Study Of Optical Micro/Nanofiber Sensors Based On Microfluidic Chips

As a typical waveguide at the micro-nanoscale, micro/nanofiber has shown great advantages for miniaturized and highly sensitive sensors owing to its low loss, strong optical field confinement, large fraction of evanescence field and mechanical flexibility. Typical micro/nanofiber based sensing structures including bi-conical micro/nanofiber, optical gratings, circular cavities, Mach-Zehnder interferometers and functionally coated/doped micro/nanofibers, have been intensively studied for physical, chemical and biological sensing such as refractive index, humidity, temperature, strain, electric current, concentration and so on. Microfluidics manipulate fluidics at micro-scale, providing an excellent platform for low sample cost, high-throughput chemical, biological and medical analysis. But highly sensitive detection is a great challenge for such little volume liquid.In this thesis we propose two detection methods with microchannel parallel or perpendicular to the bi-conical micro/nanofiber. For the parallel one, the bi-conical micro/nanofiber has a long interaction length with the sample in the detection microchannel, and the evanescence field outside the micro/nanofiber excite the fluorescence of the sample, then the fluorescence couple into the micro/nanofiber. Utilizing this structure, we performed low sample cost (nL scale), highly sensitive (the detection limit for R6G and quantum dots are 100 pM and 10 pM, respectively) fluorescence detection. For the perpendicular structure, the detection length between micro/nanofiber and sample is short (-2.5μm), leading to the detection volume down to femto-liter. Utilizing this structure, we performed fluorescence detection of fluorescein down to about 66 molecules, and with a detection sensitivity of 7×10-4 RIU for refractive index sensing. These two integration structures not only make best use of the advantages of micro/nanofibers with low loss, strong optical field confinements and flexibility, but also take advantages of the excellent platform that microfluidic chip provide for low sample cost, high-throughput chemical and biological analysis, leading to miniaturized, robust and highly sensitive sensors.In addition, we propose a localized and rapid heating method for single and stream droplets in a microfluidic chip using the photothermal effect of gold nanorods. This heating method own advantages such as low power cost (< 20 mW), rapid time response (<1s), large temperature range (from room temperature to about 95℃), providing a powerful means for temperature control of chemical, biological and medical applications in droplet microfluidics.