Gluconate stabilized silver nanoparticles as a colorimetric sensor for Pb2+

Synthesis and functionalization of silver nanoparticles (Ag-NPs) were simultaneously accomplished with highly water soluble gluconate anions (Gluc(-)). The gluconate functionalized silver nanoparticles (Gluc-Ag-NPs) were found to be anionic in nature with zeta potential (zeta) value of -55 +/- 2 mV at pH 7.92 and were made apply for a chemo-sensor probe for Pb2+. The particles belong to face-centered-cube (FCC) crystal system and have pseudospherical shape with diameter 9.57 +/- 2 nm. Although free gluconates are reputed complexing agent for various metal ions, we have found, when they are in the state of adsorption onto the Ag-NPs surface, bind selectively Pb2+ in aqueous solution over other metal ions including Al3+, Ba2+, Cu2+, Cd2+, Ca2+, Fe3+, Hg2+, K+, Mg2+, Mn2+, Na+, Ni2+, and Zn2+. Binding onsets association followed by aggregation of particles, which is a kinetic effect and leads to quenching of surface Plasmon band intensity at 395 nm and subsequently appearing of a band at 524 nm. The phenomenon results color change of the particles. The study of aggregation kinetics at UV-vis spectroscopy tool helps to evaluate Gluc(-)-Pb2+ association constant (K-asso = 3.42 x 10(5) M-1) and critical coagulation concentration (CCC = 1.91 mu M) values. The developed system is simple and highly sensitive to detect Pb2+ ions colorimetrically with limit of detection (LOD), 0.2029 mu M. The system showed excellent recovery results when it was tested for determining Pb2+ from tap-water samples spiked with the same.