Green synthesized silver nanoparticles for selective colorimetric sensing of Hg2+ in aqueous solution at wide pH range.

In the present study, the syntheses of crystalline silver and gold nanoparticles (NPs) has been demonstrated in a green and environmentally friendly approach using citrus fruit extracts (lemon, Citrus limon (Cl-1) and sweet orange, Citrus limetta (Cl-2)). In addition, potentially hazardous metal ion sensing properties of these NPs in aqueous solution has been explored. Cl-1 and Cl-2 that predominantly contained citric and ascorbic acid, exhibited different reducing abilities towards silver and gold ions into NPs. Cl-1 reduces silver ions into AgNPs only in the presence of sunlight whereas AuNPs from gold ions were formed without exposure to sunlight. In contrast, Cl-2 converts both silver and gold ions into the corresponding NPs in the absence of sunlight. The colorimetric sensor studies of these green synthesized AgNPs (Cl-1-AgNPs) showed selective sensing of the potentially hazardous Hg(2+) ion in water at micromolar concentrations. More importantly, green synthesized Cl-1-AgNPs sensor systems detected Hg(2+) ions in water in a wide pH range (3.2 to 8.5).