Selectivity of silver nanoparticle sensors: Discrimination between silver nanoparticles and Ag+

The selectivity of four sensors for silver nanoparticles detection is studied. Three of them are based on the chemical interaction of the silver nanoparticle and the thiol group of Cysteine, 1,6-hexadithiol and 8-mercaptoquinoline covalently bound to an electrode and the fourth on electrostatic attraction between a negatively charged nanoparticles and the protonated amine of cysteamine bound to a gold electrode. The sensor based on cysteamine was selective to silver nanoparticles and was not affected by Ag(I). The 8-mercaptoquinoline based sensor did not bind silver nanoparticles and was selective to Ag(I), Cysteine and 1,6-hexaditiol based sensors bound both silver nanoparticles and Ag(I), this caused the decrease of the signal for silver nanoparticles which disappeared when the concentrations of Ag(I) and silver nanoparticles are of the same magnitude. 1,6-hexaditiol based sensor was selected to determine the concentration of silver nanoparticles in a health care product whose Ag(I) concentration was low enough not to interfere. Information about the size of the nanoparticles can also be obtained if the diffusion of the oxidation products of a nanoparticle is independent of its neighboring nanoparticle.