Pulse-modulated Radiofrequency Research Articles

Application of a pm-rf-APGD-type plasma brush for deactivation of antibiotics from liquid solutions leads to impaired development of drug resistance by bacterial pathogens

The presence of antibiotics residuals in the natural environment contributes to development and spread of drug resistance determinants among bacteria, often including clinically significant human pathogens. To tackle with this threat, we constructed a plasma brush, generating pulse-modulated radio-frequency atmospheric pressure glow discharge (pm-rf-APGD), named pm-rf-APGD-type plasma brush, intended for degradation of biologically active pharmaceuticals from both single- and five-component solutions of ciprofloxacin (CFX), enrofloxacin (EFX), ofloxacin (OFX), doxycycline (DXC), and trimethoprim (TMP). The mean antibiotics removal efficiency, achieved mainly due to the action of reactive oxygen species (ROS), was 93.3 %. This removal efficiency corresponded to a mean 62.7% decrease in the antibacterial activities. We revealed the transformation products resulting from an oxygen attack and/or internal fragmentation of the treated pharmaceuticals. Based on a laboratory evolution study, bacterial exposure to the pm-rf-APGD-treated drug lead to significantly lower rates of antibiotic resistance development in juxtaposition with a long-term exposure to the sublethal dose of the active molecules. Thus, we anticipate a great potential of high-throughput, continuous flow, eco-friendly pm-rf-APGD-type plasma brush for routine decontamination processes in the future disposal pipelines of pharmaceuticals-containing wastewaters.

Biosafe removal of diclofenac from wastewaters by a continuous-flow mode cold atmospheric pressure plasma system

Diclofenac (DCF) is not only a versatile non-steroidal anti-inflammatory drug, but also an emerging water pollutant. There is an urgent need for innovative technology of wastewater treatment to reduce the impact of DCF on the environment. Thus, we examined the applicability of pulse-modulated radio-frequency atmospheric pressure glow discharge (pm-rf-APGD) for degradation of 1.56–50.0 mg L-1 DCF from both aqueous solutions and synthetic wastewaters. The removal rates varied from 84.0 ± 3.8% to 100.0 ± 0.1% for the aqueous solution and increased together with the decreasing concentration of DCF. For synthetic wastewaters, the DCF removal was enclosed in the range from 21.0 ± 1.0% to 74.8 ± 0.1%. The energy efficiencies varied from 0.0116 to 0.312 g kW-1h-1 for aqueous solutions and from 0.00779 to 0.0087 g kW-1h-1 for synthetic wastewaters, respectively. By application of ultraperformance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS) and gas chromatography-mass spectrometry (GC-MS), the pm-rf-APGD-driven DCF degradation pathways were revealed to involve decomposition, nitration, and dehalogenation reactions yielding dichloroaniline, nitro-diclofenac and 8-chlorocarbazole-1-acetic acid, respectively, before achieving the total decomposition of DCF to carbon dioxide, water, chlorides, nitrates and amines. Notable increases in the contents of the radicals, i.e., H2O2 in addition to NO2- and NO3-, were observed in the plasma-treated DCF solutions in contrast to the controls. Finally, no cytotoxic activity of the pm-rf-APGD-treated DCF solutions was demonstrated on model non-malignant human endothelial cells (HUVEC) and human immortalized keratinocytes (HaCaT). We anticipate that the described continuous-flow pm-rf-APGD-based reaction discharge system might be applied for biosafe removal of DCF from the effluents originating from wastewater treatment plants.

Comparison of pulse-modulated and continuous operation modes of a radio-frequency inductive ion source

The paper describes an experimental study of the characteristics of a pulse-modulated radio-frequency (RF) discharge sustained at low pressures, typical of the operating modes of RF gridded ion sources. The motivation for the study is the question of whether the RF pulse-modulated mode can increase the efficiency of the ion source. The ion current values extracted from an RF inductive ion source operating in continuous and pulse-modulated modes were compared. The experimental data were also compared with the parameter calculations based on a 0D numerical model of the discharge. The measurements showed that the pulse-modulated operation mode of the RF ion source had a noticeable advantage when the power of the RF generator was 140 W or lower. However, as the generator power increased, the advantage was lost because the pulse-modulated operation mode, having a higher RF power instant value, entered the region of existence sooner than the continuous mode, where the ion production cost begins to grow with RF power.

