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Low temperature plasma technology is proving to be at the frontier of emerging medical technologies with real potential to overcome escalating healthcare challenges including antimicrobial and anticancer resistance. However, significant improvements in efficacy, safety, and reproducibility of plasma treatments need to be addressed to realize the full clinical potential of the technology. To improve plasma treatments recent research has focused on integrating automated feedback control systems into medical plasma technologies to maintain optimal performance and safety. However, more advanced diagnostic systems are still needed to provide data into feedback control systems with sufficient levels of sensitivity, accuracy, and reproducibility. These diagnostic systems need to be compatible with the biological target and to also not perturb the plasma treatment. This paper reviews the state-of-the-art electronic and optical sensors that might be suitable to address this unmet technological need, and the steps needed to integrate these sensors into autonomous plasma systems. Realizing this technological gap could facilitate the development of next-generation medical plasma technologies with strong potential to yield superior healthcare outcomes. Refereed/Peer-reviewed

Refereed/Peer-reviewed This study compares how a helium plasma jet activates peracetic acid (PAA) from tetraacetylethylenediamine (TAED) and acetic acid (AA). Hydrogen peroxide (H2O2) generated from the plasma jets reacts with TAED resulting in the formation of PAA which further dissociates into AA. The by-product AA can also react with H2O2 to form PAA, which might also be useful for antimicrobial applications when coupled with plasma. Equivalent concentrations of TAED and AA solutions are used to compare the formation of PAA after activation with a helium plasma jet. Our results showed that the concentrations of both H2O2 and PAA in plasma-activated TAED (PAT) are higher than plasma-activated AA (PAAA), and that PAT is more efficient in reducing the growth of Pseudomonas aeruginosa and Staphylococcus aureus; the pathogens commonly found in wounds. The results are attributed to the presence of more acetyl donor groups in TAED, resulting in the formation of higher concentrations of PAA and H2O2.

An unresolved issue in the physics of lightning is an explanation for lightning proceeding to the ground by successive luminous steps separated by ‘dark’ times of many microseconds. There is also no explanation of the structure of the dark column connecting the streamer step with the cloud that can be km in length, is electrically conducting, yet has a very low sustaining electric field. It is proposed that these two processes can be explained by the accumulation of singlet delta metastable oxygen molecules excited in the corona pulses of lightning. The step time is necessary for the excitation of large metastable densities to produce significant metastable detachment of electrons from negative ions. The detached electrons form a highly conducting step, initially luminous, that causes a redistribution of electric fields and an increase in the potential and electric fields at the end of the step to make possible a further step by ionization. These features are supported by calculations of densities of electrons, positive ions, negative ions and singlet delta metastable oxygen molecules for the first 7 μs of a discharge chosen to be initiated by a 50 cm sphere of charged hail particles. The calculated corona streamers produce metastable densities of 1017 cm−3 near the corona source. These metastables, by electron detachment, produce a conducting cylinder 10 m long with a radius of 1 cm and an electron density ∼1012 cm−3 that is attributed to being the first step and a lightning ‘leader’. These conducting regions develop within them very low electric fields. Successive steps are likely to combine to form the long conductive columns of lightning that exist before the return stroke. Electron densities in the leader and the column are an equilibrium between electron production by metastable detachment and electron loss by attachment to neutral oxygen molecules, requiring no electric field.

Antibiotics are commonly used as the first line of defense in the treatment of infectious diseases. However, the rise of antimicrobial resistance (AMR) is rendering many antibiotics less effective. Consequently, effective non-antibiotic antimicrobial strategies are urgently needed to combat AMR. This paper presents a strategy utilizing cold plasma for the "on-demand"activation of acetyl donor molecules. The process generates an aqueous-based antimicrobial formulation comprising a rich mixture of highly oxidizing molecules: peracetic acid, hydrogen peroxide, and other reactive oxygen and nitrogen species. The synergistic potent oxidative action between these molecules is shown to be highly effective at eradicating common wound pathogenic bacteria (Pseudomonas aeruginosa and Staphylococcus aureus) and at inactivating a virus (SARS-CoV-2). Refereed/Peer-reviewed

Current methods used to treat non-muscle invasive bladder cancer are inadequate due to a high recurrence rate after surgery and occurrence of adverse events such as interstitial pneumonia following intravesical instillation therapy. Low-temperature plasma is a new form of physical therapy that provides a rich source of reactive oxygen species (ROS). Oxidative solutions, created by pre-treatment of aqueous media with plasma before application to target cells, lead to the destruction of cancer cells through oxidative stress pathways. This study focuses on the effects of plasma activated media (PAM) in bladder cancer cells. PAM treatment increases up regulation of p21 and down regulation of Cyclin D and CdK4 leading to cell cycle arrest, and concomitantly depolarises the mitochondrial membrane leading to increased mitochondrial ROS production. Cell cycle arrest and increased mitochondrial ROS production induce apoptosis in bladder cancer cells in vitro and in a bladder cancer tumour in vivo via the pro-apoptotic caspase 3/cytochrome c pathway. These observations highlight the potential of plasma activated solutions as a new adjuvant therapy in the clinical treatment of bladder cancer.

A conical assembly of six plasma jets arranged in a rectangular pattern for biomedical applications is presented. The conical configuration increases the separation distance between individual tubes within the assembly that reduces interference between individual plasma jets and enables the jets to converge at the output, facilitating more uniform treatment as opposed to plasma jet arrays operated in parallel. Electrical and optical diagnostics of the plasma discharges and measurements of H2O2 and [Formula: see text] production in de-ionized water are used to characterize the potential suitability of the device for biomedical applications. Particularly, it was found that the efficiency in H2O2 (an important bacterial disinfection agent) production by the conical assembly of six plasma jets was more than nine-fold higher compared to its single plasma jet counterpart and that this could be achieved at a biocompatible temperature of below 300 K. Therefore, the device may find use in biomedical applications, particularly where larger area treatments are required such as for certain wounds and cancer tumors that can span areas of tens of cm2.

