Surface Sterilization with Non-thermal Atmospheric Pressure Plasma Jet
M. Amini1, M. Ghoranneviss1, M. Rahimi1, A. Sari1, S. Mirpour1, A. Najafi2, Z. Ghorannevis1
1
Plasma Physics Research Center, Science and Research Branches, Islamic Azad University, Tehran, Iran
2
Department of Microbiology, Medical Branch, Islamic Azad University, Tehran, Iran
Abstract: An atmospheric–pressure plasma needle was used to sterilization of surface. Using a plasma jet to
achieve sterilization is a possible alternative to conventional sterilization means as far as sterilization of heatsensitive materials. In this experiment we evaluated the effect of He/N2 plasma treatment on Staphylococcus
aureus, using RF power Non-thermal atmospheric pressure plasma needle. Plasma needle consists of a needle, a
gas supply and a high–frequency generator. The needle has three fittings: an electrical feed through, gas inlet and
nozzle. The most important features are inside the nozzle. At the center of the nozzle is a tungsten neurology
needle, with a diameter of 0.3 mm and its length is 7 mm. the needle was concentric with a cylindrical glass-tube
nozzle, which has an inside diameter of D=0.8 mm and an outside diameter of 2.8 mm. The needle electrode was
powered by 13.56 MHZ radio-frequency to provide a return current a grounded metal plate was positioned below
the plastic Petri dish.
Keywords: Plasma jet, Surface sterilization, He/N2 plasma
1. Introduction
Low–pressure plasmas have been researched since
much time ago. Non-thermal plasmas have many
applications
such
as
surface
sterilization.
Sterilization is a physical or a chemical act or a
process that eliminates all forms of life, especially
Microorganisms. And it’s better than sterilization
with ethylene oxide, autoclave and oven, because its
advantage. In addition to their practical side, design
simplicity, and low Operational cost, nonequilibrium atmospheric pressure plasmas exhibit
unique features, which have provided the base for
numerous applications [3] Advantage of plasma
sterilization is the possibility, under appropriate
conditions, [1], of achieving such a process at
relatively low temperatures [2]. Plasma sterilization
uses gasses that have no biological property on their
own. But when plasma is ignited, it can kill bacteria
[2]. There for Sterilization with plasma is a safe
process for operator and material. The rate of
sterilization depends on a type of gases, a distance
(between nozzle and surface), and an RF power. In
this paper we present the effect of these parameters
on the rate of sterilization.
2. Experimental Setup
The Plasma needle consists of a needle, a gas supply
and a high–frequency generator. The needle has
three fittings: an electrical feed through, gas inlet
and nozzle. The most important features are inside
the nozzle. At the center of the nozzle is tungsten
neurology needle, with a diameter of 0.3 mm and its
length is 7 mm. the needle was concentric with a
cylindrical glass-tube nozzle, which has an inside
diameter D=0.8 mm and an outside diameter of 2.8
mm. the needle electrode was powered by 13.56
MHZ radio-frequency. To provide a return current a
grounded metal plate was positioned below the
plastic Petri dish. The working gas was pure helium
(with purity percentage of 99.999) gas while the
total gas flow rates were kept constant at 1 liter/min.
This rate was kept Constant during all of the
experiments. Moreover, 2% of pure Nitrogen (N2)
was mixed to pure He gas into some experiments. In
order to investigate the effect of exposure time, RF
power and distance between plasma plume and
Sample were performed. In first series of
experiments, pure He gas and mixture gas treatment
time varied from 10 to 180 s in a fixed 5 mm
distance between the electrode’s tip and bacteria
sample. In the second series of experiments, in a
constant exposure time (90 s) power supply varied
from 20 to 35 watt while distance between the
needle’s tip and sample was fixed in 5mm and the
working gas was N2/O2 gas. In third series of
experiments, in a constant exposure time (90 s) the
distance between the needle’s tip and Petri dishes
changed from 5 mm to 20 mm and the working gas
was N2/O2 gas. The temperature of the plasma was
measured by thermocouple during the Experiments.
