Metrology of Ar-N2/O2 Mixture Atmospheric Pressure Pulsed DC Jet Plasma and its Application in Bio-Decontamination

Abstract

Atmospheric pressure plasma jets are gaining a lot of attention due to their widespread applications in the field of bio-decontamination, polymer modification, material processing, deposition of thin film, and nanoparticle fabrication. Herein, we are reporting the disinfection of Pseudomonas aeruginosa, Staphylococcus aureus, and Escherichia coli bacteria using plasma jet. In this regard, Ar-O₂, Ar-N₂, and Ar-O₂-N₂ mixture plasma is generated and characterized using optical and electrical characterization. Variation in plasma parameters like electron temperature, electron density, and reactive species production is monitored with discharge parameters such as applied voltage and feed gas concentration. Results show that the peak average power consumed in Ar-O₂, Ar-N₂, and Ar-O₂-N₂ mixture plasma is found to be 4.45, 2.93, and 4.35 W respectively, at 8 kV. Moreover, it is noted that by increasing applied voltage, the electron temperature, electron density, and reactive species production also increases. It is worth noting that electron temperature increases with increase in oxygen concentration in the mixture (, while it decreases with increase in nitrogen concentration in the mixture (Ar-N₂). Similarly, a decreasing trend in electron temperature is noted for Ar-O₂-N₂ mixture plasma. On the other hand, a decreasing trend in electron density is noted for all the mixtures. Reduction in viable colonies of Pseudomonas aeruginosa, Staphylococcus Aureus, and Escherichia coli were confirmed by the serial dilution method. The inactivation efficiency of pulsed DC plasma generated, in the Ar-N₂ mixture at 8 kV and 6 KHz, was evaluated against P. aeruginosa, S. aureus and E. coli bacteria by measuring the number of surviving cells versus plasma treatment time. Results showed that after 240 s of plasma treatment, the number of survival colonies of the mentioned bacteria was reduced to less than 30 CFU/mL.

Figure 1

(a) Schematic diagram of the experimental setup; (b) real-time discharge in developed KINPen (photograph courtesy of “Naqib Ullah”. Copyright 2023).

Figure 2

Current–voltage waveform of discharge at 8 kV voltage and 6 kHz fixed pulsed frequency in (a) Ar–O₂ and (b) Ar–N₂ mixture plasmas.

Figure 3

Evolution of (a) instantaneous discharge power at 8 KV and (b) average discharge power verses applied voltage in Ar–O₂, Ar–N₂, and Ar–O₂–N₂ mixture plasma, recorded at 6 kHz frequency and 1500 SCCM total gas flow rate.

Figure 4

Optical emission spectra of (a) Ar–O₂, (b) Ar–N₂, (c) Ar–O₂–N₂, and (d) normalized intensities of UV radiation, reactive nitrogen, and oxygen species, recorded at 8 kV applied voltage, 6 kHz fixed frequency, and 1500 SCCM flow rate.

Figure 5

Variations of electron temperature (at 8 kV applied voltage, 6 kHz fixed frequency, and 1500 SCCM gas flow) vs (a) applied voltages and (b) molecular gas concentration.

Figure 6

Variations of electron number density (at 8 kV applied voltage, 6 kHz fixed frequency, and 1500 SCCM flow rate) vs (a) applied voltages and (b) molecular gas concentration.

Figure 7

(a) Recorded Ar–I 763.5 nm line and Voigt Fit, (b) electron density vs applied voltage, and (c) electron density vs molecular gas concentration (at 8 kV applied voltage, 6 kHz fixed frequency, and 1500 SCCM total gas flow).

Figure 8

Growth of E. coli (a) 10⁵ CFU/mL, (b) 10⁷ CFU/mL, (c) 10⁹ CFU/mL, and (d) treated for 240 s (photograph courtesy of “Naqib Ullah”. Copyright 2023).

Figure 9

Number of survival colonies after Ar–N₂ (Ar-1000 SCCM and N₂-500 SCCM) plasma treatment at 8 kV voltage and 6 kHz frequency.