Label-free liquid crystal immunosensor for detection of HBD-2

A label-free liquid crystal (LC) immosensorsensor based on the orientation changes of LC was developed for the detection of HBD-2 (human beta-defensin-2) through competitive immunoassay. HBD-2 was tethered onto the semassembled film surface on a glass slide via a cross-linker glutaradehyde. The DMOAP/APTES/GA (N,N-dimethyl-N-octadecyl (3-aminopropyl) trimethoxysilyl chloride/(3-aminopropyl) trimethoxysilane/glutaraldehyde) mixed self-assembled monolayers formed by both long and short alkyls could cause vertical alignment uniformly of liquid crystal. The specific binding of anti-HBD-2 antibody and HBD-2 induced the homeotropic-to-tilted transition of liquid crystal, making a visible optical change observed under the crossed polarized light and achieving the detection of HBD-2. The average gray-scale intensity of optical appearances has a good linear relationship with the concentration of HBD-2 when the concentration of HBD-2 is in the range of 1-10 ng mL(-1) and the linear correlation coefficient is 0.9956. The limit of quantification is 0.53 ng mL(-1) for the HBD-2. This study offers a simple, highly sensitive and specific, label -free method for HBD-2 detection.