Colorimetric determination of copper(II) using a polyamine-functionalized gold nanoparticle probe

A branched polyethyleneimine was used to functionalize gold nanoparticles (AuNPs). It is found that copper ions rapidly induce the aggregation of such AuNPs, this resulting in a color change from red to purple. The effect can be exploited for visual (bare-eye) detection or instrumental quantification of Cu(II) by measuring the ratio of absorbances at 650 and 520 nm at pH 4 and after a 7-min incubation time. The method works in the 0.1 to 10 μM Cu(II) concentration range and with a 30 nM limit of detection. It exhibits fairly good selectivity over other common metal ions. The standard addition method was successfully applied to the determination of Cu(II) in (spiked) tap and lake waters.