Biosensors for mercury and manganese ions by using biosynthesized silver nanoparticles

Drinking water resources are scarce and are gradually depleting throughout the world. Water contamination by heavy metals is making the situation worse because it makes water unsuitable for potable use. Heavy metals are hazardous to any aquatic ecosystem, as these adversely influence the food chain and consequently human health. In the present study, Curcuma longa-mediated silver nanoparticles (T-AgNPs)-based sensors are reported to detect heavy metals by naked-eye and ultraviolet (UV)-based methods. A sharp UV peak at 400 nm (C-AgNPs) and a broader peak at 440 nm (T-AgNPs) were recorded. Scanning electron microscopy revealed the spherically shaped morphology of silver nanoparticles (AgNPs) with sizes of 30–50 nm (T-AgNPs) and 20–25 nm (C-AgNPs). The results of Fourier transform infrared spectroscopy indicated that compounds containing functional groups (–C–H, >C=C<, >C=O) played an important role in the reduction and capping of the AgNPs. C-AgNPs (K2) after interaction with manganese (Mn) (II) ions led to the prominent deepening of the yellowish color. In contrast, biological AgNPs (K4) led to the formation of a prominent complex. Green-synthesized AgNPs allowed single-step, cost-effective, colorimetric detection of manganese (II) and mercury (Hg) (I) in the aqueous solution.