7 research outputs found

    DNA-graphene interactions during translocation through nanogaps

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    <div><p>We study how double-stranded DNA translocates through graphene nanogaps. Nanogaps are fabricated with a novel capillary-force induced graphene nanogap formation technique. DNA translocation signatures for nanogaps are qualitatively different from those obtained with circular nanopores, owing to the distinct shape of the gaps discussed here. Translocation time and conductance values vary by ∼ 100%, which we suggest are caused by local gap width variations. We also observe exponentially relaxing current traces. We suggest that slow relaxation of the graphene membrane following DNA translocation may be responsible. We conclude that DNA-graphene interactions are important, and need to be considered for graphene-nanogap based devices. This work further opens up new avenues for direct read of single molecule activitities, and possibly sequencing.</p></div

    Fabrication procedure for the graphene nanogap devices studied here.

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    <p>(A) Diagram of graphene placed by wedge transfer on top of prefabricated trench in SiO<sub>2</sub> substrate. A nanogap with width <i>w</i> is formed. A micropore is fabricated by electron-beam lithography over the nanogap location. (B) Optical microscope image of a graphene nanogap device with micropore at the same fabrication stage as Fig 1A, placed on an etched trench (yellow) in a 300 nm thick SiO<sub>2</sub> substrate (purple). Contrast has been enhanced. The fabricated micropore changes the color of the SiO<sub>2</sub> substrate and trench, making the trench appear brighter yellow and the fraction of uncovered unetched SiO<sub>2</sub> more purple. The image has 50% increased contrast and 30% reduced brightness. (C) Diagram of a graphene nanogap transferred to a measurement device with a ∼ 25 μm hole that the nanogap/micropore assembly is centered on. (D) Optical microscope image with enhanced contrast of a graphene nanogap device ready for transverse conductance measurements at the fabrication stage shown in Fig 1C.</p

    Event detection and classification.

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    <p>(A) Raw current traces are recorded as described without DNA (black) and with DNA (red, blue). Eventual determination of rectangular and exponential events are indicated by blue square and red triangle, respectively. A dip in the control experiment (×) is discarded as a possible event as described in the text. (B) Narrow-band noise is removed from the traces and eventual event position is indicated. (C) Events are fitted with rectangular (blue) or exponential (red) traces depending on which fits better statistically.</p

    Model for breaking a graphene sheet.

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    <p>(A) Breaking a graphene sheet of thickness <i>t</i> over a trench of width <i>L</i> and depth <i>h</i>. The graphene shape is estimated by balancing the bending energy <i>E</i><sub><i>B</i></sub> up to the point <i>p</i> with the surface binding energy <i>E</i><sub><i>S</i></sub>, leading to a nanogap width <i>w</i>. (B) Expected nanogap width <i>w</i> as a function of suspended length <i>L</i> for two values of surface adhesion energy <i>ε</i> (see text).</p

    Nonlinear correction of electron-beam deflection.

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    <p>(A) Optical image of Au alignment markers and selected markers with enhanced contrast for coordinate analysis (red circles). (B) SEM image of same device as A and selected markers with enhanced contrast (red circles). (C) Residual error in <i>x</i> coordinate of SEM beam deflection (black circles) that scales linearly with the SEM <i>x</i> coordinate (red line). (D) Residual error (black circles) in SEM <i>y</i> coordinate scaling linearly with the SEM <i>y</i> coordinate (red line).</p

    Recorded translocation of dsDNA through graphene nanogap with resistance of ∼ 36 MΩ.

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    <p>(A) Typical rectangular (blue, top) and exponential (red, bottom) translocation event. (B) Analysis of rectangular (blue squares) and exponential translocation events (red triangles, pointing up for Δ<i>G</i> > 0 and down for Δ<i>G</i> < 0). The solid lines are fits of the data to Δ<i>G</i> ∝ 1/<i>τ</i>. The error bars indicate the range of geometrical standard deviation.</p

    Effect of local nanogap geometry on translocation events, showing gaps and associated event data.

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    <p>(A) Illustration of continuously changing gap width over the length of the gap. As DNA translocates through the gap, its passage is characterized by the gap width at its point of traversal. (B) DNA passes through the upper gap, causing a rectangular conductance change. (C) DNA passes through the middle gap more slowly due to the narrower gap diameter. (D) DNA forces the edges of the lower gap to bend outward, which then relax to their equilibrium position once it has passed, causing an exponential decay event.</p
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