COPPER-BASED POINT-OF-CARE SENSOR FOR HEAVY METAL DETERMINATION IN PUBLIC HEALTH APPLICATIONS A dissertation submitted to the Graduate School of the University of Cincinnati in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY in the Department of Electrical Engineering and Computing Systems of the College of Engineering and Applied Science 2015 by Xing Pei B.S., Peking University, China, 2009 Committee Chair: Ian Papautsky, Ph.D. ABSTRACT This work describes development of the first copper (Cu)-based sensor for determination of heavy metals, such as zinc (Zn), lead (Pb) and cadmium (Cd). Heavy metals require careful monitoring, yet current methods are too complex for a point-of-care (POC) system. Electrochemistry offers a simple approach to metal determination, but traditional electrodes are difficult or expensive to microfabricate, preventing wide-spread use. The sensor described in this work features a new low-cost electrode material which offers simple fabrication, while maintaining competitive electrochemical performance. The sensors of this work were fabricated by photolithography and electroplating to form the three electrodes used for anodic stripping voltammetry (ASV): a Cu working electrode, a Cu auxiliary electrode, and a Cu/CuCl2 reference electrode. They were demonstrated to be sufficiently stable for at least one electrochemical measurement through the careful examination of each electrode. For the metals of interest, the Cu-based sensors exhibited limit of detection (LOD) of 140 nM (9.0 ppb) for Zn, 21 nM (4.4 ppb) for Pb and 118 nM (13 ppb) for Cd. The sensor was also used to demonstrate measurements in biological (blood, serum) and environmental (surface water) sample matrices. These results demonstrate the advantageous qualities of this POC electrochemical sensor for public health applications, which include a small sample volume (µL-scale), reduced cost, short response time and high accuracy at low concentrations of analyte. ACKNOWLEDGMENTS First, I would like to thank my advisor Dr. Ian Papautsky for his guidance during this work. His attitude, patience, awareness of details in experiments and records, and perspective of the project, set an excellent example as a productive researcher and professor. He showed me constant support and encouragement during my path towards an independent researcher. This invaluable experience will provide energy for the rest of my life. I would like to thank other members of my committee, Dr. William R. Heineman, Dr. Adam Bange, Dr. Chong Ahn and Dr. Fred Beyette. A special thank you to Dr. Heineman for his insights in electrochemistry and suggestions for methodology. His kindness infects all surrounding people. I would like to thank Dr. Bange for his help to validate our results and his ideas to solve problems during research. Dr. Ahn for wonderful courses in microfabrication, his enthusiasm, and insightful questions during the progress of this work. Dr. Beyette for cooperation with this work, and the opportunities to work with people from another area. I would like to thank Ron Flenniken and Jeff Simkins for the cleanroom access and facilities and their hard work and valuable time for device fabrication. And thank you to Dr. Necati Kaval for easy access and professional help of facilities in Department of Chemistry. I would also like to thank all my lab mates from BioMicroSystems Laboratory. Special thanks to Dr. Preetha Jothimuthu, for her mentorship and valuable experience, and Wenjing Kang, for her company and high standard of cleanliness. Thanks to Dr. Woohyuck Choi, Taher Kagalwala, Dr. Li Shen, Michael Ratterman, Josi Herren, Dr. Jian Zhou, Dr. Ananda Banerjee, Nivedita, Xiao Wang, Yuguang Liu, Prithvi Raj Mukherjee and Richard Murdock, for the simple and friendly environment for study and research, and warmness as a group. I would like to thank collaborators from other labs, Dr. Robert Wilson, Dr. Wei Yue, Ram Kumar, Geethanga De Silva and Benjamin Zerhusen from Dr. Heineman and Dr. Beyette’s groups for their efforts in this work. Finally, I would like to thank my friends and family. My host family, John and Cynthia Featherstone, for their help for me to settle down in a foreign country. Thanks to my dojo sister, Zhizhen Wu, for her enterprising and easygoing attitude in work and life. More importantly, my parents and sister on the other side of this planet, whom magically make me feel safe and supportive without too many words. Peace. TABLE OF CONTENTS LIST OF FIGURES ....................................................................................................................... iii LIST OF TABLES ......................................................................................................................... vi LIST OF ABBREVIATIONS ....................................................................................................... vii CHAPTER 1 INTRODUCTION .....................................................................................................1 State of the art in metal determination .................................................................................3 Scope of work ....................................................................................................................10 Chapter summaries.............................................................................................................12 CHAPTER 2 COPPER-BASED ELECTROCHEMICAL SENSOR ...........................................13 Experimental methods .......................................................................................................15 Cu auxiliary electrode ........................................................................................................16 Cu/CuCl2 reference electrode ............................................................................................19 Cu working electrode .........................................................................................................23 Summary ............................................................................................................................26 CHAPTER 3 DETERMINATION OF METALS IN BUFFER ....................................................27 Determination of Zn ...........................................................................................................27 Determination of Pb ...........................................................................................................34 Determination of Cd ..........................................................................................................41 Summary ............................................................................................................................46 CHAPTER 4 DETERMINATION OF MULTIPLE METALS ....................................................47 Zn determination in presence of Pb ...................................................................................48 Pb determination in presence of Zn ...................................................................................51 Pb determination in presence of Cd ...................................................................................52 Cd determination in presence of Pb ...................................................................................54 Summary ............................................................................................................................56 CHAPTER 5 DETERMINATION OF METALS IN REAL WORLD SAMPLES ......................57 Zn in serum ........................................................................................................................58 Pb in blood .........................................................................................................................63 Pb and Cd in surface water ................................................................................................69 i Summary ............................................................................................................................75 CHAPTER 6 CONCLUSIONS .....................................................................................................77 APPENDIX ....................................................................................................................................80 REFERENCES ............................................................................................................................109 ii LIST OF FIGURES Figure Page 1. Illustration of ASV of Pb, Cd and Zn on a solid Cu working electrode (WE). .................. 4 2. (a) Schematic of the electrochemical cell, working electrode (WE), auxiliary electrode (AE), and reference electrode (RE). (b) Photograph of the sensor with a mini-USB potentiostat connection. ................................................................................... 14 3. Fabrication process diagram for Cu-based sensor with Cu/CuCl2 RE. (a) Metal evaporated onto glass slides. (b) Electrode patterned by photolithography and wet etching. (c) Polymer well bonded by plasma discharge. (d) RE formatted by electrodeposition. .............................................................................................................. 15 4. Stability of Cu as an AE. (a) Images of un-oxidized Cu AE, and Cu AEs that have undergone 20 min and 60 min of oxidation. (b) Chronopotentiometry of Pt and Cu AEs under current of 10 µA. The curve for 200 nm Cu AE is an average of four measurements (n = 4), with the inset