Determination of nickel(II) at nanomolar levels using iodide-responsive gold-copper nanoparticles as colorimetric probes.

The authors present a colorimetric method for the quantification of Ni(II) at nanomolar levels. It is based on the use of iodide-responsive copper-gold nanoparticles (Cu-Au NPs) combined with the Ni(II)-catalyzed glutathione (GSH)-oxygen reaction system. In the presence of Ni(II), the catalytic reaction between GSH and oxygen is can triggered. This leads to the formation of GSSG which is bulky and hinders the access of iodide to the surface of the Cu-Au NPs. Concomitantly, the color of the solution containing the Cu-Au NPs changes from gray to red. Based on these findings, a method was developed for the quantitation of Ni(II) that has a detection limit as low as 0.54 nM. This is 1-3 orders of magnitude lower than that of previously reported optical methods. The assay has excellent selectivity for Ni(II), is rapid, cost-effective, portable, and allows for bare eye observation. Conceivably the method is suitable for field detection of Ni(II) in biological, food, and environmental samples. Graphical Abstract A sensitive colorimetric strategy for Ni(II) through the combination of iodide-responsive Cu-Au NPs with Ni(II)-catalyzed the oxidation of GSH by oxygen was presented.