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Structure and switching of single-stranded DNA tethered to a charged nanoparticle surface

Using a molecular theory, we investigate the temperature-dependent self-assembly of single-stranded DNA (ssDNA) tethered to a charged nanoparticle surface. Here the size, conformations, and charge properties of ssDNA are taken into account. The main results are as follows: i) when the temperature is lower than the critical switching temperature, the ssDNA will collapse due to the existence of electrostatic interaction between ssDNA and charged nanoparticle surface; ii) for the short ssDNA chains with the number of bases less than 10, the switching of ssDNA cannot happen, and the critical temperature does not exist; iii) when the temperature increases, the electrostatic attractive interaction between ssDNA and charged nanoparticle surface becomes weak dramatically, and ssDNA chains will stretch if the electrostatic attractive interaction is insufficient to overcome the elastic energy of ssDNA and the electrostatic repulsion energy. These findings accord well with the experimental observations. It is predicted that the switching of ssDNA will not happen if the grafting densities are too high.