Green biomimetic silver nanoparticles as invigorated colorimetric probe for Hg2+ ions: A cleaner approach towards recognition of heavy metal ions in aqueous media

In this report, we described an environment friendly synthesis procedure for cleaner production of silver nanoparticles (AgNPs) through biochemical reduction of Ag+ ions using aqueous extract of Vigna mungo beans. The primary phytochemical analysis of V. mungo beans revealed that seeds contain flavonoids, phenolic acids and proteins, which play a dual role of reducing as well as stabilizing agents. The stabilized AgNPs were analyzed using different spectrophotometric and electron microscopy techniques such as UV-visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM). The AgNPs were identified to be well distributed and having spherical morphology, as observed from TEM measurement and displayed a plasmon resonance absorption band around 430 nm during absorption spectroscopic analysis. Further, AgNPs were employed for their significant application of extremely selective and responsive colorimetric recognition of mercuric (Hg2+) ions, deprived of any prior surface reformation with organic ligands. On adding Hg2+ ions, the yellowish-brown colloidal solution of AgNPs transformed to colorless, accompanying the blue shifting and broadening of plasmon band, ascribing to disintegration of Ag nuclei. The response of various metal ions such as transition metals, alkali and alkaline earth metals and interference of various metal ions have also been investigated. Different dilutions of Hg2+ ions were also considered and detection limit (LOD) around 0.13 mu M (130 nM) for Hg2+ ions was calculated. Centered on these outstanding outcomes, we anticipated that biogenically prepared AgNPs have capability to employed for probing the Hg2+ ions in waste water reservoirs through a low cost and one step assay protocol as it does not need any pre-functionalization of nanoparticles with organic molecules/ligands.