Gold colloid solutions were prepared,by reduction of Au(III) with Sn(II) in both acidic (HO) and alkaline (carbonate) media, and characterized by electron microscopy, X-ray diffraction and light absorption spectra. Depending on the colloid preparation conditions, metal particles of 5-30 nut in size were obtained. Light absorption spectra of the Au colloid solutions contain an absorption band at 500-600 nm, typical of small gold particles. According to XRD data, colloid particles contain the metallic Au and SnO2 phases. The colloid formation rate and colloid solution stability depend on solution pH; the alkaline colloid solutions are formed more slowly and are more stable. The gold nanoparticles adsorbed on the dielectrics surface were found to initiate the electroless copper deposition process. The glassy carbon (GC) electrode modified by Au nanoparticles (200-900 ng cm(-2) Au) was found to be an electrocatalyst for dimethylamine borane, borohydride, hydrazine, and formaldehyde oxidation in alkaline solutions. The activity of the reducers can be arranged as follows: DMAB > NaBH4 > N2H4 > CH2O (c) 2007 Elsevier Ltd. All rights reserved.