In the ‘Plasma–Liquid Interactions’ Special Topic Collection, researchers explore the richness and full breadth of plasma– liquid interactions and their applications. The collection contains two perspective articles that discuss key questions related to fundamental processes at the plasma–liquid interface. Researchers introduce the concept of plasma-driven solution electro chemistry (PDSE) inspired by comparing plasma–liquid interactions with conventional electrolysis and develop ten questions that should be answered to enable researchers to make transformational advances in plasma–liquid interactions for a variety of applications. The Perspective by Vanraes and Bogaert focuses on that same plasma–liquid interface but emphasizes the gas phase processes rather than liquid-phase processes Refereed/Peer-reviewed

To investigate the potential role of the hydroxyl radical (•OH) in cold atmospheric plasma (CAP) jet treatment, two fluorescence-based methodologies are utilised to measure DNA strand breaks. The first comprises a model system of a double-stranded DNA oligomer, where the respective strand ends are tagged with fluorophore and quencher molecules; and the second, a cell culture system reporting DNA strand breaks using the γ-H2AX assay. During the various CAP jet treatments, optical emission spectroscopy is used to detect the •OH in the gas phase and electron spin resonance is used to detect the •OH in solution. The CAP jet production of the •OH is shown to correlate to CAP jet induced DNA damage both with the DNA model and in biological cells. Results indicate that the CAP jet induces a higher degree of DNA damage when the CAP plume is in contact with the target solution. The potential of a ‘plasma screen’ based upon a hydrogel film, as a method to remove the DNA-damaging •OH species from reaching skin cells, is shown to significantly reduce DNA damage whilst facilitating the delivery of hydrogen peroxide. These findings could aid in the development of CAP jet-based applications where DNA damage is the objective (e.g. in cancer treatment) and others where it is to be avoided, e.g. in open-wound treatment and dermatology.

The mechanisms of plasma in medicine are broadly attributed to plasma-derived reactive oxygen and nitrogen species (RONS). In order to exert any intracellular effects, these plasma-derived RONS must first traverse a major barrier in the cell membrane. The cell membrane lipid composition, and thereby the magnitude of this barrier, is highly variable between cells depending on type and state (e.g. it is widely accepted that healthy and cancerous cells have different membrane lipid compositions). In this study, we investigate how plasma-derived RONS interactions with lipid membrane components can potentially be exploited in the future for treatment of diseases. We couple phospholipid vesicle experiments, used as simple cell models, with molecular dynamics (MD) simulations of the lipid membrane to provide new insights into how the interplay between phospholipids and cholesterol may influence the response of healthy and diseased cell membranes to plasma-derived RONS. We focus on the (i) lipid tail saturation degree, (ii) lipid head group type, and (iii) membrane cholesterol fraction. Using encapsulated molecular probes, we study the influence of the above membrane components on the ingress of RONS into the vesicles, and subsequent DNA damage. Our results indicate that all of the above membrane components can enhance or suppress RONS uptake, depending on their relative concentration within the membrane. Further, we show that higher RONS uptake into the vesicles does not always correlate with increased DNA damage, which is attributed to ROS reactivity and lifetime. The MD simulations indicate the multifactorial chemical and physical processes at play, including (i) lipid oxidation, (ii) lipid packing, and (iii) lipid rafts formation. The methods and findings presented here provide a platform of knowledge that could be leveraged in the development of therapies relying on the action of plasma, in which the cell membrane and oxidative stress response in cells is targeted. Refereed/Peer-reviewed

Electrically generated cold atmospheric plasma is being intensively researched for novel applications in biology and medicine. Significant attention is being given to reactive oxygen and nitrogen species (RONS), initially generated upon plasma-air interactions, and subsequently delivered to biological systems. Effects of plasma exposure are observed to millimeter depths within tissue. However, the exact nature of the initial plasma-tissue interactions remains unknown, including RONS speciation and delivery depth, or how plasma-derived RONS intervene in biological processes. Herein, we focus on current research using tissue and cell models to learn more about the plasma delivery of RONS into biological environments. We argue that this research is vital in underpinning the knowledge required to realize the full potential of plasma in biology and medicine. Physical effects of plasma can be seen to depths of several hundred micrometers within tissue.Plasma-derived RONS are likely to be delivered millimeters into tissues.Speciation reveals that RONS delivered by plasma into tissue fluid and tissue are predominately stable secondary RONS - for example, H 2 O 2 , NO 2 - , and NO 3 - .The plasma generation of RONS within a hydrated target is influenced by the target matrix that can enhance or reduce the RONS concentrations and act as a reservoir of RONS.It is likely that the concentration of these plasma-derived RONS exceeds hundreds of micromoles, even at depths of several millimeters within tissue.Oxygen concentration at the time of plasma treatment significantly influences RONS generation within a hydrated proteinaceous target. Refereed/Peer-reviewed

This study investigates how addition of a 2nd ground electrode in an argon plasma jet influences the production of hydrogen peroxide (H2O2) in deionised water (DIW). Briefly, plasma is ignited by purging argon gas through a quartz tube at 1 l min−1 and applying a sinusoidal voltage of 7 kV (peak–peak) at 23.5 kHz to a high voltage stainless steel needle electrode sealed inside the quartz tube surrounded by one or two copper ring(s) that served as the ground electrode(s) situated downstream of the high voltage electrode. The mechanisms of H2O2 production are investigated through the electrical and optical plasma properties and chemical analysis of the treated DIW. We discover that the addition of a 2nd ground electrode results in higher accumulation of charges on the inner wall surface of the quartz tube of the plasma jet assembly resulting in an increase in the discharge current and dissipated power. This further leads to an increase in the electron temperature that more than doubles the H2O2 production through dissociative recombination of water vapour molecules, whilst still maintaining a biological tissue tolerable gas temperature. The double ground electrode plasma jet is shown to be highly effective at reducing the growth of common wound pathogens (Pseudomonas aeruginosa and Staphylococcus aureus) in both planktonic and biofilm states whilst inducing a low level of cytotoxicity in HaCaT keratinocyte skin-like cells under certain conditions. The information provided in this study is useful in understanding the complex physicochemical processes that influence H2O2 production in plasma jets, which is needed to optimise the development of plasma sources for clinical applications.

