(Invited) Electrostatic Field and Non-Thermal Plasma for Handling and Processing Bio-Molecules and Cells

Abstract

Electrostatic field is an important tool for handling fine objects such as biological molecules and cells. Non-thermal plasma generates reactive radicals. Long life-time radicals can migrate in liquids to penetrate membranes of cells and tissues. Electrophoresis, or Coulombic force has been widely used in biology for separation of cells and molecules. Dielectrophoresis in non-uniform AC-field uses gradient force. Since AC voltage can be applied to conductive liquid with minimum generation of bubbles, dielectrophoresis is an important tool for handling living cells and micro-organisms. Due to polarization, gradient force appears on particles of neutral charge, and magnitude and direction of the gradient force depend on the frequency response of the objects. Gradient force can be generated using a focused laser without using fixed electrodes. Biological cells are pulled into the laser focus where E-field is high, and they are trapped. This is called laser tweezers, and is a convenient tool for handling microbes and fine objects with diameter range between 0.2 – 5 micro-meter. Laser tweezers cannot hold DNA molecules of random-coiled shape, because they are too thin (2 nm diameter). The globule transition of DNA molecules can be used to fold random-coiled DNA into a solid globule DNA. This transition is reversible, controlled by concentration of counter ions in medium. Globule DNAs, therefore, can be stretched again. Globule DNAs are manipulated by laser tweezers. Droplet-in-oil emulsion is a suitable container to be manipulated using electrostatic force or laser tweezers. This emulsion system can be used to conduct PCR amplification starting from single fragment of DNA. High electric field causes reversible or irreversible puncture of membrane of cells. This phenomenon can be used for cell fusion, infection of genes and chemicals, cell fusion, or sterilization. To punctuate cell membranes, reactive radicals are also effective. Radicals are generated in NTP and injected into liquid. Certain long-lived radicals migrate in the liquid and penetrate into cells through membrane or protein shell. E.coli or B. subtilis spore in liquid was exposed to NTP, either DBD(dielectric barrier discharge) or a plasma jet with Ar or He. Analysis using decay of GFP (green fluorescent protein) fluorescence proved that oxidative radicals are penetrating through the membrane into cells. Exposure of NTP to Bacteriophages indicated that protein shells are damaged at first, and that double stranded DNA is stronger than that of single stranded genes of the phages. In conclusion, electrostatic force and NTP are effective tools for handling and for processing biological particles including cells, viruses and molecules. Wide range of applications are still to be developed. Several examples will be reported of the application of electrostatic field and NTP in handling and processing of cells and single DNA molecules.