Extended Limits of Detection (LoD) up to Subparts Per Trillion for Lead (Pb) Compounds in Water Using Laser-Scribed SERS Sensors Adorned with AgAu Bimetallic Nanoparticles

Abstract Lead (Pb) contamination in water is a critical environmental and health concern, demanding rapid, sensitive, and reliable detection techniques. We report surface-engineered nanostructured platforms fabricated by laser scribing as surface-enhanced Raman scattering (SERS) sensors for Pb detection. Sequential surface patterning of silver-coated silicon (Si) substrates immersed in AgAu bimetallic nanocolloids using ultraviolet (UV) and infrared (IR) lasers enables precise nanostructuring and controlled generation of densely packed plasmonic hotspots. Alloyed AuAg nanoparticle-adorned nanosphere-on-mirror (NPoM) SERS substrates achieve femtomolar detection of rhodamine 6G, highlighting ultrasensitivity. The optimized SERS substrates exhibit exceptional performance in detecting various lead compounds in water, such as PbO, PbS, PbI2, Pb­(NO3)2, and Pb­(CH3COO)2, with detection limits reaching down to 10–11 to 10–13 M. The lowest detection limit achieved for PbO (0.022 ppt (parts per trillion)) is approximately 670,000 times lower than the US EPA’s permissible lead concentration in drinking water (15 ppb). The sensor shows excellent signal homogeneity (RSD = 4.66% for PbO at 10–9 M), strong linearity (R2 = 0.992) over a wide range, and operational stability for 35 days. This facile, scalable, and label-free SERS platform offers trace-level Pb detection in aqueous environments, holding strong potential for real-time environmental monitoring and public health surveillance.