SERS-based sensing of heavy metal ions and methylene blue using nanosecond laser ablated silver nanoparticles

Ligand-free silver nanoparticles (Ag NPs) were synthesized by nanosecond (ns) pulsed laser ablation of a bulk silver target in double distilled water (DW). The surface plasmon resonance (SPR) peak at 407 nm was observed from the UV-visible absorption spectrum. XRD and SAED analysis confirmed the crystallinity of face-centered cubic Ag NPs. The nanoparticle size with an average diameter of 21 ± 6 nm was confirmed from the TEM images. The obtained Ag NPs were employed as SERS substrates for the detection of dye molecule methylene blue (MB), and heavy metal contaminants such as lead nitrate and cadmium chloride. The SERS enhancement was dominated by electromagnetic mechanisms, with additional contributions from charge-transfer interactions and plasmon-mediated interfacial effects. The analytical enhancement factors were estimated to be ∼10⁹ for MB and ∼10¹⁰ for lead nitrate and cadmium chloride and detection limits down to picomolar (pM) concentrations were achieved without any additional chemical functionalization. These findings highlight the practical applicability of laser ablated Ag NPs as highly sensitive SERS substrates for detection of organic pollutants and toxic metal ions.