The maximum temperature of the He plasma in the
remote area, afterglow region (about 20 mm), and
discharge zone, for 3 min treatment period were,
29oC, 30oC and 45oC, respectively. These
temperatures reached to, 30o C, 34oC and 55o C for
He/N2 plasma Treatment.
this. It should be considered that in discharge zone
plasma density and temperature are higher than
remote area and afterglow region [9]. The formula of
the GE is determined as equation .1: (1)
Figure 1: Schematic of Plasma needle
Figure 2: Plasma needle
3. Results and Discussion
Fig. 3 and Fig. 4 show the effect of different
exposure time on the sterilization of bacteria. It can
be found from the figures that by increasing the
plasma treatment time the sterilization rate enhances.
In addition, we observed that in pure He plasma
treatment, after 180 s, sterilization was completed
while in He/N2 plasma after 90 s sterilization was
completed. These tests performed in afterglow
region. Fig. 5 shows the germicidal effect when the
power supply varied from 5 to 20 watt. Fig. 6 shows
the germicidal effect when the distance (between
plasma plume and surface) varied from 5 to 20 mm,
after 20 mm it reached to the remote area of plasma.
The results show that by increasing the distance
from 5 to 20 mm, germicidal effect decreases.
Approaching to needle tip and transition from
afterglow region to discharge zone could influence
Where, Nf and Ni are the Colony Forming Unit
(CFU) numbers of plasma treated plates and in
control (1.5*108), respectively [10].
In the present study we proved that cold plasma
could be utilized to eliminate S. Areus. Our
experiments show that reactive rate goes up with RF
power. Increasing the RF power effect on
sterilization rate by two ways. At first causes that
density of charged particle is increased. Charged
particle can play a very significant role in the rupture
of the outer membrane of bacterial cells [3]. Also
some amount of heat is produced by increasing RF
power [3] and heat has sterilized property. In this
line H. S. Uhma et. al., proved that in pure He
plasma treatment, even after 180 s sterilization did
not complete but we obtained complete Sterilization
after 180 s. This difference is because of using
different bacterial samples (bacillus cereus vs. s.
areus) may have a large effect on the results [5].
Sureshkumar et. al. also tried to eliminate
Staphylococcus aureus by two different of nitrogen
and nitrogen–oxygen mixture. They can eliminate
the number of bacterial colonies within 5 min
treatment. This difference may occur because of
many conditions such as: operating gas, power
supply, pressure, bacteria different resistance and the
distance between nozzle and sample colonies.
Previous experiments proved that low pressure N2–
O2 plasma produce a large amount of UV radiation
[6, 7]. M. Laroussi et. al. [8] also reported that
active radicals such as anions play the most
important role in the elimination of bacteria.
Figure 3. Effect of treatment time of He gas on
sterilization rate.
predominately emitted by the irradiative deexcitation of excited NO molecules and partially by
the de-excitation of OH molecules [4]. Ion
bombardment is another destructive factor for
germicidal effect, which increased by decreasing
distance between plasma and samples [9]. Our
results demonstrated this hypothesis.
Conclusion:
Figure 4. Effect of treatment time of He/N2 gas on
sterilization rate.
The main goal of this paper was to study the effects
of plasma treatment on s.aureus. The treatment of s.
aureus bacteria was performed in order to study the
deactivation of harmful bacteria. We found that the
plasma needle treatments are available to produce
surface properties that are cause bacteria
elimination. This properties varies with the plasma
power, treatment durance and electrode sample
distance. Moreover, it was found that the germicidal
effect is improved by adding nitrogen gas to He
plasma. Our goal in this study is to provide some
preliminary result from effective agent in
atmospheric pressure plasma sterilization and the
future topics of our work group are followed the
mechanisms of plasma sterilization.
References
Figure 5. Effect of power supply on sterilization rate (for
He/N2 plasma).
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Figure 6. Effect of different distances between He/N2
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