Portable Electrochemical Sensing Platform: from Hardware to Software

PORTABLE ELECTROCHEMICAL SENSING PLATFORM: FROM HARDWARE TO SOFTWARE

KARTHK GANGADHARA

Presented to the Faculty of the Graduate School of

The University of Texas at Arlington in Partial Fulfillment

of the Requirements

for the Degree of

MASTER OF SCIENCE IN COMPUTER SCIENCE

THE UNIVERSITY OF TEXAS AT ARLINGTON

MAY 2020

Acknowledgements

Firstly, I would like to thank my advisor Dr. Sungyong Jung for giving me this opportunity.

I have learnt a lot of valuable things from him. When I joined his lab in December 2018, I had no idea of how to conduct research, he taught me various aspects of research by being extremely patient and motivated me from time to time. I will be indebted to him for the rest of my life.

I would also like to thank my committee members Dr. Jean Gao, and Dr. Dajiang Zhu for their consent and time to serve on my thesis defense committee and evaluate my work.

I take this opportunity to thank all current and previous members of my lab, ISCS – Special thanks to Ms. Hyusim Park, without your guidance, help and support this work would have been impossible. I would also like to thank Mr. Manu Chilukuri, Ms. Shanthala Lakshminarayana, Mr.

Younghun Park, Ms. Pallavi Vinubhai Bharoliya and Ms. Ruthya Chikkaputte Gowda. I had a wonderful time working with you all and I will always cherish it.

Finally, I would like to thank my parents and my sisters for being my constant source of motivation and for all the love and support.

April 30, 2020 4

Abstract

PORTABLE ELECTROCHEMICAL SENSING PLATFORM: FROM HARDWARE TO SOFTWARE

Karthik Gangadhara, M.S

The University of Texas at Arlington, 2020

Supervising Professor: Sungyong Jung

Recent advances in the electrochemical biosensors is increasing the popularity of the point of care devices since the electrochemical sensor can provide low cost, portability, detectability, experimental simplicity, and capacity to provide real time monitoring. The point of care devices has been used in various biomedical applications such as blood glucose monitors, pregnancy tests, HIV tests, hemoglobin level tests etc. However, the existing portable devices are limited to a specific sensing mechanism due to the inability to include the various electrochemical sensing techniques into a compact formfactor. Thus, there is a need for miniaturized all-in-one electrochemical sensing platform for the point of care devices.

In this research, we present a portable electrochemical sensing platform designed and implemented from hardware to software for the point-of-care device to accommodate widely used electrochemical sensing mechanism including amperometry, voltammetry. To control the systems interfacing with the smart-devices and computers as well as displaying the obtained data, an android application and a graphical user interface were developed in open-source 5 programming using commercial-off-shelf components which consists of a microcontroller unit with readout circuit, a multiplexer, and wired communication unit.

We performed experiments on proposed system. The Potentiostat dummy cell array tests was performed for the aqueous phase detection and test results showed the linear response, which is important in electrochemical sensing system.

Table of Contents

Acknowledgements ...... 3

Abstract ...... 4

List of Figures ...... 9

List of Tables ...... 11

Chapter 1 Introduction ...... 12

Chapter 2 Background...... 17

2.1 Electrochemistry ...... 17

2.2. Electrochemical Cell ...... 18

2.2.1 Galvanic cell (Voltaic Cell) ...... 19

2.2.2 Electrolytic Cell ...... 19

2.3. Electrochemical Sensors ...... 24

2.3.1 Potentiometric sensors ...... 24

2.3.2 Conductometric sensors ...... 27

2.3.3 Voltammetric sensors ...... 29

2.3.4 Electrochemical Impedance Spectroscopy (EIS) ...... 40

2.4. Measurement Instrumentation ...... 42

2.4.1 Potentiostat and Galvanostat ...... 42

2.4.2 Potentiostat/galvanostat operation ...... 43 7

2.4.3 Measurement Software ...... 45

2.4.4 Applications of Potentiostat/Galvanostat ...... 46

2.5 Existing Works : Portable Electrochemical sensing systems ...... 47

2.5.1 The universal Wireless electrochemical detector (UWED): ...... 47

2.5.2 Universal mobile electrochemical detector (UMED): ...... 48

2.5.3 Dstat: ...... 48

Chapter 3 Proposed System ...... 51

3.1. Hardware Design and Implementation ...... 52

3.2. Software Design and Implementation ...... 56

3.2.1. Firmware Design ...... 56

3.2.2. Graphical User Interface Design (GUI) ...... 61

3.3. Test Setup and Result ...... 67

3.3.1 Cyclic Voltammetry ...... 69

3.3.2 Square wave Voltammetry ...... 71

3.3.3. Linear Sweep Voltammetry ...... 72

3.3. 4. Amperometry ...... 74

3.3.5 Anode Stripping Voltammetry ...... 76

3.3.6. Chrono Amperometry ...... 78

Chapter 4. Conclusion ...... 81 8

References ...... 83

List of Figures

Figure 2.1. Hydrofluoric acid Redox Reaction ...... 18

Figure 2.2. Electrolytic cell ...... 20

Figure 2.3. Electrolytic cell Redox Reaction...... 21

Figure 2.4. Simple schematic of two electrode configuration where EA is the applied voltage and C and W are the counter and working electrodes, respectively...... 22

Figure 2.5. Simple schematic of three electrode configuration where EA is the applied voltage and C, W, and R are the working and counter and reference electrodes, respectively. .. 23

Figure 2.6 Simple schematic of two electrode configuration for potentiometry ...... 25

Figure 2.7 Cyclic voltammetry Input and output plot ...... 31

Figure 2.8 Anode stripping voltammetry Input and output plot ...... 33

Figure 2.9 Linear Sweep voltammetry Input and output plot ...... 34

Figure 2.10 Square wave voltammetry Input and output plot ...... 35

Figure 2.11 Chrono Amperometry Input and output plot ...... 37

Figure 2.12 Amperometry Input and output plot with respect to time...... 39

Figure 2.13. Experimental EIS system set up using three electrode mode...... 41

Figure 2.14. Schematic representation of a three-electrode controlled potential apparatus. X1 on an amplifier indicates it is a unity gain amplifier ...... 44

Figure 3.1. Block diagram for PSoC based Electrochemical sensing platform ...... 52

Figure 3.2. PSoC based Electrochemical sensing PCB board top and bottom layout ...... 54

Figure 3.3. PSoC electrochemical sensing PCB board unpopulated front side ...... 55

Figure 3.4. PSoC electrochemical sensing PCB board unpopulated front side ...... 56 10

Figure 3.5. PSoC electrochemical sensing PCB board populated front and back ...... 56

Figure 3.6 Voltage Control Circuit ...... 58

Figure 3.7 Current Measuring Circuit ...... 60

Figure 3.8 Other peripheral components ...... 60

Figure 3.9 Firmware Flowchart...... 62

Figure 3.10 Python Environment and associated packages...... 64

Figure 3.11 GUI initialization, control, and data acquisition flowchart...... 66

Figure 3.12 PSoC-Stat Graphical User Interface ...... 67

Figure 3.13. Updated GUI with SWV, LSV and Chrono Amperometry techniques ...... 68

Figure 3.14. PCB board electronic measurement using dummy cell...... 69

Figure 3.15. Potentiostat 50K Dummy Cell ...... 70

Figure 3.16. PCB board electronic measurement plot...... 71

Figure 3.17. PCB board electronic measurement plot for SWV...... 73

Figure 3.18. PCB board electronic measurement plot for LSV...... 74

Figure 3.19. PCB board electronic measurement plot for amperometry...... 76

Figure 3.20. anode stripping voltammetry dummy cell test plot...... 78

Figure 3.21. chrono amperometry result plot for ±900mV ...... 79

Figure 3.22. chrono amperometry result plot for +900mV to 0V ...... 80 11

List of Tables

Table 2.1. Comparison of different potentiostat ...... 50

Table 3.1. Part List ...... 55

Table 3.2. sample of CV response with dummy cell...... 72

Table 3.3. sample of SWV response with dummy cell...... 74

Table 3.4. sample of LSV response with dummy cell...... 75

Table 3.5. sample of Amperometric response with dummy cell...... 76

Table 3.6. sample of ASV response with dummy cell...... 78

Table 3.7. chronoamperometry result with dummy cell for pulse ±900mV...... 80

Table 3.8. chronoamperometry result with dummy cell for pulse +900mV to 0V...... 81

Chapter 1

Introduction

The impact of the sensors and sensing system is enormous and electrochemical sensors are one of the most active areas of analytical research in many fields, including clinical and environmental analysis as they offers a tremendous promise for scaling down sensing systems, with features that include high sensitivity, inherent miniaturization, low cost, low-power requirements, and high compatibility with advanced micromachining and microfabrication technologies.

Electrochemical sensors are devices that converts chemical energy into electrical energy and gives information about the composition in real time with the help of transducers. In this way, the chemical energy of the selective interaction between the chemical species and the sensor is transduced into an analytically useful signal. They are the largest and oldest group of chemical sensors. They use simplest procedures and instrumentation. They attract great interest nowadays because they are easy to miniaturize and integrate into automatic systems, without compromising analytical characteristics.

Based on the type electrical magnitude used for the transduction of the recognition incident the electrochemical sensors are classified into following families: [1]. Potentiometry,

Conductometry, Impedometry and Voltammetry/Amperometry. The potentiometry measures changes of membrane potential, conductometry measures changes of conductance, the change of current for electrochemical reaction with applied voltage in case of voltammetry and current for the applied constant voltage in case of amperometry. 13

Among the four, analytical chemists routinely use voltammetric techniques for the quantitative determination of a variety of dissolved inorganic and organic substances. The biological chemist uses voltammetric technique for variety of purposes like study of redox reactions in various media, absorption processes on surfaces, reaction mechanisms and the electron transfer and its kinetics, and transport, speciation, and thermodynamic properties of solved species. Voltammetric methods are also applied to the determination of compounds of pharmaceutical interest and for the analysis of complex mixtures[2].

This is mainly because in voltammetry input signals are varied therefore It can detect multiple chemicals species. It is simple and easy to conduct and has various sub techniques depending on the type of signal used as input, the most used waveforms are linear scan, differential pulse, and triangular and square wave. The cyclic voltammetry and square wave voltammetry techniques are more sensitive compared to EIS.

The main devices used to electrochemistry is the potentiostat and galvanostat [3]. The potentiostat involves controlling the voltage while measuring the current passing between them, whereas galvanostat controls the current while measuring the voltage across the electrodes. For this minimum 2-electrode configuration is required. In potentiostat, the electrode must pass a current while maintaining the standard voltage between them for the accurate measurements.

Because a current passing through an electrode causes change in interstitial potential, a voltage change occurs that interferes with keeping the voltage between the electrode’s constant, a third electrode is habitually used for a 3-electrode configuration. In the 3-electrode configuration, the chemical reactions occur on the working electrode surface while the reference electrode provides a stable reference potential, and not should not pass current, and an auxiliary electrode provides 14 enough current to the solution to keep the potential between the reference and working electrode at the desired voltage[4].

