Wettability-based ultrasensitive detection of amphiphiles through directed concentration at disordered regions in self-assembled monolayers


Wettability-based molecular detection is emerging to enable portable and fast chemical detection within droplets. However, current detection methods can only respond to changes in a droplet’s bulk wetting properties, leading to poor detection limits. We report a design principle that overcomes this fundamental limitation by locally concentrating analytes within a droplet’s contact line to modulate the local surface roughness, which further affects droplet mobility. This mechanism enables the detection of molecules even at minute concentrations where droplets’ bulk wetting properties are unchanged. This design can be implemented to functional surface devices that can readily sort microliter aqueous droplets into discrete groups with different amphiphile concentrations and molecular sizes, which have potential for early disease diagnostics and environmental water quality monitoring.