DNA-NEMS sensor from diamond

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In this application we will realize and optimize DNA-NEMS (Nano-Electro-Mechanical-Systems) structures on diamond for electrochemical detection of DNA hybridization. The dissimilar kinetic behavior of electrically manipulated single and double-stranded DNA will be applied as sensor principle. The DNA marker molecules will be redox-labeled and covalently bonded to a diamond working electrode. The counter electrode will be a Diamond Scanning Electro-Chemical Microscopy (SECM) Tip which is part of a scanning probe microscope and which can be place with nano-meter accuracy to optimize the geometry. The target DNA will be label free. To cause a redox current, the DNA will be exposed to ac electric fields where the redox label is moving between working and counter electrodes. Fourier-transform lock-in detection will be applied to monitor the redox current amplitude and phase. These experiments will be performed on micro- to nano-electrodes with electrode diameters ranging from 200 micrometer (micro-electrode) to 200 nm (nano-electrode) in electrolyte solutions with varying salt concentrations (3 mM to 1000 mM). Due to a change of flexibility from ss- to ds-stranded DNA molecules the variation of current amplitude and phase will be characterized in detail. The sensor area will be miniaturized with the goal to reach highest sensitivity, reproducibility and fast sensing. The dissimilar kinetic behavior of ss- and ds-DNA will be characterized in detail to deduce the ss/ds discrimination parameters from a) frequency response, b) electric field response and c) variations in oscillating height amplitudes.