A single molecule detection method for understanding mechanisms of electric field-mediated interstitial transport of genes.

The interstitial space is a rate limiting physiological barrier to non-viral gene delivery. External pulsed electric fields have been proposed to increase DNA transport in the interstitium, thereby improving non-viral gene delivery. In order to characterize and improve the interstitial transport, we developed a reproducible single molecule detection method to observe the electromobility of DNA in a range of pulsed, high field strength electric fields typically used during electric field-mediated gene delivery. Using agarose gel as an interstitium phantom, we investigated the dependence of DNA electromobility on field magnitude, pulse duration, pulse interval, and pore size in the interstitial space. We observed that the characteristic electromobility behavior, exhibited under most pulsing conditions, consisted of three distinct phases: stretching, reptation, and relaxation. Electromobility depended strongly on the field magnitude, pulse duration, and pulse interval of the applied pulse sequences, as well as the pore size of the fibrous matrix through which the DNA migrated. Our data also suggest the existence of a minimum pulse amplitude required to initiate electrophoretic transport. These results are useful for understanding the mechanisms of DNA electromobility and improving interstitial transport of genes during electric field-mediated gene delivery.