Comparing Study on Formation of Large Discharge Currents in Atmospheric Pulse-Modulated Radio Frequency Discharges

In recent years, pulse-modulation is introduced in atmospheric radio frequency (RF) discharges to further control the discharge operation. In this article, a comparing study is performed by a 1-D fluid model to investigate the formation of large discharge currents (LDCs) in the first RF cycle during the power-on phase in an atmospheric pulse-modulated RF discharge controlled by dielectric barriers. The current–voltage characteristics and helium metastable (He*) distributions show the enhancement of a pulsed voltage on the ignition of RF discharge, which agrees well with the experimental observation. On the other hand, in a dielectric barrier discharge driven by a sinusoidal voltage of 500 MHz, double LDCs are observed in the positive and negative half-cycles, respectively, and the large pulse rise rate of applied voltage essentially influences the distribution of charged particles in the first cycle during the power-on phase. In this study, according to computational data the reverse electric field near the anode contributes greatly to the generation of LDCs in both types of discharge, and the appropriate discharge conditions are suggested to optimize the pulse-modulated RF discharges in applications.

Numerical study on peak current in pulse-modulated radio-frequency discharges with atmospheric helium–oxygen admixtures

Atmospheric pressure pulse-modulated radio-frequency (rf) plasmas have drawn growing attention due to their potential in applications. By selecting appropriate modulation parameters, the diffused and large-volume plasma can be generated in the pulse-modulated rf plasma with plenty of reactive oxygen species, which is essential for the biomedical application of helium–oxygen plasmas. In this paper, by means of a fluid model, the formation of the peak current in the first period (PCFP) in a pulse-modulated rf helium–oxygen discharge driven by a sinusoidal voltage is discussed, the existence of a reverse field near the anode caused by the negative and positive charges contributes greatly to the mechanism of PCFP. In the simulation, as oxygen admixture increases, the negative ions of O− and become dominative anions in the sheath region, which can’t be driven to the anode very quickly to build a reverse field, thus the PCFP eventually disappears. This study can effectively enhance the understanding of different transportation behavior of heavy negative ions and electrons, and further optimize pulse-modulated rf discharges with helium–oxygen mixtures in various applications.

Application of pulse-modulated radio-frequency atmospheric pressure glow discharge for degradation of doxycycline from a flowing liquid solution.

Doxycycline (DOX), an antibiotic commonly used in medicine and veterinary, is frequently detected in natural waterways. Exposition of bacteria to DOX residuals poses a selective pressure leading to a common occurrence of DOX-resistance genetic determinants among microorganisms, including virulent human pathogens. In view of diminishment of the available therapeutic options, we developed a continuous-flow reaction-discharge system generating pulse-modulated radio-frequency atmospheric pressure glow discharge (pm-rf-APGD) intended for DOX removal from liquid solutions. A Design of Experiment and a Response Surface Methodology were implemented in the optimisation procedure. The removal efficiency of DOX equalling 79 ± 4.5% and the resultant degradation products were identified by High-Performance Liquid Chromatography–Diode Array Detection, Liquid Chromatography Quadruple Time of Flight Mass Spectrometry, Ultraperformance Liquid Chromatography–Tandem Mass Spectrometry, total organic carbon, total nitrogen, Attenuated Total Reflectance Furrier Transform–Infrared, and UV/Vis-based methods. The pm-rf-APGD-treated DOX solution due to the generated Reactive Oxygen and Nitrogen Species either lost its antimicrobial properties towards Escherichia coli ATCC25922 or significantly decreased biocidal activities by 37% and 29% in relation to Staphylococcus haemolyticus ATCC29970 and Staphylococcus aureus ATCC25904, respectively. Future implementation of this efficient and eco-friendly antibiotic-degradation technology into wastewater purification systems is predicted.

