Silver nano-colloid particles embedded on Langmuir-Blodgett film matrix of stearic acid serving as a SERS active sensor for detecting the herbicide 'Paraquat'.

The herbicide Paraquat, widely used for efficient weed control, poses significant health risks to humans viz., severe toxicity to vital organs and induction of neurodegenerative disorder like Parkinson's disease, underscoring the urgent need for developing sensitive detection methods for the herbicide. This study aims at fabricating a novel SERS-active substrate SA-LB/Ag (silver nano-colloids adsorbed on Langmuir-Blodgett film of stearic acid), as a SERS based sensor having high sensitivity, uniformity, and reproducibility to detect ultra-trace amounts of paraquat. The sensor was built up by immersing bilayer LB films of SA in silver nano-colloid suspension, prepared by mixing silver nitrate and sodium borohydride with vigorous stirring. Quantitative evaluations establish a significant linear regression across the concentration spectrum (100 ppm to 75 ppb) of paraquat, with a remarkable 15 ppb limit of detection (LOD) value. In practical terms, this SERS based sensor exhibits notable proficiency in detecting paraquat residues in (a) agricultural water from rice and vegetable fields and environmental water from adjoining water-logged areas, and (b) soil extracts of the agricultural fields. Moreover, the minimum toxic concentration of paraquat at the developmental stage of zebrafish embryos and larvae is found to be approximately 20 ppb, implying that the SA-LB/Ag sensor is sensitive enough to determine the limiting toxic level of paraquat for animal systems. Thus, the designed sensor holds far-reaching implications in ensuring food safety, monitoring the environment, and framing regulatory measures for paraquat use.