Optical Chemical Sensor Systems based on Photosensitive Hybrid Sol-Gel Glass

B.D. MacCraith, S. Aubonnet, H. Barry, C. von Bültzingslöwen, J.-M. Sabattié, C.S. Burke

Optical Sensors Laboratory - National Centre for Sensor ResearchDublin City University - Ireland

Sol-gel solution Concentration of

the catalyst (mol/l)

pH

Sample A 0.1 (HCl) 0.58

Coudray preparation 0.01 (HCl) 0.92

Sample B 0.01 (HCl) 1.64

Sample C 0.01 (NaOH) 6.14

Sample D 0.1 (NaOH) 7.12

Sample E 1 (NaOH) 10.74

Tailoring the microstructure

Basic RecipeMAPTMS / Zirconium propoxide

TEOS / methacrylic acidRu tris diphenyl phenanthroline

water acid / base catalyst (cf. table)

0 20 40 60 80 100

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

2.8

pH=10.74 KSV

=0.0169 pH=7.12 K

SV =0.0137

pH=6.14 KSV

=0.0115 pH=1.64 K

SV =0.0105

pH=0.58 KSV

=0.0097 Coudray K

SV =0.000833

% O2

I0 / I

Stern-Volmer plots

4 Doped Materials: Oxygen SensingThe luminescence of ruthenium poly-pyridyl complexes is

quenched reversibly by oxygen (Dynamic Quenching)

Such complexes (e.g. Ru tris diphenyl phenanthroline) can be excited by blue LEDs and emit in red

Quenching process described by Stern-Volmer equation

I0 / I = 1 + KSV [ O2]

where I0 is the unquenched luminescence intensity

The Stern-Volmer constant Ksv is a direct measure of sensitivity

KSV D, the diffusion coefficient of O2 in the matrix

2 ObjectivesTo demonstrate the capability of doped photo-patternable sol-gel

glass for sensor applications.To investigate the tunability of such sensor systemsTo exploit the photolithographic properties of these materials to

prepare a range of sensor configurations.To demonstrate the usefulness of this system for micro-total-analysis

(Lab-on-a-chip) devices.

1 IntroductionMuch interest in hybrid organic-inorganic sol-gel glasses that can be

photo-patterned by UV irradiation.Principal application is the fabrication of integrated optic devices for

telecommunication applications, e.g. splitters, DWDM’s.These materials have considerable potential for chemical sensing

systems, including optodes (doped materials) and micro-total-analysis (Lab-on-a-chip) devices.

5 Sensor Configurations Photosensitive sol-gel glass can be used to

produce a range of useful sensing configurations, e.g. integrated optic structures and arrays of sensor spots

The fluorescence is captured in each waveguide and can be observed at the channel output.Average ridge thickness of 14.5m

200 m

Photopatterned array of doped sensor spots

DetectorArray

SensorSpot

Waveguide

Blue LED

6 Microsystems (Lab-on-a-chip)Major developments in miniaturised

sensor systems with high levels of integration and functionality, e.g. -TAS (micro-total-analysis systems)

Key -TAS elements include microfluidic channels and patterned surfaces

UV-photolithographic sol-gel materials can be used for rapid prototyping, templating of PDMS (poly-dimethyl siloxane), and patterning of surfaces.

UV-cured sol-gel ridges (50 m width)

Silicon substrate

PDMS micro channels

PDMS drop

7 Conclusions

UV-curable sol-gel materials combine the versatility of the sol-gel process with the capabilities of photolithography.

Tunable doped sensor materials, waveguide sensor structures and sensor arrays can be fabricated with this process.

Future work: micro-optical sensor chips and multi- analyte sensor systems

3 Photosensitive Sol-Gel PreparationPrinciples: Presence of UV curable moiety (MAPTMS -

methacryloxypropyl-trimethoxysilane) enables spatially selective curing of sol-gel matrix.

The Photoinitiator splits into radicals upon UV illumination (Step 1).

The photoinitiator radicals react with the unsaturated groups of MAPTMS (Step 2).

The reaction propagates by radical addition to unsaturated groups of MAPTMS (Step 3).

The non-polymerised MAPTMS is washed away using Isopropanol

CH2

CH3

O

O

Si(OCH3)3O

.

O

OH

O

.OH .UV

.CH3

O

O

Si(OCH3)3

H

CH3

O

O

Si(OCH3)3

CH2

Step 1

Step 2

Step 3

Photoinitiator

MAPTMS

Mask

IPA wash

Substrate

Photosensitive layer

Substrate

UV light

Photopatterning