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

1. 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 Research Dublin City University - Ireland • 1 Introduction • Much 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. • 2 Objectives • To demonstrate the capability of doped photo-patternable sol-gel glass for sensor applications. • To investigate the tunability of such sensor systems • To 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. • 3 Photosensitive Sol-Gel Preparation • Principles: 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 Photoinitiator Step 1 Mask Photosensitive layer Step 2 Substrate MAPTMS UV light IPA wash Step 3 UV Substrate Photopatterning 4 Doped Materials: Oxygen Sensing • The 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 Tailoring the microstructure Basic Recipe MAPTMS / Zirconium propoxide TEOS / methacrylic acid Ru tris diphenyl phenanthroline water acid / base catalyst (cf. table) Stern-Volmer plots Blue LED Sensor Spot Waveguide 200 mm Detector Array • 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 Photopatterned array of doped sensor spots Average ridge thickness of 14.5m The fluorescence is captured in each waveguide and can be observed at the channel output. • 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. 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 Silicon substrate UV-cured sol-gel ridges (50 mm width) PDMS drop PDMS micro channels