Modulation of molecular hybridization and charge screening in a carbon nanotube network channel using the electrical pulse method.

In this paper, we investigate the effect of electrical pulse bias on DNA hybridization events in a biosensor platform, using a Carbon Nanotube Network (CNN) and Gold Nano Particles (GNP) as an electrical channel. The scheme provides both hybridization rate enhancement of bio molecules, and electrical measurement in a transient state to avoid the charge screening effect, thereby significantly improving the sensitivity. As an example, the probe DNA molecules oscillate with pulse trains, resulting in the enhancement of DNA hybridization efficiency, and accordingly of the sensor performances in Tris-EDTA (TE) buffer solution, by as much as over three times, compared to the non-biasing conditions. More importantly, a wide dynamic range of 10(6) (target-DNA concentration from 5 pM to 5 µM) is achieved in human serum. In addition, the pulse biasing method enables one to obtain the conductance change, before the ions within the Electrical Double Layer (EDL) are redistributed, to avoid the charge screening effect, leading to an additional sensitivity enhancement.

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.

Multi-order dynamic range DNA sensor using a gold decorated SWCNT random network.

A novel electrical DNA biosensor is presented, which consists of gold (Au) nanoscale islands and a single-walled carbon nanotube (SWCNT) network on top of a concentric Au electrode array (also referred to as the CGi). The decorated Au islands on the SWCNT network provide ideal docking sites for ss-DNA probe (p-DNA) molecules. They also provide better adhesion between the SWCNT network and the chip substrate. In addition, the concentric electrode gives asymmetric current voltage characteristics in the solution and provides more flexible bias options to the electrodes. The sensor system is applied to a DNA sensor after functionalization with a 25 mer p-DNA (5'-HSC(6)-C(18)-GCCATTCTCACCGGATTCAGTCGTC-3'), hereafter called the [CGi+p-DNA]. The response of the DNA sensor has been measured in both real-time during hybridization with the complementary target ss-DNAs (t-DNA) and the static mode after the hybridization and washing steps. A wide dynamic range from the 100 fM to 1 µM has been achieved from the real-time mode and the static mode. Moreover, it is shown that the sensor system differentiates partially mismatched (single nucleotide polymorphism (SNP), half mismatch, noncomplementary) t-DNA, as well. The [CGi] sensor platform can be easily extended to target specific biological recognition elements such as aptamers or proteins.