Enhancing detection sensitivity in quantitative protein detection based on dye-doped liquid crystals

A quantitative protein assay and label-free immunodetection based on dye-doped liquid crystal (DDLC) was developed in this study. The black dye incorporated as the dopant in the DDLC mixture features a high dichroic ratio and wide visible-light absorption band so that the level of disturbance in DDLC orientation in the presence of biomolecules can be readily observed with the naked eye. Due to the absorption and anisotropic features of DDLC, transmission spectrometry was exploited to establish a quantitative method for DDLC-based biosensing. Our results indicate that the transmittance of DDLC decreased with increasing concentration of bovine serum albumin (BSA), a common protein standard, and the detection sensitivity can be improved by using linearly polarized light during spectral measurement. A linear correlation between the spectral parameters of DDLC and BSA concentration was thus derived to facilitate protein quantitation. As a demonstration of clinical relevance, a label-free DDLC-based immunoassay for the cancer biomarker CA125 was manifested by reacting CA125 with immobilized anti-CA125 antibody. The transmittance of DDLC decreased with increasing concentration of CA125, but when a nonspecific protein such as BSA was reacted with the anti-CA125 antibody, the transmission spectrum was similar to that in the absence of CA125, suggesting that immunodetection via the DDLC-based biosensing platform was specific. It is evident from this study that with its unique dichroic and optical properties, DDLC is a potential biosensing material with capabilities of both qualitative detection as required in rapid screening as well as quantitative bioassay as in cancer screening.