DNA Biosensors for Medical Diagnosis

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Most of biosensors rely on proteins such as enzymes and antibodies, while DNA is also an important host molecule in biological affinity reactions. DNA-immobilized electrode may be a usuful tool for medical diagnosis. We immobilized DNA double strands on a Au electrode via chemisorption. Cyclic voltammograms of ferrocyanide were taken with the DNA-modified electrode. When adding DNA-binding molecules, the CV peak currents increased with increasing concentration of them. The peak current showed a sigmoidal relationship with the logarithmic concentration of the added compound. The sensor comprising DNA was confirmed to be a useful tool for evaluation of the interaction between DNA and DNA-binding molecules. In addition, this DNA-modified electrode was found to respond to anti-DNA antibody which specifically binds to double helical DNA.Anti-DNA antibodies has been used as marker molecule of Systemic Lupus Erythematossus (SLE). We also developed a novel electrochemical technique for gene detection in which the sandwich-type complex from oligodeoxynucleotide (ODN) immobilized on Au electrode, target DNA,and the ferrocenyl ODN is formed to give a response. Differential pulse voltammograms for the modified electrode showed a significant anodic peak due to the oxidation of ferrocene moiety of the probe DNA,when the electrode was treated with the target DNA.On the other hand, only a slight peak was observed for the modified electrode which was treated similarly with the mismatch control. These results indicate that the target was recognized by means of complementary base-pairing with the ODN immobilized on thw electrode.