Highly selective nanomolar level colorimetric sensing of Cr3+ through biosynthesized gold nanoparticles in the presence of Cr6

Our work exhibits a green method of formation for gold nanoparticles (AuNPs) from its precursor salt, tetra-chloroaurate through the reducing and capping action of Ziziphus mauritiana leaves (ZmL) extract with the assistance of heat in aqueous medium. The formation of so called ZmL-AuNPs was confirmed via color change of solution mixture to ruby red which was further confirmed by surface plasmon resonance (SPR) band at 521 nm using ultraviolet-visible (UV–Vis) spectroscopy. Further characterization of ZmL-AuNPs includes Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), X-ray diffraction (XRD) technique, and zeta-potential analysis (ZPA) respectively. The synthesized ZmL-AuNPs were probed and recognized to perform as a highly sensitive and selective colorimetric sensor for the detection of Cr3+ in the presence of other expected interfering cations including Cr6+. Importantly, the developed ZmL-AuNPs based colorimetric sensor functioned linearly in the range of 16–283 nM of Cr3+, based on aggregation induced decrease in absorption along with red shift in the resulting spectra exhibiting R2 value of 0.9977. The limit of detection and limit of quantification for Cr3+ were estimated as 0.48 nM and 1.6 nM respectively. The developed colorimetric sensor was effectively used for detecting Cr3+ in real water samples.