Sensitive electrochemical immunosensor based on enlarged and surface charged gold nanoparticles mediated electron transfer

A simple and sensitive electrochemical immunosensor for the detection of protein biomarker interleukin-6 (IL-6) based on gold nanoparticles (AuNPs) as label was reported. The signal of the immunosensor was originated from enlarged and positively charged AuNPs mediated electron transfer between insulating self-assemble monolayer (SAM) modified electrode and K3Fe(CN)6 solution. The gold electrode was first modified with SAM to block the electron transfer between the electrode and K3Fe(CN)6 solution. After the preparation of the immunosensor, the AuNPs attached onto electrode was enlarged and positively charged when treated in solution containing HAuCl4, ascorbic acid and cetyltrimethylammonium bromide (CTAB). The enlarged and positively charged AuNPs then mediated electron transfer between the electrode and K3Fe(CN)6 solution, creating redox current that is proportional to the concentration of IL-6 detected. The reported immunosensor has high sensitivity and wide linear range. This novel signal amplification strategy can be applied to the detection of different kinds of protein biomarkers.