In the recent years various portable potentiostat designs related to discrete integrated circuits and printed circuit board have reported. The printed circuit boards usually include a chipset or a microcontroller with the analog devices to create potentiostat or galvanostat [5][6][7]. Most of the potentiostats are limited to around 0.1±0.2 mA of current and

±1.5 V voltage this is due to as they have mostly been designed for analytical chemistry purposes and to avoid the electrolysis of water. The most common electrochemical techniques used in these devices are cyclic voltammetry, amperometry and potentiometry. There are some which include pulse based voltammetric techniques such as square wave voltammetry [4][6][13] and differential pulse voltammetry. There exist wireless communication incorporated modules like uMed and UWED design making them a good fit for remote healthcare applications [14].

The existing commercial portable devices are limited to a specific sensing mechanism.

There are Electrochemical systems which includes all the electrochemical sensing techniques to provide a wide range detection and measurement capabilities. Unfortunately, not many products can be considered as portable. This is due to the inability to include the various electrochemical sensing techniques into a compact formfactor. Most of commercial products are heavy and big.

The product should have small size, light weight and be budget friendly.

This demand stimulates progress aimed at development of novel portable Electrochemical sensing platform from hardware to software to accommodate all the voltammetric electrochemical sensing mechanisms namely, cyclic voltammetry, linear sweep voltammetry, 15 anode stripping voltammetry, amperometry, chronoamperometry and lastly, square wave voltammetry with custom built open-source software programs to control the systems.

Our proposed system includes programable system on chip (PSoC) which has built in analog components such as ADC, TIA and opamp which can be used to build potentiostat without using any external analog components, which significantly reduces the size of the board with good form factor making it good fit for the portable electrochemical sensing applications and also of low cost device compared to the above mentioned papers.

To control the various techniques of the device, a graphical user interface (GUI) was developed in the python programming language. The GUI provides various options to users. The users can select different electrochemical technique by selecting the appropriate notebook[16].

The data is displayed using the matplotlib library. The GUI also provides features to save the experimental result into a excel file. The experimental controls such as selecting the voltage range, current range, adjusting the experimental duration are some of the GUI added functionalities.

This dissertation is organized as follows.

Chapter 1 introduces to the need for portable electrochemical sensing/monitoring platform. Current devices to perform electrochemical sensing is described in brief. It also covers the research objective and motivations.

Chapter 2 covers the background of electrochemistry and electrochemical sensing techniques. It also surveys in detail current potentiostat circuit architectures used for various sensing techniques with advantages and drawbacks. 16

Chapter 3 presents the proposed architecture for portable electrochemical sensing platform from hardware to software. This chapter presents all the theory with required analysis showing advantages of the present architecture over others. Applications build with the proposed system and their experimental results and measurement results are presented to validate the circuit performance.

Chapter 4 concludes the dissertation by summarizing the work and detailing the advantages of the work. 17

Chapter 2

Background

2.1 Electrochemistry

Electrochemistry is the study of movement of electrons during the chemical reactions. It was discovered by Faraday. Electro chemical reactions produces or consumes free electrons with two main processes know as oxidation-reduction (“redox”), the once where electrons exchange. Example of a redox reaction,

Hퟐ + Fퟐ → 2HF (1)

Which can be written as follows:

Oxidation Hퟐ → 2H + +2e − (2)

Reduction F2 + 2e−→ 2F− (3)

Overall reaction H2 + F2 → 2H + 2F − (4)

As shown in the above equation, the Hydrogen loses two electrons to undergo oxidation, it is called as reducing agent or reductant. Fluorine gains two electrons to undergo reduction is known as oxidizing agent or oxidant. The redox reaction is shown in Figure 2.1 below. The

Electrochemical methods are a class of techniques which study an analyte by measuring the voltage or current in an electrochemical cell [17][18][19]][20].

Electrochemical reactions occur in a solution containing dissolved ions knows as electrolyte. The electrolyte aids the current flow. Strong electrolytes with solvent-electrolyte combinations were chosen in electrochemistry. A few volts of interfacial potential differences are corresponding to a thin layer of electrolyte attached to the electrode surface. The interfacial 18 potential difference is very small. This create a potential gradient across the electrode/electrolyte surface. The interfacial potential difference, E, of an electrode can be calculated using the Nernst equation [19]:

푅푇 퐸 = 퐸° + ln (퐶표/퐶R) (5) 푛퐹

where 퐸° is the standard potential of the electrode, R is the molar gas constant, T is temperature, F is Faraday's constant and Co and CR are the concentration of the oxidized and reduced forms of the species, respectively [22].

Figure 2.1. Hydrofluoric acid Redox Reaction[63]

2.2. Electrochemical Cell

Electrochemical cells are broadly divided into two sub-types, galvanic and electrolytic. In galvanic cells the electrodes are connected via wire. The reactions start spontaneously. while in electrolytic cell a potential more than cell operating potential is required to be applied to lead the electrochemical process. Both galvanic and electrolytic cells will consist of two electrodes (an 19 anode and a cathode), which can be made of the same or different metals, and an electrolyte in which the two electrodes are immersed.

2.2.1 Galvanic cell (Voltaic Cell)

Galvanic cells are used in DC electrical power. The basic galvanostat consists of a semi- porous membrane separating the electrolyte and others includes two half cells bridged with a salt bridge. The salt bridge contains an inert electrolyte like potassium sulfate whose ions will diffuse into the separate half-cells to balance the building charges at the electrodes. A Galvanic

Cell induces a spontaneous redox reaction to create a flow of electrical charges, or electricity.

Non-rechargeable batteries are examples of Galvanic cells. A Reaction is spontaneous when the change in Gibb’s energy[15], ∆G is < 0. Electrons flow from the anode. [23][24][25][27].

2.2.2 Electrolytic Cell

An electrolytic cell is a cell which requires an outside electrical source to initiate the redox reaction. Electrolysis is the process of how the electric energy drives the non-spontaneous reactions. Whereas the galvanic cell used a redox reaction to make electrons flow, the electrolytic cell uses the source of electricity to cause the redox reaction. In an electrolytic cell, electrons are forced to flow in the opposite direction. Since the direction is reversed of the voltaic cell, the E0 cell for electrolytic cell is negative. Also, to force the electrons to flow in the opposite direction, the electromotive force that connects the two electrode-the battery must be larger than the magnitude of cell potential E0. This additional requirement of voltage is called overpotential[23][26][25][27]. Electrolytic cell for the example shown in Figure 2.2. 20

An Electrolytic cell is one kind of battery that requires an outside electrical source to drive the non-spontaneous redox reaction. Rechargeable batteries act as Electrolytic cells when they are being recharged. A reaction is non-spontaneous when Gibbs free energy, ∆G is > 0. Must supply electrons to the cathode to drive the reduction, so cathode is negative. Must remove electrons from the anode to drive the oxidation, so anode is positive.

Figure 2.2. Electrolytic cell [27].

To understand the redox reaction, Solve the Redox equation.

Oxidation 퐶푢(푆) ⟶ 퐶푢2+(푎푞) + 2푒− (6)

Reduction 퐴푔2+(푎푞) + 2푒− ⟶ 퐴푔(푠) (7)

The most common form of Electrolytic cell is the rechargeable battery or electroplating.

The reaction is redox reaction is shown pictorially in Figure 2.3. 21

Figure 2.3. Electrolytic cell Redox Reaction [63].

The Electrolytic cells used for the electrochemical analysis comes with different electrode configuration. The two electrode and three electrode configurations are explained here.

2.2.2.1 Two Electrode Configurations

This configuration consists of a Working Electrode where the chemistry of interest occurs and a Counter Electrode which acts as the other half of the cell. The applied potential (EA) is measured between the working and counter electrode and the resulting current is measured in the working or counter electrode lead as in Figure 2.4.

The counter electrode in the two-electrode setup serves two functions. It completes the circuit allowing charge to flow through the cell, and it also maintains a constant interfacial potential, regardless of current. maintaining both requirements is an impossible task under most conditions. In a two-electrode system, it is very difficult to maintain a constant counter electrode potential (eC) while current is flowing. This is due to Interfacial potential changes when the 22 current changes. This fact, along with a lack of compensation for the voltage drop across the solution (iRS) leads to poor control of the working electrode potential (eW) with a two-electrode system. The roles of passing current and maintaining a reference voltage are better served by two separate electrodes [35].

Figure 2.4. Simple schematic of two electrode configuration where EA is the applied voltage and

C and W are the counter and working electrodes, respectively.

2.2.2.2 Three Electrode Configurations

The three electrode system remedies many of the issues of the two-electrode configuration. The three-electrode system consists of a working electrode, counter electrode, and reference electrode. The reference electrode’s role is to act as a reference in measuring and controlling the working electrode potential, without passing any current. The reference electrode should have a constant electrochemical potential at low current density. Additionally, since the reference electrode passes negligible current, the iR drop between the reference and working 23

electrode (iRU) is often very small. Thus, with the three-electrode system, the reference potential is much more stable, and there is compensation for iR drop across the solution. This translates into superior control over working electrode potential. The most common lab reference electrodes are the Saturated Calomel Electrode and the Ag/AgCl electrode. Setup is illustrated in the Figure 2.5.

In the three-electrode configuration, the only role of the counter electrode is to pass all the current needed to balance the current observed at the working electrode. The counter electrode will often swing to extreme potentials to accomplish this task [36].

Figure 2.5. Simple schematic of three electrode configuration where EA is the applied voltage

and C, W, and R are the working and counter and reference electrodes, respectively.

2.3. Electrochemical Sensors

The Electrochemical sensors are the devices that gives information of the composition of the system by undergoing oxidation reduction process. Electrochemical sensors usually consists of two basic components, a chemical (molecular) recognition system which is the main part of the sensor and a physiochemical transducer which is a device that converts the chemical response into a signal(current, potential, or concentration) that can be detected by modern electrical instruments. Electrochemical sensors are broadly classified into four categories [20]:

2.3.1 Potentiometric sensors

Potentiometric sensors, in which the open circuit electrochemical cell potential is measured, which according to the Nernst equation[19] is proportional to the logarithm of the concentration of the chemical species of interest. Potentiometric sensors are commonly used when the concentration of chemical specie to be measured changes over several orders of magnitude (e.g., in the case of pH measurements). In cases, where the concentration changes over only one or two orders of magnitude (e.g., in the case of glucose concentration in physiological fluids), a sensor with a linear relationship between response and concentration is preferable (such as Amperometric sensors) rather than logarithmic response.

Potentiometry is one of the methods of electroanalytical chemistry. It is usually employed to find the concentration of a solute in solution. In potentiometric measurements, the potential between two electrodes is measured using a high impedance voltmeter.

Use of a high impedance voltmeter is important because it ensures that current flow is negligible. Since there is no net current, there are no net electrochemical reactions, hence the 25 system is in equilibrium. At its most fundamental level, a potentiometer consists of two electrodes inserted in two solutions connected by a salt bridge (see Figure 2.6 below). The voltmeter is attached to the electrodes to measure the potential difference between them. [21][22].

Figure 2.6. Simple schematic of two electrode configuration for potentiometry[64].

The reference electrode potential is known, and the other electrode is the test electrode whose potential needs to be find out. Test electrodes are dipped in its own ionic solution whose concentration is to be detected, or a carbon rod electrode sitting a solution which contains the ions of interest in two different oxidation states. The Nernst equation[13] is used to find out the concentration of the test solution.

