Elucidating the synthesis mechanism, characterization, and colorimetric sensor applications of biogenic gold nanoparticles derived from Cassia grandis fruit extract

Abstract

Cassia grandis (CG) fruit extract, traditionally used in folk medicine, has found a new role as an eco-friendly material for synthesizing and stabilizing biogenic AuNPs, particularly for glucose and vitamin C detection. Based on the phenomenon related to Rayleigh scattering, the synthesis conditions have been optimized at a temperature of 100 °C for 50 min with 0.5 mM of Au3+ in an extract ratio of 1:5. The formation mechanism and catalytic mechanism of the biogenic AuNPs in the TMB oxidation is also elucidated in detail. The morphological properties of the synthesized AuNPs were investigated using FT-IR, XRD, SEM-EDS, TEM, and DLS. The AuNPs are approximately 16.95 ± 2.57 nm in diameter, exhibiting a spherical structure. Notably, the AuNPs synthesized and stabilized by CG-extract phytochemicals demonstrate a zeta potential of −40.33 mV, surpassing that of nanoparticles derived from several other natural extracts. Even after one month of storage, this value decreased by approximately 7.5 %. Moreover, under the established optimal conditions, the colorimetric assay using CG-AuNPs showed remarkable sensitivity and selectivity for both glucose and vitamin C, with LODs of 8.68 and 5.26 μM in linear ranges of 10–800 and 5–50 μM, respectively.