Colorimetric detection of mercury(II) in aqueous media with high selectivity using calixarene functionalized gold nanoparticles

A facile strategy for the preparation of water soluble gold nanoparticles functionalized by dithiocarbamate derivative of calixarene and application of this material as colorimetric sensor for metal ions in aqueous media is reported. This material selectively detects Hg2+ in aqueous media in presence of a large number of metal ions with a sharp colour change, detectable by naked eyes. No significant interference from other metal ions used in this study is noted. The stability of the functionalized nanoparticles in water is examined with variation in pH and found that it is highly stable in the pH range of 4.4-7.8. At the optimum conditions, it exhibited a dynamic response for Hg2+ in the concentration range of 0.2 mu M to 100 mu M of metal ion with the detection limit of 40 ppb. Detail spectroscopic and microscopic studies revealed that the visual colour change from red to violet and the shifting of SPR band is due to assembly of gold nanoparticles into arrays through the bare surfaces by dipole-dipole interaction. The bare surfaces of gold nanoparticles were generated by the displacement of calixarene derivative from the surface of the functionalized gold nanoparticles due to strong complexation between Hg2+ and calixarene derivative. The HRTEM images, UV-vis spectral study and results of DLS measurements are consistent to support this conclusion. For practical application, this new material is successfully tested for detection of Hg2+ in drinking water as real sample. (C) 2014 Elsevier B.V. All rights reserved.