Silver nanoparticle synthesis assisted by micelles for the development of a colorimetric nanobiosensor capable of detecting contaminants in water

We report the synthesis of silver nanoparticles (Ag NPs) functionalized with L-cysteine (Ag-cys NPs) for colorimetric detection of contaminants: Hg²⁺, Pb²⁺, Cr⁶⁺ (CrO₄²⁻/Cr₂O₇²), and As³⁺ in water samples. AgNPs synthesized were obtained in water from the mixture of the cationic and non-ionic surfactants, cetyltrimethylammonium bromide (CTAB) and nonylphenol ethoxylate (NP-10), respectively. Physicochemical characterization demonstrated a monomodal distribution of spherical nanoparticles with an average size of 8.25 nm. The stability of the Ag-cys NPs was evaluated by determining the surface charge, which was found to be +27.95 mV, indicating the stability of Ag-cys NPs against flocculation. The interaction between Ag-cys NPs and solutions of contaminants was studied. This was done by measuring the shift in LSPR band of Ag NPs covered with cys in the region of 400–450 nm. We observed a change or disappearance of color visually, indicating aggregation or oxidation of the Ag NPs. Concentration of cys, as well as the pH of the nanoparticles, were crucial in studying the aggregation process. This is a preliminary study in search of benefits such as low cost, in situ usability, ease of use, and rapid response making it a potential alternative to traditionally employed spectroscopic methods.