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Atmospheric pressure plasma: a high-performance tool for the efficient removal of biofilms.

Fricke K, Koban I, Tresp H, Jablonowski L, Schröder K, Kramer A, Weltmann KD, von Woedtke T, Kocher T - PLoS ONE (2012)

Bottom Line: In general, contamination of surfaces by micro-organisms is a major source of problems in health care.Physical plasmas offer a huge potential to inactivate micro-organisms and to remove organic materials through plasma-generated highly reactive agents.The impact of plasma etching on biofilms is localized due to the limited presence of reactive plasma species validated by optical emission spectroscopy.

View Article: PubMed Central - PubMed

Affiliation: Leibniz Institute for Plasma Science and Technology eV, INP Greifswald, Greifswald, Germany. k.fricke@inp-greifswald.de

ABSTRACT

Introduction: The medical use of non-thermal physical plasmas is intensively investigated for sterilization and surface modification of biomedical materials. A further promising application is the removal or etching of organic substances, e.g., biofilms, from surfaces, because remnants of biofilms after conventional cleaning procedures are capable to entertain inflammatory processes in the adjacent tissues. In general, contamination of surfaces by micro-organisms is a major source of problems in health care. Especially biofilms are the most common type of microbial growth in the human body and therefore, the complete removal of pathogens is mandatory for the prevention of inflammatory infiltrate. Physical plasmas offer a huge potential to inactivate micro-organisms and to remove organic materials through plasma-generated highly reactive agents.

Method: In this study a Candida albicans biofilm, formed on polystyrene (PS) wafers, as a prototypic biofilm was used to verify the etching capability of the atmospheric pressure plasma jet operating with two different process gases (argon and argon/oxygen mixture). The capability of plasma-assisted biofilm removal was assessed by microscopic imaging.

Results: The Candida albicans biofilm, with a thickness of 10 to 20 µm, was removed within 300 s plasma treatment when oxygen was added to the argon gas discharge, whereas argon plasma alone was practically not sufficient in biofilm removal. The impact of plasma etching on biofilms is localized due to the limited presence of reactive plasma species validated by optical emission spectroscopy.

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Intensity of excited plasma-generated species in the Ar and Ar/O2 gas discharge.Overview optical emission spectra in the visible range (680–850 nm) of Ar plasma (5 slm Ar) and Ar/O2 plasma (5slm Ar+0.05 slm O2) measured at a distance of 7 mm to the jet-nozzle by means of a dual channel fiber optical spectrometer (Avantes AvaSpec 2048-2-USB2). The spectra were relative calibrated, normalized to the exposure time, and analyzed using the software Spectrum Analyzer. In the upper spectrum excited species generated in the Ar gas discharge are shown, in particular atomic Ar in the range of 680–850 nm. The inset figure shows the emission spectrum of Ar plasma in the UV range (300–430 nm) which exhibits emission lines of OH at 309 nm and of the 2nd positive system of N2 at 337–391 nm. The lower spectrum exhibits excited species generated in Ar/O2 plasma which is dominated by emission lines of atomic Ar and additional emission lines of atomic O at 777.4 nm and 844.6 nm. Not shown is the emission spectrum in the UV range due to the absence of emission lines.
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pone-0042539-g004: Intensity of excited plasma-generated species in the Ar and Ar/O2 gas discharge.Overview optical emission spectra in the visible range (680–850 nm) of Ar plasma (5 slm Ar) and Ar/O2 plasma (5slm Ar+0.05 slm O2) measured at a distance of 7 mm to the jet-nozzle by means of a dual channel fiber optical spectrometer (Avantes AvaSpec 2048-2-USB2). The spectra were relative calibrated, normalized to the exposure time, and analyzed using the software Spectrum Analyzer. In the upper spectrum excited species generated in the Ar gas discharge are shown, in particular atomic Ar in the range of 680–850 nm. The inset figure shows the emission spectrum of Ar plasma in the UV range (300–430 nm) which exhibits emission lines of OH at 309 nm and of the 2nd positive system of N2 at 337–391 nm. The lower spectrum exhibits excited species generated in Ar/O2 plasma which is dominated by emission lines of atomic Ar and additional emission lines of atomic O at 777.4 nm and 844.6 nm. Not shown is the emission spectrum in the UV range due to the absence of emission lines.

