# Biological Decontamination by Microplasma
## 1 Introduction  
Microplasma technology proved to be a more economical and ecological alternative to classic technologies for flow control, air treatment, the surface treatment of polymers and glass, or biomedical applications [1, 2]. Among biomedical applications, nonthermal plasma is of interest for the sterilization of bacterial contaminations, since traditional methods could encounter limitations due to acquired resistance to antibiotics [3, 4, 5]. Moreover, nonthermal plasma is a more feasible alternative than other methods that use chemicals or heat. Biological decontamination can be achieved using atmospheric-pressure nonthermal plasma with various types of plasma sources that can be classified considering their electrode geometry or the frequency of excitation [6]. The electrode geometry furthermore determines if the decontamination process is carried out for flat surfaces, complex geometries, or is a localized process [7, 8]. Previous studies showed how nonthermal plasma can be used for the bacterial decontamination, i.e., _Escherichia coli_[9, 10, 11, 12], _Pseudomonas aeruginosa_[13, 14, 15], and _Staphylococcus_aureus_[16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32]. To inactivate these bacterial strains with nonthermal plasma, air was used as a discharge gas [9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 27; 28; 29; 30; 31; 32], nitrogen [15; 18], oxygen [31], mixtures of argon with oxygen [16; 26; 31], argon with air or helium with air [19]. Nonthermal plasma in a dielectric-barrier-discharge (DBD) configuration was mostly used [9; 10; 11; 12; 14; 15; 16; 17; 18; 19; 20; 22; 24; 25; 26; 27; 28; 29; 30; 32]. Other configurations were direct-current (DC) microjet and corona discharge [13; 23; 31]. Although industrial-type nonthermal plasma systems are already produced [9; 11], the discharge voltage is still high (more than 10 kV). Studies were also carried out by researchers that reduced the discharge voltage required for nonthermal plasma generation below 5 kV [12; 18; 24; 27]. As also mentioned by [PERSON] et al. [10], the majority of nonthermal plasma devices used for plasma medicine applications are based on high-voltage devices that are expensive and difficult to operate. This research describes the use of microplasma as a type of atmospheric nonthermal plasma. It is a type of surface DBD that is generated facing two grid electrodes with a micrometer-size dielectric material in between. Due to the micrometer-size thickness of the dielectric material, a high-intensity electric field generates microplasma at relatively low discharge voltages of about 1 kV. Conventionally, nonthermal plasma is generated at tens of kilovolts. Because low discharge voltages are necessary to generate microplasma, less electrical insulation is required along with small-size power supplies and reactors. Also, microplasma is generated at atmospheric pressure; thus, costly vacuum enclosures are not necessary. The system of electrodes presented in this paper has the high voltage electrode covered on the back side with a dielectric layer, while the microplasma is generated at the surface of the grounded electrode, making the system safe to use. Moreover, the electrode can be scaled to larger or smaller surfaces, while the voltage required to ignite the discharge remains the same. The electrode is also flexible; thus, it can be bent and folded to fit various shapes. A portable decontamination system using microplasma could be fabricated due to the small size of the electrode system and power supply, thus making microplasma a more economical, safer, and accessible technology for the sterilization of bacteria. A DBD plasma system similar to the one in this research was reported by [PERSON] et al. [12] although the discharge voltages are higher, over 2 kV. The particle kinetics shows that microplasma produces effectively reactive species and charged particles at gas temperatures near the room temperature.