Emission spectroscopy of atmospheric microplasma
for biomedical application
Marius Blajan ,Tatsuya Ishii, Masahiro Yamada, and Kazuo Shimizu
Innovation and Joint Research Center, Shizuoka University, 3-5-1 Jyouhoku, Hamamatsu, 432-8561, Japan, E-mail：blajanmarius@yahoo.com

Introduction
Microplasma can be found in many applications. In thelast years, the technology was used also for biomedicalapplications. Although there is an interest for application
driven research, microplasma phenomena are not fully
understood.
Microplasma which is atmospheric pressure non thermal
plasma could be used for the sterilization and inactivation
processes of a wide spectrum of microorganism or
removal of odors inside the houses or buildings. The
factors which contribute to the inactivation andsterilization processes of bacteria such as generation ofradicals and UV light, could be study with emission
spectroscopy method.

About microplasma

Microplasma electrodes are metallic electrodes covered
with a dielectric layer.
Small discharge gaps (0∼100) μm and assumed specificdielectric constant of εr = 104：►a high intensity electric field (107 ∼ 108 V/m) around 1kV.
Electrode size was 20 mm versus 40 mm. Electrode has
holes to flow for gas, which diameter is Ø 2mm and its
aperture ratio of 36%. Discharge gap was set at 50 μm.

Species(system)

Transition

Peak Position(nm)

N2 second
positive

C3Π→B3Π

315; 337.1; 357.7;
375.5; 380.5; 400.0

N2+ first
negativeB2Σu+→X2Σg+427.8

OH (3064 – Åsystem)

A2Σ+→X2Π

306.4; 307.8; 308.9

H-γ

2P0 → 2D

434.1

List of detected systems and peaks for themicroplasma in air with water droplets

Microplasma electrodes.

Emission spectrum of microplasma

Inactivation of bacteria by microplasma using
carrier gas air or nitrogen containing waterdroplets

List of detected systems and peaks for themicroplasma in N2 gas with water droplets

Emission spectrum of the microplasma discharge wasmeasured in N2 gas, N2 gas with water droplets, air and
air with water droplets.
Spectrum were obtained at discharge voltage -1.4 kV,
rise time of 80 ns, pulse width of 500 ns, and dischargefrequency of 1 kHz.

Species(system)

Transition

Peak Position(nm)

N2 second
positive

C3Π→B3Π

315; 337.1; 357.7;
375.5; 380.5; 400.0

N2+ first
negativeB2Σu+→X2Σg+

427.8

Excitation of nitrogen molecules in the ground state bydirect electron impact and spontaneous radiation offormed excited state of nitrogen:►the lifetime of photomultiplier signal of N2 SPS was
about 40 ns

Experimental setup(a)Waveforms of discharge voltage, discharge
current and emission signal of microplasma (N2SPS 337.1 nm) in N2 with water droplets.
An experimental setup.
Emission spectra were measured by an ICCD camera,a spectrometer and by a photomultiplier tube. A pulse
generator was used to trigger the Marx Generator andthe ICCD camera.
Compositions of gases used in experiments were N2with water droplets and air with water droplets.
Experiments were carried out in atmospheric pressure
and the gas flow rate was set at 5 L/min. Water droplets
were added in the carrier gas using a medical nebulizer.

Active radical species have etching effect to break thebacteria cell wall, and UV affects DNA directly to cut theirstructure

(b)

(a)

(c)

An experimental Marx Generator.
A Marx generator with 4 stages MOSFET switches:
output voltage up to -1.8 kV peak (negative pulse, risetime 80 ns, pulse width 500 ns ～ 1 µs, frequency 1 kHz～24 kHz).
Trigger signal for ICCD camera was set at 1 µs.
Capacitors are charged in parallel connection at a given
voltage V (500 V in this case).
MOSFET switches are closed, capacitors aredischarging in series connection：►output voltage 4V (2 kV in this case).

Emission spectrum of microplasma discharge in(a) N2 and air containing water droplets ; (b) N2and N2 with water droplets; (c) air and air withwater droplets.
Electron impact dissociation of H2O leads to theproduction of H and OH radicals.
e + H2O → e + H + OH
Air which used as carrier gas with water droplets, leads
to the generation of active species and ozone bymicroplasma.
e + O2 → e+ O(3P) + O(1D)O + O2 + M → O 3 + M
O(1D) + H2O → 2 OH
With oxygen in the carrier gas, any peaks of OH were notobserved due to the quenching effect of oxygen atomand ozone.
OH + O → O2 + H
OH + O3 → HO2 + O2

Waveforms of discharge voltage, discharge
current and gate signal for ICCD camera.

(b)

Images of B. subtilis by SEM a) Living B. subtilis(x 10000); (b) Sterilized B. subtilis by nitrogenplasma (x10000).

Conclusion
1)Analysis of emission spectrum shows► N2 SPS, N2 FNS, OH 3064 – Å system and H-γ bandsystem for the microplasma discharge in N2 gas withwater droplets.
► N2 SPS, N2 FNS, and H-γ band system for
microplasma discharge in air with water droplets withlower intensities comparing with emission spectrum of
microplasma discharge in N2 with water droplets due tothe quenching effect of oxygen atom and ozone.
2)Lifetime of emission signal measured by aphotomultiplier tube corresponding to wavelength 337.1
nm of N2 SPS was about 40 ns.