1.  Sol-gel grating coupler fabrication by solvent assisted micromoulding (SAMIM).  Comparison of grating couplers fabricated by SAMIM with those fabricated using the conventional embossing procedure.  Sol-gel ridge fabrication by micromoulding in capillaries (MIMIC).  Deposition of an array of sensor spots using a PDMS stamp. 3 Fabrication of PDMS grating  Liquid PDMS base and curing agent mixed in 10:1 weight ratio and cast onto master.  Cured @ 70°C for 1hr.  PDMS stamp removed from master.  Identical fabrication process for PDMS sol- gel stamp. Applications of soft lithography in the optical sensing domain C. S. Burke, H. McEvoy, B. D. MacCraith, C. McDonagh School of Physical Sciences/N.C.S.R., Dublin City University, Dublin 9, Ireland 8 Profilometer map of sol-gel ridge formed by MIMIC 7 Sol-gel ridge fabrication by MIMIC  PDMS mould with recessed channel placed on substrate.  Drop of sol placed at entrance to mould.  Sol wicks through channel by capillary action.  Sol is cured and mould is removed. 9 Deposition of an array of oxygen sensing spots by “stamping”  MTEOS-derived sol doped with Ru(dpp) 3.  PDMS stamp consisting of raised cylindrical “poles” (1mm radius).  Stamp dipped into sol and brought into contact with glass slide, then removed.  Spots cured @ 70°C for 17hrs.. 1 Introduction  Soft lithography is a set of patterning techniques employing a poly(dimethylsiloxane) (PDMS) stamp or mould as a patterning element.  PDMS (“silicone rubber”), is elastomeric, making the patterning of non-planar surfaces possible.  A range of examples of the application of these techniques to optical sensing is presented here. 2 Objectives 10 CCD image of fluorescence from array of sensor spots.  Array of sensor spots patterned with PDMS stamp.  Note fluorescence quenching by O 2 stream flowing on the right. 11 Conclusions  Soft lithographic techniques have been used to fabricate sol-gel grating couplers, ridges and an array of sensing spots.  Straightforward implementation of these techniques and the versatility of a PDMS patterning element have been demonstrated.  These properties and the quality of the finished product ensure a definite role for soft lithography in the future of optical sensor fabrication. 12 Future applications  Fabrication of microfluidic systems in PDMS for use in flow injection analysis.  Tailoring the surface properties of a substrate through microcontact printing of self-assembled monolayers on its surface - applications in chemical and biological assays. 4 Sol-gel grating coupler fabrication by SAMIM  PDMS grating “inked” with methanol and pressed onto sol-gel layer.  Cured @ room temperature for 24 hours.  PDMS master peeled off. 5 Comparison of Embossing and SAMIM techniques SAMIM  Requires only low pressures for effective grating fabrication.  Low-cost: can use PDMS masters frequently without deformation of grating characteristics.  PDMS grating fabrication does not damage masters. Embossing  High pressure technique - difficult to regulate.  Degradation of masters due to cleaning procedure - more costly technique. 6 AFM images of gratings fabricated by SAMIM and conventional embossing  Embossed grating.  Period = 1.66mm.  Grating made by SAMIM.  Period = 1.66mm.