Comparative analysis of electrical detection methods of DNA synthesis.

The incorporation of a complementary deoxynucleotide (dNTP) into a self-primed single-stranded DNA (ssDNA) attached to the surface of a sensor electrode generates an H+ charge that can be either trapped on the sensor surface or diffused into the surrounding solution. Electrical detection methods of DNA synthesis are based on these H+ kinetic mechanisms. The detection method that uses ISFET, which is related to the surface trapping mechanism, showed a better sensing signal than the induced charge detection method, which is related to the diffusion of H+ into the surrounding solution. The trapping reaction should be well-controlled, however, so that it would be stable under various surface conditions and temperatures. Moreover, the reaction should be reversible, and the reaction parameters should be well-sustained in the subsequent synthesis cycles. For the induced charge method, the AC current level was too small to be detected using an ordinary amplifier circuit with the same sensor size as that of ISFET. Consequently, the sensor operation sustainability and signal-to-noise ratio characteristics should be addressed carefully in the selection of the proper sensor type.