Real Time And Label Free Biosensing Technology And Applications Based On Whispering Gallery Mode Microcavity

In the recent years,optical biosensors have developed rapidly,and have found applications in biomedical research,environmental monitoring and homeland security.Whispering gallery mode(WGM)optical microcavities possess ultrahigh quality factor and small mode volume,enabling the enhancement of light-matter interactions.WGM optical microcavities are considered one of the most promising systems in optical biosensors.At present,the single nanoparticle and single molecule optical response have been experimentally demonstrated.However,dynamic reaction process is important topic in biosensing,there have been few demonstrations yet that these systems can be used to investigate the dynamics of a biochemical reaction.Moreover,there are still issues to be solved in practical applications.In this thesis,we focus on monitoring dynamic reaction process using WGM optical microcavity,and demonstrate o method of packaging the coupling systems of WGM optical microcavity and fiber taper.The main content is divided into the following three parts:Fabrication of WGM microcavity and fiber taperThe fabrication of ultrahigh quality factor WGM microcavity play important role in biosensing research.We successfully fabricate fiber taper and ultrahigh quality factor microbubble cavity using hydrogen flame heating and CO2 laser heating techniques.In the experimental,the coupling systems of WGM microcavity and fiber taper is built for further biosensing research.Monitoring of hydrogel phase transition in an ultrahigh-Q microbubble resonatorWe fabricate ultrahigh quality factor WGM microbubble cavity and filled with PNIPA hydrogel.Monitoring of hydrogel phase transition in WGM microbubble cavity-based sensors is firstly demonstrated by continuously monitoring both wavelength shift and linewidth broadening simultaneously.Experimentally,the thermo-sensitive hydrogel phase transition is optically controlled by change the heating laser power(?1550 nm)?During a hydrophilic to hydrophobic transition process,an overall wavelength red shift and a distinct linewidth broadening over 10 times are observed,respectively.The WGM linewidth broadening unambiguously reveals the hydrogel phase transition due to the enhanced light scattering,and the refractive index changes are detected by monitoring wavelength shift.Note that compared with the wavelength shift sensing mechanism,the WGM linewidth broadening is immune to the noises including thermal noise and laser frequency noise in practical measurements.This work demonstrate that optical microbubble cavities are promising platform for further investigating the biochemical dynamics and molecule kinetics.Packaged microbubble cavity for versatile optical sensingwe experimentally realize a robust and ultrahigh-Q PMBR for practical optical sensing.The MBR and fiber taper are packaged in a moisture curable polymer with low refractive index.The longterm stability and thermal response of a PMBR are demonstrated.Moreover,the PMBR is used for in situ measurement of hydrogel hydrophilic-hydrophobic transition by continuously monitoring both the WGM wavelength shift and linewidth broadening,which results from the changes of refractive index and light scattering of the hydrogel,respectively.The refractive index changes of hydrogel during the transition process is explicitly modelled.Our work steps further for optical microfluidic sensing in practical scenarios.