Fabrication of Ag nanoparticles by γ-irradiation: Application to surface-enhanced Raman spectroscopy of fungicides

This paper is concerned with the surface enhanced Raman scattering (SERS) activity of silver colloids obtained by a radiolytic method. Ag nanoparticles were successfully prepared by γ-radiolysis of Ag+ aqueous solution containing t-BuOH or i-PrOH at room temperature without the addition of aggregating or stabilizing substances. The metal colloids were characterised by UV/vis spectroscopy and scanning electron microscopy. Many experimental conditions were tested (i.e. Ag+ concentration, dose and OH scavenger alcohol) in order to obtain the best controlled size of nanoparticles as well as the high stability of colloidal silver with time. The use of relatively low irradiation doses and Ag+ concentrations allowed to obtain very stable suspensions of Ag nanoparticles without adding any colloid stabiliser, a source of further spurious bands in the Raman spectra. The suitability of the γ-irradiated colloids in SERS spectroscopy was tested by using thiram, a known fungicide. Micro-SERS and SERS spectra of good quality were achieved at very low concentration of adsorbate, without the overlapping of impurities normally present in conventional citrate colloidal suspensions of Ag nanoparticles.