This paper describes a novel enzymatic amplification strategy for ultrasensitive electrochemical immunosensing. This approach utilizes glucose oxidase for the enzymatic deposition of gold nanoparticies onto an indium tin oxide (ITO) electrode surface using a novel gold developer solution consisting of 20 mM of glucose, 20 mM of NaSCN, 0.5 mM of p-benzoquinone (PBQ) and 1 mM of AuCl(4)(-) dissolved in 0.1 M of pH 7.5 phosphate buffer solution. The amount of gold deposited was quantified electrochemically by monitoring the reduction of gold oxide in an aqueous solution of 0.5 M of H(2)SO(4), which was correlated to the amount of antigens in the solution. The effectiveness of this strategy was demonstrated experimentally through the construction of an immunosensor for the detection of mouse IgG using a sandwich immunoassay in a linear dynamic range of 5 pg/ml to 50 ng/ml. A good mean apparent recovery in the range of 88-102 was obtained over the entire linear dynamic range of the sensor response in the serum samples. This suggested that the immunosensor would be useful for the testing of proteins in real clinical samples.