Enhanced ligand exchange for ultrasensitive neonicotinoid detection in soil water via surface-enhanced Raman...

Neonicotinoids (neonics), including imidacloprid (IMD), clothianidin (CLO), and thiamethoxam (THI), account for over 25 % of the global pesticide market and pose significant risks to ecosystems and human health. To address the urgent need for reliable, rapid, and cost-effective monitoring of these emerging contaminants, an ultrasensitive analytical method based on optimized ligand exchange-enabled surface-enhanced Raman spectroscopy (SERS) was developed. The synergistic effects of protons and halides on the SERS detection of IMD, CLO, and THI using citrate-capped gold nanoparticles (AuNPs) were investigated. At pH 1, citrate was fully protonated and readily desorbed from AuNP surfaces, allowing neonics to adsorb and enhancing their SERS signals. Chloride ions further facilitated citrate desorption and served as molecular bridges between neonics and AuNPs. In addition to increased neonic adsorption, extensive AuNP aggregation and SERS hot spot formation were induced, leading to amplified SERS intensities. By combining protons and halides, detection sensitivity was significantly improved, enabling IMD, CLO, and THI detection at concentrations as low as 2-5 nM. This method was successfully applied to detect neonics in real soil water samples, providing a simple, highly sensitive approach for in-situ monitoring of neonicotinoids in agricultural runoff.