Synthesis, design and characterization of a distributed feedback grating based non-linear optical chemosensor

Abstract

Current optical chemosensors that operate by a 3R sensing approach - recognize, relay and report -- generate a measurable luminescent signal in the presence of targeted analyte. However, the advancement of chemical sensing into the micro- and nanoscale regimes necessitates the development of new signaling transduction strategies. There are just too few sensing active sites on the micro- and nano-patterned structures to permit species detection, resulting in the compromise of device sensitivity and performance. This thesis work addresses these challenges by adopting a multidisciplinarv approach in combining chemistry, materials and optical sciences in the development of a chemical and biological sensor. The platform with which we have focused our efforts is the Distributed Feedback (DFB) laser cavity. The waveguide materials synthesized are Si and Ti inorganic matrices that were optimized for optical waveguiding by determining the appropriate film thickness, refractive index and film smoothness. Amplified stimulated emission was achieved for a Rhodamine 6G doped SiO₂/TiO₂ slab waveguide. Imprinting of the DFB architecture onto these thin films was successfully achieved using soft lithography techniques and lasing was observed for these devices (Q-factor [approx.] 245). We have explored analyte detection capabilities of these DFB structures by attempting to spoil the gain of the cavity, and by using them as simple diffraction gratings for chemical sensing. Optical sensors are not limited to chemical and biological sensing, and we have applied the 3R approach to understanding the flow and transport properties in microdomains.

(cont.) In the final Chapter, new optical probes for measuring slow flows in microchannels are discussed. This thesis includes a detailed synthetic and photophysical study of reversible caged dye tracers with a [Cp*Ru]⁺ metal head group for the Molecular Tagging Velocimetry technique.