Surfactant-Mediated Droplet Spreading Analysis on Liquid Crystal-Infused Porous Surfaces: A Label-free Biosensor for Sensitive Lipopolysaccharide Detection.

Lipopolysaccharide (LPS), a potent endotoxin from Gram-negative bacteria, poses significant clinical and industrial challenges, necessitating sensitive and reliable detection methods. In clinical diagnostics, early LPS detection is essential for timely intervention in sepsis, where endotoxemia drives systemic inflammation. In the biopharmaceutical industry, stringent LPS monitoring ensures the safety of therapeutic proteins, as even trace levels can trigger severe immune responses. We present a novel biosensing platform for LPS detection based on the spreading behavior of surfactant-laden droplets on liquid crystal-infused porous surfaces (LCIPS). Aqueous droplets containing cetyltrimethylammonium bromide (CTAB) exhibit large spreading areas due to enhanced surface wetting on LCIPS. The addition of an LPS-specific aptamer reduces droplet spreading by forming a CTAB-aptamer complex. Upon LPS introduction, preferential aptamer-LPS binding competitively disrupts this complex, restoring droplet spreading, with the final droplet spreading area (DSA) proportional to LPS concentration. Systematic optimization of CTAB (50 μM) and aptamer (0.1 μM) concentrations enables detection sensitivity down to 0.051 EU/mL, with performance validated against a commercial endotoxin testing system. The platform exhibits high specificity for intact LPS and maintains robust functionality across complex sample matrices, including tap water, drinking water, and injectable solutions. This simple, label-free, and cost-effective biosensor holds strong potential for sepsis diagnostics, pharmaceutical quality control, and environmental monitoring.