Effects of Thermal Boundary Resistance on Thermal Management of Gallium-Nitride-Based Semiconductor Devices: A Review.

Wide-bandgap gallium nitride (GaN)-based semiconductors offer significant advantages over traditional Si-based semiconductors in terms of high-power and high-frequency operations. As it has superior properties, such as high operating temperatures, high-frequency operation, high breakdown electric field, and enhanced radiation resistance, GaN is applied in various fields, such as power electronic devices, renewable energy systems, light-emitting diodes, and radio frequency (RF) electronic devices. For example, GaN-based high-electron-mobility transistors (HEMTs) are used widely in various applications, such as 5G cellular networks, satellite communication, and radar systems. When a current flows through the transistor channels during operation, the self-heating effect (SHE) deriving from joule heat generation causes a significant increase in the temperature. Increases in the channel temperature reduce the carrier mobility and cause a shift in the threshold voltage, resulting in significant performance degradation. Moreover, temperature increases cause substantial lifetime reductions. Accordingly, GaN-based HEMTs are operated at a low power, although they have demonstrated high RF output power potential. The SHE is expected to be even more important in future advanced technology designs, such as gate-all-around field-effect transistor (GAAFET) and three-dimensional (3D) IC architectures. Materials with high thermal conductivities, such as silicon carbide (SiC) and diamond, are good candidates as substrates for heat dissipation in GaN-based semiconductors. However, the thermal boundary resistance (TBR) of the GaN/substrate interface is a bottleneck for heat dissipation. This bottleneck should be reduced optimally to enable full employment of the high thermal conductivity of the substrates. Here, we comprehensively review the experimental and simulation studies that report TBRs in GaN-on-SiC and GaN-on-diamond devices. The effects of the growth methods, growth conditions, integration methods, and interlayer structures on the TBR are summarized. This study provides guidelines for decreasing the TBR for thermal management in the design and implementation of GaN-based semiconductor devices.

Evaluation of cold atmospheric pressure plasma irradiation of water as a method of singlet oxygen generation.

We used cold atmospheric pressure plasma jet to examine in detail 1O2 generation in water. ESR with 2,2,5,5-tetramethyl-3-pyrroline-3-carboxamide, a secondary amine probe, was used for the detection of 1O2. Nitroxide radical formation was detected after cold atmospheric pressure plasma jet irradiation of a 2,2,5,5-tetramethyl-3-pyrroline-3-carboxamide solution. An 1O2 scavenger/quencher inhibited the ESR signal intensity induced by cold atmospheric pressure plasma jet irradiation, but this inhibition was not 100%. As 2,2,5,5-tetramethyl-3-pyrroline-3-carboxamide reacts with oxidizing species other than 1O2, it was assumed that the signal intensity inhibited by NaN3 corresponds to only the nitroxide radical generated by 1O2. The concentration of 1O2 produced by cold atmospheric pressure plasma jet irradiation for 60 s was estimated at 8 µM. When this 1O2 generation was compared to methods of 1O2 generation like rose bengal photoirradiation and 4-methyl-1,4-etheno-2,3-benzodioxin-1(4H)-propanoic acid (endoperoxide) thermal decomposition, 1O2 generation was found to be, in decreasing order, rose bengal photoirradiation ≥ cold atmospheric pressure plasma jet > endoperoxide thermal decomposition. Cold atmospheric pressure plasma jet is presumed to not specifically generate 1O2, but can be used to mimic states of oxidative stress involving multiple ROS.

Genome editing by introduction of Cas9/sgRNA into plant cells using temperature-controlled atmospheric pressure plasma.

