Biosensing with Silicon Photonics

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Biosensing with silicon photonics

Kristinn B. Gylfason KTH Micro and Nanosystems [email protected]

KTH – Micro and Nanosystems

IR cameras Transdermal drug delivery systems Silicon microneedles (www.flir.com) IR bolometer

Photonic ring resonator biosensors

RF filter Micro fuel cell (www.myfuelcell.se)

RF switch

Lab-on-a-Chip Polymer microfluidics Outline

• Why do we need biosensors sensors?

• Biosensor definition.

• The fundamentals of photonic waveguide based biosensing

• Silicon waveguides as biosensors.

• Liquid sample handling for photonic biosensors.

• Reducing temperature sensitivity. Why do we need biosensors?

• When intruded by a disease causing virus or bacterium, the body releases biomolecules called antibodies into the blood. • The antibodies attach selectively to a part of the intruder called the antigen, to label it for attack by the immune system.

• Accurate disease diagnosis requires the measurement of the concentration of these antibodies.

• The concentration is very low (ng/ml), and there are other biomolecules in blood of much higher concentration (mg/ml).

• By fixing an antigen on a biosensor surface, the attachment of antibodies can be measured with high selectivity.

Image from Wikipedia More applications of biosensors

• Medical diagnostics

• Drug development

• Explosives and narcotics detection

• Environmental monitoring

6 Outline

• Why do we need biosensors sensors?

• Biosensor definition.

• The fundamentals of photonic waveguide based biosensing

• Silicon waveguides as biosensors.

• Liquid sample handling for photonic biosensors.

• Reducing temperature sensitivity. What are biosensors?

Some commercial examples:

• In general, biosensors are devices to characterize a chemical quantity: the analyte

Attana QCM: www.attana.com Corning EPIC: www.corning.com • Biosensors can be used to: - Determine analyte concentration - Study the kinetics of chemical reactions of the analyte

Biacore SPR: www.biacore.com Roche Accu-Chek: www.accu-chek.com

8 The formal definition of a biosensor

For example:

1 Analytes: IUPAC definition: [K+] [Antibody] “A biosensor is a self-contained [Virus] integrated device which is [CO2] capable of providing selective Recognition: quantitative analytical DNA Antigen information using a biological recognition element which is in Enzyme direct spatial contact with a Transduction: QCM transducer element.” SPR EC

1 IUPAC: International Union of Pure and Applied chemistry 9 Analytes

• Biosensors can be used to study: - Ions: K+, Cl-, Ca2+, …

- Gasses: CO2, NH3, … - Sugars - Alcohols - Oligonucleotides (short single stranded DNA chains) - Various proteins and peptides: Antibodies, antigens - Viruses - and more …

10 Biological recognition elements

Double stranded DNA • The fundamental idea of biosensing is using the work done by biological evolution to create highly selective biomolecular pairings. • Using one part of the pair as a recognition element allows selective measurement of the other part. • The biological recognition system provides selectivity and translates information from the biochemical domain (often an analyte concentration C) into chemical or physical output. • Biological recognition elements can be: - Oligonucleotides (short single stranded DNA chains) - Enzymes 11 - Antigens/Antibodies …

Biological recognition elements

Double stranded DNA • The biological binding reactions generally work only in water.

• This is a serious limitation for biosensors that are adversely affected by the viscous damping of liquids.

• For example: Resonating micromechanical cantilevers have shown mass detection limits of: - zeptograms (10-21) in vacuum [1] - but nanograms (10-9) in liquid [2]

[1] Y. T. Yang, et al., Nano Letters 6, 583 (2006) [2] T. Braun, et al., Nature Nanotechnology 4, 179 (2009) 12 Transducer elements

• The purpose of the transducer is to transform the output from the recognition system to a form suited for data analysis and storage (usually electrical). • Often the output of the recognition system is a mass change (∆m) or a charge change (∆q). • Most often these quantities are eventually translated to a frequency change (∆f) or a current change (∆i) of an electrical signal. • Complete biosensors can thus be described by their transduction chains. For example: ∆C  ∆q  ∆i or ∆C  ∆m  ∆f

13 Classification of biosensors

Analyte Recognition Transduction Ions Enzymes Electrochemical Dissolved gasses Enzymes Electrochemical Vapors Antibodies Piezoelectric Receptor proteins Optical Substrates Enzymes Electrochemical (molecules upon Membrane receptors Piezoelectric which enzymes Whole cells Optical act) Plant or animal tissue Calorimetric Antibody/Antigen Antigen/Antibody Electrochemical Virus Piezoelectric Optical Surface plasmon Various proteins Receptor proteins Electrochemical Piezoelectric Optical Surface plasmon

14 Outline

• Why do we need biosensors sensors?

