An on-chip glass sphere resonator for label-free detection

An on-chip glass sphere resonator with prism coupler in microchannel for label-free detection is presented in this paper. A micro glass sphere in polytetrafluoroethylene (PTFE) coated microchannel and two optical fibers for light input and output are integrated onto a polydimethylsiloxane (PDMS) chip. In the experiments, the glass spheres have diameters ranging from 50 ¿m to 120 ¿m and the PTFE films with thicknesses ranging from 200 nm to 1000 nm are coated for the tuning of coupling ratio. Experimental results show that the maximum quality factor (Q-factor) of the resonator reaches 3.1 × 10³ and the measurements of refractive index has accuracy of 6 × 10^-5 RIU, which corresponds to the label-free protein concentration detection with accuracy of 0.4%. The on-chip glass sphere resonator has features as high stability, low cost, high sensitivity and label-free detection, which promises potential applications in environmental monitoring, real time chemical analysis and biological measurement.