Ignition dynamics of radio frequency discharge in atmospheric pressure cascade glow discharge

A cascade glow discharge in atmospheric helium was excited by a microsecond voltage pulse and a pulse-modulated radio frequency (RF) voltage, in which the discharge ignition dynamics of the RF discharge burst was investigated experimentally. The spatio-temporal evolution of the discharge, the ignition time and optical emission intensities of plasma species of the RF discharge burst were investigated under different time intervals between the pulsed voltage and RF voltage in the experiment. The results show that by increasing the time interval between the pulsed discharge and RF discharge burst from 5 μs to 20 μs, the ignition time of the RF discharge burst is increased from 1.6 μs to 2.0 μs, and the discharge spatial profile of RF discharge in the ignition phase changes from a double-hump shape to a bell-shape. The light emission intensity at 706 nm and 777 nm at different time intervals indicates that the RF discharge burst ignition of the depends on the number of residual plasma species generated in the pulsed discharges.

Numerical Study on Operation Optimization of Atmospheric Radio-Frequency Glow Discharges Modulated by Pulses

In recent years, pulse-modulated radio frequency (RF) plasmas have gained considerable interest in applications due to the advantages in reducing gas temperature and power consumption. In this article, the optimizations of operation mode in atmospheric pulse modulation RF discharges are investigated by a 1-D fluid model. From simulation data, the breakdown voltage and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${{\alpha -{\gamma }}}$ </tex-math></inline-formula> mode transition voltage both decrease as the duty cycle increases; however, a minimum breakdown voltage can be observed while altering the modulation frequency at a constant duty cycle, and the transition voltage always increases with the modulation frequency. The underpinning physics of the operation regime in pulsed RF discharges is discussed in detail by investigating the effects of the duration of the power-on phase based on the computational results. Increasing the number of applied RF cycles during the power-on phase contributes greatly to the breakdown and mode transition. This study can effectively deepen the understanding of the effects of pulse modulation in RF discharges and suggest ways to further optimize the pulse-modulated RF discharges.

The investigation of Pulse-Modulated GSM-900 MHz electromagnetic field effects on the electrochemotherapy mechanisms in vivo

ABSTRACT Electrochemotherapy (ECT) as a tumor treatment modality is approved for cutaneous and subcutaneous tumors. The purpose of the present study was to examine the effect of 900 MHz radiofrequency (RF) pulse-modulated by 217 Hz EMFs similar to those emitted by mobile phones on the mechanisms of ECT in vivo including: tumor hypoxia and immune system response, and on tumor volume.4 T1 cells were injected subcutaneously into the right flank of Balb/c mice. The mice were exposed to RF fields at specific absorption rate (SAR) 2 W/kg for 10 min/day and then treated with ECT. Two protocols of ECT were used: ((70 V/cm-5 kHz) and 70 V/cm-4 kHz)). Tumor hypoxia was analyzed through HIF-1α immuonohistochemistry assay. Interleukin 4 (IL-4) and IFN-γ levels were estimated by enzyme-linked immunosorbent assay (ELISA) technique to evaluate immune system response. Also, tumors volume changes were measured for 24 days following the treatment. The results showed that pulse-modulated RF fields could increase hypoxia induced by ECT, significantly (about 13% in ECT (70 V/cm-5 kHz) and 11% in ECT (70 V/cm-4 kHz)). However, these fields did not have significant effect on immune system response (the levels of IL-4 and IFN-γ) and tumor volume changes induced by ECT. Our results indicated that pulse-modulated RF fields could not affect tumor volume changes in ECT with the frequency of 5 kHz and voltage of 70 V/cm efficacy in vivo. However, investigating the role of other environmental intervening factors on this protocol of ECT is recommended in further studies.

Modeling study on the enhancement of atmospheric pulse-modulated radio-frequency discharge assisted by pulsed voltage

In this paper, we performed a one-dimensional fluid model to study the mechanism and optimization of pulse-modulated Radio-Frequency (RF) discharges at atmospheric pressure assisted by short pulse voltages. The evolution of discharge current density, helium metastable (He*) density, and total electron density from the simulation demonstrates that the ignition of RF discharge could be effectively enhanced by the short pulsed discharge, and a large Peak Current in the First Period (PCFP) can be produced, which agrees well with the experimental measurements. Due to the assistance of pulsed voltage, a strong electric field could be formed near the anode with the same polarity of that near the cathode, which can reaccelerate the electrons near the anode to generate a large PCFP. Based on the simulation results, reducing the time interval and increasing the pulse rise rate are very helpful to enhance the ignition of subsequent RF discharge by strengthening the electric field near the anode. It is shown that by choosing the appropriate time interval and pulse rise rate, the pulse-modulated RF discharge assisted by the pulsed discharge can be effectively modulated and optimized for applications.

