ROS and RNS formed in water sprayed through transient spark in air and their bactericidal effects

Transcription

1 ROS and RNS formed in sprayed through transient spark in air and their bactericidal effects Zdenko Machala, Barbora Tarabová, Karol Hensel, Libuša Šikurová Faculty of Mathematics, Physics and Informatics, Comenius University, Bratislava, Slovakia Petr Lukeš, Eva Špetlíková Institute of Plasma Physics, Academy of Sciences, Prague, Czech Republic

2 Research objectives Recent studies show that the bactericidal effects of atmospheric pressure cold air plasmas in contact with are dominantly due to reactive oxygen and nitrogen species (ROS/RNS). We investigated: Bactericidal effects in treated by DC-driven transient spark discharge in air at 1 atm DC - easy operation, low-cost power supplies Air - cheap, convenient for medical treatments, precursor of ROS/RNS Chemical effects induced in electro-sprayed through transient spark focus at ROS/RNS 1. changes of ph, electrolytic conductivity 2. hydrogen peroxide H 2 O 2 3. nitrites NO 2 and nitrates NO 3 4. peroxynitrites O=N-OO Oxidative stress of cell membranes induced by plasma treatment

3 Experimental setup flow rate. ml/min Diagnostics Peroxides H 2 O 2 colorimetry based on Ti(SO 4 ) 2 Nitrites NO 2-, nitrates NO - 3 ion chromatography (1 mm sensitivity) Peroxynitrites O=N-O-O- DCFH-DA fluorescence spectroscopy (qualitative tests) ph, conductivity probes Bactericidal effect CFU plate count method Oxidative stress TBARS analysis

4 Transient spark discharge U (kv) / I(A) needle-to-plate, -mesh, electrodes, d = 1 cm ambient air, p = 1 atm streamer-to-spark transition U max ~ kv, I mean ~ 1 ma, I max ~ 2-3 A pulse duration <2 ns, f ~ 1 khz P=1-2 W non-equilibrium plasma t (ns) U I U (kv) / I(A) Z. Machala et al. IEEE Trans. Plasma Sci. (28) Z. Machala et al. J Phys. D: Appl. Phys. (2) M. Janda et al. Plasma Sources Sci. Technol. (211, 212) t (ms) U I

5 Transient spark + electro-spray d = 8 mm Q =. ml/min U = 9 kv

6 Periodic streamer-to-spark Streamer phase: ionization e -, N 2 + excitation of N 2 C, B UV-VIS radiation, metastable N 2 A formation electron attachment O 2 - Spark phase: ionization e -, N 2 + dissociation of N 2, O 2, H 2 O N, O, OH, H; their excitation VIS radiation Relaxation phase: reactions of species living >1 μs NO x, O 3, 2. khz 6 khz

7 Treated bacterial suspensions Escherichia coli (CCM 394) suspended in: Initial bacterial concentration ~1 7 CFU/mL Water: NaH 2 PO 4 solution (mimics tap ) (σ =.6 ms/cm, ph.3) PB: phosphate buffered solution Na 2 HPO 4 /KH 2 PO 4 (σ =. ms/cm, ph 6.9) Saline: physiological saline (NaCl) solution (σ = 6.3 ms/cm, ph 7) PBS: physiological saline (NaCl) solution with Na 2 HPO 4 /KH 2 PO 4 phosphate buffer (σ = 6 ms/cm, ph 6.8)

8 Bactericidal effect of plasma ph drops: (. 3), saline (7 3) Conductivity increases: ( ms/cm), saline: ( ms/cm) Bactericidal effect: up to ~7 log reduction complete sterilization Long-term bactericidal effect: slightly stronger than immediately after plasma - plasma activated - long lived species (H 2 O 2 ) Log reduction after plasma hours later saline E. coli inactivation in and saline, directly after plasma treatment and h later.

9 Effect of ph - vs. buffered Comparison of bio-decontamination in buffered/non-buffered solution Water and saline with dilute phosphate buffer (PB, PBS); ph fixed at 6.9 ph change: drop in non-buffered (. 3), little change in buffered (6.9 6) Bactericidal effect: much lower in PB (1 log) than in (6. logs) Long-term bactericidal effect: stronger in (~7 logs) but substantial also in PB (~3. logs) Log reduction after plasma hours later PB E. coli inactivation in non-buffered and PB buffered solution, directly after plasma treatment and h later.

10 Chemical effects vs. buffered Water (non-buffered): Acidification: ph. ~3 Conductivity.6 ~1.1 ms/cm Nitrites NO 2 ~.2 mmol/l Nitrates NO 3 ~1 mmol/l Peroxides H 2 O 2 ~.7 mmol/l PB: non-acidic environment ph little drop 6.9 ~6 Conductivity stays at.6 ms/cm Nitrites NO 2 ~.6 mmol/l Nitrates NO 3 ~.9 mmol/l Peroxides H 2 O 2 ~.4 mmol/l c [mm] High concentrations of NO 2- and NO treatment time per volume ~1.2x1 s/l very small droplets (~2 nl) sprayed through the plasma (3 ms time of flight) PB NO2- NO3- H2O2 NO 2-, NO 3- and H 2 O 2 concentrations in and PB solutions after plasma treatment.

