However, when the concentration of P-gp was high enough to be detected by the conventional technologies, such as western blotting and confocal laser scanning microscopy, the effectiveness of the drug couldn't be recovered at this stage.4–7 Considering the challenge and promising applications, it was urgent to develop an ultrasensitive approach to identify the expression of P-gp in cells and then demonstrate the drug resistance of those cancer cells, especially at that early stage. The gene discussed is PGP; the disease is cancer.