Previously, we developed a technique to introduce a superfolder green fluorescent protein (sGFP) fusion protein directly into plant cells using atmospheric-pressure plasma. In this study, we attempted genome editing using CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats/CRISPR associated protein 9) system using this protein introduction technique. As an experimental system to evaluate genome editing, we utilized transgenic reporter plants carrying the reporter genes L-(I-SceI)-UC and sGFP-waxy-HPT. The L-(I-SceI)-UC system allowed the detection of successful genome editing by measuring the chemiluminescent signal observed upon re-functionalization of the luciferase (LUC) gene following genome editing. Similarly, the sGFP-waxy-HPT system conferred hygromycin resistance caused by hygromycin phosphotransferase (HPT) during genome editing. CRISPR/Cas9 ribonucleoproteins targeting these reporter genes were directly introduced into rice calli or tobacco leaf pieces after treatment with N2 and/or CO2 plasma. Cultivation of the treated rice calli on a suitable medium plate produced the luminescence signal, which was not observed in the negative control. Four types of genome-edited sequences were obtained upon sequencing the reporter genes of genome-edited candidate calli. sGFP-waxy-HPT-carrying tobacco cells exhibited hygromycin resistance during genome editing. After repeated cultivation of the treated tobacco leaf pieces on a regeneration medium plate, the calli were observed with leaf pieces. A green callus that was hygromycin-resistant was harvested, and a genome-edited sequence in the tobacco reporter gene was confirmed. As direct introduction of the Cas9/sgRNA (single guide RNA) complex using plasma enables genome editing in plants without any DNA introduction, this method is expected to be optimized for many plant species and may be widely applied for plant breeding in the future.

Pre- and Post-Harvest Conditions Affect Polyphenol Content in Strawberry (Fragaria × ananassa).

The strawberry fruit contains abundant polyphenols, such as anthocyanins, flavan-3-ol, and ellagitannin. Polyphenol enrichment improves the quality of strawberries and leads to a better understanding of the polyphenol induction process. We measured the total polyphenol content of strawberry fruits under different growth conditions, developmental stages, and treatment conditions during pre-harvest and post-harvest periods. High fruit polyphenol content was observed in cold treatment, which was selected for further analysis and optimization. A transcriptome analysis of cold-treated fruits suggested that the candidate components of polyphenols may exist in the phenylpropanoid pathway. Coverage with a porous film bag excluded the effects of drought stress and produced polyphenol-rich strawberry fruits without affecting quality or quantity. The degree of stress was assessed using known stress indicators. A rapid accumulation of abscisic acid was followed by an increase in superoxide dismutase and DPPH (2,2-Diphenyl-1-picrylhydrazyl) activity, suggesting that the strawberry fruits responded to cold stress immediately, reaching the climax at around 6 days, a trend consistent with that of polyphenol content. These findings enhance our understanding of the mechanism of post-harvest polyphenol accumulation and the value of strawberries as a functional food.

Temperature-controlled atmospheric-pressure plasma treatment induces protein uptake via clathrin-mediated endocytosis in tobacco cells.

Previously, we developed a method that uses temperature-controlled atmospheric-pressure plasma to induce protein uptake in plant cells. In the present work, we examined the mechanism underlying such uptake of a fluorescent-tagged protein in tobacco leaf cells. Intact leaf tissue was irradiated with N2 plasma generated by a multi-gas plasma jet and then exposed to the test protein (histidine-tagged superfolder green fluorescence protein fused to adenylate cyclase); fluorescence intensity was then monitored over time as an index of protein uptake. Confocal microscopy revealed that protein uptake potential was retained in the leaf tissue for at least 3 h after plasma treatment. Further examination indicated that the introduced protein reached a similar amount to that after overnight incubation at approximately 5 h after irradiation. Inhibitor experiments revealed that protein uptake was significantly suppressed compared with negative controls by pretreatment with sodium azide (inhibitor of adenosine triphosphate hydrolysis) or sucrose or brefeldin A (inhibitors of clathrin-mediated endocytosis) but not by pretreatment with genistein (inhibitor of caveolae/raft-mediated endocytosis) or cytochalasin D (inhibitor of micropinocytosis/phagocytosis), indicating that the N2 plasma treatment induced protein transportation across the plant plasma membrane via clathrin-mediated endocytosis.

Resin Cement-Zirconia Bond Strengthening by Exposure to Low-Temperature Atmospheric Pressure Multi-Gas Plasma.

