Sensitive and accurate detection of cancer cells plays a crucial role in clinical diagnosis, treatment and prognosis of tumors. In this paper, we report a new electrochemical method for highly selective and sensitive detection of cancer cells by using small molecule-linked DNA as probes. The methodology is based on the fact that exonuclease I can catalyze the digestion of folate-linked DNA probes that are immobilized on an electrode surface; however, in the presence of the target cells, such as human breast cancer MCF-7 cells, the probes can be protected from digestion upon the binding with folate receptor that is over-expressed on the cell surface. Consequently, cancer cells can be efficiently detected by monitoring the status of the probe DNA with electrochemical techniques. In this study, the protection to exonuclease I-catalyzed digestion has also been proven by electrochemical studies. Moreover, the proposed method has been proven to linearly detect MCF-7 cells in a wide range from 10(2)-10(6) cell mL(-1) with a low detection limit of 67 cell mL(-1), which can also easily distinguish the folate receptor-negative normal cells, for instance, islet β cells. The reproduction of the detection is also satisfactory, since the relative standard deviations for three independent measurements of different concentration of MCF-7 cells are all within 10%. By replacing the small molecules linked on the DNA probe, other cancer cells can also be detected by making use of this proposed method. Therefore, our cytosensor may have great potential in clinical applications.
Keywords: Cancer cells; Electrochemical techniques; Exonuclease I; Folate; Folate receptor.
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