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Description
The electrical conductivity of DNA remains to be controversial with various studies, which reports DNA properties varying from insulator to extreme conductivity (superconductive). This study investigates experimentally the electrical behavior and performance of a double-stranded Lambda DNA ( ?DNA) wire on two and three dimensional (2- and 3-D) electrodes by suspending the DNA thereby eliminating the effect of substrate that is thought to be the culprit of inconsistent results. The 2-D DNA platform design developed in this study helped to obtain an optimized 3-D platform. The 3-D chip architecture is made of layers of a negative photoresist (SU8) and gold layered on silicon dioxide substrate. The DNA attachments on 3-D and 2-D electrodes were demonstrated based on the following methods: oligo-DNA self assembly, electrostatic, and electrical field attractions. Electrical results based on I-V and R-V curves showed measurable and significant conductivity through the DNA wire that we believe could establish it as a semi-conductor. A mathematical model based on I-V data as well as an electrical circuit model for ?DNA are also developed in this study. An equivalent electrical circuit was created in PSpice where DNA is modeled as a voltage-controlled current source. This is important because having models of DNA molecules in the form of equivalent electronic circuits would be useful in the design of nanoelectronic circuits and devices. The research presented here is characterized by a significant departure from previous studies and made unique contributions by (1) DNA assembly on 3-D structures, which showed lower resistance and higher conductivity in comparison to 2-D or flat electrodes. (2) 3-D DNA platform structure demonstrated better stability than 2-D structure. (3) Additionally, these high aspect-ratio 3-D electrodes prevented the suspended DNA from contacting the substrate. This helps to collect more accurate resistance measurements. (4) design of narrow and tapered electrode tips helped to guide and attract DNA electrostatically between two gold posts. (5) Furthermore, design of four electrodes in this study had an advantage that almost no current flowed in the sense wires, thus the voltage drop was extremely low. This allowed more precise measurements than traditional two sensing probes.
