This thesis presents the development of a refractometric sensor based onquantum dot-embedded polystyrene microspheres. The technique uses opticalresonances within a microsphere, known as Whispering-Gallery Modes (WGMs), whichproduce narrow spectral peaks. The basic theory of WGMs is reviewed and specificallydiscussed for biosensing application.The spectral shifts of WGM peaks are sensitive to changes in the local refractiveindex. In the experiments, two-photon excited luminescence from the quantum dotscouples into several WGMs within the microresonator. By optimizing the detection area,the spectral visibility of the WGMs is improved. The spectral shifts are measured as thesurrounding index of refraction changes. The experimental sensitivity is about five timesgreater than that predicted by Mie theory.The sensor element is based on commercially available dielectric microsphereswith a diameter about 10 ?m. Thus, the technique is more economic and suitable forsensing applications, compared to microspheres of 100 ?m in size which can only bemade in the laboratory.
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