Unveiling the Neglected Role of Silver Ions' Leaching for Recovered Functionality of Carboxylate SAMs on Ag

The full release of surface-enhanced Raman spectroscopy (SERS) potential relies on modification of the substrate surface. However, chemical functionalization on silver substrates has, in some cases, resulted in anomalous behaviors that are difficult to explain. In this study, we investigate the role of Ag⁺ leaching from a silver surface in disrupting the performance of carboxyl-terminated self-assembled monolayers (SAMs). Using 4-mercaptobenzoic acid (4-MBA) as a model, we demonstrate that Ag⁺ released during SAM formation coordinates with carboxylate groups, inducing both aberrant SERS responses and multilayer adsorption that cannot be removed by conventional rinsing. To address this issue, we introduce a deoxygenation treatment─immersing freshly deposited AgNRs in KBH₄ solution under inert atmosphere─to remove surface oxides and suppress Ag⁺ release. Treated Ag-4-MBA nanosensors exhibit restored, stable, and accurate pH responsiveness and reliably detect 30 ppm gaseous acetic acid. Our findings elucidate Ag⁺ interference on carboxyl and develop a robust strategy to enhance the reliability of silver-based SERS sensors, paving the way for their broader applications in molecular sensing.