The purpose of this study was to investigate the effect of gas species used for low-temperature atmospheric pressure plasma surface treatment, using various gas species and different treatment times, on zirconia surface state and the bond strength between zirconia and dental resin cement. Three groups of zirconia specimens with different surface treatments were prepared as follows: untreated group, alumina sandblasting treatment group, and plasma treatment group. Nitrogen (N2), carbon dioxide (CO2), oxygen (O2), argon (Ar), and air were employed for plasma irradiation. The bond strength between each zirconia specimen and resin cement was compared using a tension test. The effect of the gas species for plasma irradiation on the zirconia surface was investigated using a contact angle meter, an optical interferometer, an X-ray diffractometer, and X-ray photoelectric spectroscopy. Plasma irradiation increased the wettability and decreased the carbon contamination on the zirconia surface, whereas it did not affect the surface topography and crystalline phase. The bond strength varied depending on the gas species and irradiation time. Plasma treatment with N2 gas significantly increased bond strength compared to the untreated group and showed a high bond strength equivalent to that of the sandblasting treatment group. The removal of carbon contamination from the zirconia surface and an increase in the percentage of Zr-O2 on the zirconia surface by plasma irradiation might increase bond strength.

DNA Damage Response After Ionizing Radiation Exposure in Skin Keratinocytes Derived from Human-Induced Pluripotent Stem Cells.

PURPOSE: Epidermal cells are positioned on the body surface and thus risk being exposed to genotoxic stress, including ionizing radiation (IR), ultraviolet rays, and chemical compounds. The biological effect of IR on the skin tissue is a significant problem for medical applications such as radiation therapy. Keratinocyte stem cells and progenitors are at risk for IR-dependent tumorigenesis during radiation therapy for cancer treatment. To elucidate the molecular mechanism of genome stability in epidermal cells, we derived skin keratinocytes from human-induced pluripotent stem cells (iPSCs) and analyzed their DNA damage response (DDR). METHODS AND MATERIALS: Skin keratinocytes were derived from iPSCs and designated as first- (P1), second- (P2), and third- (P3) passage cells to compare the differentiation states of DDR. After 2 Gy gamma-ray exposure, cells were immunostained with DNA double-strand break markers γ-H2AX/53BP1 and cell senescence markers p16/p21 for DDR analysis. DDR protein expression level, cell survival, and apoptosis were analyzed by western blotting, WST-8 assay and TUNEL assay, respectively. DDR of constructed 3D organoid modeling was also analyzed. RESULTS: P1, P2, and P3 keratinocytes were characterized with keratinocyte markers keratin 14 and p63 using immunofluorescence, and all cells were positive to both markers. Derived keratinocytes showed high expression of integrin α6 and CD71 (real-time (qRT)-PCR ratio: iPSCs: integrin α6: 1.12, CD71: 1.25, P1: integrin α6: 7.80, CD71: 0.43, P2: integrin α6: 5.53, CD71: 0.48), suggesting that P1 and P2 keratinocytes have potential as keratinocyte progenitors. Meanwhile, P3 keratinocytes showed low expression of integrin α6 and CD71 (qRT-PCR ratio: P3: integrin α6: 0.55, CD71: 0.10), suggesting differentiated keratinocytes. After IR exposure, the P1 and P2 keratinocytes showed an increase in DNA repair activity by a γ-H2AX/53BP1 focus assay (P1: γ-H2AX: 28.0%, 53BP1: 17.0%, P2: γ-H2AX: 37.7%, 53BP1: 28.3%) but not in P3 keratinocytes (P3: γ-H2AX: 74.7%, 53BP1: 63.7%) compared with iPSCs (γ-H2AX: 57.0%, 53BP1: 55.0%). Furthermore, in derived keratinocytes, expression of the cellular senescence markers p16 and p21 were increased compared with iPSCs (P16: non irradiated, iPSCs: 0%, P1: 12.5%, P2: 14.5%, P3: 29.7%, IR, iPSCs: 0%, P1: 19.5%, P2: 34.8%, P3: 64.5%). DDR protein expression, cellular sensitivity, and apoptosis activity decreased in derived keratinocytes compared with iPSCs. CONCLUSIONS: We have demonstrated the derivation of keratinocytes from iPSCs and their characterization of differentiated states and DDR. Derived keratinocytes showed progenitors like character as a result of DDR. These results suggest that derived keratinocytes are useful tools for analyzing the effects of IR, such as DDR on the skin tissue from radiation therapy for cancer.

Endoscopic Hemostasis in Porcine Gastrointestinal Tract Using CO2 Low-Temperature Plasma Jet.

