Detection of phosphatidylserine by using liquid crystal supported on the gold-deposited waveform surfaces with the annexin V-based signal enhancement

Tumor cells expose phosphatidylserine (PS) on their plasma membrane; thus, secreted PS-positive exosomes in the bloodstream could be used as biomarkers for cancer. In this study, we report a label-free liquid–crystal-mediated PS sensor employing PS antibodies, which were immobilized on waveform surfaces, with annexin V-based signal enhancement. When PS-annexin V clusters bind to the antibody, there is an orientational transition of the liquid crystal, which is supported on PS antibody-immobilized surfaces. The binding of PS-annexin V clusters to PS antibodies was confirmed by analyzing the surface topography using atomic force microscopy and an ellipsometer; the binding kinetics were determined using the surface plasmon resonance technique. This sensor could sensitively detect PS at the threshold of 0.9 ng/mL in HEPES buffer and 0.92 ng/mL in human serum and showed high selectivity, due to its specific interaction with the antibody. Thus, the proposed method is a promising platform for PS detection, not only for clinical diagnostics but also for the identification of low levels of PS in a biological environment.