An approach for studying the adsorption and desorption behaviors of single-stranded DNA（ ssDNA） molecules on the mica surface by the surface forces apparatus（ SFA） is reported,which can be used to characterize the precise thickness,configuration and mechanical properties of ssDNA layers on the mica surface at a certain buffer solution. The formation of ss DNA layers is first studied by tuning the ssDNA concentrations, and the experimental results indicate that the ss DNA concentration of 100 ng / μL is ideal for forming a ssDNA monolayer structure on the mica surface, and the hardwall value measured to be 1.04 nm under this circumstance is regarded as the thickness of the ssDNA monolayer confined on mica. The desorption behavior of ssDNA molecules from the mica surface is further studied by observing and comparing different shapes of the force-distance curves under certain conditions. It is found that the desorption of ss DNA molecules from the mica surface occurs as the monovalent salts are added into the gap buffer. It is inferred that the competition effect between monovalent and divalent salts can induce the release of ssDNA from substrate.The results also reveal that 10 mmol / L monovalent salts（ Na~＋）is sufficient for the desorption of ssDNA from mica. This work provides an applicable method to study the binding mechanism of ss DNA molecules on inorganic substrates.