BACKGROUND: Recently, atmospheric low-temperature plasma (LTP) has attracted attention as a novel medical tool that might be useful for achieving hemostasis. However, conventional plasma sources are too big for use with endoscopes, and the efficacy of LTP for achieving hemostasis in cases of gastrointestinal bleeding is difficult to investigate. In this study, to solve the problem, we developed a 3D-printed LTP jet that has a diameter of 2.8 mm and metal body for endoscopic use. The characteristics, hemostasis efficacy, and safety were investigated. MATERIALS AND METHODS: On investigating the basic characteristics of the developed plasma jet, the electron densities, gas temperatures, and reactive species were measured by emission spectroscopy and thermocouple. To evaluate the efficacy of such hemostatic treatment, porcine gastrointestinal bleeding was treated with the device. In addition, to investigate the safety of such treatment, the CO2 LTP-treated tissue was compared with tissue that was treated with clipping-based or argon plasma coagulation-based hemostasis for 5 d, and hematoxylin and eosin staining was used to evaluate tissue damage in the treated regions. RESULTS: The measurement of emission spectroscopy, power, and electron density of various gas plasmas suggested that a high-density (1014 cm-3) LTP of CO2 was generated by the LTP jet, and the gas temperature was 41.5°C at 3 mm from the outlet of the LTP jet. The CO2 LTP achieved hemostasis of oozing blood by 70 ± 20 s. In addition, the CO2 LTP resulted in earlier recovery than clipping-based or argon plasma coagulation-based hemostases, and the treated regions had no damage by the CO2 LTP treatment. CONCLUSIONS: These results indicated that the developed LTP plasma jet has the potential to be used for endoscopic hemostasis.

Influence of Gas Temperature in Atmospheric Non-Equilibrium Plasma on Bactericidal Effect.

In this study, the relationship between plasma gas temperature and the bactericidal effects on five of bacteria (Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Enterococcus faecalis and Bacillus cereus (spore)) in liquid was investigated using a temperature-controllable plasma source. We determined that the bactericidal ability improved as the plasma gas temperature increased. Specifically, the bactericidal ability on E. coli of 80-℃ plasma was enhanced by as much as 6.3 times compared to that of 10-℃ plasma. The relationship between plasma gas temperature and the amount of hydroxyl radical, singlet oxygen, hydrogen peroxide, and ozone introduced into the solution was investigated. Our results also showed that each reactive species production increased by 2.1, 9.0, 1.6, and 17 times, respectively, with 80-℃ compared to 10-℃ plasma. The relationship between the bactericidal ability and amount of reactive species indicated that singlet oxygen and ozone introduced to the solution mostly influenced the bactericidal ability as the plasma gas temperature increased. We conclude that the plasma gas temperature is the crucial parameter for plasma sterilization.

Development of a Dual Plasma Desorption/Ionization System for the Noncontact and Highly Sensitive Analysis of Surface Adhesive Compounds.

We developed a dual plasma desorption/ionization system using two plasmas for the semi-invasive analysis of compounds on heat-sensitive substrates such as skin. The first plasma was used for the desorption of the surface compounds, whereas the second was used for the ionization of the desorbed compounds. Using the two plasmas, each process can be optimized individually. A successful analysis of phenyl salicylate and 2-isopropylpyridine was achieved using the developed system. Furthermore, we showed that it was possible to detect the mass signals derived from a sample even at a distance 50 times greater than the distance from the position at which the samples were detached. In addition, to increase the intensity of the mass signal, 0%-0.02% (v/v) of hydrogen gas was added to the base gas generated in the ionizing plasma. We found that by optimizing the gas flow rate through the addition of a small amount of hydrogen gas, it was possible to obtain the intensity of the mass signal that was 45-824 times greater than that obtained without the addition of hydrogen gas.

Investigation of blood coagulation effect of nonthermal multigas plasma jet in vitro and in vivo.

