Shear acoustic wave biosensor for detecting DNA intrinsic viscosity and conformation: A study with QCM-D

Direct biosensors are devices operating by monitoring the amount of surface-bound analyte. In this work a new approach is presented where a label-free acoustic biosensor, based on a QCM-D device, and solution viscosity theory, are used to study DNA intrinsic viscosity. The latter is quantitatively related to the DNA conformation and specifically the molecule's shape and size, in a manner that is independent of the amount of bound DNA mass. It is shown that acoustic measurements can clearly distinguish between ds-DNA of same shape (straight rod) but various sizes (from 20 to 198 bp (base pairs)) and same mass and size (90 bp) but various shapes (straight, bent, triangle). These results are discussed in the broader context of coil and sphere-like molecules detected on surfaces. A mathematical formula is presented relating the length of straight, surface- protruding DNA to the acoustic ratio Delta D/Delta f. The development of real-time rapid techniques for the characterization of DNA intrinsic curvature as well as DNA conformational changes upon interaction with proteins is of significance to analytical biotechnology due to the large number of DNA sequences and potential DNA bending proteins involved in genome analysis and drug screening. (C) 2008 Elsevier B.V. All rights reserved.