Quantification of Bax protein on tumor cells based on electrochemical immunoassay

Bax protein is a pro-apoptotic member of Bcl-2 family proteins on cells and exhibits a close relationship with drug resistance of tumor cells. Its quantification can provide significant information for cancer treatment and research. A valid and sensitive electrochemical method for quantitative analysis of Bax protein on tumor cells was developed using thionine–graphene composites (TH–GN) based on a competitive immunoreaction. Bax protein and horseradish peroxidase were assembled on the TH–GN modified electrode to construct an electrochemical biosensor. The binding of Bax antibody could decrease the responses of the developed biosensor due to the strong steric hindrance effect and this effect was weakened in the presence of tumor cells or free Bax protein. Under optimal conditions the peak current change derived from the differential pulse voltammetry (DPV) measurements (ΔIDPV) was proportional to the cell concentration from 2.5 × 103 to 1.6 × 105 cells mL−1 with a detection limit of 800 cells mL−1. The average amount of Bax protein on single MCF-7 cell and MCF-7/ADR cell were calculated to be (1.2 ± 0.2) × 1011 molecules and (7.2 ± 1.1) × 1010 molecules, respectively. It indicates that the decrease of Bax protein is one of important reasons resulting in drug resistance of tumor cells.