For example, to find the concentration of Ag+ in a silver nitrate solution, reference electrode should consist of silver metal in a know 0.1 M silver nitrate solution. The test 26 electrode is silver in silver nitrate solution of wish to find the concentration. Since no current flows the cell is at equilibrium.

Ag+ ⇋ Ag (8)

The potential measured by the voltmeter, Ecell is related to the reference electrode potential and test electrode potential as follows:

퐸푐푒푙푙 = 퐸푟푒푓푒푟푒푛푐푒 − 퐸푡푒푠푡 (9)

Now, Ereference and Etest can both be expanded using the Nernst Equation:

0 푅푇푙푛(퐾푒푞) 퐸 = 퐸 + − (10) 푟푒푓푒푟푒푛푐푒 퐴푔/퐴푔 푛퐹

Therefore, at temperature of 298 K:

0 + 퐸푟푒푓푒푟푒푛푐푒 = 퐸퐴푔/퐴푔+ − 0.059푙표푔10(1/[퐴푔푟푒푓푒푟푒푛푐푒]) (11)

Similarly,

0 + 퐸푡푒푠푡 = 퐸퐴푔/퐴푔+ − 0.059푙표푔10(1/[퐴푔푡푒푠푡]) (12)

Now we can substitute equation 11 to equation 12 into equation 9, we can also assume

+ [퐴푔푟푒푓푒푟푒푛푐푒] is constant. So, after rearranging, we get:

+ −[(퐸푐푒푙푙 + 0.059)/0.059] [퐴푔푡푒푠푡] = 10 (13)

The potential reading from the voltmeter is Ecell .which can used to calculate the concentration of the silver Ions in the test solution.

The application of potentiometry are as follows. To determine the cell potential as described above. Potentiometric titration is used for all types of volumetric analysis: acid base, precipitimetry[51], complexometry[50] and redox. It is used when it is not easy or impossible to detect the end point by ordinary visual methods i.e. For high colored or turbid solutions. For very dilute solutions and when there is no available indicator[27]. 27

2.3.2 Conductometric sensors

Conductometric sensors, in which the conductance of the electrochemical cell is measured by an alternating current bridge method. In this kind of sensor mostly the resistive component of the impedance of the chemical specie is measured. The measurement is performed at one fixed frequency [30].

Conductometry is the measurement of the electrical conductivity of a solution. The conductance is defined as the current flow through the conductor. The unit for the conductance is Siemens (S) which is the reciprocal of Ohm's (Ω−1). It is mainly used for the determination of the physico-chemical properties of the compounds. The main principle involved in this method is that the movement of the ions creates the electrical conductivity. The movement of the ions is mainly depended on the concentration of the ions.

퐴+퐵− + 퐶+퐷− ⟶ 퐴퐷 + 퐶+퐵− (14) where A+B− is the solution of strong electrolyte; C+D− is the solution of the reagent. Here the ionic concentration of A+ is determined by reacting the electrolyte solution with the reagent solution so that the A+ ions are replaced by the C+ ions. This replacement of the ions with the other ions shows the conductance increase or decrease. This is done mainly by the replacement of the hydrogen ion with another cation.

The theory is mainly based on Ohm's law which states that the current (I) is directly proportional to the electromotive force (E) and inversely proportional to the resistance (R) of the conductor:

퐼 = 퐸/푅 (15) 28

The conductance is defined as the reciprocal of the resistance. The resistance is expressed by the following equation:

푅 = 휌푙/푎 (16)

where 휌 is the resistivity; 푙 is the length; 푎 is the cross-sectional area of the homogenous material. Therefore,

퐶 = 1/푅 = 푘/푙푎 (17) where K is the conductivity; l is the length; a is the cross-sectional area of the homogenous material. Then the molar conductivity is defined as the conductivity due to 1 mole and it is expressed by the following formula:

훬 = 1,000푘/퐶 (18) where K is the conductivity; C is the concentration of the solution in mol/l. The sample solution is placed on the cell which is composed of platinum electrodes. These are calibrated with the help of known conductivity of the solution, for example, standard potassium chloride solution. Cell constant is defined as the conductivity of the cell.

푐푒푙푙 푐표푛푠푡푎푛푡 = 0.002765 / 표푏푠푒푟푣푒푑 푐표푛푑푐푢푡푖푣푖푡푦 (19)

The conductometry is used for determination of Sulphur dioxide in air pollution studies.

Determination of soap in oil. Determination of accelerators in rubber. Determination of total soap in latex. Specific conductance of water. To check water solubility in rivers and lakes. To determine alkalinity of fresh water, salinity of sea water. To determination of deuterium ion concentration in water – deuterium mixture. Food microbiology for tracing micro-organisms and tracing the antibiotics[30].

2.3.3 Voltammetric sensors

In Voltammetric sensors, the voltage is applied across the electrodes of the electrochemical cell and the current flowing between them is measured. The measured current is due to the response of chemical species of interest. By applying linear, square, or cyclic voltammetry, improved selectivity and sensitivity is achieved.

In voltammetry, the applied voltage and the redox current follows a well define law. The applied potential controls the concentration of the oxidation and reduction species at the electrode (CO and CR) and the rate of the reaction(k0) as described by Nernst[25] or Butler–Volmer equations[33], respectively. When diffusion is involved the material flux between the electrode and the solution controls the redox current based on Fick’s law[34]. The interplay between these processes is responsible for the characteristic features observed in the Volta gram of various techniques. For a reversible electrochemical reaction described by below equation.

O + 푛푒− ⟺ R (20)

The application of potential E forces the respective concentrations O and R at the surface of the electrode to the ratio according to Nernst equation:

0 0 푅푇 퐶푅 퐸 = 퐸 − ln ( 0) (21) 푛퐹 퐶푂

Where,

R – molar gas constant (8.3144 J mol–1K–1),

T – Absolute Temperature (K),

n – Number of electrons transferred,

F – Faraday constant (96,485 C/equiv), and

E0 – The standard reduction potential. 30

When the applied potential to the electrode is changed, the ratio of the concentration changes satisfying equation 13. The variables for current, potentials and concentration can be expressed using Butler-Volmer equation:

푖 = 푘0{퐶 푒−훼휃 − 퐶 푒(1−훼)휃} (23) 푛퐹퐴 푂 푅

Where,

푛퐹(퐸−퐸0) 휃 = (24) 푅푇

K0 – heterogeneous rate constant,

훼 – transfer coefficient,

A – Area of the electrode.

Depending on the type of signal used the voltammetric techniques are further classified into subcategories as follows:

2.3.3.1 Cyclic Voltammetry(CV)

Cyclic voltammetry (CV) has become an important and widely used electroanalytical technique in many areas of chemistry. It is widely used for the study of redox processes, for understanding reaction intermediates, and for obtaining stability of reaction products. This technique is based on varying the applied potential at a working electrode in both forward and reverse directions (at some scan rate) while monitoring the current [32].

For example, the initial scan could be in the negative direction to the switching potential.

At that point, the scan would be reversed and run in the positive direction. One full cycle analysis 31

Input is provided in the Figure 2.7 shows the potential applied to between the WE and RE for the cyclic voltammetry measurement and the resultant response.

Figure 2.7 Cyclic voltammetry Input and output plot

The important parameters in a cyclic voltammogram are the peak potentials (Epc , Epa) and peak currents (ipc , ipa) of the cathodic and anodic peaks, respectively. If the electron transfer process is fast compared with other processes such as diffusion, the reaction is said to be electrochemically reversible, and the peak separation is

△ 퐸푝 = |퐸푝푎 − 퐸푝푐| = 2.303 푅푇/푛퐹 (25)

0 For reversible reaction at 25 C with electrons △ 퐸푝 should be 0.0592/n V, or about 60 mV for one electron. Irreversibility due to a slow electron transfer rate results in △ 퐸푝 > 0.0592/n

V, greater, 70 mV for a one-electron reaction.

The reduction potential (E0) for a reversible couple is given by,

퐸 +퐸 퐸0 = 푝푎 푝푐 (26) 2

For a reversible reaction, the concentration is related to peak current by the Randles–

Sevcik [25] expression (at 25 °C): 32

5 3/2 0 1/2 1/2 푖푝 = 2.686 × 10 푛 퐴푐 퐷 푣 (27)

Where,

ip – peak current in amps,

D – the diffusion coefficient (cm2 s–1),

A – Area of the electrode (cm2),

c0 – Concentration in mol cm–3, and

n – Scan rate in Vs–1.

The Applications of cyclic voltammetry are as follows. Determination of band gap of semiconductor. To determine the oxidation state of central metal atom in many metal complexes.

To determine electron transfer where it is one or two electron transfer. It provides supplementary fluorescence spectrometry.

2.3.3.2 Anode Stripping Voltammetry(ASV)

Anode stripping voltammetry (ASV) is most widely used for trace metal detection. Anodic

Stripping Voltammetry is a method to demonstrate the presence of multiple metals in water.

There are two steps. First, the analyte species in the sample solution is concentrated onto or into a working electrode. During the second step, the precontracted analyte is measured or stirred from the electrode by the application of potential scan. Figure 2.8 shows the ASV with cyclic voltammetry scan. A is the cleaning step and B is the electroplating and equilibrium step, C is the stripping step [26]. 33

The resultant plot for the Anode stripping voltammetry is shown in the Figure 2.8. The response is like the one obtained for the cyclic voltammetry with exceptional sensitivity due to the preconcentration step.

Figure 2.8 Anode stripping voltammetry Input and output plot.

Advantages and applications are as follows. ASV allows researchers to detect multiple types of dissolved metal in one experiment. Researching water quality using ASV is also fast and accurate. An ASV test is very easy to perform on site by taking a sample of the water and testing it with the potentiostat linked to a laptop or tablet.

The metal film formed during the reduction step concentrates the metal particles at the electrode, so the detection of very low concentrations (ppb range) of metal ions is possible.

Anodic Stripping Voltammetry is widely used for testing drinking water quality, surface water and sewage or wastewater – water that leaves the treatment plant before being discharged into surface water. [35]. 34

2.3.3.3 Linear Sweep Voltammetry(LSV)

In linear sweep voltammetry (LSV) a fixed potential range is employed much like potential step measurements. However, in LSV the voltage is scanned from a lower limit to an upper limit as shown Figure 2.9 below.

Figure 2.9 Linear Sweep voltammetry Input and output plot

The voltage scan rate (v) is calculated from the slope of the line. Clearly by changing the time taken to sweep the range we alter the scan rate. The characteristics of the linear sweep voltammogram recorded depend on several factors including the rate of the electron transfer reaction(s), The chemical reactivity of the electroactive species, The voltage scan rate. Typical response plot for the LSV is shown in Figure 2.9.

LSV mainly used in irreversible reactions. one example,[37] linear voltammetry was used to examine direct methane production via a biocathode. Since the production of methane from

CO2 is an irreversible reaction.