BACKGROUND: Nonthermal atmospheric pressure plasma (NTAPP) has recently received attention as a novel tool in medicine. It is thought that plasma components yield plasma effects such as sterilization, blood coagulation, and wound healing. These effects are produced without thermal damage. We investigated the blood coagulation effect of NTAPP by using a multigas plasma jet. MATERIALS AND METHODS: Multigas plasma jets can generate NTAPP by several gas species. In this study, argon, oxygen, helium, nitrogen, mock air, and carbon dioxide were used to generate NTAPP, and blood coagulation times were compared with each plasma-treated sample. The NTAPP blood coagulation effects on whole blood with four different anticoagulants were investigated. In addition, in this study, the effects of plasma treatment on porcine tissues and organs were investigated as in vivo experiment. RESULTS: A tendency to coagulate later with argon gas plasma than others was shown. There were no significant differences between oxygen, helium, nitrogen, mock air, and carbon dioxide. Whole blood with each anticoagulant demonstrated fast coagulation by NTAPP treatment. Fast control of the bleeding lesions on porcine stomach and liver by plasma treatment was observed, and no tissue damage due to the plasma treatment was detected by optical microscope. CONCLUSIONS: These experiments suggest the potential of various gas NTAPPs as a novel medical device to control bleeding lesions.

Development of a High-Density Microplasma Emission Source for a Micro Total Analysis System.

To achieve a highly sensitive and onsite analysis of a small amount samples, a microplasma-based micro total analysis systems (µ-TAS) device was developed. A dielectric barrier discharge (DBD) that can generate a stable plasma at atmospheric pressure was generated in a microchip and used as the plasma source. The use of DBD suppresses the temperature rise of the electrodes and enables operation for long times because of a reduction of the electrode damage due to suppression of the current via dielectric interposing between the electrodes. It is expected that the analytical system can be miniaturized because helium plasma is generated in the microchannel contained in the microchip. Emissions from gaseous Cl, Br, and I were analyzed using the plasma source, and it was found that the detection limits for these analytes were 0.22, 0.18, and 0.14 ppm, respectively. The calibration curves for gaseous Cl, Br, and I were also plotted obtaining correlation coefficients of 0.975, 0.955 and 0.986, respectively, and showing good linearity for the developed plasma source.

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.

Irradiation effects of low temperature multi gas plasma jet on oral bacteria.

The purpose of this study is to evaluate the sterilization effects of a newly developed low temperature multi gas plasma jet on oral pathogenic microorganisms (Streptococcus mutans [S. mutans], Lactobacillus fermentum [L. fermentum], Aggregatibacter actinomycetemcomitans [A. actinomycetemcomitans]). Plasma gas which generated from O2, N2, Ar and 50% (O2+N2) was irradiated to the microbes. Effect of O2 plasma irradiation on S. mutans under scanning electron microscopy (SEM) was also observed. O2 plasma was directly applied to dental plaque on human extracted tooth. Then, the depth of enamel resorption area was noted by nanoscale hybrid microscope. O2 had the best sterilizing effect for all microbes. The potent bactericidal effect of plasma irradiation was also observed by SEM. Decalcification of enamel was noted significantly lower in plasma irradiated tooth surface compared to no plasma exposure group. These findings revealed that multi gas plasma jet has great potential to be used for dental treatment.

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.

Development of Desolvation System for Single-cell Analysis Using Droplet Injection Inductively Coupled Plasma Atomic Emission Spectroscopy.

With a view to enhance the sensitivity of analytical instruments used in the measurement of trace elements contained in a single cell, we have now equipped the previously reported micro-droplet injection system (M-DIS) with a desolvation system. This modified M-DIS was coupled to inductively coupled plasma atomic emission spectroscopy (ICP-AES) and evaluated for its ability to measure trace elements. A flow rate of 100 mL/min for the additional gas and a measurement point -7.5 mm above the load coil (ALC) have been determined to be the optimal parameters for recording the emission intensity of the Ca(II) spectral lines. To evaluate the influence of the desolvation system, we recorded the emission intensities of the Ca(I), Ca(II), and H-ß spectral lines with and without inclusion of the desolvation system. The emission intensity of the H-ß spectral line reduces and the magnitude of the Ca(II)/Ca(I) emission intensity ratio increases four-fold with inclusion of the desolvation system. Finally, the elements Ca, Mg, and Fe present in a single cell of Pseudococcomyxa simplex are simultaneously determined by coupling the M-DIS equipped with the desolvation system to ICP-AES.

Microbial Inactivation in the Liquid Phase Induced by Multigas Plasma Jet.

