Cheng-Yu Bao

Genetic effects of radio-frequency, atmospheric-pressure glow discharges with helium

Due to low gas temperatures and high densities of active species, atmospheric-pressure glow discharges (APGDs) would have potential applications in the fields of plasma-based sterilization, gene mutation, etc. In this letter, the genetic effects of helium radio-frequency APGD plasmas with the plasmid DNA and oligonucleotide as the treated biomaterials are presented. The experimental results show that it is the chemically active species, instead of heat, ultraviolet radiation, intense electric field, and/or charged particles, that break the double chains of the plasmid DNA. The genetic effects depend on the plasma operating parameters, e.g., power input, helium flow rate, processing distance, time, etc.

Atmospheric and room temperature plasma (ARTP) as a new powerful mutagenesis tool

Developing rapid and diverse microbial mutation tool is of importance to strain modification. In this review, a new mutagenesis method for microbial mutation breeding using the radio-frequency atmospheric-pressure glow discharge (RF APGD) plasma jets is summarized. Based on the experimental study, the helium RF APGD plasma jet has been found to be able to change the DNA sequences significantly, indicating that the RF APGD plasma jet would be a powerful tool for the microbial mutagenesis with its outstanding features, such as the low and controllable gas temperatures, abundant chemically reactive species, rapid mutation, high operation flexibility, etc. Then, with the RF APGD plasma generator as the core component, a mutation machine named as atmospheric and room temperature plasma (ARTP) mutation system has been developed and successfully employed for the mutation breeding of more than 40 kinds of microorganisms including bacteria, fungi, and microalgae. Finally, the prospect of the ARTP mutagenesis is discussed.

Novel mutation breeding method for Streptomyces avermitilis using an atmospheric pressure glow discharge plasma

Aims:  Avermectins are major antiparasitic agents used commercially in animal health, agriculture and human infections. To improve the fermentation efficiency of avermectins, for the first time a plasma jet generated by a novel atmospheric pressure glow discharge (APGD) was employed to generate mutations in Streptomyces avermitilis.

Discharge characteristics of atmospheric-pressure radio-frequency glow discharges with argon/nitrogen

In this letter, atmospheric-pressure glow discharges in γ mode with argon/nitrogen as the plasma-forming gas using water-cooled, bare copper electrodes driven by radio-frequency power supply at 13.56MHz are achieved. The preliminary studies on the discharge characteristics show that, induced by the α-γ coexisting mode or γ mode discharge of argon, argon-nitrogen mixture with any mixing ratios, even pure nitrogen, can be employed to generate the stable γ mode radio-frequency, atmospheric-pressure glow discharges and the discharge voltage rises with increasing the fraction of nitrogen in the argon-nitrogen mixture for a constant total gas flow rate.

Studies on the Physical Characteristics of the Radio-Frequency Atmospheric-Pressure Glow Discharge Plasmas for the Genome Mutation of Methylosinus trichosporium

In this paper, both simulations and experiments are conducted to investigate the physical characteristics of the radio-frequency atmospheric-pressure glow discharges (RF APGDs) first. The experimental and modeling results show that there are abundant chemically reactive species, e.g., electrons, helium metastables and ions, with high number densities in the discharge region. The corresponding plasma jet temperatures are in the range of 27°C - 39°C with the power input lower than 120 W, which is suitable for the treatment of the biomolecules or cells. Then, a prototype, which is the so-called atmospheric and room-temperature plasma mutation system, is designed with the RF APGD plasma generator as the core component. As an example, it is used for the mutation breeding of Methylosinus trichosporium OB3b. The experimental results show that the RF APGD plasma source is an environmentally friendly and efficient tool for the genome mutation of microorganisms to construct mutant library with large diversity.

