Jörg Ehlbeck

Low temperature atmospheric pressure plasma sources for microbial decontamination

The aim of this paper is to provide a survey of plasma sources at atmospheric pressure used for microbicidal treatment. In order to consider the interdisciplinary character of this topic an introduction and definition of basic terms and procedures are given for plasma as well as for microbicidal issues. The list of plasma sources makes no claim to be complete, but to represent the main principles of plasma generation at atmospheric pressure and to give an example of their microbicidal efficiency. The interpretation of the microbicidal results remain difficult due to the non-standardized methods used by different authors and due to the fact that small variations in the setup can change the results dramatically.

Antimicrobial treatment of heat sensitive products by miniaturized atmospheric pressure plasma jets (APPJs)

The technological potential of non-thermal plasmas for the antimicrobial treatment of heat sensitive materials is well known. Despite a multitude of scientific activities with considerable progress within the last few years, the realization of industrial plasma-based decontamination or sterilization technology remains a great challenge. This may be due to the fact that an antimicrobial treatment process needs to consider all properties of the product to be treated as well as the requirements of the complete procedure, e.g. a reprocessing cycle of medical instruments. The aim of this work is to demonstrate the applicability of plasma-based processes for the antimicrobial treatment on selected heat sensitive products. The strategy is to use modular, selective and miniaturized plasma sources, which are driven at atmospheric pressure and adaptable to the products to be treated.

Antimicrobial Effects of UV and VUV Radiation of Nonthermal Plasma Jets

Radio-frequency-driven plasma jets in argon at atmospheric pressure have been shown to emit a significant amount of UV and VUV radiation. There is an increasing interest in the use of UV and VUV photons in many fields of research and in industry, in particular for life-science applications. In order to study the antimicrobial effect of plasma-emitted UV and VUV radiation, microbiological tests and plasma diagnostics are combined. In particular, quantitative values of irradiance are estimated. The VUV emission of the plasma jet is dominated by the emission of argon excimer (Ar2). The recorded spectra between 115 and 180 nm also include several atomic emission lines of nitrogen and oxygen. The UV emissions are due to molecular bands of NO, OH, and N2. The best antimicrobial effect is observed by means of direct plasma treatment. UV and VUV emissions have a lower effect, and there is no difference observed between these two components.

Characterization of the global impact of low temperature gas plasma on vegetative microorganisms.

Plasma medicine and also decontamination of bacteria with physical plasmas is a promising new field of life science with huge interest especially for medical applications. Despite numerous successful applications of low temperature gas plasmas in medicine and decontamination, the fundamental nature of the interactions between plasma and microorganisms is to a large extent unknown. A detailed knowledge of these interactions is essential for the development of new as well as for the enhancement of established plasma‐treatment procedures. In the present work we introduce for the first time a growth chamber system suitable for low temperature gas plasma treatment of bacteria in liquid medium. We have coupled the use of this apparatus to a combined proteomic and transcriptomic analyses to investigate the specific stress response of Bacillus subtilis 168 cells to treatment with argon plasma. The treatment with three different discharge voltages revealed not only effects on growth, but also clear evidence of cellular stress responses. B. subtilis suffered severe cell wall stress, which was made visible also by electron microscopy, DNA damages and oxidative stress as a result of exposure to plasma. These biological findings were supported by the detection of reactive plasma species by OES measurements.

Determination of absolute Ba densities during dimming operation of fluorescent lamps by laser-induced fluorescence measurements

Investigations of fluorescent lamps (FL) are often focused on the electrodes, since the lifetime of the lamps is typically limited by the electrode lifetime and durability. During steady state operation, the work function lowering emitter material, in particular, barium, is lost. Greater barium losses occur under dimming conditions, in which reduced discharge currents lead to increased cathode falls, the result of the otherwise diminished heating of the electrode by the bombarding plasma ions. In this work the barium density near the electrodes of (FL), operating in high frequency dimming mode is investigated using the high-sensitivity method of laser-induced fluorescence. From these measurements we infer barium loss for a range of discharge currents and auxiliary coil heating currents. We show that the Ba loss can very easily be reduced by moderate auxiliary coil heating.

