Redox-Triggered Interfacial Reconstruction as an Analytical Transduction Mechanism for Optical Detection of Arsine...

Arsine (AsH3) is widely used in semiconductor manufacturing yet poses severe health risks, motivating sensitive on-site monitoring for personnel safety. We report a liquid crystal (LC)-based optical sensor that translates arsine-triggered surface chemistry into an orientational transition. The sensing cell consists of nematic 4-cyano-4'-pentylbiphenyl (5CB) doped with 0.1 wt % 4'-hexyl-[1,1'-biphenyl]-4-carboxylic acid (HBCA) on an HAuCl4-derived reactive gold-coated substrate. In the absence of arsine, HBCA preferentially adsorbs at the coating and enforces homeotropic LC alignment (dark under crossed polarizers). Exposure to AsH3 initiates a redox-triggered interfacial reconstruction process in which AsH3 reduces surface Au(III)-Clx species to Au(0) and promotes nanoscale restructuring, collectively disrupting HBCA-Au interactions. The resulting anchoring change induces a homeotropic-to-nonhomeotropic (planar/hybrid) LC transition with a clear dark-to-bright optical readout. Mechanistic evidence from in situ Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and density functional theory (DFT) calculations supports the proposed pathway. The sensor exhibits high selectivity toward AsH3 over common solvent vapors and achieves a practical optical detection limit of 10 ppb. This work introduces interfacial redox-driven reconstruction as a programmable analytical transduction mechanism for gas sensing and provides a broadly applicable design principle for translating reactive interfacial chemistry into LC-amplified optical outputs.