Session SR1: Biological and Emerging Applications II

Cold atmospheric plasma sterilization: from bacteria to biomolecules

Although ionized gases have been known to have biological effects for more than 100 years, their impact on the practice in healthcare service became very significant only recently. Today, plasma-based surgical tools are used for tissue reduction and blood coagulation as surgical procedures. Most significant however is the speed at which low-temperature gas plasmas are finding new applications in medicine and biology, including plasma sterilization, wound healing, and cancer therapies just to name a few. In the terminology of biotechnology, the ``pipeline'' is long and exciting. This presentation reviews the current status of the field with a particular emphasis on plasma inactivation of microorganisms and biomolecules, for which comprehensive scientific evidence has been obtained. Some of the early speculations of biocidal plasma species are now being confirmed through a combination of optical emission spectroscopy, laser-induced fluorescence, mass spectrometry, fluid simulation and biological sensing with mutated bacteria. Similarly, fundamental studies are being performed to examine cell components targeted by gas plasmas, from membrane, through lipid and membrane proteins, to DNA. Scientific challenge is significant, as the usual complexity of plasma dynamics and plasma chemistry is compounded by the added complication that cells are live and constantly evolving. Nevertheless, the current understanding of plasma inactivation currently provides strong momentum for plasma decontamination technologies to be realized in healthcare. We will discuss the issue of protein and tissue contaminations of surgical instruments and how cold atmospheric plasmas may be used to degrade and reduce their surface load. In the context of plasma interaction with biomolecules, we will consider recent data of plasma degradation of adhesion proteins of melanoma cells. These adhesion proteins are important for cancer cell migration and spread. If low-temperature plasmas could be used to degrade them, it could form a control strategy for cancer spread. This adds to the option of plasma-triggered programmed cell death (apoptosis). Whilst opportunities thus highlighted are significant and exciting, the underpinning science poses many open questions. The presentation will then discuss main requirements for plasma sources appropriate for their biomedical applications, in terms of the scope of up-scaling, the ability to treat uneven surfaces of varying materials, the range of plasma chemistry, and the control of plasma instabilities. Finally a perspective will be offered, in terms of both opportunities and challenges.   

Sterilization and Mechanism of Microorganisms on A4 Paper by Dielectric Barrier Discharges Plasma at Atmospheric Pressure

This study investigated the microorganisms' sterilization and mechanism by a DBD plasma device at atmospheric pressure. The device including a transfer system and two roller-electrodes is driven by sine-wave high voltages at frequencies of 15 kHz. Normal A4 papers were used to study the effects of the sterilization on their surfaces by analyzing the number of the living bacteria cells. The state of Escherichia coil's DNA were also measured by agarose gel electrophoresis after sterilization to analyze the inactivation mechanisms. Experimental results indicated that microorganisms on the surface of A4 Papers almost were destroyed while the papers went through the device and there was no any damage of the paper during the process. The main reason engendered bacteria death was due to the double chains of the DNA broken by the plasma.   

Sterilization of Surfaces with a Handheld Atmospheric Pressure Plasma

Low temperature, atmospheric pressure plasmas have shown great promise for decontaminating the surfaces of materials and equipment. In this study, an atmospheric pressure, oxygen and argon plasma was investigated for the destruction of viruses, bacteria, and spores. The plasma was operated at an argon flow rate of 30 L/min, an oxygen flow rate of 20 mL/min, a power density of 101.0 W/cm$^{3}$ (beam area = 5.1 cm$^{2})$, and at a distance from the surface of 7.1 mm. An average 6log$_{10}$ reduction of viable spores was obtained after only 45 seconds of exposure to the reactive gas. By contrast, it takes more than 35 minutes at 121$^{\circ}$C to sterilize anthrax in an autoclave. The plasma properties were investigated by numerical modeling and chemical titration with nitric oxide. The numerical model included a detailed reaction mechanism for the discharge as well as for the afterglow. It was predicted that at a delivered power density of 29.3 W/cm$^{3}$, 30 L/min argon, and 0.01 volume{\%} O$_{2}$, the plasma generated 1.9 x 10$^{14}$ cm$^{-3}$ O atoms, 1.6 x 10$^{12}$ cm$^{-3}$ ozone, 9.3 x 10$^{13}$ cm$^{-3}$ O$_{2}(^{1}\Delta _{g})$, and 2.9 x 10$^{12}$ cm$^{-3}$ O$_{2}(^{1}\Sigma ^{+}_{g})$ at 1 cm downstream of the source. The O atom density measured by chemical titration with NO was 6.0 x 10$^{14}$ cm$^{-3}$ at the same conditions. It is believe that the oxygen atoms and the O$_{2}(^{1}\Delta _{g})$ metastables were responsible for killing the anthrax and other microorganisms.   