Mentions: To gain further insight into the mechanism of biofilm etching and to identify reactive plasma species that are involved in the surface effects induced by plasma exposure, the plasma was characterized by performing optical emission spectroscopy. The spectral characteristics in the ultraviolet/visible (UV/VIS) range of Ar and Ar/O2 plasma are plotted in Fig. 4. The emission spectrum of the Ar gas discharge was mainly dominated by atomic lines of Ar between 670 and 850 nm in the visible range. Furthermore, emission lines of OH at 309 nm and of the second positive system of molecular nitrogen N2 at 337 nm were identified in the UV range (240–400 nm). The OH radical was probably formed from water vapors present in the ambient air [27]. In contrast, the optical emission spectrum of Ar/O2 plasma showed additional emission lines of high intensity of atomic oxygen at 777.4 nm and 844.6 nm in the visible region which were caused by dissociative excitation and direct excitation processes. Neither emission lines of OH nor of N2 were observed in the UV range of Ar/O2 plasma. Consequently, the admixture of oxygen resulted in collisional quenching of N2 and OH lines [28] which suppressed the excitation and production mechanisms. Since the previous results indicated a reduced etching efficacy by using Ar plasma, it is most likely that UV radiation had a little effect on biofilm etching. Furthermore, the comparison of the ratio of the intensity of the emission lines of O (IO) at 844.6 nm and Ar (IAr) at 750.4 nm of both gas discharges revealed an IO/IAr ratio of 0.6 for Ar/O2 plasma and an IO/IAr ratio of 0.05 for Ar plasma. Hence, the portion of oxygen in the spectrum of Ar/O2 plasma is remarkable higher. Deduced from these results it can be assumed that reactive oxygen species played a major role for biofilm removal and hence, that plasma-assisted etching was mainly a chemically driven process.


Atmospheric pressure plasma: a high-performance tool for the efficient removal of biofilms.

Fricke K, Koban I, Tresp H, Jablonowski L, Schröder K, Kramer A, Weltmann KD, von Woedtke T, Kocher T - PLoS ONE (2012)

Intensity of excited plasma-generated species in the Ar and Ar/O2 gas discharge.Overview optical emission spectra in the visible range (680–850 nm) of Ar plasma (5 slm Ar) and Ar/O2 plasma (5slm Ar+0.05 slm O2) measured at a distance of 7 mm to the jet-nozzle by means of a dual channel fiber optical spectrometer (Avantes AvaSpec 2048-2-USB2). The spectra were relative calibrated, normalized to the exposure time, and analyzed using the software Spectrum Analyzer. In the upper spectrum excited species generated in the Ar gas discharge are shown, in particular atomic Ar in the range of 680–850 nm. The inset figure shows the emission spectrum of Ar plasma in the UV range (300–430 nm) which exhibits emission lines of OH at 309 nm and of the 2nd positive system of N2 at 337–391 nm. The lower spectrum exhibits excited species generated in Ar/O2 plasma which is dominated by emission lines of atomic Ar and additional emission lines of atomic O at 777.4 nm and 844.6 nm. Not shown is the emission spectrum in the UV range due to the absence of emission lines.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3412829&req=5

