Colorimetric detection of Cr3+ based on gold nanoparticles functionalized with 4-mercaptobenzoic acid

Herein, we report the construction of a colorimetric probe used to detecting Cr3+ ions in aqueous solution based on functionalized gold nanoparticles. We investigated 4-mercaptobenzoic acid, 4-nitrobenzenethiol, and a mixture of 4-mercaptobenzoic acid and 4-nitrobenzenethiol as ligands for Cr3+ ions to functionalize the gold nanoparticles, respectively. The results showed that the three probes were all aggregated in the presence of Cr3+ ions, which induces a color change from ruby to violet. Moreover, gold nanoparticles modified with 4-mercaptobenzoic acid exhibit a higher response toward Cr3+ than the two other probes, which can be detected by the naked eye and UV-vis absorption spectroscopy. The detection time was rapid (within 25 min). A linear relationship was obtained from 20 to 25 mu M between the ratio of the absorbance observed at 635 nm and 520 nm (A635 nm/A520 nm) with the limit of detection was 5 x 10(-6) M. This method exhibited excellent selectivity for Cr3+ ions over other tested heavy metal ions, anions, and organic molecules in the absence of another shielding reagent of metal ion. The system was successfully utilized to detect Cr3+ ions in simulated samples.