Synergistic Au/Ag-based SERS platform for sensitive detection of malachite green

Introduction: Malachite green (MG), a toxic and carcinogenic triphenylmethane dye widely used in aquaculture, has been restricted in many regions due to health and environmental concerns; however, it remains prevalent in some areas because of its low cost and strong efficacy. Although various methods have been employed to detect MG, surface-enhanced Raman scattering (SERS) offers rapid, high-sensitivity analysis by leveraging noble metal nanostructures and their localized surface plasmon resonance. Methods: The SERS method for detecting MG leverages the localized surface plasmon resonance (LSPR) of gold (Au) and silver (Ag): these noble metal nanoparticles (NPs) create ``hot spots'' that concentrate electromagnetic energy. When MG molecules are adsorbed onto the Au/Ag surface, their Raman scattering signal is significantly amplified, allowing for detection at low concentrations. By employing a multilayer structure containing Au and Ag, the LSPR effect is optimized, resulting in a higher detection efficiency compared to single-layer metal substrates. Results: Characterization via UV-Vis spectroscopy and XRD confirmed that Au and Ag NPs exhibit distinct plasmon absorption peaks (407 and 526 nm, respectively) and the (111) lattice plane at 2q = 38.2◦. HR-TEM and FE-SEM revealed that the Au NPs are spherical (30.46-nm diameter), and the Ag NPs measure 20 nm in diameter. SERS experiments with MG indicated that the P/Au/Ag substrate provides the highest enhancement, detecting MG down to 10−9 M. Conclusions: The P/Au/Ag substrate for SERS-based MG detection was successfully fabricated and characterized, achieving a detection limit of 10−9M. The robust multilayer structure, boosted by the synergy between Au and Ag, holds significant potential for trace-level detection of various contaminants in environmental monitoring and food safety.