HYBRID GLASS AND SOL-GEL STRUCTURES

FOR BIO-CHEMICAL SENSING

Nasuhi YurtEmre Araci

Sergio MendesSeppo Honkanen

Alan KostNasser 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

Modulator Generator

Linear Non-Linear

Intrinsic Extrinsic

Evanescent Field Core

RefractiveAbsorptive

A Linear, guided wave evanescent field absorption based biosensor

DEVICE FUNCTIONALITY

Absorption based sensingSignature 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 indicesWavelength of operation

Single mode structures Less noise in the sensing signal

Core

y

z

E(y) ~ e-ky

Pin

WAVEGUIDE SELECTION

1.35

1.4

1.45

1.5

0.20.4

0.60.8

11.2

1.41.6

1.82

x 10-6

0.05

0.1

0.15

0.2

ns

thickness

Fra

ctio

n o

f Eva

ne

sce

nt W

ave

Fra

cti

on

of

Ev

an

es

ce

nt

Fie

ld

Thickness of the ridge, t Buffer l

ayer index

w

t

Percentage Overlap of Fundamental Mode with Overlayer - 630 nm - BGG31 20 min thermal

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

1.32 1.34 1.36 1.38 1.4 1.42 1.44 1.46 1.48

overlayer index

ove

rlap

1.0 um 1.25 um 1.5 um 2.0 um

Percentage Overlap of Fundamental Mode with Overlayer

Overlayer index

Sol-gel Ion-exchangeSensitive solution

Sol-gel ridge wg

Ion-exchanged Surface wg

Glass buffer & substrate

SiliconSubstrate

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

(NO3)-

Ag+

Na+

Si4+

O2-

Gla

ssS

alt

Mel

t

x Borosilicate GlassSilver Nitrate

(α ~ 0.5)

n(633nm)=1.52Δn=0.062D=0.028 μm2/minT= 300 oCt= 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 AgNO3

Titanium Removal, Dicing, Polishing

UV lightPhotomask

Photoresist

Titanium

Glass

Ti wet etch

Ion-exchange

Furnace Salt Melt

Thermocouple Sample holder

ACHIEVING SINGLE MODE WAVEGUIDES

Single mode Multimode modeλ = 532 nmT = 310 C0

Ag Concentrationcontours

SimulatedGuided modes

Near Field picture of

guided modes

2μm opening20 min

4μm opening30 min

Single modeLimits

Vertically: ~50 minLaterally: ~20 min for 4μm opening

CYTOCHROME-C PROTEIN

λ = 532 nm

λ = 632 nm

A distinct protein extracted from horse heart

pH

-7 b

uff

er

solu

tio

n

So

lid

Gla

ss S

urf

ace

Ionic Interactions

Protein

Adsorbs and forms a monolayer

Cyt-C absorption Spectrum

A close-packed monolayer is 22 pmol/cm2

10μM

WAVEGUIDES IN ACTION

Pin Pout

Corning 0211 Substrate

Plastic Pool

cc

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 integrationfor selective micro pool fabrication

COMPOSITE ION-EXCHANGE AND SOL-GEL SENSING DEVICE

Fiber PinFiber Pout

Corning 0211 Glass Substrate

UV patterned sol-gel micro-pool

Silver Ion-exchange Surface channel waveguide

Adsorbed monolayerOf Cyt-C Molecules

Sol-gel with Tapered edges

pH-7 buffersolution

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 hydrolizewith 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 modeInput Fiber

Multimode fiber

Lock-in AmpComputer

Detector

Pool Sensitive Agents

INITIAL RESULTS

Sensitivity to Red Light. Sensitivity to Green Light.

0.6 dB

Multimode waveguides

Improvements:1. Single mode Waveguides2. Noise reduction in characterization setup3. 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

d=250μm

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