Monodispersed AuNPs synthesized in a bio-based route for ultra selective colorimetric determination of Ni(II) ions

Abstract

Nanoparticle (NP) systems with controllable and adjustable response sensor characteristics are promising for the colorimetric sensing of heavy metal ions in aqueous systems. In this article, uniform gold nanoparticles (AuNPs) with a mean diameter of 31.16 ± 6.67 nm have been achieved with the inexpensive and easily affordable differential centrifugation technique. Thereafter, they are deployed for Ni(II) ions colorimetric determination. Plant phytochemicals (mostly GC, EGC, CG and ECG polyphenols) that exist as natural reducing agents in mature green tea leaves were explored for the synthesized AuNPs. Subsequently, various spectroscopic and imaging methods such as UV–Vis spectroscopy, X-ray diffractometer (XRD), field emission transmission electron microscopy (FETEM), and X-ray photoelectron spectroscopy (XPS) have been applied for a greater insight into the morphological and structural characteristics of the green method synthesized AuNPs. The colorimetric sensing ability of the AuNPs for Ni(II) ionic identification in aqueous tap water system (0.001 to 1 mg/L) has been quantified in terms of the limit of detection (LOD) and limit of quantification (LOQ) values of 0.001 and 0.005 mg/L respectively. Furthermore, the metal-ligand interaction between AuNPs and Ni(II) ions resulted in a noticeable shift in color, and from the pink (λmax= 528 nm) to purple hue (λmax= 556 nm). The FETEM analysis assured clustering tendencies of AuNPs upon exposure to Ni(II) ions. The XPS analysis conveyed the coordination of positively charged Ni(II) ions with the surface-bound negative charged functional groups (–OH, C = O) of the AuNPs. These findings confirmed the practical relevance of the AuNPs for application as a potential colorimetric sensory system.