2.3.3.4 Square wave voltammetry(SWV)

The excitation signal in SWV consists of a symmetrical square-wave pulse of Fixed amplitude superimposed on a staircase waveform of fixed step height, where the forward pulse of the square wave coincides with the staircase step. The net current is obtained by taking the difference between the forward and reverse currents (Ifor – Irev) and is centered on the redox potential. Typical Square wave voltammetric Input plot is shown in the Figure 2.10 below.

The typical response plot for the square wave voltammetry for a redox reaction is shown in Figure 2.10. The SWV has several advantages and is used in determination of some species in trance levels and in electrochemical detection in HPLC [32][38].

Figure 2.10 Square wave voltammetry Input and output plot

The scan rate of the square wave voltammetry is inversely dependent upon the time per step, τ:

푚푉 퐸 (푚푣) 푆푐푎푛 푟푎푡푒 ( ) = 푠푡푒푝 (28) 푠 τ(s)

Where,

Estep – Amplitude of the step voltage, 36

τ – Time per step.

During the scan, the current is recorded at the end of the forward pulse and at the end of the reverse pulse, meaning it is sampled twice per cycle. Waiting till the end of the pulse to sample the current avoids involving the charging current.

The frequency, f, used in square-wave voltammetric experiments is generally from about

1 to 125 Hz. Such a high f means that square-wave voltammetry is usually much faster than other pulsed experiments.

Applications are as follows: SWV is very sensitive, often allowing direct analyses at the ppb (parts per billion) level and even the low ppt (parts per trillion) level when used in a stripping mode. SWV requires less time per sweep than older techniques such as differential pulse polarography. A SWV sweep can often be recorded in less than ten seconds, in contrast with a differential pulse polarogram that typically requires more than two minutes for data acquisition.

The square-wave frequency can be used to differentiate between processes with fast and slow kinetics. In some cases, kinetically fast processes can be measured without interference from slower processes that occur in the same potential range.

Other techniques, such as cyclic voltammetry, are generally preferred over SWV for mechanistic and kinetic studies. However, square-wave voltammetry’s sensitivity allows mechanistic and kinetic measurements in solutions that are too dilute for more conventional study.

SWV is generally performed on a stationary solid electrode or a hanging mercury drop electrode. The SWV script in the Pulse Voltammetry software provides for mercury-drop 37 generation, solution de-aeration, and experiment sequencing suitable for the most common applications for square-wave voltammetry.

2.3.3.5 Chrono Amperometry

In chronoamperometry electrochemical analytical technique, the potential of the working electrode is stepped, and the resulting faradaic current is measured as a function of time. As shown in the Figure 2.11 the applied potential is instantaneously jumped from one value to another.

Figure 2.11 Chrono Amperometry Input and output plot

The resultant current is measured. The current rises instantaneously after the changes in the voltage and then begins to drop as a function of time. Chronoamperometry is a time- dependent technique where a square-wave potential is applied to the working electrode. The current of the electrode, measured as a function of time, fluctuates according to the diffusion of an analyte from the bulk solution toward the sensor surface. 38

Chronoamperometry can therefore be used to measure current–time dependence for the diffusion-controlled process occurring at an electrode. It is a sensitive technique which does not require labeling of the analyte or bioreceptor and has been applied in many studies independently or alongside other electrochemical techniques such as CV[40].

The characteristic shape of the resulting chronoamperogram can be represented by the

Cottrell equation[31]

푛퐹퐴퐶0퐷1/2 푖 = (29) 푡 휋1/2푡1/2

Where,

n – The moles of electrons involved in the reaction.

F – The Faraday constant.

A – The area of the electrode (cm2),

C0 – The concentration of the analyte in the bulk solution (mol./dm3),

D – The diffusion coefficient (cm2/s) and

t – Time (s).

Consequently, i will be proportional to t− 1/2.

It is used in wide range of applications such as in measuring the concentration by measuring I vs conc. at any fixed time. It can analyze the shape of the current-time curve to study coupled chemical reactions. There are better ways to do both with more modern techniques

Chronoamperometry is important because it is a fundamental method on which other techniques are based. 39

2.3.3.6 Amperometric sensors

Amperometry is a special type of voltammetry, where the voltage applied across the electrodes of the electrochemical cell is kept constant while its current is measured. The measured current is a function of the concentration of the electroactive species. The response will have high linearity if the current is limited by the rate of the mass transfer and not by the rate of charge transfer. Typical voltage Input and current output plots are illustrated in Figure 2.12. below [41].

Figure 2.12 Amperometry Input and output plot with respect to time.

The Magnitude of the measured current is proportional to the concentration of the oxidized and reduced analyte. The Amperometric methods is highly dependent on the applied potential. However, the electrode material and the composition of the supporting electrolyte can also influence it. This steady state diffusion current is the direct measure of the concentration of the electroactive species in the solution.

Some of the applications are, Amperometric titrations are used for redox; precipitation[59] and complexometric titrations[58] of the reducible inorganic or organic ions. For 40 conventional acid-base titrations it is not useful. In the determination of moisture by Karl fisher reagent, the end point is located by amperometry. Factors like surface area completely disappear from Amperometric titrations.

2.3.4 Electrochemical Impedance Spectroscopy (EIS)

Electrochemical Impedance Spectroscopy (EIS) is an electrochemical technique to measure the impedance of a system in dependence of the AC potentials frequency. EIS systems characterize the time response of chemical systems using low amplitude alternating current (AC) voltages over a range of frequencies. Using an electrode setup consisting of a working, reference, and counter electrodes a known AC voltage is passed from the working electrode through an electrolytic solution and into the counter electrode. Quantitative measurements are produced by the EIS and enable the evaluation of small-scale chemical mechanisms at the electrode interface and within the electrolytic solution. Therefore, EIS is useful in determining a wide range of dielectric and electrical properties of components in research fields studying batteries, corrosion, etc.

The Figure 2.13 shows the experimental setup for EIS system with 3 electrodes. An electrochemical cell is used to for the chemical reaction and is connected to the electrochemical spectrometer to obtain the electrical response of an electrolytic solution. EIS systems are operated using computer programs specifically designed for EIS testing. 41

Figure 2.13. Experimental EIS system set up using three electrode mode[55].

When the voltage is passed through the electrolytic solution, from the WE to RE, its acts as resistors to impede electron flow. The resulting voltage recorded by the RE is used to determine the electrolyte resistance by comparing the input and output voltage. The excitation signal is expressed as a function of time, has the form

퐸푡 = 퐸표 sin (휔푡) (30)

Where, 퐸푡 is the potential at time t, 퐸0 is the amplitude of the signal and 휔 is the radial frequency. The frequency f and radial frequency 휔 is related as follows

휔 = 2휋푓 (31)

In a linear system, the response signal, It , is shifted in phase and has a different amplitude than I0.

퐼푡 = 퐼0 sin (휔푡 + 휙) (32)

An expression analogous to Ohm’s law allows us to calculate the impedance of the system as:

퐸푡 퐸0 sin (휔푡) sin (휔푡) 푍 = = = 푍0 (33) 퐼푡 퐼0 sin (휔푡+휙) sin (휔푡+휙) 42

EIS is used in corrosion for rate determination, inhibitor and coatings, passive layer

Investigations. In Coatings evaluation used for dielectric measurements and corrosion protection.

In batteries to determine state-of-charge, materials selection, electrode design. In electrode deposition for bath formulation, surface pretreatment, deposition mechanism, deposit characterization. In Electro-Organic synthesis to determine reaction mechanism. In

Semiconductors for photovoltaic work and dopant distributions[56][57].

2.4. Measurement Instrumentation

The basic components of a modern electroanalytical systems are a potentiostat/galvanostat, computer, and the electrochemical cell. In some cases, the potentiostat/galvanostat and computer are bundled into one package, whereas in other systems the computer and the A/D and D/A converters and microcontroller are separate, and the potentiostat can operate independently. Potentiostats and galvanostats are electrochemical instruments used in electrochemistry, battery and fuel cell testing, corrosion control, voltammetry, biomedical research, surface imaging, and related applications.

2.4.1 Potentiostat and Galvanostat

Potentiostats are used to keep the potential (voltage) between a working electrode and a reference electrode at a constant value. With potentiostats, the signal from the reference electrode is fed through an impedance transformer which amplifies the input current but leaves the voltage unchanged. An input resistor protects the buffer from static loads, and a capacitor 43 reduces the intrinsic noise. Like potentiostats, galvanostats function as electronic amplifiers with low feedback. A simple galvanostat produces a constant voltage with a resistor connected in series. To force the flow of a near-constant current through a load, this resistor needs to function at considerably higher levels than the load resistor. A more complex galvanostat can feed a constant current ranging from a few picoamperes (pA) to several amperes (A).

2.4.2 Potentiostat/galvanostat operation

A basic potentiostat can be modeled as an electronic circuit consisting of four components: the electrometer, the I/E converter, the control amplifier, and the signal. The Figure 2.14 is the schematic representation of 3 electrode controlled potential apparatus. The working of various parts are as follows:

2.4.2.1 Electrometer

The electrometer circuit measures the voltage difference between the working and the reference electrode. It acts as a feedback signal within the potentiostat, and I is the voltage signal that is measured and displayed to the user. Its output serves two purposes. An ideal electrometer has infinite impendence and zero current. The reference electrode does pass a very small amount of current. Current through the reference electrode can change its potential, but this current is usually so close to zero that the change is negligible.

The capacitance of the electrometer and the resistance of the reference electrode form an RC circuit. If the RC time constant is too large it can limit the effective bandwidth of the electrometer. The electrometer bandwidth must be higher than the bandwidth of all other components in the potentiostat. 44

Figure 2.14. Schematic representation of a three-electrode controlled potential apparatus. X1

on an amplifier indicates it is a unity gain amplifier[44].

2.4.2.2 The I/E Converter

The current to voltage converter measures the cell current. The cell current is forced through a current measurement resistor, Rm . The resulting voltage across this resistor is a measure of cell current. During an experiment, cell current can change by several orders of magnitude. Such a wide range of current cannot be accurately measured by a single resistor. 45

Modern potentiostats have several Rm resistors and an “I/E auto ranging” algorithm that selects the appropriate resistor and switches it into the I/E circuit under computer control.

The bandwidth of the I/E converter depends strongly on its sensitivity. Unwanted capacitance in the I/E converter along with Rm forms an RC circuit. To measure small currents,

Rm must be sufficiently large. This larger resistance, however, increases the RC time constant of the circuit limits the I/E bandwidth. For instance, no potentiostat can measure 10nA at 100 kHz.

2.4.2.3 The Control Amplifier

The control amplifier compares the measured cell voltage to the desired cell voltage and drives current into the cell to force these voltages to be the same. The control amplifier works on the principle of negative feedback. The measured voltage enters the amplifier in the negative or inverting input. Therefore, a positive perturbation in the measured voltage creates a decrease in the control amplifier output, which counteracts the initial change.

The potentiostat simplified schematic in Figure 2.14 becomes a galvanostat when the feedback is switched from the cell voltage signal to the cell current signal. The instrument then controls the cell current rather than the cell voltage. The electrometer output can still be used to measure the cell voltage.