pone-0042539-g004: Intensity of excited plasma-generated species in the Ar and Ar/O2 gas discharge.Overview optical emission spectra in the visible range (680–850 nm) of Ar plasma (5 slm Ar) and Ar/O2 plasma (5slm Ar+0.05 slm O2) measured at a distance of 7 mm to the jet-nozzle by means of a dual channel fiber optical spectrometer (Avantes AvaSpec 2048-2-USB2). The spectra were relative calibrated, normalized to the exposure time, and analyzed using the software Spectrum Analyzer. In the upper spectrum excited species generated in the Ar gas discharge are shown, in particular atomic Ar in the range of 680–850 nm. The inset figure shows the emission spectrum of Ar plasma in the UV range (300–430 nm) which exhibits emission lines of OH at 309 nm and of the 2nd positive system of N2 at 337–391 nm. The lower spectrum exhibits excited species generated in Ar/O2 plasma which is dominated by emission lines of atomic Ar and additional emission lines of atomic O at 777.4 nm and 844.6 nm. Not shown is the emission spectrum in the UV range due to the absence of emission lines.
Mentions: To gain further insight into the mechanism of biofilm etching and to identify reactive plasma species that are involved in the surface effects induced by plasma exposure, the plasma was characterized by performing optical emission spectroscopy. The spectral characteristics in the ultraviolet/visible (UV/VIS) range of Ar and Ar/O2 plasma are plotted in Fig. 4. The emission spectrum of the Ar gas discharge was mainly dominated by atomic lines of Ar between 670 and 850 nm in the visible range. Furthermore, emission lines of OH at 309 nm and of the second positive system of molecular nitrogen N2 at 337 nm were identified in the UV range (240–400 nm). The OH radical was probably formed from water vapors present in the ambient air [27]. In contrast, the optical emission spectrum of Ar/O2 plasma showed additional emission lines of high intensity of atomic oxygen at 777.4 nm and 844.6 nm in the visible region which were caused by dissociative excitation and direct excitation processes. Neither emission lines of OH nor of N2 were observed in the UV range of Ar/O2 plasma. Consequently, the admixture of oxygen resulted in collisional quenching of N2 and OH lines [28] which suppressed the excitation and production mechanisms. Since the previous results indicated a reduced etching efficacy by using Ar plasma, it is most likely that UV radiation had a little effect on biofilm etching. Furthermore, the comparison of the ratio of the intensity of the emission lines of O (IO) at 844.6 nm and Ar (IAr) at 750.4 nm of both gas discharges revealed an IO/IAr ratio of 0.6 for Ar/O2 plasma and an IO/IAr ratio of 0.05 for Ar plasma. Hence, the portion of oxygen in the spectrum of Ar/O2 plasma is remarkable higher. Deduced from these results it can be assumed that reactive oxygen species played a major role for biofilm removal and hence, that plasma-assisted etching was mainly a chemically driven process.

Bottom Line: In general, contamination of surfaces by micro-organisms is a major source of problems in health care.Physical plasmas offer a huge potential to inactivate micro-organisms and to remove organic materials through plasma-generated highly reactive agents.The impact of plasma etching on biofilms is localized due to the limited presence of reactive plasma species validated by optical emission spectroscopy.

View Article: PubMed Central - PubMed

Affiliation: Leibniz Institute for Plasma Science and Technology eV, INP Greifswald, Greifswald, Germany. k.fricke@inp-greifswald.de

ABSTRACT

Introduction: The medical use of non-thermal physical plasmas is intensively investigated for sterilization and surface modification of biomedical materials. A further promising application is the removal or etching of organic substances, e.g., biofilms, from surfaces, because remnants of biofilms after conventional cleaning procedures are capable to entertain inflammatory processes in the adjacent tissues. In general, contamination of surfaces by micro-organisms is a major source of problems in health care. Especially biofilms are the most common type of microbial growth in the human body and therefore, the complete removal of pathogens is mandatory for the prevention of inflammatory infiltrate. Physical plasmas offer a huge potential to inactivate micro-organisms and to remove organic materials through plasma-generated highly reactive agents.

Method: In this study a Candida albicans biofilm, formed on polystyrene (PS) wafers, as a prototypic biofilm was used to verify the etching capability of the atmospheric pressure plasma jet operating with two different process gases (argon and argon/oxygen mixture). The capability of plasma-assisted biofilm removal was assessed by microscopic imaging.

Results: The Candida albicans biofilm, with a thickness of 10 to 20 µm, was removed within 300 s plasma treatment when oxygen was added to the argon gas discharge, whereas argon plasma alone was practically not sufficient in biofilm removal. The impact of plasma etching on biofilms is localized due to the limited presence of reactive plasma species validated by optical emission spectroscopy.

Show MeSH
Related in: MedlinePlus