Selective colorimetric and electrochemical detections of Cr(III) pollutant in water on 3-mercaptopropionic acid-functionalized gold plasmon nanoparticles.

Gold plasmon nanoparticle (AuNP) was applied to the detection and the quantification of pollutant Cr(III) in water. It was synthesized by the chemical reduction of tetrachloroauric(III) acid with sodium citrate as a reducing and capping agent and was modified with 3-mercaptopropanoic acid (3-mpa) to improve the sensing recognition for the metal ion in the colorimetric detection. The 3-mpa-deposited AuNP selectively bound Cr(III) among the other 14 metal cations, resulting in the redshift of the gold plasmon band from 521 nm to 670 nm. The colorimetric quantification examination of the Cr(III) using the plasmon intensity approved the high sensitivity with the low limit of detection (0.34 ppb). Meanwhile, for the electrochemical detection, AuNP was electrochemically deposited on indium tin oxide glass substrate, modified with 3-mpa, attached Cr(III), and subsequently capped with 3-mpa-deposited AuNP. The cathodic current peak at -0.84 V versus the metal ion concentration revealed the linearity at a wide concertation range of 200-5000 ppb. As a result, the proposed colorimetric and electrochemical sensing techniques, which are the simple and facile detectors, can be complementarily employed with a high selectivity, sensitivity and wide analyte concentration range for the quantification of Cr(III) in aqueous solutions.