Selective visual detection of Pb(II) ion via gold nanoparticles coated with a dithiocarbamate-modified 4'-aminobenzo-18-crown-6

We have developed a crown ether based selective colorimetric sensing scheme for the determination of Pb(II) ion by using gold nanoparticles modified with dithiocarbamate derivative of 4'-aminobenzo-18-crown-6 that acts as a colorimetric probe. Monodisperse Au-NPs were prepared by reacting 4'-aminobenzo-18-crown-6 with carbon disulfide to generate the dithiocarbamate ligand which was then added to the Au-NPs to form a supramolecular assembly on their surface. The Au-NPs modified in this way undergo aggregation in the presence of Pb(II) ions, and this causes the color to change from red to blue. The Pb(II)-induced aggregation can be monitored by using UV-visible spectrometry and even with the bare eye. The absorbance ratio (A(650nm)/A(520nm)) is linearly related to the concentration of Pb(II) in the 0.1 to 75 mu M range (with a correlation coefficient of 0.9957), and the detection limit is 50 nM which is lower than the allowable level (75 nM) as defined by the US EPA. The method was successfully applied to the determination of Pb(II) in spiked water samples.