Aurothiomalate as an electroactive label for the determination of immunoglobulin M using glassy carbon electrodes as immunoassay transducers

A new electroactive label was used for monitoring immunoassays for the determination of human immunoglobulin M (IgM) using glassy carbon electrodes as supports of the immunological reactions. Aurothiomalate, a gold (1) complex, was bound to rabbit IgG anti-human IgM (RIgG-Au). The IgM was adsorbed on the electrode surface and then the immunological reaction with gold-labelled RIgG was carried out for an hour following non-competitive and competitive procedures. The analytical signal was based on the catalytic effect of gold deposited on the electrode surface upon silver electrodeposition. The gold (1) bound to the RIgG was electrodeposited in a 0.1 M HCl at -1.00 V for 5 min, and then, oxidised in a 0.1 M H2SO4 Solution, at + 1.40 V for 1 min. Then, silver electrodeposition at -0.14 V for 1 min followed by an anodic stripping voltammetry were carried out in aqueous 1.0M NH3-2.0 x 10(-4) M AgNO3. For both immunoassay formats, calibration curves in the range of 7.5 x 10(-11) to 1.0 x 10(-1) m of IgM were obtained with an estimated detection limit of 2.8 x 10(-11) M (25 ng/ml). Moreover, the levels of IgM in synthetic serum were evaluated, applying the method of standard additions following both formats competitive and non-competitive. These samples were previously pretreated in order to remove most of the albumin and IgG, which interfered in the electrochemical detection. (c) 2005 Elsevier B.V. All rights reserved.