Biological Effects of Intense Subnanosecond Electrical Pulses

The application of nanosecond pulses to biological cells, which has been shown to lead to electroporation of not only the cell membrane, but also the membranes of subcellular structures, has spawned a new field of research: bioelectrics. A new domain of pulsed electric field interactions with cell structures and functions opens up when the pulse duration is reduced to values such that membrane charging becomes negligible, and direct electric field molecule effects determine the biological mechanisms. For mammalian cells, this holds for pulse duration of one nanosecond or less. In addition to entering a new domain of electric field-cell interactions, entering the subnanosecond temporal range will allow us to use wideband antennas, rather than needle or plate electrodes, to generate large pulsed electric fields with reasonable spatial resolution in tissue. In order to study the biological effect of subnanosecond pulses we have developed a sub-ns pulse generator. The generated voltage pulses have 160 kV amplitude, 200 ps rise-time, and 800 ps pulse width, and are delivered to a cylindrical Teflon chamber with polished flat electrodes at either end. Length and diameter of the chamber are 3 and 2 mm, respectively, resulting in a volume of approximately 10 muL. We have started applying subnanosecond pulses to B16 (mouse melanoma) cells. First experiments at extremely high electric fields of 950 kV/cm show that with a relatively small number of pulses, programmed cell death can be initiated