We investigated a new approach to control protein and cell attachment inside 96-well polystyrene plates. The wells were first coated with bovine serum albumin (BSA) to inhibit cell and protein attachment. The BSA-coated wells were then treated with a helium microplasma jet for increasing times that resulted in gradual removal of BSA from the surface. It was found that the amount of enzyme and cell attachment could be controlled in the wells where BSA was only partially removed by the microplasma jet. In addition to the surface coverage of BSA, the new surface chemistry induced by the microplasma jet treatment also had an important role in the control of enzyme and cell attachment. In summary, microplasma jet treatment of BSA-coated polystyrene wells is a simple and effective method for controlling enzyme and cell attachment. This might find use for high-throughput screening of new cell culture platforms where control over the level protein, enzyme or cell adherence is needed in order to maintain a specific cell function. Refereed/Peer-reviewed

Advances in digital technologies have opened new opportunities for creating more reliable, time‐ and cost‐effective, safer and mobile methods of diagnosing, managing and treating diseases. A few examples of advanced nano‐ and digital technologies are already FDA‐approved for diagnosing and treating diseases. Plasma treatment is still emerging as a new healthcare technology, but it is showing a strong potential for treatment of many diseases including cancers and antimicrobial‐resistant infections, with little or no adverse side effects. Here, we argue that with the ever‐increasing complex healthcare challenges facing communities, including the ongoing COVID‐19 pandemic, it is critical to consider combining unique properties of emerging healthcare technologies into a single multimodal treatment modality that could lead to unprecedented healthcare benefits. In this article, we focus on the healthcare opportunities created by establishing a nexus between plasma, nano‐ and digital technologies. We argue that the combination of plasma, nano‐ and digital technologies into a single multimodal healthcare package may significantly improve patient outcomes and comfort, and reduce the economic burden on community healthcare, as well as alleviate many problems related to overcrowded healthcare systems., Establishing a credible link between plasma, nano‐ and digital technologies could open new opportunities for the development of superior multimodal healthcare strategies. Here, we provide an overview of how to establish a nexus between plasma, nano‐ and digital technologies, and demonstrate how this beneficial link may be utilised in personalised medicine, using the recent COVID‐19 pandemic as a pertinent case study.

We investigate the use of a DC-pulse-driven non-thermal atmospheric-pressure He plasma jet in the regulation of hydrogen peroxide (H2O2), nitrite (NO2&minus, ), nitrate (NO3&minus, ), and oxygen (O2) in deionized (DI) water. The production of these molecules is measured by in situ UV absorption spectroscopy of the plasma-activated water (PAW). Variations in the pulse polarity and pulse width have a significant influence on the resultant PAW chemistry. However, the trends in the concentrations of H2O2, NO2&minus, NO3&minus, and O2 are variable, pointing to the possibility that changes in the pulse polarity and pulse width might influence other plasma variables that also impact on the PAW chemistry. Overall, the results presented in this study highlight the possibility of using DC-pulse-driven plasma jets to tailor the chemistry of PAW, which opens new opportunities for the future development of optimal PAW formulations across diverse applications ranging from agriculture to medicine.

We explore how to configure an argon atmospheric-pressure plasma jet for enhancing its production of hydrogen peroxide (H2O2) in deionised water (DIW). The plasma jet consists of a quartz tube of 1.5 mm inner diameter and 3 mm outer diameter, with an upstream internal needle electrode (within the tube) and a downstream external cylindrical electrode (surrounding the tube). The plasma is operated by purging argon through the glass tube and applying a sinusoidal AC voltage to the internal needle electrode at 10 kV (peak–peak) with a frequency of 23.5 kHz. We study how the following operational parameters influence the production rate of H2O2 in water: tube length, inter-electrode separation distance, distance of the ground electrode from the tube orifice, distance between tube orifice and the DIW, argon flow rate and treatment time. By examining the electrical and optical properties of the plasma jet, we determine how the above operational parameters influence the major plasma processes that promote H2O2 generation through electron-induced dissociation reactions and UV photolysis within the plasma core and in the plasma afterglow; but with a caveat being that these processes are highly dependent on the water vapour content from the argon gas supply and ambient environment. We then demonstrate how the synergistic action between H2O2 and other plasma generated molecules at a plasma induced low pH in the DIW is highly effective at decontaminating common wound pathogens Gram-positive Staphylococus aureus and Gram-negative Pseudomonas aeruginosa. The information presented in this study is relevant in the design of medical plasma devices where production of plasma reactive species such as H2O2 at physiologically useful concentrations is needed to help realise the full clinical potential of the technology.

This review critically examines the multiple effects of low-temperature, atmospheric pressure plasma stress on the “on top” (collectively termed cutaneous) materials, to reveal the effects of this stress on the materials that lay underneath, collectively termed sub-cutaneous materials. Plasma generated reactive agents presents stress and trigger relayed effects within the cutaneous layers, leading to transcutaneous penetration of the plasma-induced stress into sub-cutaneous materials. Among the many possibilities from the areas spanning soft matter and life sciences, the effects of reactive plasma agents help improve the outcomes of cutaneous wound healing, reduce skin cancer tumors, and eradicate biofilms on biomedical implant materials. Cutaneous materials include animal skin or laboratory models using soft matter such as liquid media, gels, and cell cultures. Here we examine permeable interfaces of cutaneous materials and sub-cutaneous living tissues subjected to low-temperature atmospheric-pressure plasmas as a multi-modal reactive system producing stress on materials through multiple reactive agents including radicals, excited atoms and molecules, ions, heat, UV, and electric fields. Interaction of plasma-radiative stress with cutaneous materials leads to the unexpected, yet effective transmission of the reactive agents through to sub-cutaneous tissues, potentially systemically through the body. We examine the penetration of plasma-generated stress through the skin or skin models leading to the many interesting effects. In a broader context, this knowledge is relevant to several fields of materials science and engineering from soft matter to biomaterials and may help advance diverse applications ranging from non-thermal processing of soft and flexible materials for flexible electronics and soft robotics to direct skin disease treatment in vivo. Refereed/Peer-reviewed

We employed UV-vis spectroscopy to monitor real-time changes in the oxygen tension and concentration of reactive oxygen and nitrogen species (RONS) in deionized (DI) water during treatments with helium (He) and argon (Ar) gas plasma jets. He and Ar gas jets are both shown to de-oxygenate DI water with He being more efficient than Ar, whilst the plasma jets deliver and regulate the concentrations of hydrogen peroxide (H 2 O 2 ), nitrite (NO 2 - ) and nitrate (NO 3 - ) in DI water. The H 2 O 2 and NO 3 - production efficiency varied between He and Ar plasma jets, but was similar for NO 2 - . Whilst DI water fully equilibrated with ambient air prior to treatment (de-oxygenated by both plasma jets) when DI water was first de-oxygenated by an inert gas jet treatment, both plasma jets were found to be capable of oxygenating DI water. These insights were then used to show how different combinations of plasma jet and inert gas jet treatments can be used to modulate O 2 tension and RONS chemistry. Finally, potential further improvements to improve control in the use of plasma jets in regulating O 2 and RONS are discussed. © 2018 The Japan Society of Applied Physics.

