A synergistic coordination strategy for colorimetric sensing of chromium(III) ions using gold nanoparticles

We report a simple, facile, and reliable colorimetric system for detection of chromium(III) ions (Cr 3+ ) using citrate- and thiourea-modified gold nanoparticles (AuNPs). The colorimetric sensing strategy is based on the synergistic coordination interaction of citrate and thiourea toward Cr 3+ on the surface of AuNPs, leading to the aggregation of AuNPs which produces a color change from red to purple. Under the optimal conditions, this colorimetric sensing system shows an excellent selectivity and sensitivity for Cr 3+ , and the limit of detection (LOD) is estimated to be 0.05 μM at a signal-to-noise ratio of 3, which is far below the current standard stipulated by U.S. Environmental Protection Agency (1.9 μM). Moreover, this LOD is one and a half orders of magnitude lower than those of previously reported modified AuNPs-based colorimetric methods. Visual color change can be observed when 50 μM of Cr 3+ was introduced to the sensing system. Furthermore, this colorimetric sensing system can be employed for detection of Cr 3+ in diluted natural water samples.