Bifunctionalization of silver nanoparticles with 6-mercaptonicotinic acid and melamine for simultaneous colorimetric sensing of Cr3+ and Ba2+ ions

In this study, silver nanoparticles (Ag NPs) were bifunctionalized with 6-mercaptonicotinic acid (MNA) and melamine (MA) for simple, rapid and simultaneous colorimetric detection of Cr3+ and Ba2+ ions in water samples. The bifunctionalized Ag NPs were confirmed by UV-visible, FT-IR, dynamic light scattering (DLS), transmission electron microscopy (TEM), and atomic force microscopic (AFM) techniques. The bifunctionalized Ag NPs were induced to aggregate quickly with Cr3+ and Ba2+ ions through color change from yellow- to reddish brown (Cr3+) and -to orange (Ba2+), respectively which was readily seen by the naked eye. The recognition mechanism is attributed to the unique structures of MNA and MA on Ag NPs surfaces, which can yield strong interactions (cooperative metal-ligand interaction) between Ag NPs and metal ions (Cr3+ and Ba2+). It was observed that the addition of metal ions could induce the aggregation of Ag NPs solutions at pH 6.0, yielding changes in color and in UV-visible absorption spectra. Using this system, good liner range was obtained in the range of 10-370 mu M, with limit of detection 64.51 and 80.21 nM for Cr3+ and Ba2+ ions, respectively. This method was successfully applied to detect metal ions (Cr3+ and Ba2+) in drinking, tap and river water samples. (C) 2014 Elsevier B.V. All rights reserved.