Hiroaki Kawano

Temperature Controllable Atmospheric Plasma Source

An atmospheric pressure plasma source in which the gas temperature can be accurately controlled from below freezing point up to a high temperature has been developed. In general plasma devices, an electrical discharge is passed through a gas at about room temperature to generate plasma, so the plasma is at a temperature higher than room temperature; moreover, the gas temperature is determined by the discharge condition such as discharge power and plasma gas flow rate, so accurate temperature control is difficult. In the plasma source that has been developed in this research, the gas that is to be supplied to the discharge unit is first cooled using a gas cooler and then heated by a heater. The gas temperature of the produced plasma is measured, and feedback is sent to the heater. Thus, plasma at a desired temperature can be generated. Gas temperature control of the plasma over a range from -54 °C to +160 °C with a standard deviation of 1 °C was realized. Spectroscopic characteristics of generated plasma were investigated. This plasma source/technique will realize that effective plasma is applicable for heat-sensitive materials such as paper, textile, polymer, and especially human tissue. Furthermore, it enables us to generate the plasma at optimal gas temperature for chemical reaction of each plasma treatment.

Atmospheric nonequilibrium mini-plasma jet created by a 3D printer

In this study, a small-sized plasma jet source with a 3.7 mm head diameter was created via a 3D printer. The jet’s emission properties and OH radical concentrations (generated by argon, helium, and nitrogen plasmas) were investigated using optical emission spectrometry (OES) and electron spin resonance (ESR). As such, for OES, each individual gas plasma propagates emission lines that derive from gases and ambient air inserted into the measurement system. For the case of ESR, a spin adduct of the OH radical is typically observed for all gas plasma treatment scenarios with a 10 s treatment by helium plasma generating the largest amount of OH radicals at 110 μM. Therefore, it was confirmed that a plasma jet source made by a 3D printer can generate stable plasmas using each of the aforementioned three gases.

Direct protein introduction into plant cells using a multi-gas plasma jet

Protein introduction into cells is more difficult in plants than in mammalian cells, although it was reported that protein introduction was successful in shoot apical meristem and leaves only together with a cell-penetrating peptide. In this study, we tried to introduce superfolder green fluorescent protein (sGFP)-fused to adenylate cyclase as a reporter protein without a cell-penetrating peptide into the cells of tobacco leaves by treatment with atmospheric non-thermal plasmas. For this purpose, CO2 or N2 plasma was generated using a multi-gas plasma jet. Confocal microscopy indicated that sGFP signals were observed inside of leaf cells after treatment with CO2 or N2 plasma without substantial damage. In addition, the amount of cyclic adenosine monophosphate (cAMP) formed by the catalytic enzyme adenylate cyclase, which requires cellular calmodulin for its activity, was significantly increased in leaves treated with CO2 or N2 plasma, also indicating the introduction of sGFP-fused adenylate cyclase into the cells. These results suggested that treatment with CO2 or N2 plasma could be a useful technique for protein introduction into plant tissues.

Imaging of the Staphylococcus aureus Inactivation Process Induced by a Multigas Plasma Jet.

To identify mechanisms underlying the bacterial inactivation process by atmospheric nonthermal plasma using a unique plasma jet that can generate various gas plasmas, Staphylococcus aureus were irradiated with carbon dioxide plasma, which produces a large amount of singlet oxygens, and nitrogen plasma, which produces a large amount of OH radicals. And damaged areas of plasma-treated bacteria were observed by field emission scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. As a result, bacteria were damaged by both gas plasmas, but the site of damage differed according to gas species. Therefore, it suggests that singlet oxygen generated by carbon dioxide plasma or other reactive species caused by singlet oxygen contributes to the damage of internal structures of bacteria through the cell wall and membrane, and OH radicals generated by nitrogen plasma or other reactive species derived from OH radicals contribute to damage of the cell wall and membrane.

Investigation of bacterial inactivation by various gas plasmas and electron microscopic observation of treated bacteria

Our group succeeded in developing a multi-gas plasma jet, which can generate plasma from various gas species. Using this plasma source, reactive species can be investigated in detail, since they can be generated selectively by the supplied gas species. This study aims to investigate the amount of reactive species generated by various gas plasmas, find reactive species that can inactivate bacteria and observe treated bacteria using electron microscope.