Ion-induced agglomeration of Ag NPs for quantitative determination of trace malachite green in natural water by SERS

Abstract

This article covers a simple one-step method that has been developed for ion-induced activation/agglomeration of silver nanoparticles. While using this method in Surface-enhanced Raman spectroscopy (SERS) we have recorded high values of signal enhancement factor (EF= 3.9 ×106). An important feature of the method is high stability of analytical signal (RSD of about 2% with analyte concentration at 1 ppb). We have shown, that in case of activation of nanoparticles with chlorides of alkaline earth metals the signal amplification proceeds according to a different mechanism rather than in case of NaCl. It was found that the synergistic action of two-charged cations (Ca2+, Mg2+, Ba2+) and chloride ions leads to the agglomeration of silver nanoparticles and the formation of “hot spots”, whereas in the case of NaCl at a concentration of up to 1 mM, only the surface modification of Ag NPs occurs. Kinetic studies have been carried out, and the mechanism of this process has been proposed. The obtained data served as a basis for the development of a simple and sensitive express method for the determination of trace amounts (in the range of 0.1–10 ppb, LOD = 0.002 ppb) of malachite green in water from natural sources. In order to compensate matrix effects we applied a standard addition method which simplified considerably the sample preparation process, increased method’s accuracy and reduced the time of analysis.