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