Single DNA molecule detection in an optical trap using surface-enhanced Raman scattering
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A spectrum (top plot) from a typical SERS measurement of a single DNA molecule plotted against a background spectrum (bottom plot). The raw data (gray line) are plotted with their smoothed counterparts (Savitzky–Galey, 30 points) for both the DNA (top plot) and background (bottom plot) spectra and are shifted for clarity. Inset: an illustration (not drawn to scale) of the DNA-bead construct in the optical trap.
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A sample of two extension curves from the data set of DNA molecules that gave a Raman signal at the conditions of Fig. 1. The curves are fit to the WLC model (solid line) [formula in (a) inset] and all curves give the expected contour length of and persistence lengths that vary between 47–57 nm. In the two examples given here, persistence values of (a) 55 nm and (b) 48 nm were found. Error bars are calculated to be far less than the size of the plotting symbols and are, therefore, not shown. Theoretical force-extension curves are included using the expected contour length and persistence lengths of 53 nm (square line) and 26 nm (triangle line) in order to further demonstrate the presence of a single DNA molecule. A camera image of the suspended DNA-bead construct is included in (b) inset.
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