Excitation of helical shape argon atmospheric pressure plasma jet using RF pulse modulation

The article reports the excitation of a helical argon atmospheric pressure plasma jet using a pulse-modulated 13.56 MHz radio frequency (RF) power source. This helical structure is observed in open ambient air, which is far different from the conventional conical shape. This helical structure originates due to the periodic pressure variation in the discharge region caused by pulse-modulated RF (2 kHz modulation frequency) and propagates downstream into the ambient air. The geometrical characteristics of the observed structure are explored using optical imaging. Moreover, the influence of various input parameters, viz., duty cycle, gas flow rate, and RF power, of the modulated pulse on the formation of a helical structure are studied. These helical structures have an implication on the plasma jet chemical features (enhancement of reactive oxygen and nitrogen species) as these are involved in an increase in air entrainment into the ionization region desired for various plasma applications.

Numerical study on optimization of atmospheric pulse-modulated radio frequency discharges in the very high frequency range

In this paper, we investigated the optimization of pulse-modulated radio frequency (rf) discharges in the range of very high frequency from 50 to 800 MHz by a fluid model. A very strong Peak Current in the First Period (PCFP) during the power-on phase can be observed only when the excitation frequency is large enough, usually larger than 50 MHz, and the reversal electric field near the anode due to the accumulation of electrons contributes greatly to the formation of this peak current from the simulation data. The highest electron temperature is achieved in the first period, while the largest electron density is usually obtained in the last period during the power-on phase. By increasing the duty cycle, the value of PCFP increases initially, then it reaches the peak value at a duty cycle of approximately 70%, and later it drops to the normal value generated in a continuous rf discharge, and the maximum electron temperature also shows the similar evolution. However, as the duty cycle is increased, the electron density is always enhanced during the power-on phase. According to the simulation results, the duty cycle and modulation frequency can be effectively applied to modulate and optimize the electron density and electron temperature for applications.

Effects of pulse-modulated radiofrequency magnetic field (RF-EMF) exposure on apoptosis, autophagy, oxidative stress and electron chain transport function in human neuroblastoma and murine microglial cells

The use of body-worn wireless devices with different communication protocols and rapidly changing exposure scenarios is still multiplying and the need to identify possible health effects of radiofrequency electromagnetic field (RF-EMF) exposure with extremely low-frequency (ELF) modulation envelops. In this study, effects of ELF-modulated 935 MHz RF-EMF on apoptosis, autophagy, oxidative stress and electron exchange in N9 microglial and SH-SY5Y neuroblastoma cells were investigated.Cells were exposed at 4 W/kg or sham-exposed for 2 and 24 h. RF-EMF exposure of both cell types did not alter apoptosis, the number of living cells nor the apoptosis-inducing factor (AIF), irrespective of the exposure duration. RF-EMF exposure for 24, but not for 2 h, increased protein levels of the autophagy marker ATG5, whereas LC3B-I and II and pERK were not altered in both cell types and exposure times investigated. A transient increase in glutathione (GSH), but not hydrogen peroxide and cytochrome c oxidase was found only in SH-SY5Y cells, indicating that short-time RF-EMF at SAR levels accepted by today's safety guidelines might cause autophagy and oxidative stress with the effect being dependent on cell type and exposure duration.Further studies are needed to evaluate possible underlying mechanisms involved in pulse-modulated RF-EMF exposure.

Etch Characteristics of Nanoscale Patterned Magnetic Tunnel Junction Stacks Using Pulse-Modulated Radio Frequency Source Plasma.

