Monitoring the Escape of DNA from a Nanopore Using an Alternating Current Signal

We present the use of an alternating current (AC) signal as a means to monitor the conductance of an alpha-hemolysin (alpha HL) pore as a DNA hairpin with a polydeoxyadenosine tail is driven into and released from the pore Specifically, a 12 base pair DNA hairpin attached to a 50-nucleotide poly-A tail (HP-A(50)) is threaded into an alpha HL channel using a DC driving voltage. Once the HP-A(50) molecule is trapped within the alpha HL channel, the DC driving voltage is turned off and the conductance of the channel is monitored using an AC voltage The escape time, defined as the time it takes the HP-A(50) molecule to transport out of the alpha HL channel, is then measured. This escape time has been monitored as a function of AC amplitude (20 to 250 mV(ac)), AC frequency (60-200 kHz), DC drive voltage (0 to 100 mV(dc)), and temperature (-10 to 20 degrees C), in order to determine their effect on the predominantly diffusive motion of the DNA through the nanopore. The applied AC voltage used to monitor the conductance of the nanopore has been found to play a significant role in the DNA/nanopore interaction The experimental results are described by a one-dimensional asymmetric periodic potential model that includes the influence of the AC voltage. An activation enthalpy barner of 1 74 x 10(-19) J and a periodic potential asymmetry parameter of 0.575 are obtained for the diffusion at zero electrical bias of a single nucleotide through alpha HL