Detection of streptavidin using liquid crystal based whispering gallery mode microbubble

Protein is a complex chemical substance essential for human survival. Traditional protein detection methods, such as colorimetry, electrochemical analysis, and enzyme-linked immunosorbent assays, have shown good specificity and accuracy for the protein detection. However, all these methods require specialized instruments, and the detection procedures are laborious and time-consuming. As a result, a rapid, sensitive, label-free protein detection method is urgently needed. Herein, we have developed an ultra-sensitive biosensor for the detection of low-concentration protein molecules, employing liquid crystal (LC)-amplified optofluidic resonator. Since the orientations of LCs highly depend on the surface biomolecular binding processes, LCs can be employed to realize the extremely sensitive detection of biomolecules. Immobilized protein molecules interfere with the orientation of LCs by reducing the vertical anchoring force from the alignment layer in which the spectral wavelength shift was monitored as a sensing parameter. A biosensing platform based on an LC-amplified optofluidic whispering gallery mode (WGM) resonator was designed and studied accordingly. Due to the simultaneous interaction of the WGM and the LCs in the optofluidic resonator, the changes caused by the injection of protein molecules will be amplified, resulting in a shift in the resonance wavelength. Total wavelength shifts scale proportionally to the molecular concentrations of the protein within a certain range. The detection limit for streptavidin (SA) can reach as low as the femtometer level, which is significantly higher than the detection limit in the classic polarized optical microscope (POM) method visible with the naked eye. In addition to SA, the LC-based optofluidic resonator can also be applied to detect a variety of protein molecules. Our study demonstrates that LC-amplified optofluidic resonator can provide a novel solution for ultrasensitive real-time characterization of biosensing and biomolecular interactions.