Colorimetric detection of Cu2+ by surface coordination complexes of polyethyleneimine-capped Au nanoparticles

A new simple colorimetric chemosensor for sensitive and selective detection of Cu2+ using polyethyleneimine (PEI)-capped Au nanoparticles (PEI/Au NPs) has been developed. PEI/Au NPs are synthesized by using PEI as reducer without adding nanoparticles seeds and stabilizing agent. Copper ions are captured by the amino groups of the PEI/Au NPs to form an absorbent complex at the surface of PEI/Au NPs, resulting in the color of PEI/Au NPs changing from wine red to purple. Under the optimal conditions, the proposed colorimetric sensor is capable of sensitively and specifically detecting Cu2+ with a detection limit of 0.29 μM and a linear range of 25-300 μM. This method is simple, fast and highly selective for Cu2+ in the presence of high concentrations of other environmentally relevant metal ions because of the great specific coordination between Cu2+ and PEI, which potentially meets the requirement of the detection in real samples. Moreover, addition of EDTA to PEI/Au NPs-Cu2+ recovers the color offering PEI/Au NPs as a promising reversible sensor for practical application.