2.4.3 Measurement Software

For the galvanostat/potentiostat controlling is software’s are essential without software, is of no use. With dedicated software one can control the instrument, apply the experimental settings, and see the measurement data in many graphical representations. Most of the software always includes free use on multiple computers and free updates. The commercial 46 potentiostat/galvanostat are sold including its own easy-to-use intuitive software, which allows the user to execute experiments immediately without any required training. Potentiostats and galvanostats differ in terms of form factor and may include integral software that runs under the

Microsoft Windows operating system (OS). Software features may include cyclic and linear voltammetry, normal and differential pulse voltammetry, user-definable programming, and chronoamperometry and chronopotentiometry. Potentiostat software with potentiostatic polarization, galvanostatic polarization, and potentiodynamic polarization is also available[47].

The software’s such as graphical user interfaces can provide various features such as

Automatic data saving during and/or after a measurement, scripting and equivalent circuit fittings, saving all the available curves and plots, measurement data and methods to a single file.

And can also provide dynamic feedback on method parameters.

2.4.4 Applications of Potentiostat/Galvanostat

The potentiostat are used in controlled potential electrolysis for the synthesis of organic and inorganic chemicals when control of the electrode potential allows a high degree of selectivity to be obtained as compared to conventional chemical approaches. output drive or output power of the instrument are key things to consider while selecting potentiostat for such applications.

Some major uses of the potentiostat related to processes in metal finishing are as follows.

Metal deposition - techniques involving the potentiostat are widely used to investigate fundamental aspects of electrocrystallisation. Electropolishing - this technique is used extensively to produce stress-free, highly polished surfaces on many metals and their alloys. Coatings - the corrosion of aluminum, magnesium[38]. 47

Galvanostats are used in battery charger research works. They are used to check the battery longevity, charging and discharging characteristics. They are also used as battery chargers.

To determine the resilience of a certain protective layer by applying an electron current on the layer, and to measure how high the potential of the layer is and how it will behave under different circumstances galvanostats are used [61][47].

2.5 Existing Works : Portable Electrochemical sensing systems

Recently there have been many potentiostat solutions designed with discrete Integrated circuits (ICs) connected to Printed Circuit Board (PCBs) to perform electrochemical analysis

[6][7][8]. The typical potentiostat performs with voltage range ±1.5 V and current range of 0.1mA to 0.2mA. The main concerns of these designs were low cost, small size, and good performance.

The universal Wireless electrochemical detector (UWED) [48], Universal mobile electrochemical detector (UMED)[49], Dstat[50] and Cheapstat[51] are the most recent papers.

2.5.1 The universal Wireless electrochemical detector (UWED):

This paper demonstrated application for the most used electrochemical techniques of potentiometry, chronoamperometry, cyclic voltammetry, and square-wave voltammetry. The working voltage range is about ± 1.5 and can measure current up to ± 0.18 mA current. The board make use of 10-bit analog to digital converter (ADC) and 0.05mV resolution digital to analog converter (DAC). It provides both wired and wireless communication mechanism.

The UWED communicates with a smartphone or a tablet using the wireless Bluetooth Low

Energy (BLE) protocol. A host program in the smartphone receives the input parameters of the 48 experiment from the user, communicates the experimental protocol to the UWED, receives the raw data as the result of the experiment from the UWED, visualizes the data for the user, stores the data, and sends the results to the Cloud[48].

2.5.2 Universal mobile electrochemical detector (UMED):

This paper describes an inexpensive, handheld device that couples the most common forms of electrochemical analysis directly to “the cloud” using any mobile phone, for use in resource-limited settings. The electrochemical methods that demonstrated are chronoamperometry, cyclic voltammetry, differential pulse voltammetry, square wave voltammetry, and potentiometry each with different uses. The combination of these electrochemical capabilities in an affordable, handheld format that is compatible with any mobile phone or network worldwide guarantees that sophisticated diagnostic testing can be performed by users with a broad spectrum of needs, resources, and levels of technical expertise. It is hardware specifications consist of ± 2 voltage range and ± 0.156 mA current range with up to 16 bit of ADC resolution. [49].

2.5.3 Dstat:

The Dstat is inexpensive, freely modifiable open-source analytical instruments that both complement and compete with commercial instruments. It demonstrated Its capabilities for low- current voltammetry in laboratory settings and found its performance to be comparable to that of a compact commercial potentiostat as well as being superior to that of a previously reported open-source instrument. DStat was also demonstrated to be useful for potentiometry (mostly 49 unique among lab-built potentiostats) with performance comparable to that of a commercial pH meter. It also provides Integration with other devices through hardware or the custom-made software as intermediary. Compared to other Potentiostats Dstat can measure up to 10mA current. The opamp used in Dstat were selected for criteria to have low noise 45 푛푉/√퐻푧 and an offset of 0.2 mV to optimize the noise and offset voltage, which is better compared to many open source potentiostats [50].

There are also many reports of single chip potentiostats manufactured with complementary metal-oxide-semiconductor (CMOS) and related technologies [52][53][54].

Table 2.1. Comparison of different potentiostat

Potentiostat Voltage Current ADC DAC Communication Sampling (V) (mA) Resolution Resolution Protocol Rate (mV) UWED ± 1.5 ±0.18 10 bits 0.05 Wired and Wireless 0.1 UMED ± 2 0.156 16 bits 0.05 Wired and Wireless 0.8 Dstat ± 1.5 10 24 bits 0.046 Wired 30 Cheapstat ± 0.99 0.05 12 bits 1 Wired 2 PSoCStat ± 2 ±0.1 12 bits 1 Wired 50

The above Table 2.1 shows the comparison of a list of different potentiostat proposed over the last decade. Among them Dstat can measure up to 10mA current. Almost all the potentiostat can perform most common electrochemical techniques such as Cyclic Voltammetry,

Amperometry and Potentiometry. The universal Wireless electrochemical detector (UWED),

Universal mobile electrochemical detector (UMED), Dstat include square wave voltammetry and differential pulse voltammetry with above techniques. The UMED and UMED also includes wireless protocols for remote operations. 50

In our research, we present a portable electrochemical sensing platform designed and implemented from hardware to software for the point-of-care device to accommodate widely used electrochemical sensing mechanism including amperometry, voltammetry. To control the systems interfacing with the computers as well as displaying the obtained data, a graphical user interface was developed in open-source programming language such as python. The low-power compact hardware was designed and fabricated using commercial-off-shelf components which consists of a microcontroller unit with readout circuit, a multiplexer, and wired communication unit.

The proposed electrochemical sensing platform accommodates electrochemical techniques such as linear sweep voltammetry, cyclic voltammetry, amperometry, anode strip voltammetry, chrono amperometry and square wave voltammetry. The custom designed python graphical user interface provides user options to select and perform each of the voltammetric experiments. The GUI was developed using python 2.7 environment provides various functional control over the sensing system.

The sensing system is design consists of a programmable system on chip unit which includes a CPU and other analog components(ADC, DAC and TIA) to build the on-chip potentiostat which help in reducing the external analog components inclusion compared to the various above mentioned board. This also helps in achieving a good formfactor and developing small and portable sensing system. Since the used components are a few including the MCU and the multiplexer, the cost of the board is also very low.

Chapter 3

Proposed System

The purpose of the proposed system is to describe the design and characterization of a portable electrochemical sensing platform from hardware to software. The proposed system includes the voltammetric technique such as cyclic voltammetry, linear sweep voltammetry, anode stripping voltammetry, amperometry, chrono amperometry and square wave voltammetry.

This system interfaces with a graphical user interface for receiving the experimental parameters and experimental protocols. This approach provides a better form factor, simplified design and reduced size and cost of the hardware. The small size is suited for the portable remote electrochemical analysis. The systems operating ranges are (± 2 V, ± 100 uA) which are sufficient for most of the electrochemical analysis in aqueous solution.

Figure 3.1. Block diagram for PSoC based Electrochemical sensing platform.

The Figure 3.1 shows the block diagram for the PSoC based Electrochemical sensing platform. The sensor plugged into the board; the board is connected to computer via USB cable.

A host program in the computer controls the experiments performed by MCU, processes, visualizes, and stores the data in the computer. The trans impedance amplifier and analog to digital convertor block in MCU are used to interpret the data from the sensor. Communication part, it has built in USB communication protocol for the data transmission. User can get the data 52 with the PC using the GUI. It will be discussed more in detail in later chapter. For the commercial sensor connection part, 3 pin sockets are used.

3.1. Hardware Design and Implementation

Most open source potentiostats cover the voltage ranges of ± 1.5 V, and voltages more than this results in electrolysis of water, making larger voltages less useful in aqueous solutions.

And most of the potentiostats are limited to around 0.1±0.2 mA of current as they have mostly been designed for analytical chemistry purposes.

To do this we use a Programmable System on a Chip (PSoC), a single IC microcontroller that includes with the CPU core, an array of other digital and analog electronic components. The electrochemical sensing system board is designed to include the PSoC 5LP CY8C5888LTI-LP097

MCU. Five pin SWD interface is used to program the MCU. microUSB is used for Wired communications, respectively.

There are some tradeoffs for the convenience of using a single chip potentiostat such as, the Opamps cannot be selected to optimize noise or the offset voltage. For example the Opamps used in the Dstat were selected for this criteria and have a noise of 6.5 푛푉√퐻푧 and an offset of

< 0.2 mV, in comparison the Opamps of the PSoC 5LP have a noise of 45 푛푉√퐻푧 and an offset of up to 12 mV (for the reference and working electrodes combined). Also, the inputs of the PSoC

5LP are programmable general-purpose input-output pins having leakage current of up to 2nA while the DStat Opamps, with their dedicated inputs designed for low currents, only have an input bias current of 200 fA. 53

Due to use of on chip components and the size of the board is significantly reduced and it is design as a good fit for remote healthcare applications.

The Figure 3.2 shows the PCB layout front and back side of it, respectively. The total size of the board is 48mmX37mm. The Figure 3.3 and 3.4 are the front and back sides of the PCB board unpopulated and the Figure 3.5 is the PCB board populated with the components completely. For the commercial sensor connection 3 pin sockets are used.

Figure 3.2. PSoC based Electrochemical sensing PCB board top and bottom layout.

The list of the major components used are listed in the Table 3.1 below.

Table 3.1. Part List

Item Part Number Manufacturer Multiplexer TMUX1208SVR Texas Instrument MCU CY8C5888LTI-LP097 Cypress

Figure 3.3. PSoC electrochemical sensing PCB board unpopulated front side

Figure 3.4. PSoC electrochemical sensing PCB board unpopulated back side.

Figure 3.5. PSoC electrochemical sensing PCB board populated front and back 56

3.2. Software Design and Implementation

The software portion for the PSoC electrochemical sensing system consists of two main sections. Which are, Firmware design and Graphical user Interface (GUI) design. The potentiostat is designed in the Firmware design section. The controlling software is designed in the GUI section.

3.2.1. Firmware Design

The Firmware for the liquid based electrochemical sensing system is developed in PSoC

4.2 developed by Cypress Semiconductor. The liquid based electrochemical system consists of

PSoC 5LP (part number CY8CKIT-059), which has integrated analog components into a single chip with an ARM Cortex-M3 CPU. The potentiostat designed for the system make use of the built-in components such as Transimpedance amplifier, VDAC, 12-bit ADC and DAC modules. The detailed

Firmware made in the TopDesign window of PSoC Creator, which will configure the analog portion of the PSoC 5LP chip.

