Bimetallic AuPt nanoparticles-based SERS substrate for high-performance endosulfan detection

Surface-enhanced Raman spectroscopy (SERS) substrates based on metallic or alloy nanomaterials have attracted increasing attention for trace pesticide detection in food and environmental samples. Endosulfan (ES), a chemically stable and hazardous organochlorine pesticide, remains difficult to be rapidly and sensitively detected at low concentration. In this work, a SERS substrate based on bimetallic AuPt nanoparticles (NPs) was developed via reduction of HAuCl₄ and H₂PtCl₆ precursors. The resulting AuPt nanomaterials were systematically characterized using TEM, HRTEM, XRD, EDS, and UV-vis, and their SERS performance was evaluated using endosulfan as a probe analyte. Among the investigated compositions, AuPt NPs with an Au : Pt molar ratio of 1 : 1 exhibited the best analytical performance, with an enhancement factor (EF) of approximately 14.3 × 10⁶, a limit of detection (LOD) of 0.05 ppm (1.225 × 10^-7 M), and a good linear relationship between log I and log C over the concentration range of 0.05-2 ppm. The developed substrate also showed good repeatability, signal uniformity, and storage stability. The enhanced SERS performance is likely associated with the combined effects of alloy composition and favorable nanoparticle morphology, particularly the formation of interparticle nanogaps that promote hotspot generation. Based on the present results, the electromagnetic contribution is considered to be the dominant enhancement mechanism, while electronic interactions between AuPt NPs and ES molecules may provide a supportive contribution. These results suggest that AuPt NPs are a promising SERS-active platform for sensitive endosulfan detection.