Fast Colorimetric Detection of Copper Ions Using L-Cysteine Functionalized Gold Nanoparticles

This communication reports an efficient visual detection method of Cu2+ by L-cysteine functionalized gold nanoparticles in aqueous solution. Upon exposure to Cu2+, the gold nanoparticle solution changed from red to blue, in response to surface plasmon absorption of dispersed and aggregated nanoparticles. This colorimetric sensor allows a rapid quantitative assay of Cu2+ down to the concentration range of 10−5 M. Recognition of Cu2+ and formation of the aggregates are proposed to occur via a 2 : 1 sandwich complex between L-cysteine and Cu2+.