Optimized colorimetric detection of chromium ions (Cr3+) using black garlic-Ag nanoparticles

Abstract

In this study, AgNPs were synthesized using black garlic (BG) extract and applied for precise and sensitive colorimetric detection of chromium (Cr³⁺) ions in solution. The nanoparticles (BG-AgNPs) were characterised using UV-visible spectroscopy, FTIR, SEM, TEM and XPS analysis. The UV-visible absorbance peak appeared at 411 nm. The pattern of X-ray diffraction (XRD) confirmed a face-centered cubic (FCC) structure of the AgNPs. The SEM images displayed a fusiform (spindle-shaped) morphology of the AgNPs. Transmission electron microscopy (TEM) images presented the sphere-shaped nature of the nanoparticles having a mean diameter of 16.02 ± 1.75 nm. The addition of Cr³⁺ ions turned the brownish BG-AgNP solution colourless. The sensor displayed a linear response to Cr³⁺ concentrations between 2 nM and 20 nM, with a limit of detection (LoD) of 0.07 nM. Optimal sensor performance was achieved at pH 7 and a temperature of 45 °C. Selectivity tests confirmed minimal interference from other metal ions. These results indicate that the developed nanosensor is exceptionally efficient and ultrasensitive at precisely detecting low concentrations of Cr³⁺ ions in environmental applications. A computational study with one of the most abundant compounds during the early stages of the aging process of black garlic formation, γ-glutamyl-S-allylmercaptocysteine (GSAMC), showed a binding energy of −6.67 kcal mol⁻¹ for the formation of GSAMC-AgNPs and −8.82 kcal mol⁻¹ for the formation of the GSAMC-AgNP-Cr complex.