Surface-engineered silver nanoplates to enhance humidity sensing

Vapor sensing critically depends on the interaction between vapor molecules and functional surfaces. In this work, we enhance the sensitivity of silver nanoplates for humidity detection by precisely tuning their surface hydrophilicity with different thiol monolayers. Upon exposure to water vapor, localized surface plasmon resonance (LSPR) shifts were found to strongly depend on surface chemistry: hydrophilic 4-mercaptobenzoic acid coatings induced a pronounced maximum shift (∼15 nm), whereas a hydrophobic benzyl mercaptan layer resulted in minimal shifts (∼3 nm). This clear correlation between wettability and plasmonic response provides a precise route to improve LSPR sensor sensitivity. Finite-Difference Time-Domain simulations linked the observed spectral shifts to variations in the thickness of the adsorbed water layer, providing a connection between the model and the water-layer thickness. Silver nanoplates also exhibited fast and reproducible responses, confirming their suitability for real-time humidity monitoring. Overall, this study introduces a robust surface-chemistry-based approach to boost the sensitivity and reliability of LSPR humidity sensors for practical applications.