This study compares the differences in the viability of skin cells after culturing in cell medium supplemented with helium (He) plasma jet-treated serum and Dulbecco's Modified Eagle Medium (DMEM). HaCaT and HDFa cells were used as surrogates for the two major cell types of skin, i.e., keratinocytes and fibroblasts, respectively. A reduction in cell viability was observed for cells cultured in cell media supplemented with He plasma jet-treated serum and DMEM: however, cells were more sensitive to the He plasma jet-treated serum. HaCaT cells were more sensitive to He plasma jet-treated serum compared to HDFa cells. The decrease in the viability of HaCaT cells was not directly attributed to excessive oxidative stress (i.e., from reactive oxygen species generated by the He plasma jet). A possible explanation for the decrease in cell viability is that the He plasma jet treatment results in modification of the serum or DMEM, which decreases the bioavailability and/or bioefficacy of their essential components. In response to nutrient-deficiency, the cells may undergo autophagy, which can lead to a different form of cell death compared to apoptosis and necrosis. It will be important in the future to elucidate what essential components in cell media/serum are modified by plasma jets or other plasma sources utilised in biology and medicine research, and how these modifications alter cellular response. Refereed/Peer-reviewed

Plasma-activated water ( PAW) is receiving much attention in biomedical applications because of its reported potent bactericidal properties. Reactive oxygen and nitrogen species (RONS) that are generated in water upon plasma exposure are thought to be the key components in PAW that destroy bacterial and cancer cells. In addition to developing applications for PAW, it is also necessary to better understand the RONS chemistry in PAW in order to tailor PAW to achieve a specific biological response. With this in mind, we previously developed a UV-vis spectroscopy method using an automated curve fitting routine to quantify the changes in H2O2, NO2 %, NO3 % (the major long-lived RONS in PAW), and O-2 concentrations. A major advantage of UV-vis is that it can take multiple measurements during plasma activation. We used the UV-vis procedure to accurately quantify the changes in the concentrations of these RONS and O-2 in PAW. However, we have not yet provided an in-depth commentary of how we perform the curve fitting procedure or its implications. Therefore, in this study, we provide greater detail of how we use the curve fitting routine to derive the RONS and O-2 concentrations in PAW. PAW was generated by treatment with a helium plasma jet. In addition, we employ UV-vis to study how the plasma jet exposure time and treatment distance affect the RONS chemistry and amount of O-2 dissolved in PAW. We show that the plasma jet exposure time principally affects the total RONS concentration, but not the relative ratios of RONS, whereas the treatment distance affects both the total RONS concentration and the relative RONS concentrations. (C) 2018 The Japan Society of Applied Physics Refereed/Peer-reviewed

The influence of the electrical and optical properties of a spatially varying He microplasma on the gradient surface modification of an adsorbed protein layer inside a microfluidic chip was investigated. Microplasma was generated inside a native polydimethylsiloxane (PDMS) microchannel. Excited and metastable states of He and N2 (from air) potentially played a major role in the removal/modification of protein during the discharge period. In-between discharge events, N2(A) metastables can also induce bond breaking and surface modification. The purge time of the feed gas was shown to be important in the use of small scale microplasma sources for surface processing or protein modification. Refereed/Peer-reviewed

© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Chronic wounds are a major socio-economic problem. Bacterial infections in such wounds are a major contributor to lack of wound healing. An early indicator of wound infection is an increase in pH of the wound fluid. Herein, we describe the development of a pH-responsive drug delivery device that can potentially be used for wound decontamination in situ and on-demand in response to an increase in the pH of the wound environment. The device is based on a porous silicon film that provides a reservoir for encapsulation of an antibiotic within the pores. Loaded porous silicon is capped with dual plasma polymer layers of poly(1,7-octadiene) and poly(acrylic acid), which provide a pH-responsive barrier for on-demand release of the antibiotic. We demonstrate that release of the antibiotic is inhibited in aqueous buffer at pH 5, whereas the drug is released in a sustainable manner at pH 8. Importantly, the released drug was bacteriostatic against the Pseudomonas aeruginosa wound pathogen. In the future, incorporation of the delivery device into wound dressings could potentially be utilized for non-invasive decontamination of wounds.

Despite growing interest in the application of atmospheric plasma jets as medical treatment strategies, there has been comparatively little research on the potential genotoxic and cytotoxic effects of plasma jet treatment. In this study, we have employed the cytokinesis block micronucleus cytome (CBMN-Cyt) assay with WIL2-NS B lymphoblastoid cells to test the potential genotoxicity, as well as the cytotoxicity, of toxic species generated in cell culture media by an argon (Ar) plasma jet. Elevated levels of cell death (necrosis) and occurrence of chromosomal damage (micronuclei MN, nculeoplasmic bridge NPBs and nuclear bus, Nbuds) were observed when cells were exposed to plasma jet-treated media. These results provide a first insight into how we might measure the genotoxic and cytotoxic effect of plasma jet treatments (both indirect and direct) in dividing human cells.

Cold atmospheric pressure plasma jets (plasma) operated in ambient air provide a rich source of reactive oxygen and nitrogen species (RONS), which are known to influence biological processes important in disease. In the plasma treatment of diseased tissue such as subcutaneous cancer tumors, plasma RONS need to first traverse an interface between the plasma-skin surface and second be transported to millimeter depths in order to reach deep-seated diseased cells. However, the mechanisms in the plasma generation of RONS within soft tissues are not understood. In this study, we track the plasma jet delivery of RONS into a tissue model target and we delineate two processes: Through target delivery of RONS generated (primarily) in the plasma jet and in situ RONS generation by UV photolysis within the target. We demonstrate that UV photolysis promotes the rapid generation of RONS in the tissue model target's surface after which the RONS are transported to millimeter depths via a slower molecular process. Our results imply that the flux of UV photons from plasma jets is important for delivering RONS through seemingly impenetrable barriers such as skin. The findings have implications not only in treatments of living tissues but also in the functionalization of soft hydrated biomaterials such as hydrogels and extracellular matrix derived tissue scaffolds. Refereed/Peer-reviewed

We investigate an approach for the patterning of reactive oxygen and nitrogen species (RONS) onto polystyrene using atmospheric-pressure microplasma arrays. The spectrally integrated and time-resolved optical emission from the array is characterized with respect to the applied voltage, applied-voltage frequency and pressure; and the array is used to achieve spatially resolved modification of polystyrene at three pressures: 500, 760, and 1000 Torr. As determined by time-of-flight secondary ion mass spectrometry (ToF-SIMS), regions over which surface modification occurs are clearly restricted to areas that are exposed to individual microplasma cavities. Analysis of the negative-ion ToF-SIMS mass spectra from the center of the modified microspots shows that the level of oxidation is dependent on the operating pressure, and closely correlated with the spatial distribution of the optical emission. The functional groups that are generated by the microplasma array on the polystyrene surface are shown to readily participate in an oxidative reaction in phosphate buffered saline solution (pH 7.4). Patterns of oxidized and chemically reactive functionalities could potentially be applied to the future development of biomaterial surfaces, where spatial control over biomolecule or cell function is needed. Refereed/Peer-reviewed

