Hierarchical multiscale computations of ion transport in synthetic nanopores

There is a growing interest in investigating transport and electrochemical phenomena in synthetic membrane nanopores because of the possibility of mimicking selective ion transport found in protein channels in cell membranes of living systems and also towards development of single molecule detection systems. Several experimental (Gu et al., 2001; Jirage et al., 1997; Kuo et al., 2001) approaches such as the track etch method and the ion beam method have been used with increasing success in recent years to characterize the ionic transport through nanopores of varying diameters. We first performed two level multiscale simulations combining the continuum Poisson Nernst Planck theory and the molecular dynamics simulations to obtain current-voltage characteristics of nanopores in a silicon dioxide membrane and to investigate the effects of the complex phenomena of conductivity and self diffusion of ions due to the confinement in nanopores. Statistical analysis from molecular dynamics simulations were used to obtain mobility and diffusion coefficient in SiO/sub 2/ nanopores 5nm in length and diameters of 3 nm, 2nm and 1.2nm in 1M KCl and NaCl solutions. The data from these simulations showed that the mobility and diffusion coefficient decreases with decrease in diameter and is significantly different from the bulk especially for diameters less than 2 nm. The transport coefficients obtained were used in a continuum based Poisson-Nernst-Planck solver in a multiscale framework to obtain the I-V curves. The partial charges were obtained using DFT and semiempirical AMI, which closely matches the data for silica clusters in literature. Preliminary results indicate that the presence of partial charges on the pore walls alter the transport coefficient because the counter ions stick to the walls for pores of small diameters.