Magnetic tunnel junctions (MTJs) patterned with 70 × 70 nm² square arrays were etched in a CH₄/O₂/Ar gas mixture by pulse-modulated inductively coupled plasma reactive ion etching (ICPRIE). A good etch profile of MTJs with etch slope of approximately 82° was achieved by adjusting the on-off duty ratio of the plasma and pulse frequency. Langmuir probe analysis and optical emission spectroscopy confirmed that the balance between the formation of the passivation layer as an etch byproduct and sputtering effect is responsible for the etch selectivity and etch profile with a high degree of anisotropy. It is concluded that the application of pulse-modulated plasma on ICPRIE can be an effective method to obtain the anisotropic etch profile of nanometer-scale MTJs.

Application of Oil-in-Water Nanoemulsion Carrying Size-Defined Gold Nanoparticles Synthesized by Non-thermal Plasma for the Human Breast Cancer Cell Lines Migration and Apoptosis

In this work, the gold nanoparticles (AuNPs) were synthesized using pulse-modulated radio-frequency atmospheric pressure glow discharge (pm-rf-APGD). By tailoring selected operating parameters of the pm-rf-APGD reaction-discharge system, the experimental conditions for the synthesis of raw-AuNPs with controlled optical and structural properties were found. The colloidal suspension of the size-controlled raw-AuNPs was mixed with an aqueous solution of gelatine and turmeric oil to produce an oil-in-water (O/W) nanoemulsion. AuNPs loaded into the nanoemulsion were characterized using ultraviolet–visible absorption spectrophotometry, dynamic light scattering, scanning electron microscopy supported by energy dispersive X-ray spectroscopy, and transmission electron microscopy equipped with selected area X-ray diffraction. Additionally, attenuated total reflectance Fourier-transform infrared spectroscopy was used to confirm the efficient functionalization of the AuNPs by nanoemulsion component. It was revealed that AuNPs were mostly spherical with an average size of 4.6 ± 1.0 nm and a face-centered cubic crystal system. The developed O/W nanoemulsion carrying AuNPs was applied towards the human breast cancer cell lines MCF7 and MDA-MB-231. It was found that it exhibited the cytotoxicity towards the breast cancer cells while were non-cytotoxic towards the non-tumour breast cells MCF10A. Moreover, it also inhibited the migration of the invasive cancer breast cells (line MDA-MB-231) and hence, could prevent the breast cancer metastasis.

Controlled formation of iron oxide nanoparticles by pulse-modulated RF discharge at atmospheric pressure

Iron oxide nanoparticles of various sizes have been experimentally obtained in a capacitively coupled plasma of a radio frequency (RF) discharge at atmospheric pressure in constant and pulse-modulated modes of the RF discharge. Elemental analysis of the obtained nanoparticles by X-ray photoelectron spectroscopy (XPS) and IR Fourier spectroscopy shows that the iron oxide nanoparticles are a mixture of FeO (II) and Fe2O3 (III) oxides. In the constant mode of discharge burning, the obtained nanoparticles with an estimated average size of 5–50 nm are formed as agglomerates of tangled chains. In the pulse-modulated mode of discharge burning, the particles with an estimated average size of 330 or 640 nm depending on the mode of discharge modulation are obtained.

Immunotropic effects in cultured human blood mononuclear cells exposed to a 900MHz pulse-modulated microwave field.

ABSTRACTThe specific biological effect of electromagnetic field (EMF) remains unknown even though devices present in our daily lives, such as smartphones and Wi-Fi antennae increase the environmental level of electromagnetic radiation. It is said that the human immune system is able to react to discrete environmental stimuli like EMF. To investigate the effect of 900 MHz microwave stimulation on the immune system our research aimed to analyze lymphocyte proliferation and observe and assess the basic immunoregulatory activities using a newly developed and improved anechoic chamber. Samples of mononuclear cells (PBMC) isolated from the blood of healthy donors were exposed to 900 MHz pulse-modulated radiofrequency radiation (20 V/m, SAR 0.024 W/kg) twice (15 min each) or left without irradiation (control group). Subsequently, the control and exposed cells were set up to determine several parameters characterizing T cell immunocompetence and monocyte immunogenic activity. Although the microcultures of PBMC exposed to radiofrequency radiation demonstrated higher immunogenic activity of monocytes (LM index) and T-cell response to concanavalin A than control cultures after first exposure, this parameter decreased after a second stimulation. Saturation of the interleukin-2 (IL-2) receptor rose significantly after the second day of exposure. On the other hand, response to mitogen dropped after EMF stimulation. The results suggest that PBMC are able to overcome stress caused by mitogens after stimulation with 900 MHz radiation.

