Optimized silver selenide quantum dots for surface-enhanced infrared absorption spectroscopy detecting venlafaxine

The contamination of aquatic environments by pharmaceuticals is a critical global concern, as a consequence of their persistence, bioaccumulation, and adverse effects on ecosystems and public health. To effectively mitigate this issue, it is essential to adopt a preventive approach based on regular monitoring of contaminants. Hence, this study reports the optimization of a green synthesis of silver selenide (Ag_xSe) quantum dots (QDs) as efficient signal amplifiers via surface-enhanced infrared absorption (SEIRA) spectroscopy. The QDs synthesis was performed in water using glutathione (GSH) and ascorbic acid as the stabilizing and reducing agent, respectively. The synthesis procedure was optimized using a Box-Behnken multivariate design approach, identifying critical parameters that influence the resulting optical response. Ag_xSe-GSH QDs exhibited an emission maximum around 700 nm and an average diameter of 6 nm. Total reflection X-ray fluorescence (TXRF) confirmed the expected presence and molar proportion of Ag and Se in the non-stoichiometric molar ratio of Ag:Se 7:1. Venlafaxine (VEN) was selected as a model pharmaceutical to evaluate QDs performance in SEIRA following two deposition strategies: (i) layered deposition (LD) and (ii) mixed deposition (MD). The following SEIRA experiments comparing MD and LD QDs resulted in more repeatable signals for the MD-QDs with IR signal amplification of up to 38-fold. The lowest detectable VEN concentration via SEIRA was 0.113 mmol L^-1, demonstrating the potential of SEIRA, augmented by Ag_xSe QDs, for monitoring pharmaceutical contaminants in aqueous matrices.