Research On Biosensing Effects Of Novel Optical Microcavities And Microcavity Lasers

Label-free optical biosensors use optical ways to detect biological analytes in their natural forms. These high-sensitive and low-detection-limit biosensors are easy in pre-processing, immune to electromagnetic interference, capable of real time monitoring, remote control and multi-channel detection. They have vast applications in fundamental biomedical researches, health care, environmental monitoring and homeland security.Among all the optical sensors, optical microcavity is one of the most promising sensing structures. Optical microcavities confine the light in a micro-scale area, meanwhile maintain the high Q feature (104?109). They have superb sensing ability, theoretically, even are capable of single molecule detection. Also, the sensing area of microcavity is tiny, which allows optical integration and simultaneous multi-specie detection and makes them very favorable in real application.In this thesis we will systemically characterize and optimize optofluidic ring resonator biosensor, and design and realize a novel biosensing structure based on single-mode coupled microcavity laser.The thesis focuses on the following aspects:1. I investigated the ultimate sensing capability of optofluidic ring resonators in bulk refractive index (RI) detection and label-free small molecule surface mass density detection in the region close to the detection limit. The noise equivalent detection limit of bulk refractive index and surface mass density are 3.8×10-8 RIU and 0.18 pg/mm2, respectively, which break the barriers of 10-7 RIU and 1 pg/mm2 typically encountered in many optical label-free biosensors. These results represent the best sensing performance of microcavity biosensors and set the benchmark for microcavity biosensors and for comparisons with other label-free optical biosensors.2. I theoretically analyzed the ability of 3-dimensionally confined optofluidic ring resonators (OFRRs) for detection of a single nanoparticle in water and in air. Through optimization, the sensitivity is enhanced at lest 10 times, as compared to that of a solid microsphere biosensor. Combined with the lowest reported noise level, the smallest detectable nanoparticle is estimated to be less than 10 nm in radius, which is close to the size of a single protein molecule.3. I designed and experimentally realized a novel label-free optical biosensor based on single mode coupled microcavity laser. We demonstrated that the surface adsorption of bio analyte changes the coupling condition and leads to single mode laser hopping. By applying the sensing scheme based on mode hopping process monitoring, the lowest detectable concentration of BAS protein solution about 80 pg/mm2 is experimentally achieved, which is comparable to that of ultrahigh Q passive microcavity biosensors, but with much simplified experimental setup. Our results for the first time show the possibility of using a microcavity laser to achieve ultra-sensitive optical sensing.