There is a growing literature database that demonstrates the therapeutic potential of cold atmospheric plasma (herein referred to as plasma). Given the breadth of proposed applications (e.g. from teeth whitening to cancer therapy) and vast gamut of plasma devices being researched, it is timely to consider plasma interactions with specific components of the cell in more detail. Plasma can produce highly reactive oxygen and nitrogen species (RONS) such as the hydroxyl radical (OH•), peroxynitrite (ONOO-) and superoxide () that would readily modify essential biomolecules such as DNA. These modifications could in principle drive a wide range of biological processes. Against this possibility, the reported therapeutic action of plasmas are not underpinned by a particularly deep knowledge of the potential plasma-tissue, -cell or -biomolecule interactions. In this study, we aim to partly address this issue by developing simple models to study plasma interactions with DNA, in the form of DNA-strand breaks. This is carried out using synthetic models of tissue fluid, tissue and cells. We argue that this approach makes experimentation simpler, more cost-effective and faster than compared to working with real biological materials and cells. Herein, a helium plasma jet source was utilised for these experiments. We show that the plasma jet readily induced DNA-strand breaks in the tissue fluid model and in the cell model, surprisingly without any significant poration or rupture of the phospholipid membrane. In the plasma jet treatment of the tissue model, DNA-strand breaks were detected in the tissue mass after pro-longed treatment (on the time-scale of minutes) with no DNA-strand breaks being detected in the tissue fluid model underneath the tissue model. These data are discussed in the context of the therapeutic potential of plasma. Refereed/Peer-reviewed

With ambient mass spectrometry, we followed the transport of neutral gas species and ionic species through a 3.2 mm thick agarose tissue model target during He non-thermal atmospheric pressure plasma (NT-APP) jet treatment. We found that the neutral gas species are unable to efficiently penetrate the agarose target. But both positively and negatively charged ionic species readily penetrate through the agarose target, following an initial time-lag period of several minutes. Interestingly, we also found that the ionic species are easily hydrated. The trends in the He NT-APP jet transport of ionic species observed in this study correlate well with the He NT-APP jet transport of reactive oxygen and nitrogen species (RONS) through agarose tissue model targets that was investigated in previous studies. Therefore, mass spectrometry might prove to be a useful tool in the future for analyzing the dosages of NT-APP-generated RONS in real biological tissues. Refereed/Peer-reviewed

The effect of oxidation, oxygenation, and de-oxygenation arising from He gas jet and He plasma jet treatments on the viability of skin cells cultured in vitro has been investigated. He gas jet treatment de-oxygenated cell culture medium in a process referred to as "sparging." He plasma jet treatments oxidized, as well as oxygenated or de-oxygenated cell culture medium depending on the dissolved oxygen concentration at the time of treatment. He gas and plasma jets were shown to have beneficial or deleterious effects on skin cells depending on the concentration of dissolved oxygen and other oxidative molecules at the time of treatment. Different combinations of treatments with He gas and plasma jets can be used to modulate the concentrations of dissolved oxygen and other oxidative molecules to influence cell viability. This study highlights the importance of a priori knowledge of the concentration of dissolved oxygen at the time of plasma jet treatment, given the potential for significant impact on the biological or medical outcome. Monitoring and controlling the dynamic changes in dissolved oxygen is essential in order to develop effective strategies for the use of cold atmospheric plasma jets in biology and medicine. Refereed/Peer-reviewed

A challenge in cancer therapy is the destruction of tumours, where there is the potential issue of cancer cells residing within hypoxic tissue. The concept of hypoxic regions within tumours dates back to 1909 and it has long been suspected that under low oxygen tension, cells are “afforded” radiation protection. It has been shown many decades ago, that raising the concentration of oxygen in tissues can significantly improve the outcomes in radiotherapy. For example, in 1953, a meta-analysis of 83 randomised trials showed a clear benefit from raising tissue oxygen tension during radiation therapy, with the clearest benefits seen in cancers of neck and head [1]. However, there are only a limited number of ways to raise oxygen tension in tissues, which include breathing pure oxygen at or above standard temperature and pressure, or hypoxic modification by the means of an administered drug (e.g. nimorazole) [2, 3, 4]. Recently, we (and other research groups) have shown that cold atmospheric plasma jets not only readily deliver reactive oxygen and nitrogen species (RONS) into tissue, but concomitantly raise the oxygen tension in tissue. Combined RONS and oxygen delivery, may significantly elevate oxidative stress in cancer cells, resulting in destruction of these cells within hypoxic tumours. In this presentation, I will provide a brief historical overview of research on the modification of hypoxia in cancers; I will then discuss results that have shown how plasma jets can be used to treat hypoxia in tumours (through delivery of RONS and oxygen into tissues). I will also discuss the potential opportunities, challenges and limitations of the plasma technology for treatment of hypoxic cancer tumours.

Dr. S. A. Al-Bataineh, E. J. Szili, P. J. Gruner, R. D. Short, D. A. Steele Mawson Institute, University of South Australia, Mawson Lakes, SA 5095, Australia Fax: þ61 (0)8 8302 5689; E-mail: sameer.al-bataineh@unisa.edu.au C. Priest, H. J. Griesser Ian Wark Research Institute, University of South Australia, Mawson Lakes, SA 5095, Australia N. H. Voelcker Flinders University, School of Chemical and Physical Sciences, Bedford Park, SA 5042, Australia Current address: Mawson Institute, University of South Australia, Mawson Lakes, SA 5095, Australia Surface modification of materials with microscale features through plasma treatment or deposition is of high value, and is considered one of the great challenges in plasma-based materials processing. This article reports a versatile method for the fabrication of microcavity plasma array devices. A 7 7 microcavity plasma array device (each cavity was 250mm in diameter and separated by 500mm) was used in this study to demonstrate the capability of these devices for localised, non-contact surface treatment/polymer deposition. The device can be reused multiple times for plasma treatment and polymerisation. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) imaging and region of interest (ROI) analysis, in addition to surface hydration, were employed to characterise the micropatterns on microplasma-treated PS. The results showed that microplasma treatment/ deposition could be spatially confined to regions exposed to the individual ignited microcavities. However, the results also demonstrated that the size of the treated spots tended to increase with increasing treatment time until they eventually overlapped resulting in a homogeneous surface treatment confined to the size of the array. Similarly, the concentration of oxygen quantified on the treated spots reached saturation after 75 s of treatment. The versatility of the device was demonstrated by depositing an array of octadiene plasma polymer (ODpp) onto a silicon substrate as confirmed by XPS imaging and ROI analysis. A key advantage of these microcavity array devices is that they can be easily integrated into manufacturing and do not require contact with the substrate surface to impart well-defined chemical modifications on materials surfaces.

