Optofluidic Bragg grating sensors for chemical detection

This thesis reports the development and potential applications of direct UV written Bragg grating refractometers for detection of chemical analytes. The technique of direct UV writing uses the localised refractive index increase of a photosensitive planar glass layer upon exposure to a tightly focussed UV beam to fabricate a wide range of integrated optical devices. One such device, the Bragg grating, can be used as an optical sensor for changes in refractive index. This thesis reports upon the advancements made to such optical Bragg grating devices towards the development of practical “lab-on-a-chip” microfluidic chemical sensors. This has been achieved through improvements in the fabrication processes and the inclusion of a high-index overlayer, shown to enhance the sensitivity by over an order of magnitude. A novel method for compensating for fluctuations in temperature is introduced; with it demonstrated that this technique can be applied towards the fabrication of an athermal Bragg grating device. The encapsulation of such highly sensitive refractometers within a microfluidic channel allows for realtime measurements of the dynamic composition of a fluid. This technology has been further developed to allow for chemical reactions to both occur, and to be monitored upon the microfluidic sensor surface. It is also demonstrated that using such a functionalised surface allows for chemical specificity to be introduced to these highly sensitive optical sensors, with examples of both copper and sodium selective sensors presented