Theory of DNA translocation through narrow ion channels and nanopores with charged walls

Translocation of a single-stranded DNA molecule through genetically engineered α -hemolysin channels with positively charged walls is studied. It is predicted that transport properties of such channels are dramatically different from neutral wild-type α -hemolysin channels. We assume that the wall charges compensate a fraction x of the bare charge qb of the DNA piece residing in the channel. Our predictions are as follows. (i) At small concentration of salt the blocked ion current decreases with x. (ii) The effective charge qs of the DNA piece, which is very small at x=0 (neutral channel) grows with x and at x=1 reaches qb. (iii) The rate of DNA capture by the channel grows exponentially with x. Our theory is also applicable to translocation of a double-stranded DNA molecular in narrow solid state nanopores with positively charged walls.