The scanning force microscopy of DNA in air and in n-propanol using new spreading agents

We present recent advances in DNA specimen preparation technique for scanning force microscopy (SFM) based on spreading on mica in the presence of cationic and non-ionic detergents. Reproducible DNA imaging in air and in n-propanol has been achieved in the presence of the non-ionic detergent 2,4,6-tris(dimethylaminomethyl) phenol (DMP-30) or the cationic detergent cetylpyridinium chloride (CP) in a microdrop containing nanograms of DNA. In an alternative procedure, a microdrop of detergent is applied to the surface just prior to the DNA. Quantitative image analysis yields as the apparent molecular dimensions of the DNA a width of ∼ 7 nm and a height of ∼ 0.7 nm, and delineates the problems of DNA metrology by SFM.