Electronic profiling of synthetic DNA using Schottky junctions / Souhad M.A Daraghma

Souhad M.A , Daraghma (2020) Electronic profiling of synthetic DNA using Schottky junctions / Souhad M.A Daraghma. PhD thesis, Universiti Malaya.

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Abstract

Deoxyribonucleic acid (DNA) has attracted a lot of attention lately owing to the discovery of its semiconducting property and is considered as an interesting material that could find applications in nanotechnology and electronic devices. In-depth understanding of its charge transfer mechanism is however required for effective development of DNA-based technology. This unfortunately remains still a non-trivial task despite the numerous theoretical and experimental studies that have been conducted to date. The complexity of the previously employed methods, and their lack of accuracy has made it difficult to grasp the clear understanding of the electronic behaviors of the DNA molecules under varying conditions. Previously, introduced by our very own research group, Schottky junction based-DNA (metal-semiconductor) was fabricated and proved to be a simple, rapid and cost-effective method for characterizing the electronic properties of DNA. In our current work, attempt has been made to uncover the charge transfer mechanism by fabricating Schottky junctions incorporating synthetic DNA strands so that accurate electrical conductivity of various DNA structures and sequences could be quantitatively investigated and differentiated. Initially, the current-voltage (I-V) profiles and related solid-state parameters such as turn-on voltage, series and shunt resistance, ideality factor and saturation current were obtained for DNA thin film prepared using Langmuir Blodgett (LB) technique. Tris base, boric acid (TBE) buffer was employed for the first time instead of deionized water as the subphase in this study since DNA tends to dissolve in water due to its hydrophilicity. Pure DNA thin film deposited on indium tin oxide (ITO) substrate was integrated with copper (Cu) tape electrodes to fabricate the Schottky junction. The electronic parameters of the fabricated contact (Cu/DNA-film/ITO) were observed to demonstrate excellent electrical conductivity and low resistance. However, due to lengthy and time-consuming film preparation process of the LB technique, a droplet-based DNA method was further utilized to enable a simpler and practical method for rapid electrical characterization of the different DNA samples. This was achieved by means of a printed circuit board (PCB) integrating gold (Au) electrodes with applied DNA droplets to form the Au/DNA/Au Schottky junctions. Synthetic single-stranded (ss) and double-stranded (ds)DNA samples having different bases and base pair sequences were measured in positive and negative voltage regions and its characteristic DNA electronics studied. Interestingly, dsDNA demonstrated greater conductance than ssDNA and DNA with G-C base pair sequence has higher conductance than A-T sequence while the nitrogenous base G has the best conductivity amongst the four DNA bases. It is therefore anticipated that the novel electronic technique introduced in this thesis may well contribute immensely towards further understanding the elusive charge transfer mechanism through DNA, and potentially other biomolecules in general.

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