This paper describes a novel transducer principle converting biomolecular binding events into changes in porous silicon structural colour. An enzyme-catalysed reaction, horseradish peroxidase (HRP) mediated oxidation of 3,3 ,5,5 -tetramethylbenzidine (TMB), induced an amplified optical detection signal on an antibody-functionalised porous silicon film, which manifested as significant changes in the Fabry–Pérot fringe pattern. Exposing porous silicon to non-oxidised TMB and oxidised TMB products and measuring the resulting effective optical thickness (EOT) changes of the porous silicon layer, an amplified signal from porous silicon was found, caused by an intermediate radical cation produced during the enzymaticcatalysed oxidation of TMB. Finally, it was shown that this system could be used to detect a human immunoglobulin (IgG) at 0.2 g/ml. This work may lead to the development of new biosensors where porous silicon acts as the sensing matrix and transducer element. Refereed/Peer-reviewed

There is considerable interest in the spatial control of plasma polymerisation such as to produce sub-millimetre features with high fidelity, versatility and reproducibility, for example, for arrays or writable specific patterns. This study reports the design of a microcavity plasma device and a method for its fabrication, with the device comprising a single cavity of � 400 mm diameter. The device can be fabricated within a short time and at low cost in a standard laboratory, with no need for a clean room facility. The device is capable of multiple operations in plasma polymerisation mode. XPS imaging combined with small-spot ROI analysis showed localised thin film deposition of an acrylic acid plasma polymer with good retention of carboxylate groups from the monomer. The device can be configured with flexibility and addressedforplasma polymer writing of complex patterns.

This report addresses the challenge of using microplasma jets to modify surfaces with precise chemistries over exact areas. We explore how different treatment conditions (time and distance) and operational parameters (voltage and frequency) influence the spatial modification of a model polymer (polystyrene) in terms of size, degree and nature of the surface modification. At 4.5 kV pk―pk , the visible glow of the microplasma jet was confined to within the capillary tube (tube inner diameter = 0.7 mm) and resulted in a narrower area of treatment compared to when the visible glow extended 3 mm into the ambient atmosphere at 8.0 kV pk―pk . Short treatment times of 15 s or less, longer capillary tube-sample separation distances of several mm and lower frequencies of 5―10 kHz were also required to reduce expansion of treatment. Low concentrations of carboxylates (

A micro-cavity discharge array (2500 cavities of 50 µm2 size) was operated in neon at atmospheric pressure to modify polystyrene (PS), fluorinated ethylene–propylene co-polymer (FEP) and polytetrafluoroethylene(PTFE) polymer surfaces and, with the injection of a polymerisable monomer (acrylic acid), to deposit patterned, thin polymeric coatings. The aim of this study was to investigate the utility of these micro-discharge sources in the surface treatment of polymers and for the patterned deposition of polymeric material. The influence of the driving frequency, treatment time and sample-array distance on polymer surface treatment was investigated. X-ray photoelectron spectroscopy (XPS) was used to explore the surface chemistry of the treated polymer surfaces and of the polymer deposits. It was found that increasing themicro-cavity discharge source driving frequency and/or treatment time and decreasing the sample-arraydistance all led to a significant decrease in surface energy as determined by water contact angle measurements. For a period of time, post treatment surface hydrophilicity degraded due to the well known“ageing effect” but stabilized after two days. Finally, it was demonstrated that the device could be used forthe localized, array sized, deposition of acrylic acid. High resolution XPS analysis of the deposit registered a C1s spectra typical of poly(acrylic acid) with a prominent peak centred at approximately 289.3 eV indicating a relatively high level retention of the original monomer functionality. These results demonstrate that microcavity discharges, operated at or near atmospheric pressure, can be used to both modify and locally depositpolymeric material. Refereed/Peer-reviewed

This work examines the biocompatibility of poly(octanediol citrate)/sebacate (p(OCS)) biodegradable polyester elastomers. The growth of human MG63 osteoblast-like cells was studied on p(OCS) films. Three types of p(OCS) films were synthesised simply by varying the concentrations of 1,8-octanediol (OD), citric acid (CA), and sebacic acid (SA) monomers at initial molar ratios of 1:1:0, 1:0.75:0.25 and 1:0.5:0.5. At these ratios, the p(OCS) films exhibit decreasing hydrophilicity as shown by the measured water contact angle values of 31, 41 and 64°, respectively. For all the samples, no difference in cell growth was detected after 1 day of cell culture. However, after 4 days, the highest number of viable cells was detected on the p(OCS) film synthesised with the intermediate CA molar ratio of 0.75. This sample also contains the median concentration of surface carboxylic acid groups and hydrophilicity. Following long-term cell culture (18 days), a statistically significant higher density of viable cells had grown on the p(OCS) films with SA molar ratios of 0.25 (P < 0.0001) and 0.5 (P = 0.002) in comparison to the material containing 100% CA and no SA. The work demonstrated that the performance of possible p(OCS) bone tissue engineering scaffolds could be improved by simply adjusting the molar ratios of CA and SA in the pre-polymer without any requirements for post-synthesis modification. Refereed/Peer-reviewed

In this study, we compare for the first time the nanomechanical properties of lipid bilayer islands on flat and porous surfaces. 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) bilayers were deposited on flat (silicon and mica) and porous silicon (pSi) substrate surfaces and examined using atomic force spectroscopy and force volume imaging. Force spectroscopy measurements revealed the effects of the underlying substrate and of the lipid phase on the nanomechanical properties of bilayers islands. For mica and silicon, significant differences in breakthrough force between the center and the edges of bilayer islands were observed for both phospolipids. These differences were more pronounced for DMPC than for DPPC, presumably due to melting effects at the edges of DMPC bilayers. In contrast, bilayer islands deposited on pSi yielded similar breakthrough forces in the central region and along the perimeter of the islands, and those values in turn were similar to those measured along the perimeter of bilayer islands deposited on the flat substrates. The study also demonstrates that pSi is suitable solid support for the formation of pore-spanning phospholipid bilayers with potential applications in transmembrane protein studies, drug delivery, and biosensing.

