Electrochemical determination of gold nanoparticles in colloidal solutions

A new method to determine the number concentration of gold nanoparticles in colloidal solutions is based on silver electrodeposition on the particles adsorbed on a carbon paste electrode. When colloidal gold was attached to a carbon paste electrode surface and then oxidised in a suitable media, the overpotential for cathodic deposition of silver was lowered relative to tha t of the carbon paste. Thus a range of potentials exists where the direct r eduction of silver ions on the carbon paste surface could be avoided whilst the process did proceed on the surface of the adsorbed gold particles. A p retreated carbon paste electrode was immersed in colloidal gold solutions f or 10 min. The modified electrode was then activated in a suitable media (0 .1 M NaOH and 0.1 M H2SO4) to form oxides on the surface of gold particles. Then, silver electrodeposition at - 0.12 V for 45 s followed by anodic str ipping voltammetry were carried out in aqueous 1.0 M NH3-2.0 x 10(-4) M AgN O3. A linear relationship was found between the area of the anodic strippin g peak and the number of colloidal gold particles cm(-3) (from 3.62 x 10(7) to 9.06 x 10(8) particles cm(-3)) and a detection limit of 1.25 x 10(7) go ld particles cm(-3) were obtained. In addition, colloids of gold with molec ules of protein (albumin) adsorbed on their particles could be determined. In this last case, a detection limit of 1.80 x 10(7) gold particles cm(-3) was obtained. (C) 2000 Elsevier Science Ltd. All rights reserved.