Geon Joon Lee

Analysis of the antimicrobial effects of nonthermal plasma on fungal spores in ionic solutions

The antimicrobial efficiency of reactive species-based control strategies is significantly affected by the dynamics of reactive species in the biological environment. Atmospheric-pressure nonthermal plasma is an ionized gas in which various reactive species are produced. The various levels of antimicrobial activity may result from the dynamic interaction of the plasma-generated reactive species with the environment. However, the nature of the interaction between plasma and environments is poorly understood. In this study, we analyzed the influence of the ionic strength of surrounding solutions (environment) on the antimicrobial activity of plasma in relation to the plasma-generated reactive species using a model filamentous fungus, Neurospora crassa. Our data revealed that the presence of sodium chloride (NaCl) in the background solution attenuated the deleterious effects of plasma on germination, internal structure, and genomic DNA of fungal spores. The protective effects of NaCl were not explained exclusively by pH, osmotic stability, or the level of reactive species in the solution. These were strongly associated with the ionic strength of the background solution. The presence of ions reduced plasma toxicity, which might be due to a reduced access of reactive species to fungal spores, and fungal spores were inactivated by plasma in a background fluid of nonionic osmolytes despite the low level of reactive species. Our results suggest that the surrounding environment may affect the behavior of reactive species, which leads to different biological consequences regardless of their quantity. Moreover, the microbicidal effect of plasma can be synergistically regulated through control of the microenvironment.

Optical and structural properties of plasma-treated Cordyceps bassiana spores as studied by circular dichroism, absorption, and fluorescence spectroscopy

To understand the killing mechanism of fungal spores by plasma treatment, the optical, structural, and biological properties of the insect pathogenic fungus Cordyceps bassiana spores were studied. A nonthermal atmospheric-pressure plasma jet (APPJ) was used to treat the spores in aqueous solution. Optical emission spectra of the APPJ acquired in air indicated emission peaks corresponding to hydroxyl radicals and atomic oxygen. When the APPJ entered the aqueous solution, additional reactive species were derived from the interaction of plasma radicals with the aqueous solution. Fluorescence and absorption spectroscopy confirmed the generation of hydroxyl radicals and hydrogen peroxide in the plasma-activated water (PAW). Spore counting showed that plasma treatment significantly reduced spore viability. Absorption spectroscopy, circular dichroism (CD) spectroscopy, and agarose gel electrophoresis of the DNA extracted from plasma-treated spores showed a reduction in spore DNA content. The magnitude of the dip in the CD spectrum was lower in the plasma-treated spores than in the control, indicating that plasma treatment causes structural modifications and/or damage to cellular components. Tryptophan fluorescence intensity was lower in the plasma-treated spores than in the control, suggesting that plasma treatment modified cell wall proteins. Changes in spore viability and DNA content were attributed to structural modification of the cell wall by reactive species coming from the APPJ and the PAW. Our results provided evidence that the plasma radicals and the derived reactive species play critical roles in fungal spore inactivation.

Effects of reactive oxygen species on the biological, structural, and optical properties of Cordyceps pruinosa spores

Effects of reactive oxygen species (ROS) on the optical, structural, and biological properties of Cordyceps pruinosa spores were studied. Both the atmospheric pressure plasma jet (APPJ) and chemically induced ROS significantly reduced the viability of C. pruinosa spores. Changes in the peak intensity of fluorescence and the depth of the dip in the circular dichroism (CD) spectrum suggested that both the APPJ and chemical induction of ROS can cause structural alteration of the spore cell wall. Fluorescence spectra of propidium iodide-stained spores indicated that alteration of cell wall (and/or membrane) permeability is involved in the change of spore viability after plasma treatment. High-performance liquid chromatography analysis of C. pruinosa ethanol extracts showed that the APPJ and chemical induction of ROS decreased the amount of ergosterol in the spores, indicating that excessive oxidative stress destroys cellular antioxidant capacity. Absorption spectroscopy, CD spectroscopy and agarose gel electrophoresis of the DNA extracted from the plasma-treated spores showed that a decrease in the DNA content and DNA degradation can be caused by either of the two treatments. The nonthermal APPJ and chemical induction were used to generate ROS in an aqueous solution. Electron spin resonance spectra provided evidence that hydroxyl radicals and singlet oxygen exist in the plasma activated water (PAW). Overall, the decline in spore viability, in antioxidative capacity, and in DNA content can be attributed to structural alteration of the cell wall and cellular damage by reactive species originating from the APPJ and the PAW.

