Methods for imaging DNA in liquid with lateral molecular-force microscopy

摘要

Shear force microscopy is not normally associated with the imaging of biomolecules in a liquid environment. Here we show that the recently developed scattered evanescent wave (SEW) detection system, combined with custom-designed vertically oriented cantilevers (VOCs), can reliably produce true non-contact images in liquid of DNA molecules. The range of cantilever spring constants for successful shear force imaging was experimentally identified between 0.05 and 0.09 Nm~(-1). Images of λ-DNA adsorbed on mica in distilled water were obtained at scan rates of 8000pixelss~(-1). A new constant-height force mapping mode for VOCs is also presented. This method is shown to control the vertical position of the tip in the sample plane with better than 1nm accuracy. The force mode is demonstrated by mapping the shear force above λ-DNA molecules adsorbed on mica in a liquid environment at different tipsample separations.