Gold nanoparticles capped with α-cyclodextrin for dual colorimetric sensing of Fe³⁺ and Cr³⁺ in tap water

A rapid colorimetric assay for the dual detection of Fe 3+ and Cr 3+ using gold nanoparticles (AuNPs) capped with α-cyclodextrin was developed. The synthesized AuNPs produced a red wine color with a particle size of 8.60 ± 1.55 nm and were stable for 9 months. Detection of Fe 3+ and Cr 3+ changed the color of the AuNPs solution to bluish purple with a detection time of <1 and 10 min, respectively. Reaction of the AuNPs with Fe 3+ and Cr 3+ also increased the particle size of the AuNPs to 16.18 ± 2.28 nm and 17.33 ± 1.71 nm, respectively. Characterization of the AuNPs using Fourier-transform infrared spectroscopy and X-ray diffraction showed that the presence of Fe 3+ would damage the structure of the AuNPs, whereas Cr 3+ would not. This colorimetric sensor is sensitive toward Fe 3+ and Cr 3+ with limits of detection of 265.92 and 430.80 μg/L, respectively. The dual ion sensing ability of the AuNPs was also assessed by individually detecting Fe 3+ and Cr 3+ in tap water samples in South Tangerang, Banten, Indonesia.