2D correlation SERS of organic ions using AuNP films at electrified soft interfaces

Abstract

This study reports the formation of gold nanoparticle (AuNP) films by electrochemical assembly at the polarized water|trifluorotoluene interface (ITIES) and their use as SERS substrates whose activity can be tuned by the interfacial potential. Using a four-electrode configuration, cyclic modulation of the interfacial potential induced the growth of AuNP films, monitored in real time by total internal reflection (TIR) UV-Vis spectroscopy. The absorbance evolution reveals two distinct growth regimes, while the interfacial double-layer capacitance (C_dl) increases steadily with the number of cycles. These electrochemically generated films were subsequently evaluated as SERS-active substrates for two cationic probes: methylene blue (MB⁺) and norfloxacin (Nor⁺). The interfacial potential governs their adsorption and distribution between the phases. To discriminate spectral responses and identify the sequence of interfacial processes as a function of applied potential, two-dimensional correlation spectroscopy using the applied potential as the external perturbation of the system was employed. The synchronous and asynchronous maps highlight potential-induced changes in adsorption states as well as competitive interactions between the probe molecules, the supporting electrolyte and the AuNPs film at the interface. Overall, these results demonstrate that electrochemically assembled AuNP films act as dynamic plasmonic substrates whose SERS performance can be modulated by potential (EC-SERS), while 2D-Correlation Spectroscopy provides a complementary approach to unravel multi-species mechanisms at liquid–liquid interfaces.