Search

A new plasma dental probe (PDP), powered with 4-6.kV ~100-ns electric pulses at repetition rates of up to 2 kHz, generates a room-temperature > 2-cm-long ~2-mm-diameter plasma plume at ambient atmospheric pressure. The shape of the plasma plume depends on the gas flow rate and the pulse voltage. Growth of Bacillus atrophaeus on nutrient agar plates is completely inhibited by exposure to both He and He/(l%)[O.sub.2] plasmas for 60 s. A 300-s treatment with the He/(l%)[O.sub.2] plasma disinfected a human tooth root canal colonized with saliva-derived biofilms, demonstrating the potential of the PDP as a simple, safe, and effective tool or adjunct for the disinfection of root canals during endodontic therapy. He/(l%)[O.sub.2] plasma is more effective than He alone for B. atrophaeus growth inhibition, and the emission spectrum of the He--[O.sub.2] plasma supports the identification of atomic oxygen as the likely primary reactive chemical species contributing to bacterial inactivation. Index Terms--Atmospheric pressure, bacteria, disinfection, plasma torch, sterilization.

1. Introduction POST-fabrication determination of thickness values for the various layers in a complementary-metal-oxide-semiconductor (CMOS) process poses measurement and analytical challenges. Process and lot-specific variations in these quantities are typically […]

Research on the electroperturbation effects of ultrashort high field pulses in cancer cells requires subnanosecond rise time, high voltage pulses delivered to low impedance biological loads. Here we present a compact solid-state pulse generator developed for this application. The pulse is generated by switching a chain of avalanche transistors configured as a tapered transmission line from high voltage to ground. The system features a built in 1400:1 capacitively compensated resistive voltage divider. The divider, with a 3 dB point at 910 MHz, overcomes challenges in the direct measurement of the high frequency components of the output pulse. The generator is capable of producing a 0.8 ns rise time, 1.3 ns wide, 1.1 kV pulse into a 50 [ohms] load at a maximum repetition rate of 200 kHz. Techniques to implement physical layouting strategies to achieve subnanosecond rise times are outlined. Problems faced in integrating the subnanosecond pulse generator with a biological load are discussed. This pulse generator will be used in experiments aimed at electromanipulation of intracellular biomolecular structures. Index Terms--Avalanche breakdown, pulse power systems, voltage dividers, bioelectric phenomena, electroperturbation, biomembranes.

Design and operation of a fast recovery diode based pulse generator is presented. The generator produces 3.5-ns-wide, 1200 V amplitude unipolar pulses or +/- 600-V bipolar pulses into 50-[ohm] load at the maximum repetition rate of 100 kHz. Pulses shorter than 10 ns are essential for the studies of biological cell response to high electric fields while avoiding ordinary electroporation effects dominant at long pulses. Bipolar pulses are used for the studies of biological cell response to high electric fields when the net transfer of charge is undesirable. The bipolar pulse is produced from a unipolar pulse with the help of a shorted transmission line. This transmission line delays and inverts the initial pulse, so the output is the sum of the initial and the inverted and delayed pulses. The use of mass-produced fast recovery surface-mount rectifier diodes in this circuit substantially simplifies the generator and results in low cost and very small footprint. Similar diode switched pulse generators have been described in the literature using mostly custom fabricated snap-recovery diodes. Here we give an example of an ordinary low-cost diode performing similarly to the custom fabricated counterpart. The diode switched circuit relaxes the requirement on the speed of the main closing switch; in our case, a low-cost power metal-oxide semiconductor field-effect transistor (MOSFET)-saturable core transformer combination. Index Terms--Biological cells, diode opening switch, fast recovery diode, ultrashort pulse electroperturbation.

Ultra-short, high-field electric pulses induce apoptosis in Jurkat T lymphoblasts but have little effect on cat glioma C6 cells even at much higher doses. Germination of Bacillus atrophaeus spores is unaffected even by exposure to millions of nanosecond, megavolt-per-meter pulses. Despite the many fundamental similarities among biological systems at the cellular level, and the well-defined physical and electrical parameters of nanoelectropulse delivery systems, a wide variety of responses to stimuli in this new bioelectromagnetic regime must be anticipated. Future studies can utilize these differences to uncover the underlying mechanisms and to exploit the relative resistances and sensitivities among cell and tissue types for the expansion of fundamental knowledge of cell biology and for practical applications in therapeutics and bioengineering. Index Terms--Apoptosis, calcium burst, electroperturbation, phosphatidylserine externalization, spore germination, ultra-short electric pulse.

Megavolt-per-meter electric pulses with durations shorter than charging time constants associated with external cell membrane dielectric properties can generate significant voltages on the membranes of intracellular structures. Nanosecond-duration, high-field (2-4 MV/m) pulses are not immediately lethal to cells and do not produce the conductive openings in the cytoplasmic membrane associated with long-pulse, low-field electroporation, but can induce profound physiological changes, including apoptosis (programmed cell death). We demonstrate rapid, non-destructive, field-dependent translocation of the plasma membrane inner leaflet phospholipid phosphatidylserine in Jurkat T lymphocytes, and we show that cells which exhibit a similar geometry in suspension, rat glioma C6 cells, are highly resistant to these pulses and respond differently even to much higher doses. Index Terms--Ultrashort electric pulse, electroporation, electroperturbation, phospholipid inversion, phosphatidylserine translocation, apoptosis.

This paper describes three pulse generators: a spark gap switched coaxial cable, a spark gap switched Blumlein, and a solid state modulator, developed for applying ultrashort electrical pulses to biological materials in culture. Recent research has shown that ultrashort pulsed electric fields can induce apoptosis in biological cells, and that pulses as short as 10 ns with field amplitude greater than 1 MV/m cause membrane phospholipid rearrangement and activation of the effector enzymes of apoptosis. Pulses of very short duration use only tens of mJ per mL per pulse to induce apoptosis and other intracellular effects without causing thermal trauma. The pulse generators discussed here, each of a different topology, deliver ns pulsed electric fields (nsPEF) to cells in liquid suspension, and can be modified to drive electrodes for external, surgical, or endoscopic treatment of tissues in situ. Index Terms--Apoptosis, Blumlein, electric field, electroperturbation, fluorescence microscopy, nanosecond, nsPEF, phospholipid inversion, pulsed electric field, pulse forming network, pulse generator, real-time, ultrashort

Nuclear Waste Daniel E. Koshland, Jr.'s editorial of 27 June 'Dealing in hot property' (p. 1585) was a flippant statement far beneath the standards of Science. The difficult problem of [...]