• Biosensor definition.

• The fundamentals of photonic waveguide based biosensing

• Silicon waveguides as biosensors.

• Liquid sample handling for photonic biosensors.

• Reducing temperature sensitivity. Interaction of light and matter: Wavelength change (refractive index)

λ 0 Speed of light in vacuum: c Wavelength in vacuum:

λ0 = c/f

λꞌ nw In water light slows down to vꞌ Wavelength in water:

λꞌ = vꞌ/f = λ0/nw

λꞌꞌ ns Wavelength in a biomolecule

solution: λꞌꞌ = λ0/ns < λꞌ

n is the material's refractive index Waveguides for light control, by microfabrication Guided wave propagation

Electric field (Ey) of the light wave in the A-A’ cross-section

Evanescent field Liquid sample ns

Core nc

Bottom nb cladding λ = λ0/neff Effective refractive index of waveguide Evanescent field

neff =f(nb, ns, nc) Evanescent field based biosensing with photonic waveguides

Liquid sample Strength of evanescent field • Cross section along guide

• Electric field of

Anti- Y the propagating bodies light wave Antigens • Biomolecule binding Core  Increased wg. effective Bottom index: cladding

Δλ/λ = Δne/ne Photonic waveguide circuits for Δλ read out

• The transduction chain of a photonic biosensor is:

∆C  ∆m  ∆n  ∆λ Overlapping evanescent fields • We need to read out ∆λ. • Lithography enables fabrication of functional photonic circuits. • The directional coupler permits nearly lossless splitting and combining of light. Directional coupler

Image from: http://www.comsol.com/wave-optics-module Ring resonators for Δλ read out Transmitted light to detector Light in at free space wavelength

λ0

OnOff resonance resonance Transmitted m = 10 mλ /n = 2πR New light 0 e trans- to detector Surface binding mission spectrum Integermλ’0/n ’e = 2πR of ring fixed

λ0 λ0 λ’0 Light in

• Off resonance  Most of light transmitted Directional coupler R=70 µm • On resonance  Light coupled to ring  Transmission minimum

• Surface binding  ne increase Light out  Resonace wavel. increase: Δλ0 Ring resonator Ring resonator sensing fundamentals

Input Pass

Quality factor Volume Surface sensitivity sensitivity

= = =

The Q limits휆 the Resonance푉 wavelength휕휆 Resonance푆 wavelength휕휆 푄achievable shift per푆 refractive index unit shift for surface푆 density change sensor resolution.Δ휆 change of top 휕cladding.푛 of surface coating.휕휎 An example ring resonator biosensor chip

Biosensor cartridge

Ring resonator transducer

70 µm Antigen-Antibody pair 1 µm

Light in Optical sensor array

750 µm Light out

24 C. F. Carlborg, K. B. Gylfason, et al., "A packaged optical slot-waveguide ring resonator sensor array for multiplex label-free assays in labs-on-chips," Lab Chip, vol. 10, pp. 281-290, Feb. 2010. Layout of sensor array optical circuit

Grating coupling

Waveguide

Ring-resonator

25 Waveguide cross-section

A-A’ Strip waveguide Slot waveguide Sample EvanescentΔnΔ waveσsp n s ΔσpΔλ Y Y Y Y Y Y Y Y Y Y

SurfaceY sensing Y Y Y nc Y Y

ΔnsΔλ Waveguide IncreasedWaveguide light-analyte nb interaction Bottom cladding Volume sensing

Time average of optical power through cross section (TE, λ=1310 nm) (TM, λ=1310 nm) Volume refractive index measurement of ethanol and methanol dilutions

Limit of detection: noise level / sensitivity = 5 x 10-6 RIU

State of the art refractometers: 10-8 RIU Selective surface bio-coating by spotting Spotting robot Chip spotted Spotts with BSA Spotting jets

Biological recognition components

Not spotted Spotted Bus Ring

Precipitated salt crystals on surface Sensor M5 Sensor M6 Coupler

28 Biosensing

(the antibody)

(the antigen)

C. F. Carlborg, K. B. Gylfason, et al. “A packaged optical slot-waveguide ring resonator sensor array for multiplex label-free assays in labs-on-chips,” Lab on a Chip, vol. 10, pp. 281-290, 2010. Outline

• Why do we need biosensors sensors?

• Biosensor definition.

• The fundamentals of photonic waveguide based biosensing

• Silicon waveguides as biosensors.

• Liquid sample handling for photonic biosensors.

• Reducing temperature sensitivity. Biosensing with silicon waveguides

The high refractive index of silicon waveguides provide two benefits for sensing: 1. Rings can be made very small without reducing Q by bending loss, 2. The evanescent electric field at the silicon surface is very high, yielding high sensitivity for surface sensing. Biosensing with silicon waveguides

Label-free detection limit of a few hundred molecules.

