Synthesis of fluorescent silver nanoclusters with potential application for heavy metal ions detection in water

Abstract

Metal nanoclusters (MNCs) are small aggregates of metal atoms with a mean diameter up to 2 nm, that when excited by electromagnetic radiation of suitable energy present an intense florescence. This optical property can be exploited in many fields such as bioimaging, drug delivery and optical sensing in environmental monitoring. In the present work, we synthesized silver nanoclusters (AgNCs) in water starting from AgNO3 and exploiting poly (methacrylic acid) (PMAA) as capping agent. The reduction of the silver ions Ag(I) to Ag(0) was promoted by the exposition of the solution to UV light radiation for 6 minutes. We studied the UV-Vis absorption and the fluorescence spectra for different pH values. The morphological characterization of the solution was accomplished by Transmission Electron Microscopy (TEM) and the statistical analysis showed that the mean diameter of the AgNCs was around 2 nm for the solution at pH = 4 which presented also the strongest fluorescence. Moreover, we studied the time stability of the absorption and fluorescence spectra. AgNCs stored in the dark at 4 °C were stable for more than 60 days. A possible application of the synthesized AgNCs deals with water monitoring by optical sensing based on the change of the fluorescence property in presence of heavy metal ions. Preliminary investigations show a high sensitivity to Pb(II) ions.