Label-free colorimetric detection of Cr(VI) in aqueous systems based on flower shaped silver nanoparticles

We herein report a green method to synthesize flower shaped silver nanoparticles (AgNPs) by employing 3,4-dihydroxyphenylalanine (L-dopa), as the reducing and capping agent for detection of Cr(VI) to the ppm level in aqueous systems. Stable nanoparticles were obtained in the alkaline medium and showed absorption maxima at 417 nm. Aggregation induced detection of Cr(VI) provides a highly selective and sensitive method with a detection limit of 0.01 ppm. Aggregation causes a dramatic color change of nanoparticles solution from dark yellow to reddish brown. The interaction between nanoparticles and metal ions characterized by ultraviolet-visible (UV-Vis) spectroscopy, Fourier transform-infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), and zeta potential analyses. The applicability of this detection method was validated through the presence of other heavy metal ions in the detection system. The findings in this work might lead to developing a very efficient nanoparticles aggregation based colorimetric sensor for chromium, keeping in view of its stability, simplicity, reproducibility, and low cost.