A simple and sensitive colorimetric detection method for hexavalent chromium (Cr(VI)) was described based on ascorbic acid (AA)-capped silver nanoparticles (AgNPs). The cross-linking between AA and Cr(III), the reductive product of Cr(VI), resulted in the aggregation of AA-capped AgNPs, and the color change from yellow to red. Control experiments with the addition of over 15 other metal ions (Cr 3+ , Pb 2+ , Zn 2+ , Hg 2+ , Cd 2+ , Co 2+ , Cu 2+ , Al 3+ , Ni 2+ , Ag + , Mn 2+ , Ba 2+ , Fe 3+ , Na + , K + , Ca 2+ , Mg 2+ ) did not result in a distinct change in the color or in the spectrum of the suspension, indicating that these ions do not interfere with the colorimetric determination of Cr(VI). The detection concentration of Cr(VI) ranged from 7.0 Â 10 À8 to 1.84 Â 10 À6 M, and the detection limit was 5 Â 10 À8 M (3d). The performance of the sensor was successfully evaluated with water samples spiked with Cr(VI), indicating that this convenient and sensitive technique offers great promise for onsite environmental monitoring of Cr(VI).

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This study describes a simple and highly selective method for the colorimetric detection of trivalent chromium (Cr3+) using tartrate-capped silver nanoparticles (AgNPs) as probe. The addition of tartrate to the initially prepared AgNPs gives tartrate-stabilized AgNPs ascribing to the electrostatic repulsion of the highly negatively charged tartrate ions covered on the surface of AgNPs. It is found that, in the presence of Cr3+ in aqueous solution, the aggregation of tartrate-stabilized AgNPs occurs. The color of AgNPs suspension changes from yellow to pink and the surface plasmon absorption band broadens and red shifts, which could be applied for the colorimetric detection of Cr3+ in aqueous solution. The utilization of tartrate-stabilized AgNPs as probe substantially increases the selectivity and sensitivity for colorimetric detection of Cr3+. Control experiments with the addition of over 14 other metal ions, such as Pb2+, Zn2+, Cr2O7(2-), Cd2+, Co2+, Cu2+, Al3+, Ni2+, Mn2+, Ba2+, Fe3+, Ca2+, Mg2+, Sr+ do not result in a distinct change in the color or in the spectrum of the suspension, indicating that these metal ions do not interfere with the colorimetric detection of Cr3+. Under the conditions employed here, A502/A393 (ratio of absorption value at 502 nm to 393 nm) is linear with the concentration of Cr3+ within a concentration range from 0.1 to 1.17 microM with a detection limit of 0.06 microM. This study may offer a simple, rapid and sensitive approach to colorimetric detection of Cr3+ in aqueous solution.