Numerical simulation of atmospheric pulse-modulated radio-frequency glow discharge ignition characteristics assisted by a pulsed discharge

A one-dimensional self-consistent fluid numerical model was developed to study the ignition characteristics of a pulse-modulated (PM) radio-frequency (RF) glow discharge in atmospheric helium assisted by a sub-microsecond voltage excited pulsed discharge. The temporal evolution of discharge current density and electron density during PM RF discharge burst was investigated to demonstrate the discharge ignition characteristics with or without the pulsed discharge. Under the assistance of pulsed discharge, the electron density in RF discharge burst reaches the magnitude of 1.87 × 1017 m−3 within 10 RF cycles, accompanied by the formation of sheath structure. It proposes that the pulsed discharge plays an important role in the ignition of PM RF discharge burst. Furthermore, the dynamics of PM RF glow discharge are demonstrated by the spatiotemporal evolution of the electron density with and without pulsed discharge. The spatial profiles of electron density, electron energy and electric field at specific time instants are given to explain the assistive role of the pulsed discharge on PM RF discharge ignition.

Contrasting Characteristics of Gas–Liquid Reactive Species Induced by Pulse-Modulated RF and kHz Sinusoidal Plasma Jets

The pulse-modulated radio frequency (RF) and kHz sinusoidal voltages are used for the excitation of two plasma jets, for which the reactive species in the plasma plumes and in the treated water are comparatively studied. With the same discharge power, it is found that concentrations of aqueous reactive species generated by the kHz sinusoidal plasma jet are higher than that of the pulse-modulated RF plasma jet, especially for the short-lived species OH. In addition, the comparison between the bacterial inactivation results is in accordance with that for the concentrations of aqueous reactive species for the two types of plasma jets. On the contrary, the emission spectra indicate that the gaseous reactive species such as OH(A) and O(3p5P) have much higher densities for the pulse-modulated RF plasma jet, which should ascribe to its higher electron density and electron temperature. Moreover, the concentrations of the aqueous reactive species and the emission intensities of the gaseous reactive species have similar variation trends for each of the plasma jets, as a function of the discharge power and the gap width. These results imply that the emission intensity could not reflect the relative concentration of an aqueous reactive species between these two plasma jets, but it could be used as an indicator of the concentration variation of an aqueous reactive species for each of the plasma jets. In addition, the phenomenon of electron trapping effect also indicates that the aqueous reactive species can be effectively generated only when more electrons act on the water sample.

Experimental investigation of the electron impact excitation behavior in pulse-modulated radio frequency Ar/O2 inductively coupled plasma

In inductively coupled plasmas (ICPs), mode transition between capacitive coupling (E mode) and inductive coupling (H mode) is a key issue. Using an intensified charge-coupled device camera, the mode transition-related behaviors of the electron impact excitation of Ar(2p1) are investigated under different discharge conditions in pulse-modulated radio-frequency (rf) Ar/O2 ICPs. The initiation time of the E-H mode transition at the initial stage of a pulse period is examined under nanosecond time-resolution for the first time. It is found that the initiation time increases with increasing the applied power (300-600 W), while it decreases with raising the duty cycle (50%-80%) or gas pressure (20-80 mTorr). Besides, we also examined the spatial-temporal electron impact excitation rate over the whole pulse period (microsecond time-resolution), especially in the H mode when the discharge is operated at the steady state. We found that as the O2 content/pressure increases, the electron impact excitation axially concentrates closer to the quartz window, and the bimodal structure becomes more prominent in the H mode. However, the excitation gets farther away from the window at higher power. In addition, the maximum value of the excitation rate appears earlier at the initial stage of a pulse period at higher pressure/O2 content.