Characteristics of kilohertz-ignited, radio-frequency atmospheric-pressure dielectric barrier discharges in argon

In this letter, ignited by a kilohertz atmospheric-pressure dielectric-barrier discharge (APDBD), the stable and uniform argon radio-frequency (rf) APDBDs are generated with lower rf ignition voltages compared to the conventional rf APDBDs without the aid of the kilohertz filamentary discharges. The experimental studies on the mechanisms of this dual-frequency APDBD method indicate that it is the filaments extending from the kilohertz electrode region to the rf electrode region that provide the seed electrons for the ignition of the rf APDBDs at the lower applied rf voltages. A 12-mm-long stable and uniform argon plasma jet is obtained using the coaxial-type plasma generator.

Discharge features of radio-frequency, atmospheric-pressure cold plasmas under an intensified local electric field

In this paper, stable atmospheric-pressure argon, nitrogen or air glow discharges driven by a radio-frequency power supply with water-cooled, bare copper electrodes are obtained by employing a newly-designed plasma generator. Due to the existence of the intensified local electric field by using an insulated tungsten wire between the two bare copper electrodes, which is also verified by the modelling results, the experimental measurements show that stable glow discharges of argon, nitrogen or air can be obtained following a local breakdown process in the vicinity of the tungsten wire under lower applied voltages between the electrodes.

The back-diffusion effect of air on the discharge characteristics of atmospheric-pressure radio-frequency glow discharges using bare metal electrodes

Radio-frequency (RF), atmospheric-pressure glow discharge (APGD) plasmas using bare metal electrodes have promising prospects in the fields of plasma-aided etching, deposition, surface treatment, disinfection, sterilization, etc. In this paper, the discharge characteristics, including the breakdown voltage and the discharge voltage for sustaining a stable and uniform α mode discharge of the RF APGD plasmas are presented. The experiments are conducted by placing the home-made planar-type plasma generator in ambient and in a vacuum chamber, respectively, with helium as the primary plasma-forming gas. When the discharge processes occur in ambient, particularly for the lower plasma-working gas flow rates, the experimental measurements show that it is the back-diffusion effect of air in atmosphere, instead of the flow rate of the gas, that results in the obvious decrease in the breakdown voltage with increasing plasma-working gas flow rate. Further studies on the discharge characteristics, e.g. the luminous structures, the concentrations and distributions of chemically active species in plasmas, with different plasma-working gases or gas mixtures need to be conducted in future work.

Characteristics of atmospheric-pressure, radio-frequency glow discharges operated with argon added ethanol

Rf, atmospheric-pressure glow discharge (APGD) plasmas with bare metal electrodes have promising prospects in the fields of plasma-aided etching, thin film deposition, disinfection and sterilization, etc. In this paper, the discharge characteristics are presented for the rf APGD plasmas generated with pure argon or argon-ethanol mixture as the plasma-forming gas and using water-cooled, bare copper electrodes. The experimental results show that the breakdown voltage can be reduced significantly when a small amount of ethanol is added into argon, probably due to the fact that the Penning ionization process is involved, and a pure α-mode discharge can be produced more easily with the help of ethanol. The uniformity of the rf APGDs of pure argon or argon-ethanol mixtures using bare metallic electrodes is identified with the aid of the intensified charge coupled device images.

Characteristics of Atmospheric Room-Temperature Argon Plasma Streams Produced Using a Dielectric Barrier Discharge Generator With a Cylindrical Screwlike Inner Electrode

In this paper, an innovative coaxial-type dielectric barrier discharge plasma generator is proposed to produce the large-volume and visibly uniform cold argon plasmas at atmospheric pressure by enhancing the local intensity and uniformity of the electric field simultaneously with the aid of a cylindrical screwlike inner electrode configuration. The experimental measurements show that the discharges transit from the initial stage after breakdown to the stable stage through a transitional stage and finally reach an unstable discharge stage with the increase of the applied voltage. The estimated values of the electron temperature and the number density of the gas discharge plasmas in the electrode region vary in a small range, i.e., 8.0-8.9 eV and (4.6-6.4) × 1011 cm-3, with increasing the applied voltage. Moreover, the plasma streams are quite uniform in the radial direction with a low gas temperature ( ~ 300 K) and an abundance of chemically reactive species in the stable discharge stage, which will be potentially a useful tool for the treatment of the heat-sensitive materials.