Highly selective colorimetric detection of Zn(II) ions using label-free silver nanoparticles

A simple and facile colorimetric method for the detection of zinc ions (Zn2+) using label-free silver nanoparticles (AgNPs) has been developed. Zn2+ ions induced the aggregation of label-free AgNPs in solution, resulting in a color change from yellow to forest green, which was accompanied by the appearance of a new surface plasmon absorption band at 635 nm. The sensitivity of label-free AgNPs towards other metal ions was negligible, with the exception of Fe3+, which caused a modest interference. The binding site and sensing mechanism for Zn2+ ions in label-free AgNPs were characterized by Fourier Transform infrared spectroscopy, ultraviolet-visible spectroscopy, and transmission electron microscopy. The aggregation of AgNPs in the presence of Zn2+ ions was inhibited by polyvinyl alcohol, which formed a shell on the surface of AgNPs. Furthermore, Zn2+ ions coordinated with BH4- on AgNPs through a triangular sixdentate binding structure, thus inducing aggregation of AgNPs in solution. The sensor conditions were optimized with 6.0 mu M of sodium dodecylbenzenesulfonate (NaDDBS) and 0.23 mM AgNPs at pH 6. The absorption ratios (A(635)/A(390)) of the label-free AgNPs solution exhibited a linear correlation with Zn2+ ion concentration within the range of 0.0 - 7.6 x 10(-6) mol L-1, with a limit of detection of 0.36 x 10(-6) mol L-1. This cost-effective sensing system allows rapid and facile determination of Zn2+ ions in various types of biological, mineral supplement, and environmental samples. (C) 2016 Elsevier B.V. All rights reserved.