K. De Vos, et al., "Silicon-on-Insulator microring resonator for sensitive and label-free biosensing," Optics Express, vol. 15, no. 12, pp. 7610-7615, 2007. Multiplexing

K. De Vos, et al., "Multiplexed antibody detection with an array of Silicon-on-Insulator microring resonators," Photonics Journal, IEEE, vol. 1, no. 4, pp. 225-235, Oct. 2009. Signal enhancement

M. S. Luchansky, et al., "Sensitive on-chip detection of a protein biomarker in human serum and plasma over an extended dynamic range using silicon photonic microring resonators and sub-micron beads," Lab Chip, vol. 11, pp. 2042-2044, 2011. Outline

• Why do we need biosensors sensors?

• Biosensor definition.

• The fundamentals of photonic waveguide based biosensing

• Silicon waveguides as biosensors.

• Liquid sample handling for photonic biosensors.

• Reducing temperature sensitivity. Challenge: Cost-efficient microfluidic integration

37 Challenge: Cost-efficient microfluidic integration

• Minimize wafer footprint of microfluidics • Bonding compatible with biofunctionalization • Extendable to wafer scale

39 Photolithography OSTE

Bonding to Si Off-Stoichiometric Thiol-Ene (OSTE) polymer technology enables new solutions for Lab-on-a Chip

Compatible with biofunctionalization

Tailor-made mechanical Patternable Injection properties wettability molding

40 OSTE: photolithography

Photolithography enables footprint efficient vias

A-A’

41 OSTE: bonding

Bonding compatible with biofunctionalized surfaces

C.F. Carlborg et al. MicroTAS 2011

42 Fabrication: concept

43 Fabrication: process

BONDING30 s in Butyl acetate 13 s

DEVELOPMENT CURING

44 A biophotonic sensor with microfabricated sample handling system Light Light out 75 µm in

A biophotonic sensor example: Refractive index sensing Refractive index sensitivity

S=50 nm/RIU Carlos

C. Errando-Herranz, K. B. Gylfason, et al., Opt. Express, vol. 21, pp. 21293-21298, Sep. 2013. Outline

• Why do we need biosensors sensors?

• Biosensor definition.

• The fundamentals of photonic waveguide based biosensing

• Silicon waveguides as biosensors.

• Liquid sample handling for photonic biosensors.

• Reducing temperature sensitivity. Temperature sensitivity

• For practical biosensing we need to reach a detection limit of 10-6 RIU. • Water has a thermo optic co-efficient -4 of κH2O = -1.1 × 10 RIU/K.  Waveguide based biosensors normally need temperature control.

(SPR-BIAcore T100) Athermal waveguides

Cross-section Optical power Thermo-optic (TE mode, λ = 1550 nm) coefficients A-A’ n = 1.3 κ = ∂n/∂T n = 3.5 Strip waveguide n = 1.5

Slot waveguide

If we can make  Athermal waveguide 50 K. B. Gylfason, et al. “On-chip temperature compensation in an integrated slot-waveguide ring resonator sensor array,” Optics Express, vol. 18, pp. 3226-3237, 2010. Athermal slot-waveguide design

h = 220 nm

C: WWrailrail ==180 240 nm A nm

C Athermal design

B: Wrail = 215 nm B Zero- contour

A: Wrail = 180 nm 51 Wslot=120 nm Temperature dependence of effective index Calculated with COMSOL Multiphysics® FEM mode solver Evaluation circuit

Mach-Zehnder Interferometer

Slot-waveguide (Si) 150 nm

Albert Lower

Top view cladding (SiO2)

K. B. Gylfason, A. Romero, et al., "Reducing the temperature sensitivity of SOI waveguide-based biosensors,“ Proc. SPIE, vol. 8431, pp. 84 310F-84 310F-15, May 2012. http://dx.doi.org/10.1117/12.922263 Summary

• By fixing a receptor to a photonic sensor surface, antibodies can be measured with high selectivity.

• Biomolecules binding within the evanescent field of a sensing waveguide shorten the wavelength of light in the guide.

• Slot waveguides are good bulk sensors, marginal benefit for surface sensing.

• However, silicon slot waveguides enable athermal photonic biosensors.

• Cost-efficient microfluidic integration on silicon sensors challenging: OSTE

Outlook

• Silicon waveguide based photonic transducers already good enough for many practical applications.

• However, benefits over existing biosensors is not clear enough yet to make an impact.

• Improvements in microfluidics integration (pumping, filtering etc.) necessary to leverage the benefits of CMOS fabrication.

• Unique features for future exploration: - Low absolute mass detection limit. - Spatial resolution by sensor arrays.