The efficacy of helium (He) and argon (Ar) plasma jets are being investigated for different healthcare applications including wound and cancer therapy, sterilisation and surface disinfections. Current research points to a potential link between the generation of reactive oxygen and nitrogen species (RONS) and outcomes in a range of biological and medical applications. As new data accrue, further strengthening this link, it becomes important to understand the controlled delivery of RONS into solutions, tissue fluids and tissues. This paper investigates the use of He and Ar plasma jets to deliver three RONS (hydrogen peroxide—H2O2, nitrite—$\text{NO}_{2}^{-}$ and nitrate—$\text{NO}_{3}^{-}$ ) and molecular oxygen (O2) directly into deionised (DI) water, or indirectly into DI water through an agarose target. The DI water is used in place of tissue fluid and the agarose target serves as a surrogate of tissue. Direct plasma jet treatments deliver more RONS and O2 than the through-agarose treatments for equivalent treatments times. The former only deliver RONS whilst the plasma jets are ignited; the latter continues to deliver RONS into the DI water long after the plasmas are extinguished. The He plasma jet is more effective at delivering H2O2 and $\text{NO}_{2}^{-}$ directly into DI water, but the Ar plasma jet is more effective at nitrating the DI water in both direct and through-agarose treatments. DI water directly treated with the plasma jets is deoxygenated, with the He plasma jet purging more O2 than the Ar plasma jet. This effect is known as 'sparging'. In contrast, for through-agarose treatments both jets oxygenated the DI water. These results indicate that in the context of direct and indirect plasma jet treatments of real tissue fluids and tissue, the choice of process gas (He or Ar) could have a profound effect on the concentrations of RONS and O2. Irrespective of operating gas, sparging of tissue fluid (in an open wound) for long prolonged periods during direct plasma jet treatment, could have implications for healthy tissue function; whilst through-tissue plasma jet treatment may provide a method to reperfuse oxygen-starved tissue. The assays described in this paper can be readily adopted (by others) and may support the future development of plasma sources to deliver specific (metered) doses of RONS.

This paper reports on the fabrication of a pSi-based drug delivery system, functionalized with an initiated chemical vapor deposition (iCVD) polymer film, for the sustainable and temperature-dependent delivery of drugs. The devices were prepared by loading biodegradable porous silicon (pSi) with a fluorescent anticancer drug camptothecin (CPT) and coating the surface with temperature-responsive poly(N-isopropylacrylamide-co-diethylene glycol divinyl ether) (pNIPAM-co-DEGDVE) or non-stimulus-responsive poly(aminostyrene) (pAS) via iCVD. CPT released from the uncoated oxidized pSi control with a burst release fashion (∼21 nmol/(cm2 h)), and this was almost identical at temperatures both above (37 °C) and below (25 °C) the lower critical solution temperature (LCST) of the switchable polymer used, pNIPAM-co-DEGDVE (28.5 °C). In comparison, the burst release rate from the pSi-pNIPAM-co-DEGDVE sample was substantially slower at 6.12 and 9.19 nmol/(cm2 h) at 25 and 37 °C, respectively. The final amount of CPT released over 16 h was 10% higher at 37 °C compared to 25 °C for pSi coated with pNIPAM-co-DEGDVE (46.29% vs 35.67%), indicating that this material can be used to deliver drugs on-demand at elevated temperatures. pSi coated with pAS also displayed sustainable drug delivery profiles, but these were independent of the release temperature. These data show that sustainable and temperature-responsive delivery systems can be produced by functionalization of pSi with iCVD polymer films. Benefits of the iCVD approach include the application of the iCVD coating after drug loading without causing degradation of the drug commonly caused by exposure to factors such as solvents or high temperatures. Importantly, the iCVD process is applicable to a wide array of surfaces as the process is independent of the surface chemistry and pore size of the nanoporous matrix being coated. Refereed/Peer-reviewed

The transport of plasma generated reactive oxygen species (ROS) across a simple phospholipid membrane mimic of a (real) cell was investigated. Experiments were performed in cell culture media (Dulbecco's modified Eagle's medium, DMEM), with and without 10% serum. A (broad spectrum) ROS reporter dye, 2,7-dichlorodihydrofluorescein (DCFH), was used to detect the generation of ROS by a helium (He) plasma jet in DMEM using free DCFH and with DCFH encapsulated inside phospholipid membrane vesicles dispersed in DMEM. The authors focus on the concentration and on the relative rates (arbitrary units) for oxidation of DCFH [or the appearance of the oxidized product 2,7-dichlorofluorescein (DCF)] both in solution and within vesicles. In the first 1 h following plasma exposure, the concentration of free DCF in DMEM was ∼15× greater in the presence of serum (cf. to the serum-free DMEM control). The DCF in vesicles was ∼2× greater in DMEM containing serum compared to the serum-free DMEM control. These data show that serum enhances plasma ROS generation in DMEM. As expected, the role of the phospholipid membrane was to reduce the rate of oxidation of the encapsulated DCFH (with and without serum). And the efficiency of ROS transport into vesicles was lower in DMEM containing serum (at 4% efficiency) when compared to serum-free DMEM (at 32% efficiency). After 1 h, the rate of DCFH oxidation was found to have significantly reduced. Based upon a synthesis of these data with results from the open literature, the authors speculate on how the components of biological fluid and cellular membranes might affect the kinetics of consumption of plasma generated ROS. Refereed/Peer-reviewed

Spatially varied surface treatment of a fluorescently labeled Bovine Serum Albumin (BSA) protein, on the walls of a closed (sealed) microchannel is achieved via a well-defined gradient in plasma intensity. The microchips comprised a microchannel positioned in-between two microelectrodes (embedded in the chip) with a variable electrode separation along the length of the channel. The channel and electrodes were 50 μm and 100 μm wide, respectively, 50 μm deep, and adjacent to the channel for a length of 18 mm. The electrode separation distance was varied linearly from 50 μm at one end of the channel to a maximum distance of 150, 300, 500, or 1000 μm to generate a gradient in helium plasma intensity. Plasma ignition was achieved at a helium flow rate of 2.5 ml/min, 8.5 kVpk-pk, and 10 kHz. It is shown that the plasma intensity decreases with increasing electrode separation and is directly related to the residual amount of BSA left after the treatment. The plasma intensity and surface protein gradient, for the different electrode gradients studied, collapse onto master curves when plotted against electrode separation. This precise spatial control is expected to enable the surface protein gradient to be tuned for a range of applications, including high-throughput screening and cell-biomolecule-biomaterial interactions. Refereed/Peer-reviewed

