Label-free electrochemical immunoassay of Bcl-2 protein expression on tumor cells

Bcl-2 protein is one of the anti-apoptotic members in Bcl-2 family proteins. It can regulate apoptosis in response to a wide variety of toxic agents, which has a close relationship with drug-resistance of tumor cells. Electrochemical impedance spectroscopy measurements were employed to quantify the cell concentration and analyze the expression of Bcl-2 protein on tumor cells and drug-resistant tumor cells based on the competitive immunoassay. Bcl-2 antibody and bovine serum albumin were adsorbed on Au nanoparticles to construct nanocomposites that could be captured on the Bcl-2 protein modified electrode. The binding of the nanocomposites resulted in a great increase of the charge-transfer resistance (Rct) due to the strong steric hindrance effect and this effect was inhibited in the presence of MCF-7 cells and MCF-7/ADR cells owing to the competitive immunoreaction between the nanocomposites and Bcl-2 proteins on cells. Under the optimal conditions, the charge-transfer resistance change (ΔRct) is proportional to the logarithm of the cells concentration from 5×10(2) to 1.6×10(6) cell mL(-1) with a detection limit of 170 cell mL(-1). The expression of Bcl-2 protein on MCF-7/ADR cells was found to be significantly higher than that in MCF-7 cells, indicating that the up-regulation of Bcl-2 protein is one of characteristics of drug-resistant tumor cells.