3.2.1.1. Voltage Control Circuit

The voltage between the Reference Electrode and the Working Electrode is controlled using the circuit shown in Figure 3.6. The PSoC 5LP MCU consists of two types of voltage digital to analog convertors. One is low resolution 8-bit VDAC and another one is the 12-bit dithering digital to analog convertor(DVDAC). The voltage control circuit make use of both the modules but one at a time. The built in opamp is used as a buffer to which voltage from selected

VDAC/DVDAC module will be provided. To select a voltage source an analog mux is used. The cons 57 with DVDAC is the noise it generates, to avoid this an external capacitor is used. The graphical user interface used to provide user option for the voltage source selection.

Figure 3.6 Voltage Control Circuit

The output of the opamp is connected to the counter electrode. Counter electrode and reference electrodes are connected via analog mux for selecting two or three electrode configurations. The current through the counter electrode will flow until the voltage across the reference electrode is same as the voltage source. The control functionalities for the voltage control unit are provided in graphical user interface.

3.2.1.2. Current Measuring Circuit

The PSoC 5LP MCU consists of 3 types of Analog to digital converters. Successive approximation ADC (SAR ADC), Delta sigma ADC and Sequencing SAR ADC. All are of 12-bit 58 resolution. In this circuit built in Trans impedance amplifier is used to convert the current from the working electrode into voltage. The trans impedance amplifier high input impedance makes the working electrode current to pass through the feedback resistor. The drop across the resistor is then digitized using the delta sigma ADC. The TIA of the PSoC MCU uses switch capacitors to produce the feedback resistance values. This range varies from 20 kiloohms to 1 Mega ohm(8 resistor values).The device is limited to 100uA as the minimum value of the resistance can be used it 20 kiloohms. Due to use of switched capacitors the measured values of the TIA sometimes vary, to rectify this an 8-bit IDAC is used. The know values of current is passed to the TIA and the respective ADC readings are then matched with the expected values. If there is deviation the correction offset is used to correct the reading. Figure 3.7 shows the arrangement of the various current measuring circuit components.

Figure 3.7 Current Measuring Circuit

3.2.1.3. Peripheral Components

Figure 3.8 Other peripheral components.

Figure 3.8 shows the other peripherals used by the device. The data read operation from the ADC and the DAC is controlled using a pulse width modulator. The PWM generates pulse that is used to trigger the interrupt service routines of the ADC/DAC. The pulse width modulator period is decided by the user, which will be provided as an input to the Firmware from the GUI.

An EEPROM is used to store the user preferences such as the number of electrodes to use, the type of voltage source to use. The Full speed USB component is used for data transmission between the firmware and the GUI.

3.2.1.4 Firmware Workflow

In the Firmware design once the required components are placed, the next step is to initialize these components and their respective interrupt routines. The flowchart of the main program and its functional calling based on commands are shown in the Figure. 3.9. below.

There are two main parts. At first when the firmware starts, the components such as

Analog to digital converter (ADC), Digital to analog converter (DAC), Trans-impedance amplifier 60

(TIA), PWD (Pulse width modulator) are initialized and put into sleep mode to save the power consumption. The main program then invokes into a forever loop where it will constantly check for the received USB commands. If the USB commands received, then the program will jump into the respective program to perform next set of operations. This workflow is shown in the first of the three flowcharts shown in the Figure 3.9.

Figure 3.9 Firmware Flowchart.

The first set of the received commands are the one to set the look up table for the potentiostat input voltage. Depending on the different type of voltammetric sensing technique, the lookup table created varies. For example, cyclic voltammetry involves creating of a triangular wave points, the square wave voltammetry involves creating of a square wave look up points for the voltage based on the user provided start and the stop voltage values. Once these lookup tables were created the main program returns to its loop to check for the next set of USB commands. This part of the programming flow is shown in the third flowchart of the Figure 3.9.

The main set of the commands are the one to run each experiment and then to return the received ADC response. Once the GUI command to run these experiments is received, depending on the experiments respective hardware components will be awaken and the DAC voltage for the electrode is set using the already created experiment specific lookup table. Once the DAC values are set, the program return the “Done” command to the GUI. The GUI after receiving the “Done” command will send another command to read the respective ADC value for the Current value readings. This part of the programming flow is shown in the second flowchart in the Figure 3.9.

There are other set of programs which handles the interrupt service routines and hardware configuration which are not included here. But are essential part of the Firmware.

3.2.2. Graphical User Interface Design (GUI)

The electrochemical sensing platform communicates with computer via Universal Serial

Bus (USB) and by sending and receiving the commands in the string format. The wired communication is provided using the inbuilt USB or COM port communication protocol. 62

The Graphical User Interface (GUI) for wired control protocols is designed using the python software language, version 2.7. We followed the GUI provided by the open source potentiostat for the further functional enhancement and modification for the portable sensing platform. The user can select different electrochemical sensing techniques by selecting the appropriate notebook. The main programming language and its libraries are illustrated in the

Figure 3.10.

Figure 3.10 Python Environment and associated packages.

The GUI development consists of python environment version 2.7. The Visual Studio Code

IDE, developed by Microsoft for which provides support for debugging, embedded Git control 63 and GitHub, syntax highlighting intelligent code completion, snippets, and code refactoring. The main framework of the GUI is built using the tkinter python library. The data is displayed using the matplotlib library. USB communication is done using pyUSB and the libusb-win32, WinUSB driver libraries. The source code is bundled has been compiled into an executable file. The packaging of the python script into an executable file is accomplished with the Pyinstaller package. Other supporting libraries such time, CSV are used for the synchronization and data saving options. All these libraries and their association are shown in the Figure 3.10. On broadly speaking, the GUI consists of two set of the programs. The initialization and then the device control and data acquisition programs.

3.2.2.1 GUI initialization

The GUI initialization involves establishing the connection with the board via USB communication protocol. The GUI will send a pre-defined command “I” the PSoC electrochemical sensing board and it will wait for the handshake signal from it. The PSoC electrochemical sensing board on receiving the command “I” will return with the USB setup string which will be used by the GUI to set the connection button with connected string in green color to indicate the connection is established. If the connection establishment is resulted in fail due to some reason, then the indicator button is set to red color and with the string “unable to connect”.

On establishing the communication, the GUI will then send the individual voltammetric sensing technique lookup table commands and electrode settings, the DAC source settings and wait for the completion response from the board. Once this established the GUI will enter the stage where it will wait for the user to select the next operation. The other voltage or current 64

Figure 3.11 GUI initialization, control, and data acquisition flowchart. 65

settings or running the experiment are the next set up of commands. This programming flow of the GUI is shown in the first flowchart which is also called as GUI initialization flowchart of Figure 3.11.

3.2.2.2 GUI device control and data Acquisition:

In this section of GUI functions, based on the user selected electrochemical sensing technique, on selecting “Run”, a command identifier for the techniques and the sensor count is sent to the sensing system board. The board on receiving the command will provide the respective voltage response to the electrode and will return the completion message.

On receiving the completion message the GUI will then send another command to continuously receive the data point for the electrodes. These read values are used to plot the data and on user request these points are exported to CSV data file. While running these commands any error occurred will be handled from the python exception handling side. 66

3.2.2.3. Finished Application

Figure 3.12 PSoC-Stat Graphical User Interface

The graphical user interface (GUI) provided by the PSoC-Stat [48] is shown in the figure

3.12. The User Interface provide measuring capabilities for the cyclic voltammetry, amperometry and anode stripping voltammetry.

The user interface has been modified with new windows for the PSoC electrochemical system to include the added electrochemical technique measurements. New windows for the square wave voltammetry, Linear sweep voltammetry and Chrono amperometry are added.

Functional modification to run each electrochemical sensing techniques are added. The

Application with added windows is shown in figure 3.13.

Figure 3.13. Updated GUI with SWV, LSV and Chrono Amperometry techniques.

3.3. Test Setup and Result

To test the board with the electrochemical techniques we used the dummy cell test setup shown in the Figure 3.14. The customized sensor board is placed in its case to isolate it from any other electrical contact.

In the experiment we used the a 50K Potentiostat dummy cell [47] described in Figure

3.15. The dummy cell consists of the 3 terminals, one for each of WE, CE, and RE. These terminals connected to their respective slot. The board USB is connected to the computer via a USB cable to control the device through the graphical user Interface. Once the board is connected, on stating the GUI, connection is established between the board and the GUI via USB communication protocol. 68

Figure 3.14. PCB board electronic measurement using dummy cell.

Figure 3.15. Potentiostat 50K Dummy Cell

To compare the performance of our PCB, we performed cyclic voltammetry electrically with commercial sensor board using the Potentiostat 50k Dummy Cell. The PSoC-Stat cyclic voltammetry performed on 50K Potentiostat Dummy cell[47] run from 900 mV to -900 mV with a scan of 10mV/s.

The Dummy cell consists of 50k resistor connected between the counter and reference electrode. The working electrode connected to the other side of the reference electrode. The

Dummy cell will produce current at working electrode proportional to the supplied ADC voltage when connected to the device.

The experimental result produced current between the Working electrode (WE) and

Counter electrode (CE) in the range of -18uA to +18uA. The resistance calculated using the applied voltage and measured current is matched with the resistor connected between counter and reference electrode.

3.3.1 Cyclic Voltammetry

The Potentiostat dummy cell experiment is performed on cyclic voltammetry with the voltage range 900mv to -900mv which produced a current between the working electrode and the counter electrode in the range of 18uA to 18uA. The result of the experiment is interpreted using the executable file.

The Figure 3.16. shows the electronic measurement performed on the bord using dummy cell. The x-axis consists of the ADC voltage applied, the y-axis contains the resultant current measured across the WE and the RE.

Figure 3.16. PCB board electronic measurement plot for CV.

Table 3.2. sample of CV response with dummy cell.

Voltage(mv) current(uA) Resistance (KΩ)

-896 -17.7774 50.4011 -880 -17.2576 50.99208 -864 -17.3096 49.91461 -848 -16.8937 50.19618 -832 -16.5299 50.33318 -816 -16.166 50.47635 -800 -16.166 49.48661 -784 -15.5422 50.44324 -768 -15.3343 50.08381 -752 -14.7625 50.93985

The resultant current of both the PSoC-Stat and the PCB board generated with respect to the provided ADC voltage. The dummy cell resistance is calculate using the Experimental data listed in the table 3.2. The average resistance measured for the board is 50.326 KΩ. which is almost in agreement with the dummy cell resistance 50 KΩ.

3.3.2 Square wave Voltammetry

For the Square wave voltammetry, a square wave pulse signal is applied between the working electrode and the reference electrode. Resultant current is measured between the working electrode and counter electrode.

The dummy cell experiment is performed on square wave voltammetry with the voltage range pulse generated in the range of -900mv to 900mv over the default DAC voltage(0V) which produced a current between the working electrode and the counter electrode in the range of -

12uA to 12uA. The result of the experiment is interpreted using the GUI.

Figure 3.17. Commercial sensor board electronic measurement plot for SWV.

