An Investigation of the Sterilization Effect of 385nm UVA-LED

An Investigation of the Sterilization Effect of 385nm UVA-LED
Tomohiro Oshita1*, Keiko Shintani2, Mai Katayama2
Takahiro Emoto1, Masatake Akutagawa1, Akira Takahashi2, and Yohsuke Kinouchi1
1
Institute of Technology and Science, The University of Tokushima, Tokushima, Japan,
2
Institute of Health Bioscience, The University of Tokushima, Tokushima, Japan
*
Corresponding author e-mail:[email protected]
ITRODUCTIO
Ultraviolet (UV) sterilization has been used for reducing the bacteria count. A UV-lightemitting diode (LED) has investigated as a simple alternative light source to standard
mercury lamp which has the high germicidal effect of UV radiation at around 260 nm. The
UVA(365nm)-LED is known to be capable of sterilization. However, the sterilization effect
and mechanism of UVA(320-400nm)-LED have not yet investigated completely. The LED
used in this study has an emission maximum at 365 and 385nm. In this paper, we compare
the effect of those different wavelengths of UVA-LED in the sterilization. Moreover, the
difference of sterilization effect between UVA (365 and 385nm) and visible radiation (405
nm) is investigated in our experiments.
MATERIALS AD METHODS
Figure 1 shows a experimental device which contains eight high power UVA-LEDs
(NCSU033A(T); Nichia Corporation, Japan). The sterilizer is installed in water-cooling heat
sink to maintain a constant temperature. In this study, DH5α strain (Escherichia coli) was
used as indicator bacteria. The bacterial suspension (150µL) was poured into wells of the
96well plate where just under the LEDs. The distance between LEDs and bacterial
suspension was 20mm.
The computer simulation is carried out for investigating the irradiance distribution for all
the geometries of LED array. Then radiant flux of the 385nm-LED is larger than that of
365nm-LED, because luminance efficiency of the 385nm-LED is better than that of the
365nm-LED. Figure 2 is a simulation result of the irradiance distribution by the sterilizers on
surface of the bacterial suspension. In this simulation, characteristic of light emission was
determined based on a specification sheet of each LED. Furthermore the drive current is
adapted for 500mA. According to Figure 2, the light intensity is increased at the center of
plate, and is decreased contrastively at the both ends of plate.
Figure 1: Experimental device
Figure 2: Computer simulation results
The number of bacteria was measured by the colony-counting method.
Before-after the UV irradiation the sterilization effect is evaluated based on the number of
colony counted that cultured bacterial suspension. And we evaluated the sterilization effect with
the following formula.
 
survival rate ( SR ) = log 10

 o 
(1)
N: Number of bacteria colonies before irradiation
N0: Number of bacteria colonies after irradiation
RESULTS
As a result of simulation result, about sterilization effect of 385nm-LED compared ends
with center, but it was not difference.
Figure 3 shows the sterilization effect for 365 and 385nm-LED at the each irradiation
energy. Based on the result, the sterilization effect of 365nm-LED was very similar to that of
385nm-LED.
385nm which is close to visible radiation was a high sterilization effect. Thus we
investigated sterilization effect of 405nm-LED which is visible radiation, but there was no
sterilization effect (Figure 4).
Figure 4: A sterilization effect of the visible light LED
Figure 3: Relationship between Irradiation energy and sterilization
COCLUSIOS
As expected, 405nm visible radiation was no effective for sterilizing, but 365 and 385nm
had the high sterilization effect. The summary of the and experimental results, we can
conclude that the sterilization effect of 385nm UV is equal to that of 365 nm UV. We showed
that the UVA sterilization is a feasible even at 385nm-UVA which is close to visible
radiation.
REFERECES
[1] M. Mori, H. Akiko, A. Takahashi, M. Nakano, N. Wakikawa, S.Tachibana, T. Ikehara, Y. Nakaya,
M. Akutagawa and Y. Kinouchi : Development of a new water sterilization device with a 365 nm UV-LED,
Medical and Biological Engineering and Computing, Vol.45, No.12, pp.1237--1241, 2007
[2]N. Yagi, M. Mori, A. Hamamoto, Xin. Lian, M. Nakano, S. Tachibana, M. Akutagawa, T. Ikehara, A.
Tkahashi, and Y. Kinouchi, The Bioelectromagnetic Society 30th Annual Meeting Abstract Collection, 62008
[3] A. Hamamoto, M. Mori, A. Takahashi, M. Nakano, N. Wakikawa, M. Akutagawa, T. Ikehara, Y. Nakaya
and Y. Kinouchi : New water disinfection system using UVA-light emitting diodes., Journal of Applied
Microbiology. In press, Vol.103, No.6, pp.2291--2298, 2007.