Stable and reusable silver nanoparticle SERS platform for pretreatment-free screening of trace malachite green in environmental water.

The rapid and sensitive detection of malachite green (MG) is critical for environmental safety due to its potential carcinogenicity and strict prohibition in aquaculture. However, practical surface-enhanced Raman scattering (SERS) monitoring is often hindered by the high cost, single-use nature, and matrix-induced degradation of commercial substrates. In this study, we systematically evaluate and validate the operational performance of a highly stable and reusable silver nanoparticle (Ag NP)-based SERS platform fabricated via a low-cost, solid-phase reduction method. The platform features a uniform network of Ag NPs with sub-10 nm nanogaps, providing high-density "hot spots". We demonstrate that the SERS platform can be successfully reused for up to 10 measurement-cleaning cycles while retaining 60% of its initial intensity, a robust performance driven by the interfacial "anchor effect" of the bottom-layer NPs. Furthermore, the platform exhibits excellent shelf life over 12 weeks with minimal performance fluctuations under vacuum storage. Most importantly, we achieved an ultra-low detection limit of 10-9 M for MG through the pretreatment-free screening of natural environmental water samples collected from the Asahi River. These findings establish a highly practical, cost-effective, and sustainable analytical framework for the trace detection of hazardous pollutants in real-world aquatic systems.