Nanoparticle-Induced Interfacial Director Straining Enables Ultrasensitive Molecular Detection at Microfluidic Liquid Crystal Interfaces.

Detecting aqueous trace pollutants is a challenge in tracking environmental and public health. We report nanoparticle-decorated liquid crystal (LC) soft interfaced microfluidic platforms for detecting trace-level aqueous analytes. Silica nanoparticles functionalized with alkyl-terminated silanes were used to decorate the LC-aqueous interfaces and induce LC strain. The response of the LC flow sensor to various analytes, including industrial dyes, pharmaceuticals, and persistent chemicals, was investigated through the optically observable LC ordering transitions. The microfluidic results, supported by nanoparticle-integrated LC droplet-based sensors, showed a limit of detection (LOD) of 0.1 ppb with LC interfaces decorated with concentrated nanoparticles. Lowering the interfacial nanoparticle loading resulted in sensors achieving an impressive 4 orders of magnitude reduction in the LOD. While LC droplet-based sensors were unable to reach this sensitivity limit, such ultralow responses were strikingly observed in microfluidic sensor platforms by leveraging the interface geometry and localized straining at LC interfaces induced by nanoparticle positioning. We show that the sensors demonstrate selectivity for analytes characterized by aromatic structures. These features hold potential for various applications, including continuous tracking of micropollutants and medical diagnostics.