Research On The Immobilization Status Of Staphylococcal Enterotoxin A Antibody In Optofluidic Biosensing

Optical microcavity biosensor is a kind of sensor which is based on the whispering gallery mode and achieves quantitative analysis. It works mainly by detecting the sensing signal change caused by the specific binding of the analyte to biological molecules immobilizated on the microcavity surface in advance. Due to the small size, high sensitivity, low sample consumption and label-free detection, optical microcavity biosensor has recently attracted increasing attentions.Owing to the structural feature, microtube simultaneously acts as the light guide channel and fluid transport channel, which simplifies the sensing system, and also has the multiplexing potential. As a result, biosensor based on microtube is very promising. In this paper, the microtube-based optofluidic biosensor is studied theoretically and experimentally and the major work completed is as follows:1. The theoretical model of the microtube resonator is established by the coupling mode theory, and transmission characteristics of the light propagating in the microtube are studied. Then from the Maxwell’s equations, distribution of the electromagnetic field in the microtube in a cylindrical coordinate system is derived. A brief overview of two different sensing mechanisms for microtube used as a biosensor is given finally.2. By using the FullWAVE simulation engine based on the finite-difference time-domain algorithm, the microring resonator, a two dimensional model Simplified from the microtube, is simulated and the light propagating states in the microring is studied. Meanwhile, resonance wavelength shift caused by respectively changing different parameters, such as the wall thickness and the effective radius of the microring, is calculated and according to the result, sensitivities with different modes are compared.3. A optofluidic biosensing experimental system based on microtube immobilizated with staphylococcal enterotoxin A antibodies on its inner wall is built by a prism coupling method, and is applicated in the surface density detection of the SEA antibody. By measuring resonance wavelength shifts corresponding to various concentrations of the antibody solutions injected into the micotube, surface densities can be obtained. Comparing with the ideal and the calculated value, it’s found that only part of SEA antibodies is immobilized and immobilization coefficient k linearly increases with concentrations before saturation concentration. This result is useful for WGM-based optofluidic biosensor development.