Conductance of individual DNA molecules measured with adjustable break junctions

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LIU, Shoupeng, 2010. Conductance of individual DNA molecules measured with adjustable break junctions [Dissertation]. Konstanz: University of Konstanz

@phdthesis{Liu2010Condu-9077, title={Conductance of individual DNA molecules measured with adjustable break junctions}, year={2010}, author={Liu, Shoupeng}, address={Konstanz}, school={Universität Konstanz} }

Liu, Shoupeng Liu, Shoupeng 2010 2011-03-24T17:53:24Z application/pdf 2011-03-24T17:53:24Z deposit-license Leitfähigkeit einzelner DNA-Moleküle gemessen mit regelbaren Bruchkontakten eng In this thesis, we described our MCBJ setup which enable us to measure the conductivity of single (or a few) molecules at different conditions, ie. in solution, in ambient or in high vacuum. We characterized the performance of setup especially in buffer solution which is not established before. The setup also enables us to monitor the change of conductivity of studied molecules during its conformational change (stretched or relaxed). With the help of this special feature, we studied the conductance of DNA molecules in two different forms, double stranded DNA and G-quadruplex. Transport properties of DNA is important mainly because its potential usage in future nano-electronics. However at present it is limited by its poor measured conductivity. In order to enhance the conductance of the metal-DNA-metal systems, we used a novel protocol to bind the DNA molecules to the gold electrodes. The terminal thymine bases are modified with protected thiol- group at 5 position of the back instead of at backbone, which allow direct coupling between &#960; system of DNA and electrodes. Strong bindings of the DNA to fresh gold surface are observed both with microscopy and during conductance measurement with MCBJ in solution. More important, we measured a higher conductance on the 21bp DNA duplex than results reported before, 0.16 ~ 0.2 mG<sub>0</sub> for single DNA conductance in vacuum. Moreover, we studied the conductance of a G-quadruplex with MCBJ. The G-quadruplex has stacked planes made by four guanine bases and trapped ions in the center channel, so it is prospected to have better conductance. We observed a stable conductance plateau during opening and closing the MCBJ, which may corresponds to the unfolding/refolding process of the G-quadruplex. The non-linear I-V curves are qualitatively explained by an "off-resonance tunneling" model. Besides these improvements, the conductance of DNA is still below the requirement to use DNA directly as a conductive nanowire, and its transport mechanism is still not fully understood. Further studies should be done as following: 1. In order to fully understand the transport properties of both DNA duplex and G-quadruplex, detailed knowledge about their band structures are desired. Although our IV curves do show non-linear S-shapes or asymmetric, but quantitative estimate of band structure are impossible because of the thermal fluctuations. This can be realized by doing the measurement at low temperature. The challenge will be modification of our MCBJ setup to fit in the low temperature chamber. The whole setup may need to be redesigned. 2. During opening and closing of the MCBJ, the molecules in the junction, DNA duplex or G-quadruplex, are stretched and further denatured. However, the stretch processes of both molecules under external forces are not well known yet. There is no experimental report on the structure of these stretched molecules. Results from computer simulations are also limited and need to be verified. Moreover in our experiment, we do see some difference on the open-close curves measured in solution and in vacuum, i.e. the long stable plateau measured with dsDNA in solution vanished when measured in vacuum. This difference is attributed to the different stretch process of DNA in solution and in vacuum. So in order to understand the measurement results with MCBJ more quantitatively, we need more knowledge about the stretched structure of molecules (DNA duplex or G-quadruplex) both in solution and in vacuum. 3.In our G-quadruplex sample, the thiol functionality is attached on the terminal thymine bases, which is not part of quartet plane. So electrons from gold electrodes are not directly coupled to the &#960; system of G-quadruplex. In future studies, it is desired to attach thiol functionality to the guanine bases. Only by this way, a good contact in the meaning of conductance measurement between G-quadruplex and gold electrodes can be established, so that we can probe the intrinsic transport properties of G-quadruplex without hindrance by the contact resistance. 4. In our experiments, the G-quadruplex sample has only 22 bases and contains three stacked quartet planes. It is needed to measure the dependence of conductance on the length of G-quadruplex, i.e. more quartet planes. More particular, we can measure the conductance of a G-wire, which is intermolecular G-quadruplex and can have length up to micrometers, by using micro-fabricated electrodes. If the conductance is good enough, it can be directly integrated into nanoelectronic circuits Conductance of individual DNA molecules measured with adjustable break junctions

Dateiabrufe seit 01.10.2014 (Informationen über die Zugriffsstatistik)

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