HYBRID GLASS AND SOL-GEL STRUCTURES FOR BIO-CHEMICAL SENSING Nasuhi Yurt Emre Araci Sergio Mendes Seppo Honkanen Alan Kost Nasser Peyghambarian

INTRODUCTION Hybrid glass technology to achieve highly selective, stable, low cost, disposable, integrated optical bio- chemical sensing devices Motivation: Ion-exchange and Sol-gel hybrid integration Planar channel waveguide technology Absorption based sensing

OPTICAL GUIDED-WAVE BIO-CHEMICAL SENSING SCHEMES ModulatorGenerator Linear Non-Linear Intrinsic Extrinsic Evanescent Field Core Refractive Absorptive A Linear, guided wave evanescent field absorption based biosensor

DEVICE FUNCTIONALITY Absorption based sensing Signature recognition of bio- chemical agents using the absorption spectra Planar guided-wave devices Potential on chip, monolithic integration with other passive and active optoelectronic components, stable, robust, compact devices.

GLASS INTEGRATED OPTICS Borosilicate Glass (0211) Excellent transparency Low cost High threshold to optical damage Rigidity Polarization insensitive components Index matching to optical fibers Most bio agents potential of interest λ regimes; From lower visible to deep UV and far infrared

EVANESCENT FIELD SENSING  Stronger evanescent tail stronger sensing signal  Important parameters: Waveguide core thickness core-cladding indices Wavelength of operation  Single mode structures Less noise in the sensing signal Core y z E(y) ~ e -ky P in

WAVEGUIDE SELECTION Fraction of Evanescent Field Thickness of the ridge, t Buffer layer index w t Percentage Overlap of Fundamental Mode with Overlayer Overlayer index Sol-gel Ion-exchange Sensitive solution Sol-gel ridge wg Ion- exchanged Surface wg Glass buffer & substrate Silicon Substrate  Very thin sol-gel waveguides needed for good overlap to the sensing agents  Ion-exchange waveguides can be fabricated very close to the surface Ion-excahnge is the choice for the waveguides Very low-loss waveguides

ION-EXCHANGE PROCESS (NO 3 ) - Ag + Na + Si 4+ O 2- Glass Salt Melt x Borosilicate Glass Silver Nitrate (α ~ 0.5) n(633nm)=1.52 Δn=0.062 D=0.028 μm 2 /min T= 300 o C t= 20 min Diffusion equation

ION-EXCHANGE WAVEGUIDE FABRICATION Process Steps  Cleaning Ti Deposition Photoresist Coating Exposure with UV  Photoresist Development Wet etching of Titanium  Ion Exchange in AgNO 3  Titanium Removal, Dicing, Polishing UV light Photomask Photoresist Titanium Glass Ti wet etch Ion-exchange Furnace Salt Melt Thermocouple Sample holder

ACHIEVING SINGLE MODE WAVEGUIDES Single modeMultimode mode λ = 532 nm T = 310 C 0 Ag Concentration contours Simulated Guided modes Near Field picture of guided modes 2μm opening 20 min 4μm opening 30 min Single mode Limits Vertically: ~50 min Laterally: ~20 min for 4μm opening

CYTOCHROME-C PROTEIN λ = 532 nm λ = 632 nm A distinct protein extracted from horse heart pH-7 buffer solution Solid Glass Surface Ionic Interactions Protein Adsorbs and forms a monolayer Cyt-C absorption Spectrum A close-packed monolayer is 22 pmol/cm 2 10μM

WAVEGUIDES IN ACTION P in P out Corning 0211 Substrate Plastic Pool c c Ion-exchange Surface waveguide Buffer solution Surface adsorbing Cyt-C protein monolayer Top View  Large pools for defining the sensitive interaction region  Inefficient to define the interaction selectivity  Liquid proof gluing needed for stability: causing disturbances  Not suitable for compact, disposable sensing elements Sol-gel and Ion-exchange hybrid integration for selective micro pool fabrication

COMPOSITE ION-EXCHANGE AND SOL-GEL SENSING DEVICE Fiber P in Fiber P out Corning 0211 Glass Substrate UV patterned sol-gel micro-pool Silver Ion-exchange Surface channel waveguide Adsorbed monolayer Of Cyt-C Molecules Sol-gel with Tapered edges pH-7 buffer solution Precise control of the sensing pool region: sizes from micrometers to millimeters Robust, stable, inexpensive, micro-patterned compact structures Tapering edges for adiabatic transition of the optical guided mode One step direct UV patterning: much easier compared to alternatives Potential for simultaneous multiple agents sensing

SOL-GEL FABRICATION In house preparation Methacryloxy propyltrimethoxysilane (MAPTMS) Zirconium(IV)-n-propoxide Photoinitiator (IGRACURE 184) mix and hydrolize with O.1 N HCl UV light Spinned and baked sol-gel Ion-exchange wg Glass substrate Gray scale mask

CHARACTERIZATION SETUP He-Ne (632nm) Green(532nm) Chopper Single mode Input Fiber Multimode fiber Lock-in Amp Computer Detector PoolSensitive Agents

INITIAL RESULTS Sensitivity to Red Light. Sensitivity to Green Light. 0.6 dB Multimode waveguides Improvements: 1.Single mode Waveguides 2.Noise reduction in characterization setup 3.Index matching gel σ σ Δ Δ Limit of detection 3

IMPROVED SIGNAL Only Buffer solution Protein added

CONCLUSIONS  First demonstration of a hybrid Ion-exchange and Solgel sensing structure and its application to the absorption based bio-chemical sensing  Applicable to wide range bio-chemical agents via absorption spectra signature recognition  Broad wavelength operation capability  Potential for simultaneous multiple agents detection using selective micro pool technology

CONTINUING WORK d=250μm 375μm  On chip referencing for improved Signal to Noise Ratio  Multiple armed devices for simultaneous multi-agent sensing  Multi-agent selective sensing regions on single chip  Various planar optical device designs are possible