A submicromolar Cr(III) sensor with a complex of methionine using gold nanoparticles

We report a combined approach for the detection of Cr(III) after the binding l-methionine (Met) and subsequent treatment with gold nanoparticles (AuNPs) by colorimetric, UV–vis absorption, and surface-enhanced Raman scattering (SERS). Both UV–vis and SERS led to a selective detection of Cr(III) at the submicromolar level. The absorbance values at 650 nm for Met–Cr(III)–AuNPs could be correlated quantitatively with the concentrations of the Cr(III) ion. The detection limit of Cr(III) was estimated be as low as 300 nM based on the absorbance measurements of the aggregated AuNPs at 650 nm. Environmental (distilled, tap, river, and sea) water samples with different ionic compositions were also tested to validate our method. After the binding the metal ion in aqueous solutions, the amino acid Met was found to be a sensitive and selective sensor for Cr(III) on the AuNPs in the water samples without interference from the other ions.