The Figure 3.17 shows the electronic measurement performed on the board using the dummy cell. The x-axis consists of the time duration, the y-axis contains the current measured across the WE and CE.

Table 3.3. sample of SWV response with dummy cell.

Voltage(mv) PSoC 5LP current(uA)

-0.585282306 -11.70564611 -0.577714 -11.55428 -0.590327843 -11.80655686 -0.582759537 -11.65519074 -0.570145694 -11.40291389 -0.587805074 -11.75610149 -0.585282306 -11.70564611 -0.562577389 -11.25154777 -0.577714 -11.55428 -0.590327843 -11.80655686

3.3.3. Linear Sweep Voltammetry

The Potentiostat dummy cell experiment is performed on Linear sweep voltammetry with the voltage range 900mv to -900mv which produced a current between the working electrode and the counter electrode in the range of 18uA to 18uA. The electrical measurement is performed the result of the experiment is interpreted using the GUI. The Figure 3.18 shows the electronic measurement performed on the commercial sensor board using the dummy cell. The x-axis 73 consists of the ADC voltage applied, the y-axis contains the current measured across the WE and

RE.

Figure 3.18. PCB board electronic measurement plot for LSV.

Table 3.4. sample of LSV response with dummy cell.

Voltage(mv) PSoC 5LP Computed current(uA) Resistance (KΩ) -890 -17.2065 51.7246 -889 -17.8644 49.7637 -888 -17.6114 50.4218 -887 -17.409 50.9506 -886 -17.4596 50.7457 -885 -17.7632 49.8221 -884 -17.4596 50.6311 -883 -17.3078 51.0174 -882 -17.5608 50.225 -881 -17.409 50.6060 74

The resultant current of the PCB board generated with respect to the provided ADC voltage. The Comparison of both the plot is shown in Table 3.4. Response obtained are almost identical indicates both the boards are producing same characteristics average current

50.5908Kohm.

3.3. 4. Amperometry

The Potentiostat dummy cell experiment is performed on amperometry with the supply voltage set to 500mv, the circuit produced a constant current of 10mv as shown in the Figure 3.21.

The result of the experiment is interpreted using the executable file.

The Figure 3.21. shows the electronic measurement performed on the bord using dummy cell. The x-axis consists of the time duration in seconds, the y-axis contains the resultant current measured.

Figure 3.19. PCB board electronic measurement plot for amperometry.

Table 3.5. sample of Amperometric response with dummy cell.

Time(sec) Current Resistance of Voltage computed from Measured (uA) dummy cell (KΩ) the result (mv) 0.001 10.03683 50 0.501842 0.002 10.34098 50 0.517049 0.003 10.08753 50 0.504376 0.004 9.986143 50 0.499307 0.005 10.08753 50 0.504376 0.006 10.13822 50 0.506911 0.007 10.29029 50 0.514514 0.008 10.49305 50 0.524653 0.009 10.08753 50 0.504376 0.01 10.49305 50 0.524653

The resultant current of the PCB board generated with respect to the provided ADC voltage. The voltage calculated using the measured current is listed in the table 3.5. The average current measured for the board is 10.23uA for the supply voltage of 500mV. which is almost in agreement with the computed value for the dummy cell resistance 50 KΩ and the supplied voltage

500mv.

3.3.5 Anode Stripping Voltammetry

The Potentiostat dummy cell experiment is performed on anode stripping voltammetry with the voltage range 900mv to -900mv which produced a current between the working electrode and the counter electrode in the range of -18uA to 18uA. The result of the experiment is interpreted using the executable file.

The Anode stripping voltammetry consists of two parts. First, the calibration of the circuit.

The Figure 3.22. shows the initial calibration performed on the board though GUI. Once the calibration is complete the second step, cyclic voltammetry is performed with dummy cell. The x- axis consists of the ADC voltage applied, the y-axis contains the resultant current measured across the WE and the RE.

The resultant current of the board generated with respect to the provided ADC voltage.

The dummy cell resistance is calculated using the Experimental data listed in the table 3.6. The average resistance measured for the board is 50.716 KΩ. which is almost in agreement with the dummy cell resistance 50 KΩ. 77

Figure 3.20. anode stripping voltammetry dummy cell test plot.

Table 3.6. sample of ASV response with dummy cell.

Voltage(mv) current(uA) Computed Resistance (K-Ohm) -896 -18.31500134 48.92164533 -880 -17.50772856 50.26351632 -864 -17.45727401 49.4922632 -848 -17.05363762 49.72546146 -832 -16.65000122 49.9699663 -816 -16.34727393 49.91657959 -800 -16.09500118 49.70487364 -784 -15.79227389 49.64452907 -768 -15.69136479 48.94411738 -752 -15.03545565 50.01511212

3.3.6. Chrono Amperometry

To perform chronoamperometry we generated two types pulse signal and checked the response with the Potentiostat dummy cell with 50K resistance.

The first pulse generated was with voltage range 900mv to -900mv which produced a current between the working electrode and the counter electrode in the range of -18uA to 18uA.

The result of the experiment is interpreted using the executable file.

The Figure 3.23. shows the result for +900mv to -900mv pulse. The test performed on the board through GUI. The x-axis consists of the time duration in seconds, the y-axis contains the resultant current measured across the WE and the RE.

Figure 3.21. chrono amperometry result plot for ±900mV

The same experiment is performed with the pulse generated from +900mv to 0. During the first half of the duration the pulse value is held at +900mv and during the remaining half, it 79 was held at 0v. The result is shown in the Figure 3.24. and the sample of the experimental data is provided in the table 3.7 and 3.8.

Figure 3.22. chrono amperometry result plot for +900mV to 0V

Table 3.7. chronoamperometry result with dummy cell for pulse ±900mV.

Time(sec) Current(uA) Computed voltage (mV) 1 17.95603 897.8014 2 17.69504 884.7519 3 17.85163 892.5816 4 17.69504 884.7519 5 18.00823 900.4113 6 17.85163 892.5816 7 17.59064 879.5322 8 17.79943 889.9717 9 17.53845 876.9223 10 17.85163 892.5816 80

The resultant current of the board generated with respect to the provided ADC voltage.

The pulse voltage is calculated suing the dummy cell resistance 50 KΩ and the read current value was ±900mV as expected.

Table 3.8. chronoamperometry result with dummy cell for pulse +900mV to 0V.

Time(sec) Current(uA) Computed Voltage (mV) 54 17.23575 0.861787 55 17.9066 0.89533 56 17.75179 0.887589 57 17.9066 0.89533 58 17.64858 0.882429 59 17.75179 0.887589 60 -0.15481 -0.00774 61 -0.15481 -0.00774 62 -0.0516 -0.00258 63 0.051604 0.00258

The table 3.8 shows the resultant current of the board generated with respect to the provided +900mv to 0V pulse signal. The pulse voltage is calculated suing the dummy cell resistance 50 KΩ and the read current value was ±900mV as expected. 81

Chapter 4.

Conclusion

In this work, a Portable Electrochemical sensing system from hardware to software for voltammetric sensing mechanism is proposed. The board is designed to work with voltage range

± 2V and current ± 0.1 mA range, respectively. The electrochemical sensing techniques included are cyclic voltammetry, anode stripping voltammetry, amperometry, linear sweep voltammetry, square wave voltammetry and chrono amperometry. The system is developed in 3 stages. They are hardware design, firmware design and graphical user interface design.

In the hardware design, the PCB board is designed for the typical electroanalytical specification, i.e. the voltage range within ± 2V in as excess of this results in electrolysis of water, making larger voltages less useful in aqueous solutions and current range ± 0.1 mA as have mostly been designed for analytical chemistry purposes. We used 3 commercial multiplexers to provide eight sensors measurement at a time which is not implemented in any of the existing opensource potentiostats. We used PSoC MCU which includes most of the analog components helps in reducing the size of the board significantly to provide portability. The MicroUSB for the wired communication protocol.

In the firmware design, the 3 electrode potentiostat is designed using the PSoC 5LP

Internal analog components such as TIA, ADC and DAC and the amplifier. This helped in reducing the size but also has its disadvantage in not able to reduce the noise significantly compared to the potentiostats designed using the discrete analog components(Opamp and TIA). 82

Finally, the graphical user interface is designed and to control the board using USB communication with opensource python 2.7 version programming language. To control the systems interfacing with the computers as well as to display the obtained data, a graphical user interface is developed.

We performed experiments on PSoC based electrochemical system. The Potentiostat dummy cell array tests was performed for the aqueous phase detection and test results showed the linear response, which is important in electrochemical sensing system.

The existing papers on electrochemical sensor implementation includes some of main voltammetric techniques. In our board, most of the voltammetric techniques are included. The sensing system was developed with programmable system on chip which eliminates the requirement of any of the external analog component for the potentiostat implementation. This

Significantly reduced cost factors and made us to reduce the board size to 50mmX40mm. This helps to achieve the portability and cost friendly (MCU and MUX).

For future work, it is intended to include other electrochemical sensing mechanisms such as Potentiometry, Conductometry, Electrochemical Impedance spectroscopy to form a more versatile, compact, cheaper, and minimally invasive solution to existing methods of commercially available universal electrochemical sensing platform. The development of an android applications to provide both GUI and to control and collect response in both wired and wireless communication protocols.

References

[1] Chapter 1 - Molecularly Imprinted Electrochemical Sensors: Past, Present, and Future Author

links open overlay panel, Daniel Antuña-Jiménez, GorettiDíaz-Díaz, M. CarmenBlanco-

López, M. JesúsLobo-Castañón, Arturo J.Miranda-Ordieres, Paulino Tuñón-Blanco

[2] Chapter 37, Voltammetric Techniques, Samuel P. Kounaves Tufts University Department of

Chemistry

[3]. Skoog DA, Holler FJ, Crouch SR. Principles of Instrumental Analysis. 7 editions. San

Francisco, CA: Brooks Cole; 2017.

[4]. Bard AJ, Faulkner LR. Electrochemical Methods: Fundamentals and Applications. 2

editions. New York: Wiley; 2000.

[5]. Kwakye S, Baeumner A. An embedded system for portable electrochemical detection. Sens

Actuators

B Chem. 2007; 123: 336±343. https://doi.org/10.1016/j.snb.2006.08.032

[6]. Nemiroski A, Christodouleas DC, Hennek JW, Kumar AA, Maxwell EJ, FernaÂndez-Abedul

MT, et al. Universal mobile electrochemical detector designed for use in resource-limited

applications. Proc Natl Acad Sci. 2014; 111: 11984±11989.

https://doi.org/10.1073/pnas.1405679111 PMID: 25092346

[7]. Huang CY, Lee MH, Wu ZH, Tseng HY, Huang YC, Liu BD, et al. A Portable Potentiostat

with Molecularly Imprinted Polymeric Electrode for Dopamine Sensing. 2009 IEEE

Circuits and Systems International Conference on Testing and Diagnosis. 2009. pp. 1±4.