Characterization of a new VHF-CCP for Sterilization

Plasma sterilization is an upcoming alternative to common sterilization methods. Reduced process times combined with a low treatment temperature lead to proper sterilization and decontamination results even for heat-sensitive materials. The capabilities of plasma sterilization were demonstrated in several laboratory setups. Based on these experiences, a new plasma reactor was developed and realized as capacitive coupled plasma discharge with a variable frequency range between 76 and 80 MHz. The reactor concept is designed to meet industrial needs. Therefore, a specialized chamber design was developed: it is composed of PEEK, a high-performance plastic, and it is shaped like a drawer to make the sterilization process easy and uncomplicated for application. Optical Emission Spectroscopy was performed to obtain detailed information about the plasma parameters. According spectra, intensities and plasma parameters will be presented in comparison to a well established ICP laboratory setup. These data are used for optimization of sterilization efficiency. Furthermore, first microbiological tests were carried out at optimized conditions.   

Pulsed plasma polymerization of Ethylene Glycol for development of ultra thin biocompatible interfaces

An investigation of the gas phase and surface phase behavior for Ethylene Glycol (EG) pulsed discharges is presented. Infrared spectroscopy was utilized to study the effect of plasma average power and its correlation to monomer selective fragmentation. This allows one to predict the proper average power range to maximize preservation of monomer functionality in film deposition processes. The main daughter species detected in the gas phase were identified as formaldehyde (CH$_{2}$O), carbon monoxide (CO), carbon dioxide (CO$_{2})$, and water (H$_{2}$O). This data allowed for the construction of a dissociative model of the EG molecule in the gas phase during discharge conditions. From this it was observed that neutral byproduct formation is the result of complex recycling processes occurring at the reactor walls. This is similar to previously reported results with a related compound: Di-ethylene glycol vinyl-ether.\footnote{G. Padron-Wells, et al., Colloids Surf. B: Biointerfaces (2008)} In addition to gas-phase chemistry and surface reactions; we will also report on the analysis of the films grown under such conditions. This will be linked to the processes deduced from the gas-phase chemistry.   

Selective Encapsulation of Heterogeneous Fullerene Ions Into Single-Walled Carbon Nanotubes

A plasma consisting of ionic heterogeneous fullerenes such as C$_{60}$ negative ions and lithium endohedral fullerene positive ions (Li@C$_{60})$ is generated by means of an electron beam impact to a sublimated Li@C$_{60}$/C$_{60}$ composite. These C$_{60}$ negative ions and Li@C$_{60}$ positive ions are selectively irradiated and encapsulated in single-walled carbon nanotubes (SWNTs) put on a substrate which is positively and negatively biased, respectively. It is found that the amount of Li@C$_{60}$ irradiation to SWNTs depends on the energy of the electron beam E$_{e}$ which ionizes the Li@C$_{60}$, and has the maximum for E$_{e} \quad \sim $ 200 eV. The electrical transport properties of the C$_{60}$ and Li@C$_{60}$ encapsulated SWNTs are investigated by fabricating them as the channels of field-effect transistor devices. The C$_{60}$ encapsulated SWNTs show the p-type electrical transport property. On the other hand, the Li@C$_{60}$ encapsulated SWNTs exhibit the ambipolar conduction or the n-type property. This result indicates that the electrical properties of the SWNTs can be controlled by the kinds of encapsulated fullerenes.