Statistical characterisation of single-stranded DNA motion near glass surface beyond diffusion coefficient

The diffusion of single-stranded DNA (ssDNA) molecules near a glass surface by total internal reflection fluorescence microscopy has been observed. Substantially smaller diffusion coefficients compared to the bulk are caused by phenomenologically different types of surface effect that is not necessarily adsorptive. In particular, preliminary treatments of the glass substrate by low and high concentrations of KOH lead to highly and much less adsorptive effects on the ssDNA molecules, respectively. These characteristics beyond diffusion coefficients are elucidated by the difference of two ensemble-averaging methods of mean square displacement for diffusion coefficients due to the nonuniformity of the molecular motion, which is further confirmed by the distribution of displacements and tracked duration.