Circular dichroism, surface-enhanced Raman scattering, and spectroscopic ellipsometry studies of chiral polyfluorene-phenylene films

To understand the chiroptical responses of polyfluorene–phenylene (PFP) films, circular dichroism (CD), surface-enhanced Raman scattering (SERS), attenuated total reflection (ATR), and spectroscopic ellipsometry studies were performed. The pristine PFP films exhibited significant CD at room temperature, and the chirality increased by thermal annealing at 120 °C (above the glass transition temperature). SERS and ATR spectra indicated that the chirality enhancement was due to the rearrangement of the polymer backbones on the glass substrate by thermal annealing and/or self-organization. In addition, comparison of PFP and polyfluorene polymers indicated that molecular structure of polymer backbone plays an important role in the chiroptical responses of the chiral polymers.

Influence of plasma-generated reactive species on the plasmid DNA structure and plasmid-mediated transformation of Escherichia coli cells

The influence of plasma-generated reactive species on the conformation of plasmid DNA (pDNA) and the transformation efficiency of Escherichia coli cells were studied. An atmospheric-pressure plasma jet (APPJ) was used to generate reactive oxygen and nitrogen species (RONS) in an aqueous solution. When E. coli cells were transformed, the transformation efficiency of E. coli with the APPJ-treated plasmid was lower than with the APPJ-untreated plasmid. Transformation efficiency was reduced due to structural modification and degradation of the pDNA by the APPJ. Plasma treatment caused structural modification of the plasmid from the supercoiled form to the linear form, and also decreased the amount of plasmid by degrading the deoxyribonucleic acid (DNA) structure accompanied by disruption of nucleobases and DNA strand breakage. The formation of linear plasmid from supercoiled plasmid by the APPJ treatment was verified through electrophoretic analysis of the NdeI restriction enzyme-cut supercoiled plasmid. The ...

New fluorene-based chiral copolymers with unusually high optical activity in pristine and annealed thin films

Polyfluorene (PF)-based chiral alternating copolymers, i.e., PFPh and PFTh, were successfully synthesized to obtain high circular dichroism (CD) in pristine thin films. By tethering chiral side-chains to the fluorene moiety, the resultant PFPh and PFTh films intriguingly exhibited high CD even in pristine films, which was attributed to the relatively low steric hindrance between the repeating units and intermolecular interactions between the polymer chains. Compared to PFTh bearing a five-membered heteroaromatic thiophene monomer, PFPh containing a six-membered aromatic benzene monomer, showed significantly enhanced CD in an annealed film. Of particular importance, results of optical microscopy and atomic force microscopy can be used to assess the CD of a chiral polymer thin film after thermal annealing.

Optical Sensing Properties of ZnO Nanoparticles Prepared by Spray Pyrolysis

We studied the optical sensing properties of ZnO nanoparticles prepared by spray pyrolysis. To investigate their optical sensing performance, we incubated peptides on ZnO nanoparticles. The photoluminescence (PL) peak intensity of peptides on the ZnO nanoparticles was higher than that of peptides on the ZnO film or on the glass plate. This observed PL enhancement is attributed to the optical confinement of ZnO nanoparticles. The low-temperature spectra displayed a strong exciton emission peak with multiple sidebands, attributed to the bound exciton and its longitudinal optical phonon sidebands. The strong exciton emission is thought to be the combined effect of optical confinement due to the nanoparticle geometry, reduction of defect emission by thermal annealing, and reduction of non-radiative relaxation at low temperatures.

Scavenging effects of ascorbic acid and mannitol on hydroxyl radicals generated inside water by an atmospheric pressure plasma jet

In this study, we have studied the scavenging effects of radical scavengers (ascorbic acid and mannitol) on •OH radicals generated inside water by an atmospheric pressure plasma jet. Plasma was generated by using a sinusoidal power supply (applied voltage: 2.4 kV, frequency: 40 kHz) at a constant argon gas flow rate of 400 sccm and it was characterized by electrical and optical measurements. The technique of ultra-violet (UV) absorption spectroscopy was applied to investigate the effects of scavenging at 3, 6 and 9 mm depths below the water surface by using terephthalic acid as a •OH radical sensitive probe. Also, the effects of scavenging were studied by changing the concentration of radical scavengers and plasma exposure time. For both radical scavengers, the reduced concentrations of •OH radicals were found to decrease with increasing depths as their production would also be reduced by decreasing intensities of plasma-initiated UVs with increasing depths. The effectiveness of ascorbic acid on the scavenging of •OH radicals appeared much stronger than mannitol at all depths inside water since the deprotonated form of ascorbic acid consumes two •OH radicals whereas mannitol consumes only one. Also, the reduced concentration of OH radicals with addition of scavengers was found to be increased under longer plasma exposure time even though the generation of OH radicals were also increased. The detailed mechanism on the formation of •OH radicals inside water has been discussed along with the causes of scavenging. These results can be an important milestone in the applications of non-thermal plasma sources requiring the reduction of •OH radicals.

Erratum to: Branch length similarity entropy-based descriptors for shape representation (Journal of the Korean Physical Society, (2017), 71, 10, (727-732), 10.3938/jkps.71.593)

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