A electrical detection of protein is developed in this paper by using self-assembled multilayer gold nanoparticles (AuNP) onto SiO2/Si substrate between gold electrodes. The electrical measurements were performed at room temperature using a probe station. The first monolayer of AuNP is formed by immobilizing AuNP on SiO2 substrate using 3-Aminopropyltrimethoxysilane (APTMS) molecules. Then, monoclonal antibody is immobilized on the top surface of the first monolayer of AuNP. The second layer of AuNP is formed through specific binding among target antigen (Hepatitis C virus, (HCV)), monoclonal antibody (2B2 by GBC in Taiwan), and conjugate of gold nanoprticle with polycolnal antibody (GP by GBC in Taiwan). The target antigen is sandwiched between monoclonal antibody and conjugate of AuNP-polycolnal antibody. The system relies on gold nanoparticles probes and nano-gap-electrode device with antibodies that specifically binding a protein target of antigen and antibodies that can sandwich the target captured by the nanoparticles probes. As shown in Fig. 1, the average diameter of gold nanoparticles is around 15 nm. A significant difference in IV curves of monolayer and multilayer of AuNP can be used to identify the target antigen in the tested sample. No significant current, which is less than 1 pA, can be measured for the monolayer of AuNP. Once the binding among antigen and antibodies occurs, a peak electrical current can be observed at V ≈ 5.9V.