Smectic liquid crystal films as potential biosensors for amphiphilic molecules

Liquid crystal (LC) biosensors have garnered tremendous interest in recent years due to their high sensitivity, rapid visual response and the ease of functionalization to interact with specific target molecules. Membrane proteins and phospholipids are amphiphilic molecules and important biomarkers indicative of human health, and previous studies have shown the effect of amphiphilic molecules on nematic LC interfaces, supporting the idea of LC biosensors. But the research showing the effect on smectic LC interfaces is lacking. Unlike the nematic phase, the smectic phase can form interesting visually observable defects called focal conic domains (FCDs), which potentially enable the possibility of quantitative results in addition to qualitative. Our research is focused on conducting studies with the thermotropic LC, 8CB (4'cyano-4'octylbiphenyl) in its smectic phase and check its feasibility and potential as a biosensor. We investigated the response of different concentrations of amphiphilic molecules and measured the lowest detectable concentrations. In our experiments, in addition to the presence of FCDs as a function of concentration, we also observed a potential correlation between the FCDs with respect to time of contact with the interface. Our findings contribute to the understanding of molecular interactions at smectic LC interfaces and demonstrate the significant potential of smectic LCs and their defects for biosensing applications, paving the way for a novel sensing platform.