Biologically green synthesis of silver nanoparticles from Citrullus lanatus extract with L-cysteine addition and investigation of colorimetric sensing of nickel(II) potential

Abstract This work presents a green synthesis of silver nanoparticles (AgNPs) using Citrullus lanatus juice extract. The biologically synthesized AgNPs and functionalized AgNPs using L-cysteine (Cys-AgNPs) were characterized by the UV-Vis spectroscopy, the FT-IR spectroscopy, and the scanning electron microscopy (SEM) analysis. The surface-plasmon resonance (SPR) bands of the AgNPs and Cys-AgNPs and appears at 420 and 415 nm, respectively. The SEM image revealed that the particles had a spherical shape and size distribution of 20–40 nm. Application of Cys-AgNPs in terms of heavy metal selectivity showed that it exhibited selectivity against nickel(II) which was confirmed by the color change from yellow to orange and the appearance of a new SPR band at 455 nm. The predicted structures of AgNPs and Cys-AgNPs showed that the complexes were formed through the electrostatic interactions and the shift of the SPR band from theoretical calculations are in accordance with experiment. Accordingly, this eco-friendly approach showed the successful application of the biologically green synthesized AgNPs modified by the L-cysteine addition for colorimetric detection of nickel(II). This proposed method could be considered as an efficient probe for the colorimetric sensing of nickel(II) with simplicity, rapidity, low cost and environmental reservation.