We demonstrated the efficacy of using a simple experimental approach, involving UV absorption spectroscopy, to monitor the transport of reactive oxygen and nitrogen species (RONS) through an agarose film (as surrogate for real tissue) into deionized (DI) water. The experiment involved placing a 4 mm thick agarose film over a quartz cuvette filled with DI water. The agarose film was exposed to a non-thermal, He atmospheric-pressure plasma jet (APPJ) and the UV absorption of the DI water was recorded in real-time. Our results indicate an accumulation of RONS within the agarose film during APPJ exposure and a subsequent time-lapsed release of RONS into the DI water. Curve fitting of the UV spectra suggested the APPJ transported and / or generated at least four RONS (NaNO2, HNO3, H2O2 and O2) through the 4 mm thick agarose film. Our approach of analyzing the delivery depth of RONS through synthetic tissue targets might find use in the future development of APPJ medical therapies and for improving our understanding of APPJ interactions with soft tissue. Refereed/Peer-reviewed

The influence of protein and molecular, ground state oxygen (O2) on the plasma generation, and transport of reactive oxygen and nitrogen species (RONS) in tissue are investigated. A tissue target, comprising a 1 mm thick gelatin film (a surrogate for real tissue), is placed on top of a 96-well plate; each well is filled with phosphate buffered saline (PBS, pH 7.4) containing one fluorescent or colorimetric reporter that is specific for one of three RONS (i.e., H2O2, NO2 −, or OH•) or a broad spectrum reactive oxygen species reporter (2,7-dichlorodihydrofluorescein). A helium cold atmospheric plasma (CAP) jet contacts the top of the gelatin surface, and the concentrations of RONS generated in PBS are measured on a microplate reader. The data show that H2O2, NO2 −, or OH• are generated in PBS underneath the target. Independently, measurements are made of the O2 concentration in the PBS with and without the gelatin target. Adding bovine serum albumin protein to the PBS or gelatin shows that protein either raises or inhibits RONS depending upon the O2 concentration. Our results are discussed in the context of plasma-soft tissue interactions that are important in the development of CAP technology for medicine, biology, and food manufacturing. Refereed/Peer-reviewed

We have examined the link between ionized-gas plasma delivery of reactive oxygen species (ROS) to immortalized keratinocyte (HaCaT) cells and cell fate, defined in terms of cell viability versus death. Phospholipid vesicles were used as cell mimics to measure the possible intracellular ROS concentration, [ROSi], delivered by various plasma treatments. Cells were exposed to a helium cold atmospheric plasma (CAP) jet for different plasma exposure times (5-60 s) and gas flow rates (50-1000 ml min-1). Based upon the [ROSi] data we argue that plasma-generated ROS in the cell culture medium can readily diffuse into real cells. Plasma exposure that equated to an [ROSi] in the range of 3.81 × 10-10-9.47 × 10-8 M, measured at 1 h after the plasma exposure, resulted in increased cell viability at 72 h; whereas a higher [ROSi] at 1 h decreased cell viability after 72 h of culture. This may be because of the manner in which the ROS are delivered by the plasma: HaCaT cells better tolerate a low ROS flux over an extended plasma exposure period of 1 min, compared to a high flux delivered in a few seconds, although the final [ROSi] may be the same. Our results suggest that plasma stimulation of HaCaT cells follows the principle of hormesis. Refereed/Peer-reviewed

The helium (He) atmospheric-pressure plasma jet (APPJ) delivery of reactive oxygen and nitrogen species (RONS) and molecular oxygen (O2) in deionized (DI) water was monitored in real time using in situ UV absorption spectroscopy. The He APPJ was used to treat DI water directly and through an agarose target as a surrogate for tissue (e.g., a skin barrier). For direct treatment, the RONS were generated immediately in the DI water, and the concentration of RONS continued to increase during the He APPJ treatment. But there was only a very minor increase in the total RONS concentration detected after the plasma and gas flow were switched off. The agarose target delayed the generation of RONS into the DI water, but the total RONS concentration continued to increase long after (25 min) the plasma and gas flow were switched off. Direct treatment deoxygenated the DI water, whereas treatment through agarose resulted in oxygenation of the DI water. A dynamic change in the ratio of H2O2, NO2-, NO3-, and O2 was detected in the DI water during He APPJ treatment and 25 min after the He and gas flow were switched off for both direct and through-agarose treatment. These results have implications for the plasma treatment of real tissue where the dynamic changes in the RONS and O2 concentrations within the tissue and tissue fluid could affect cellular and physiological processes. Refereed/Peer-reviewed

This study was designed to enhance our understanding of how reactive oxygen species (ROS), generated ex situ by ionized gas (plasma), can affect the regulation of signalling processes within cells. A model system, comprising of a suspension of phospholipid vesicles (cell mimics) encapsulating a ROS reporter, was developed to study the plasma delivery of ROS into cells. For the first time it was shown that plasma unequivocally delivers ROS into cells over a sustained period and without compromising cell membrane integrity. An important consideration in cell and biological assays is the presence of serum, which significantly reduced the transfer efficiency of ROS into the vesicles. These results are key to understanding how plasma treatments can be tailored for specific medical or biotechnology applications. Further, the phospholipid vesicle ROS reporter system may find use in other studies involving the application of free radicals in biology and medicine. Refereed/Peer-reviewed

We demonstrate the utility of a 'tissue model' to monitor the delivery of plasma jet-generated reactive oxygen species (ROS). We report on helium plasma jet interactions both across the surface and into the subsurface (defined as 150μm to 1.5 mm) of the tissue model. The model comprises a gelatin gel encapsulating a homogeneously dispersed chemical or biological reporter molecule. Jet-surface interactions result in (i) star shaped patterns that resemble those previously reported for surface-plasma streamers on insulators (as imaged by Pockels sensing) and (ii) 'filled' or hollow circular surface features, which resemble the 'killing' patterns seen in plasma jet treatments of bacterial lawns. From the data presented, we argue that in these four cases (and others) ROS may be capable of directly accessing a tissue's subsurface, as opposed to other proposed mechanisms, which involve stimulating surface reactions that trigger a cascade of biomolecular signalling events (into the tissue). The use of reporter molecules show that plasma can deliver ROS from 150μm to 1.5mm below the tissue surface. Subsurface delivery of ROS is consistent with the use of plasma to decontaminate wounds (covered by wound exudate and clotted blood), the deactivation of whole biofilms, plasma-enhanced drug delivery through skin and the destruction of solid tumours. Refereed/Peer-reviewed