Synthesis of colloidal snowflake-like silver nanoparticles and their use for SERS detection of pesticide imidacloprid at trace levels

Besides conventional methods, trace concentration detection of molecules can now be performed with the emerging surface-enhanced Raman scattering (SERS) spectroscopy. A key factor in achieving high performance in SERS is the quality of the substrate, which must exhibit a high, uniform and reproducible enhancement factor. Silver nano snowflakes (AgNSFs) meet these criteria effectively. In this report, we present a simple procedure to synthesize uniform colloidal AgNSFs, approximately 2 μm in size, by reducing aqueous silver nitrate with hydroxylamine at room temperature. These AgNSFs were then deposited onto an aluminum foil and dried to create a SERS substrate. The performance of this SERS substrate was first tested using rhodamine 6G (R6G), demonstrating detection capabilities down to a concentration of 10⁻¹⁴ M, with a SERS enhancement factor reached 2.8 × 10¹¹, and a high degree of uniformity and reproducibility (with a relative standard deviation less than 9 %). Additionally, when applied to detect the important pesticide imidacloprid (IMI), the substrate enabled detection at concentrations as low as 0.005 mg/L, with a detection limit of 0.1 μg/L (0.1 ppb). These findings suggest that the AgNSFs synthesized in this study have significant potential for application in SERS measurements, particularly in food safety and environmental monitoring applications.