Determination of absolute population densities of eroded tungsten in hollow cathode lamps and fluorescent lamps by laser-induced fluorescence

The high energy ion bombardment during instant start of a fluorescent lamp (FL) leads to intense sputtering of the electrode material including tungsten and emitter. Thus, a cold started FL often suffers from early failures due to coil fracture. The main goal of this paper is to investigate tungsten erosion. We have employed the ultra-sensitive method of laser-induced fluorescence. This technique is particularly well-suited to determining absolute population densities of neutral and singly ionized atoms of liberated electrode material. In addition to FL, our investigations have been performed also on hollow cathode lamps (HCLs). These are useful because they provide a variable source of sputtered tungsten atoms and can serve as tuning tools for precise adjustment of the laser radiation.We will present absolute atomic tungsten population densities in a commercial FL and in an HCL. Furthermore, the results of a theoretical investigation of the argon plasma and the tungsten density in the HCL are represented.

Atmospheric Pressure Plasmas for Decontamination of Complex Medical Devices

Atmospheric pressure plasma sources produce a multiplicity of different antimicrobial agents and are applicable to even complicated geometries as well as to heat sensitive materials. Thus, atmospheric pressure plasmas have a huge potential for the decontamination of even complex medical devices like central venous catheters and endoscopes. In this paper we present practicable realizations of atmospheric pressure plasma sources, namely plasma jet, dielectric barrier discharge and microwave driven discharge that are able to penetrate fine lumen or are adaptable to difficult geometries. Furthermore, the antimicrobial efficacy of these sources is given for one example setup in each case.

Microwave-based characterization of an atmospheric pressure microwave-driven plasma source for surface treatment

A plasma source operating at atmospheric pressure by continuous or pulsed microwave at 2.45 GHz with a maximum power of 1.7 kW is developed for surface treatment applications. The microwave power is coupled into a cylindrical cavity used as a process chamber. The device characteristics are studied in detail using a simple network analysis and finite integration technique simulations. Experimental results are compared with the outcome of the model. The TM01 mode in the process chamber is found to be appropriate for surface treatment. The results obtained are used to optimize and simplify the device performance and operation. It has been found that the electric field strength, responsible for plasma ignition, and the microwave power coupling into the plasma demonstrate a contradictory course—a maximum field corresponds to a minimum power in-coupled. A set of parameters representing a compromise between stable plasma ignitions and proper plasma treatment has been found.

Plasma decontamination at atmospheric pressure - basics and applications

Plasma sources, driven at atmospheric pressure gain more and more interest due to the technological advantages (avoidance of vacuum devices and batch processing). Especially nonthermal plasmas at atmospheric pressure for the antimicrobial treatment of heat sensitive materials are of rapidly growing interest. However, the realisation of industrial plasma-based decontamination or sterilisation technology remains a great challenge. This is due to the fact that an antimicrobial treatment process needs to consider all properties of the product to be treated as well as the requirements of the complete process and all boundary conditions. First the requirements for plasma-decontamination and plasma-sterilization will be discussed. Advantages and disadvantages regarding present no-plasma decontamination processes will be indicated. The applicability of plasma-based processes for the antimicrobial treatment on selected, heat sensitive products will be demonstrated. Modular and selective plasma sources will be used to match the specific requirements regarding decontamination of medical products. Nearly any complex 3-dimensional structure can be treated by the plasma sources developed. In particular catheters for intracardial electrophysiological studies as well as the antimicrobial treatment process of hollow packaging for pharmaceutical products, namely PET- bottles, will be discussed. Furthermore the contribution will report on attempts and difficulties concerning the adaptation of the plasma sources on such real products. Optical emission spectroscopy of the plasma sources and micro-biological tests will complete the investigation.

Antimicrobial Treatment of Heat Sensitive Products by Atmospheric Pressure Plasma Sources

The technological potential of non-thermal plasmas for the antimicrobial treatment of heat sensitive materials is well known. Despite a multitude of scientific activities with considerable progress within the last years the realization of industrial plasma-based decontamination or sterilization technology remains a great challenge. The aim of the work presented in this contribution is to demonstrate the applicability of plasma-based processes for the antimicrobial treatment on selected, heat sensitive products. The idea is to use modular and selective plasma sources. These plasma sources are driven at atmospheric pressure due to its technological advantages (avoidance of vacuum devices and batch processing). According to the specific requirements given by the product different plasma sources, namely rf-driven plasma jets, microwave-driven air plasmas are used.