In this paper we describe the hitherto unravelled facts on the interactions of a cold atmospheric plasma with living cells and tissues. A specially designed source, plasma needle, is a low-power discharge, which operates under the threshold of tissue damage. When applied properly, the needle does not cause fatal cell injury which would result in cell death (necrosis). Instead, it allows precise and localized cell removal by means of the so-called cell detachment. In addition, plasma can be used for bacterial disinfection. Because of mild treatment conditions, plasma disinfection can be performed in vivo, e.g. on wounds and dental cavities. Presently, one strives to obtain a better control of the operating device. Therefore, plasma has been characterized using a variety of diagnostics, and a smart system has been designed for the positioning of the device with respect to the treated surface.

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In this paper we present a parameter study on deactivation of Escherichia coli (E. coli) by means of a non-thermal plasma (plasma needle). The plasma needle is a small-sized (1 mm) atmospheric glow sustained by radio-frequency excitation. This plasma will be used to disinfect heat-sensitive objects; one of the intended applications is in vivo deactivation of dental bacteria: destruction of plaque and treatment of caries. We use E. coli films plated on agar dishes as a model system to optimize the conditions for bacterial destruction. Plasma power, treatment time and needle-to-sample distance are varied. Plasma treatment of E. coli films results in formation of a bacteria-free void with a size up to 12 mm. 104–105 colony forming units are already destroyed after 10 s of treatment. Prolongation of treatment time and usage of high powers do not significantly improve the destruction efficiency: short exposure at low plasma power is sufficient. Furthermore, we study the effects of temperature increase on the survival of E. coli and compare it with thermal effects of the plasma. The population of E. coli heated in a warm water bath starts to decrease at temperatures above 40°C. Sample temperature during plasma treatment has been monitored. The temperature can reach up to 60°C at high plasma powers and short needle-to-sample distances. However, thermal effects cannot account for bacterial destruction at low power conditions. For safe and efficient in vivo disinfection, the sample temperature should be kept low. Thus, plasma power and treatment time should not exceed 150 mW and 60 s, respectively.

Interactions of a small-size, non-thermal plasma (plasma needle) with living cells in culture are studied. We have demonstrated the non-destructive character of the plasma needle: under moderate conditions (low-power and low concentration of molecular species) the plasma needle does not heat biological samples and does not induce cell death. Treatment of living cells is restricted to the cell exterior (membrane). As a result of the interactions of plasma radicals with cell adhesion molecules, cell attachment is temporarily interrupted; the loose cells can be removed, reattached or transferred. This effect may prove very useful in fine surgery, where a part of the tissue must be removed with high-precision, without damage to the adjacent cells and without inflammatory reaction.

Aims:  A nonthermal atmospheric plasma, designed for biomedical applications, was tested for its antimicrobial activity against biofilm cultures of a key cariogenic bacterium Streptococcus mutans. Methods and Results:  The Strep. mutans biofilms were grown with and without 0·15% sucrose. A chlorhexidine digluconate rinse (0·2%) was used as a positive antimicrobial reference. The presence of sucrose and the frequency of plasma application during growth were shown to have a significant effect on the response to treatment and antibacterial activity. Conclusions:  A single plasma treatment for 1 min on biofilms cultured without sucrose caused no re‐growth within the observation period. However, with either single or repeated plasma treatments of 1 min, on biofilms cultured with 0·15% sucrose, growth was only reduced. Significance and Impact of the Study:  In summary, there may be a role for nonthermal plasma therapies in dental procedures. Sucrose and associated growth conditions may be a factor in the survival of oral biofilms after treatment.