Various gas atmospheric nonthermal plasmas were generated using a multigas plasma jet to treat microbial suspensions. Results indicated that carbon dioxide and nitrogen plasma had high sterilization effects. Carbon dioxide plasma, which generated the greatest amount of singlet oxygen than other gas plasmas, killed general bacteria and some fungi. On the other hand, nitrogen plasma, which generated the largest amount of OH radical, killed ≥ 6 log of 11 species of microorganisms, including general bacteria, fungi, acid-fast bacteria, spores, and viruses in 1-15 min. To identify reactive species responsible for bacterial inactivation, antioxidants were added to bacterial suspensions, which revealed that singlet oxygen and OH radicals had greatest inactivation effects.

Development of a gas-cylinder-free plasma desorption/ionization system for on-site detection of chemical warfare agents.

A gas-cylinder-free plasma desorption/ionization system was developed to realize a mobile on-site analytical device for detection of chemical warfare agents (CWAs). In this system, the plasma source was directly connected to the inlet of a mass spectrometer. The plasma can be generated with ambient air, which is drawn into the discharge region by negative pressure in the mass spectrometer. High-power density pulsed plasma of 100 kW could be generated by using a microhollow cathode and a laboratory-built high-intensity pulsed power supply (pulse width: 10-20 µs; repetition frequency: 50 Hz). CWAs were desorbed and protonated in the enclosed space adjacent to the plasma source. Protonated sample molecules were introduced to the mass spectrometer by airflow through the discharge region. To evaluate the analytical performance of this device, helium and air plasma were directly irradiated to CWAs in the gas-cylinder-free plasma desorption/ionization system and the protonated molecules were analyzed by using an ion-trap mass spectrometer. A blister agent (nitrogen mustard 3) and nerve gases [cyclohexylsarin (GF), tabun (GA), and O-ethyl S-2-N,N-diisopropylaminoethyl methylphosphonothiolate (VX)] in solution in n-hexane were applied to the Teflon rod and used as test samples, after solvent evaporation. As a result, protonated molecules of CWAs were successfully observed as the characteristic ion peaks at m/z 204, 181, 163, and 268, respectively. In air plasma, the limits of detection were estimated to be 22, 20, 4.8, and 1.0 pmol, respectively, which were lower than those obtained with helium plasma. To achieve quantitative analysis, calibration curves were made by using CWA stimulant dipinacolyl methylphosphonate as an internal standard; straight correlation lines (R(2) = 0.9998) of the peak intensity ratios (target per internal standard) were obtained. Remarkably, GA and GF gave protonated dimer ions, and the ratios of the protonated dimer ions to the protonated monomers increased with the amount of GA and GF applied.

Fundamental properties of a touchable high-power pulsed microplasma jet and its application as a desorption/ionization source for ambient mass spectrometry.

Plasma-based ambient desorption/ionization mass spectrometry (ADI-MS) has attracted considerable attention in many fields because of its capacity for direct sample analyses. In this study, a high-power pulsed microplasma jet (HPPMJ) was developed and investigated as a new plasma desorption/ionization source. In an HPPMJ, a microhollow cathode discharge is generated in a small hole (500 µm in diameter) using a pulsed high-power supply. This system can realize a maximum power density of 5 × 10(8) W/cm(3). The measured electron number density, excitation temperature and afterglow gas temperature of the HPPMJ were 3.7 × 10(15) cm(-3), 7000 K at maximum and less than 60 °C, respectively, which demonstrate that the HPPMJ is a high-energy, high-density plasma source that is comparable with an argon inductively coupled plasma while maintaining a low gas temperature. The HPPMJ causes no observable damage to the target because of its low gas temperature and electrode configuration; thus, we can apply it directly to human skin. To demonstrate the analytical capacity of ADI-MS using an HPPMJ, the plasma was applied to direct solid sample analysis of the active ingredients in pharmaceutical tablets. Caffeine, acetaminophen, ethenzamide, isopropylantipyrine and ibuprofen were successfully detected. Application to living tissue was also demonstrated, and isopropylantipyrine on a finger was successfully analyzed without damaging the skin. The limits of detection (LODs) for caffeine, isopropylantipyrine and ethenzamide were calculated, and LODs at the picogram level were achieved. These results indicate the applicability of the HPPMJ for high-sensitivity analysis of materials on a heat-sensitive surface.