The clusters of immunogold nanoparticles were fabricated through cross-linking immunogold nanoparticles with glutaraldehyde. A novel strategy for immunoassay signal amplification using the clusters of immunogold nanoparticles on glass slides based on electroless deposition was described. The immunoassay signal amplification through the clusters of immunogold nanoparticles was about three to four times higher than that through single immunogold nanoparticles. The purple attachments were readily discernible on glass slides by naked eye at a concentration of 0.1 pg/mL antigen in PBS solution. The indirect detection of antigen using the clusters of immunogold nanoparticles is an efficient way to improve the detection sensitivity. (c) 2006 Elsevier B.V. All rights reserved.