11 Nitrites and nitrates Dissolution of NO x in acidification NO 2 + NO 2 +H 2 O NO 2 +NO 3 +2H + NO 2 + NO + H 2 O 2 NO 2 +2H + Under acidic condition: disproportionation of NO 2 NO 3 3 NO H + +H 2 O 2 NO + NO 3 + H 3 O + HCl or HNO 3 solution of ph ~3 much weaker bactericidal effect! Acid environment + plasma agents bacterial inactivation in Log reduction PB log NO2- NO3- Bacteria log reduction and H 2 O 2 concentration in and PB solutions depending on ph after plasma treatment NO2 -, NO3 - [mm]

12 Nitrites and hydrogen peroxide NO 2- strongly decay in acidified NO 2- seems related with strong bactericidal action - acidified nitrite D. Graves, J Phys D (212) M. Traylor, J Phys D (212) Direct bactericidal effect of NO 2 - at acidic ph: 3NO H + + H 2 O 2NO + NO 3- + H 3 O + Log reduction log NO2- H2O NO2 -, H2O2 [mm] H 2 O 2 produced more in than in PB PB. H 2 O 2 seems also related with strong bactericidal action Bacteria log reduction and nitrite concentration in and PB depending on ph after plasma treatment.

13 Peroxynitrites Formation of peroxynitrites from nitrites and hydrogen peroxide at acidic ph: H 2 O 2 + NO 2 O=N-OO + H 2 O Reactivity depends on ph. Fast decay in acidic ph: O=N-OOH OH + NO 2 K. Oehmingen, Plasma Proc. Polym (21, 211) In cells: O=N-OO - NO + O 2 Other possible ONOO - formation mechanisms: O 2 + NO O=N-OO OH + NO 2 O=N-OO + H + Log reduction log ONOO- PB Bacteria log reduction of and PB after plasma treatment correlated with relative ONOO- concentrations measured as DCFH fluorescence ONOO - [a.u.]

14 Is DCFH fluorescence specific to peroxynitrites? Dichlorodihydrofluorescein diacetate (DCFH-DA) converts to highly fluorescent dichlorofluorescein (DCF) under the action of ROS Literature: DCFH much more sensitive to ONOO- than other ROS H. Possel, FEBS Lett J. P. Crow, Nitric Oxide: Biol. Chem We confirmed this experimentally by DCFH fluorescence in 1 mm H 2 O 2 solutions much weaker fluorescence signal DCFH fluorescence [a.u.] H2O2 ph~2. H2O2 ph~.6 plasma Recent cooperation with INP Greifswald confirmed low fluorescence from H 2 O 2 but non-negligible from OCl - - possible in saline solutions only (PBS)

15 Peroxone process H 2 O 2 in progressively decreased in time supports the expected phdependent reaction between NO 2 - and H 2 O 2 (peroxynitrite formation H 2 O 2 + NO 2 O=N-OO + H 2 O) H2O2 [mmol L -1 ] PB However, higher H 2 O 2 in immediately after plasma treatment compared to PB contradicts this reaction Time after plasma [h] Peroxone process between H 2 O 2 and ozone at ph >. should be considered! H 2 O O 3 2 OH + 3 O 2 Chemistry in plasma treated strongly depends on ph! Log reduction Time evolution of H 2 O 2 in plasma 1. 8 log NO2-7 treated and PB H2O Log reduction NO2 -, H2O2 [mm] PB PB 4 3 after plasma hours later

16 Oxidative stress measurement ROS peroxidation of cell membrane lipids malondialdehyde (MDA) MDA reacts with thiobarbituric acid (TBA) product quantified spectrophotometrically Measurement of the oxidative stress induced on bacteria cells by thiobarbituric acid reactive substances (TBARS) method Lower oxidative stress in buffered solutions in agreement with lower bactericidal effect Plasma treated oxidations of membranes by ROS are important Log reduction log TBARS PB Bactericidal effect of plasma treated and PB correlated with the TBARS concentrations, c(tbars) with reference concentrations subtracted. ΔC(TBARS) [nm]

17 Biofilm treatment + spray Plastic surfaces with Streptococci biofilms treated by +/- streamer corona Water electrospraying strongly enhances biofilm inactivation Perhaps due to similar -plasma chemistry? +SC -SC Z. Šipoldová and Z. Machala, IEEE Trans. Plasma Sci. (211) Z. Kovaľová et al. Eur. Phys. J. Appl. Phys. (213)

18 Summary We investigated bio-decontamination of or saline solutions by electro-spray through the cold air plasma of transient spark. The treatment leads to acidification and the production of ROS/RNS: nitrites, nitrates, peroxides and peroxynitrites. At lowered ph, nitrites are quickly oxidized to nitrates or peroxynitrites (with peroxides) - associated with the strong bactericidal effect of E. coli bacteria. At neutral ph in buffered solutions, nitrites are less oxidized and the bactericidal effect is weaker; Peroxone reaction of ozone with H 2 O 2 should be considered. The bactericidal effect correlates with the amount of the formed peroxynitrites, as well as with the oxidative stress induced in cell membranes measured by TBARS method. It seems that that the interacting nitrites and peroxides in acidic conditions are the dominant bactericidal agents in sprayed through air plasma + potential mechanism via peroxynitrites. Acknowledgements: Slovak Grant Agency VEGA 1/668/11, Slovak Research and Development Agency APVV SK-CZ-179-9, the Grant Agency of AS CR IAAX4382 and Project of Ministry of Education, Youth and Sports of the Czech Republic No. MEB Z. Machala et al., Plasma Process. Polym. (213) under review Z. Machala et al., Eur. Phys. J. D. 4 (29) Z. Machala et al., J. Phys. D: Appl. Phys. 43 (21) Z. Machala et al., NATO book, Springer (212)