Polyelectrolyte modified Ag-nanosphere: A practical approach for sensitive and selective SERS-based detection of organic pollutants

This study presents a cost-effective method for fabricating surface-enhanced Raman spectroscopy (SERS) substrates using Ag-nanospheres (AgNS) capped with Poly (diallyldimethylammonium chloride) (PDADMAC) and poly (styrene sulfonate) (PSS). AgNS synthesis involves immersing Ag-nanocrystals in a nonaqueous solution, mixed with polyelectrolytes (PEs) in an aqueous solution via ultrasonic disturbance. Resulting aggregates form stable spherical assemblies with diameters ranging from 150 nm to 450 nm, and various characterization techniques, including scanning electron microscopy with energy-dispersive X-ray, UV–visible spectrophotometry, dynamic light scattering, and zeta potential analysis, were employed to analyze their fundamental chemical and physical properties. These qualified AgNSs serve as SERS substrates for sensitive and selective identification of charged organic dye contaminants, such as rhodamine 6G (R6G) and rose bengal (RB). Sensitivity assessments with the optimized quantities of either PDADMAC or PSS-capped AgNSs demonstrate successful detection down to concentrations of 10⁻¹⁴ M for RB and 4 × 10⁻¹³ M for R6G. The same SERS substrates also enable electrostatically driven selective detection even in analyte mixtures, and an additional variation of the SERS substrate comprising a complex of PDADMAC-capped and PSS-capped AgNSs exhibited distinct SERS spectra influenced by both positively and negatively charged analytes. Finally, successful detection of two oppositely charged pesticides was achieved through electrostatic attraction, so theses PEs capped AgNS-based SERS substrate presents a promising avenue for efficiently and selectively detecting charged organic contaminants.