Highly selective and sensitive colorimetric determination of Cr3+ ion by 4-amino-5-methyl-4H-1,2,4-triazole-3-thiol functionalized Au nanoparticles.

In this work, a rapid, selective naked eyes colorimetric chemical probe for the detection of Cr3+ was developed based on functionalization of gold nanoparticles. For this purpose, surface of Au NPs was functionalized using 4-amino-5-methyl-4H-1,2,4-triazole-3-thiol (AMTT). Through colorimetric studies, it was found that in the presence of Cr3+ ions, AMTT-Au NPs instantly aggregated and resulted in a color change of the solution from red to blue. The color change of AMTT-Au NPs due to the aggregation induced by Cr3+ can be seen with even naked eyes and also by UV-Vis spectroscopy with a detection limit of 1.8μM and 0.1μM, respectively. AMTT-Au NPs showed excellent selectivity toward Cr3+ compared to other cations tested, including K+, Na+, Cs+, Fe3+, Ni2+, Cu2+, Co2+, Zn2+, Ba2+, Ca2+, Mg2+, Cd2+, Pb2+, Hg2+ ions and especially all trivalent lanthanide ions. The absorbance ratio (A650/A525) was linear toward Cr3+ concentrations in the range of 0.6-6.1μM (R2=0.996). The best response was achieved over a pH range of 3-5. Furthermore, the proposed colorimetric method based on AMTT-Au NPs was successfully used for Cr3+ ion detection in plasma sample and some water samples.