[8]. Dryden MDM, Wheeler AR. DStat: A Versatile, Open-Source Potentiostat for

Electroanalysis and Integration. PLOS ONE. 2015; 10: e0140349.

https://doi.org/10.1371/journal.pone.0140349 PMID: 26510100. 84

[7]. Beach RD, Conlan RW, Godwin MC, Moussy F. Towards a miniature implantable in vivo

telemetry monitoring system dynamically configurable as a potentiostat or galvanostat for

two- and three-electrode biosensors. IEEE Trans Instrum Meas. 2005; 54: 61±72.

https://doi.org/10.1109/TIM.2004.839757

[8]. Gopinath AV, Russell D. An Inexpensive Field-Portable Programmable Potentiostat. Chem

Educ. 2005;10: 1±6.

[9]. Sun A, Venkatesh AG, Hall DA. A Multi-Technique Reconfigurable Electrochemical

Biosensor: Enabling Personal Health Monitoring in Mobile Devices. IEEE Trans Biomed

Circuits Syst. 2016; 10: 945±954. https://doi.org/10.1109/TBCAS.2016.2586504 PMID:

28113176

[10]. Rowe AA, Bonham AJ, White RJ, Zimmer MP, Yadgar RJ, Hobza TM, et al. CheapStat: An

Open-Source, ªDo-It-Yourselfº Potentiostat for Analytical and Educational Applications.

PLOS ONE. 2011; 6: e23783. https://doi.org/10.1371/journal.pone.0023783 PMID:

21931613

[11]. Meloni GN. Building a Microcontroller Based Potentiostat: A Inexpensive and Versatile

Platform for Teaching Electrochemistry and Instrumentation. J Chem Educ. 2016; 93:

1320±1322. https://doi.org/10.1021/acs.jchemed.5b00961

[12]. Sun A, Wambach T, Venkatesh AG, Hall DA. A low-cost smartphone-based electrochemical

biosensor for point-of-care diagnostics. 2014 IEEE Biomedical Circuits and Systems

Conference (BioCAS) Proceedings. 2014. pp. 312±315.

[13]. Ainla A, Mousavi MPS, Tsaloglou M-N, Redston J, Bell JG, FernaÂndez-Abedul MT, et al.

Open-Source Potentiostat for Wireless Electrochemical Detection with Smartphones. 85

Anal Chem. 2018; 90: 6240±6246. https://doi.org/10.1021/acs.analchem.8b00850 PMID:

29658268

[14] PSoC-Stat: A single chip open source potentiostat based on a Programmable System on a

Chip Prattana Lopin1, Kyle V. Lopin2.

[15] Dictionary of Energy (Second Edition) 2015, Pages 247-273 Dictionary of Energy G Author

links open overlay panel, https://doi.org/10.1016/B978-0-08-096811-7.50007-X

[16] https://wiki.tcl-lang.org/page/tkinter.Notebook ( Cited on 05072020)

[17] Atkins, P. de Paula, J. Physical Chemistry for the Life Sciences. pg 209-225. 2006. Oxford

University Press. New York.

[18] Zumdahl, S. Zumdahl, S. Chemistry. pg 215-220. 2007. Houghton Mifflin Company. New

Jersey.

[19] Petrucci, Ralph H. General Chemistry Principles & Modern Applications. Pearson Prentice

Hall. New Jersey

[20] Jones, Atkins. Chemistry Molecules, Matter, and Change. W. Freeman and Company, New

York.

[21] Handbook of Electrochemistry 2007, Pages 3-29 https://doi.org/10.1016/B978-044451958-

0.50002-1.

[22] Advances in Inorganic Chemistry Volume 70, 2017, Pages 1-

61https://doi.org/10.1016/bs.adioch.2017.02.004.

[23] Petrucci, Harwood, Herring, and Madura. General Chemistry: Principles and Modern

Applications: Ninth Edition. New Jersey: Pearson, 2007.

[24] Professor Delmar Larsen. Lecture 2, 3, and 6. Spring 2010

[25] Rieger, Philip. Electrochemistry. 2, Illustrated. Springer Us, 1994. 112-113. Print. 86

[26] Hamann, Carl, Andrew Hamnett, and Wolf Vielstich. Electrochemistry. 2, Illustrated. Vch

Verlagsgesellschaft Mbh, 2007. 82. Print.

[27]https://chem.libretexts.org/Bookshelves/Analytical_Chemistry/Supplemental_Modules_(Ana

lytical_Chemistry)/Electrochemistry/Voltaic_Cells/Electrochemical_Cell_Conventions

(cited on 05042020).

[28] B. R. Eggins, Ed., Analytical Techniques in the Sciences: Chemical Sensors and

Biosensors. 2007.

[29] E. Wilkins and P. Atanasov, “Glucose monitoring: state of the art and future possibilities,”

Med Eng Phys, vol. 18, no. 4, pp. 273–288, Jun. 1996.

[30] M. M. Ahmadi, A Wireless Implantable Microsystem for Continuous Blood Glucose

Monitoring. University of Calgary (Canada), 2007.

[31] S. Hwang, Integrated Cmos Microsystems for Electrochemical Sensing. BiblioBazaar, 2011.

[32] Handbook of Electrochemistry 2007, Pages 3-29 https://doi.org/10.1016/B978-044451958-

0.50002-1 MadalinaCiobanu, Jeremy P.Wilburn, Morgan L.Krim, David E.Cliffel.

[33] Intuitive Analog Circuit Design 2014, Pages 53-86 https://doi.org/10.1016/B978-0-12-

405866-8.00003-6 Marc T.ThompsonPh.D.

[34] Fuel Cells and Hydrogen from Fundamentals to Applied Research 2018, Pages 15-40.

https://doi.org/10.1016/B978-0-12-811459-9.00002-5 UweReimer, Werner Lehnert,

Yaovi Holade, Boniface Kokoh.

[35] https://www.palmsens.com/anodic-stripping-voltammetry/ (cited on 05042020).

[36] https://www.ceb.cam.ac.uk/research/groups/rg-eme/Edu/linear-sweep-and-cyclic-

voltametry-the-principles (cited on 05042020). 87

[37] Cheng, Shaoan; Xing, Defeng; Call, Douglas F; Logan, Bruce E. (2009). "Direct Biological

Conversion of Electrical Current into Methane by Electromethanogenesis". Environ. Sci.

Technol. 43: 3953–3958. Bibcode:2009EnST...43.3953C. doi:10.1021/es803531g. PMID

19544913.

[38] https://www.gamry.com/application-notes/physechem/square-wave-voltammetry/ (Cited on

05042020)

[39] Cottrell, F. G. Residual current in galvanic polarization regarded as a diffusion problem. Z.

Phys. Chem., 1903, 42, 385–431

[40] Materials Science and Applications in Sensors, Electronics and Photonics Woodhead

Publishing Series in Electronic and Optical Materials 2012, Pages 366-409

[41] A. J. Bard and L. R. Faulkner, Electrochemical Methods: Fundamentals and Applications.

Wiley, 2001.

[42] Bard, Allen J. and Faulkner, Larry R. Electrochemical Methods: Fundamentals and

Applications. John Wiley and Sons, New Jersey, 2001.

[43] Heineman, William R. and Kissinger, Peter T. Laboratory Techniques in Electroanalytical

Chemistry. Dekker, New York, 1996.

[44] Gamry Instruments. Application Notes: Potentiostat Primer.

http://www.gamry.com/App_Notes‐/Potentiostat_Primer.htm.

[45] https://www.sciencedirect.com/topics/engineering/potentiostat (cited on 05042020).

[46] R H Dahm & R J Latham (1993) The Potentiostat and its Applications, Transactions of the

IMF, 71:2, 77-79, DOI: 10.1080/00202967.1993.11870993.

[47] https://www.stinstruments.com/electrochemistry/potentiostat-galvanostat-eis/#why (cited on

05042020). 88

[48] Ainla A, Mousavi MPS, Tsaloglou M-N, Redston J, Bell JG, FernaÂndez-Abedul MT, et al.

Open-Source Potentiostat for Wireless Electrochemical Detection with Smartphones.

Anal Chem. 2018; 90: 6240±6246. https://doi.org/10.1021/acs.analchem.8b00850 PMID:

29658268

[49] Nemiroski A, Christodouleas DC, Hennek JW, Kumar AA, Maxwell EJ, FernaÂndez-

Abedul MT, et al. Universal mobile electrochemical detector designed for use in

resource-limited applications. Proc Natl Acad Sci. 2014; 111: 11984±11989.

https://doi.org/10.1073/pnas.1405679111 PMID: 25092346.

[50] Dryden MDM, Wheeler AR. DStat: A Versatile, Open-Source Potentiostat for

Electroanalysis and Integration. PLOS ONE. 2015; 10: e0140349.

https://doi.org/10.1371/journal.pone.0140349 PMID: 26510100

[51] Rowe AA, Bonham AJ, White RJ, Zimmer MP, Yadgar RJ, Hobza TM, et al. CheapStat: An

Open- Source, ªDo-It-Yourselfº Potentiostat for Analytical and Educational Applications.

PLOS ONE. 2011; 6: e23783. https://doi.org/10.1371/journal.pone.0023783 PMID:

21931613.

[52] Kakerow RG, Kappert H, Spiegel E, Manoli Y. Low-power Single-chip CMOS Potentiostat.

The 8th International Conference on Solid-State Sensors and Actuators, 1995 and

Eurosensors IX. Transducers `95. 1995. pp. 142±145.

[53] Kimura M, Fukushima H, Sagawa Y, Setsu K, Hara H, Inoue S. An Integrated Potentiostat

With an Electrochemical Cell Using Thin-Film Transistors. IEEE Trans Electron Devices.

2009; 56: 2114±2119. https://doi.org/10.1109/TED.2009.2026120. 89

[54] Ayers S, Gillis KD, Lindau M, Minch BA. Design of a CMOS Potentiostat Circuit for

Electrochemical Detector Arrays. IEEE Trans Circuits Syst Regul Pap. 2007; 54:

736±744. https://doi.org/10.1109/ TCSI.2006.888777 PMID: 20514150.

[55]https://eng.libretexts.org/Bookshelves/Materials_Science/Supplemental_Modules_(Materials

_Science)/Insulators/Electrochemical_Impedance_Spectroscopy. (cited on 05082020)

[56] https://www.gamry.com/application-notes/EIS/basics-of-electrochemical-impedance-

spectroscopy. (cited on 05082020)

[57]https://eng.libretexts.org/Bookshelves/Materials_Science/Supplemental_Modules_(Materials

_Science)/Insulators/Electrochemical_Impedance_Spectroscopy. (cited on 05082020)

[58]https://chem.libretexts.org/Bookshelves/Ancillary_Materials/Laboratory_Experiments/Wet_

Lab_Experiments/General_Chemistry_Labs/General_Chemistry_Labs/Complexometric_

Calcium_Determination_(Experiment). (cited on 05082020)

[59] Pharmaceutical Analysis by P. D. Chaithanya Sudha, Chapter 7, Precipitation Titrations.

[60]https://www.globalspec.com/learnmore/sensors_transducers_detectors/electrical_electromag

netic_sensing/potentiostats_galvanostats (cited on 05082020)

[61] https://www.palmsens.com/galvanostat (cited on 05082020)

[62] https://www.palmsens.com/software/multitrace/ (cited on 05082020)

[63] https://byjus.com/jee/redox-reactions/ (cited on 05082020)

[64] https://www.chemicool.com/definition/potentiometry.html (cited on 05082020)