High-precision measurement of refractive index (RI) is very important and popular in the field of sensor, medicine, biology and molecular structure. In the context of detection of biomolecule, the optical detection of small changes in refractive index within solutions has received considerable attention recently. In the optical detection technology, label-free detection does not require the sample - usually a liquid analyte, to be marked with fluorescent dyes but rather relies on the detection of tiny refractive index changes due to bonding events, e.g., antibody-antigen interaction. The ability to detect smaller concentrations of molecules results from the smaller detection limits of changes in the refractive index.

The Ultrasensitive optofluidic resonator refractive index sensor we report combines the SPR technology and the UOMs and successfully creates an optofluidic resonator consisting of an SMHW and the prism. This new waveguide can scan for the angles of SPP and UOMs as a whole structure instead of measuring as two parts. Measuring the SPP can roughly figure out the range of refractive index and also the thickness of the waveguide. Then by using the angles of the ultrahigh-order modes we can figure out the exact value of the refractive index. By programming with Matlab, this research can automatically calculate the refractive index of the waveguide. After numerical simulation and experiments, it comes out that the precision of refractive index can reach 1.010-6 RIU as the measurement precision of the angle reaches 10-4 degree.

Publication: Zhiyuan Xiao, Hailang Dai, Xianfeng Chen, Ultrasensitive optofluidic resonator refractive index sensor, Optics Letters, 43(17), 4216-4219(2018)