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. 2007 Jun 5:4:50.
doi: 10.1186/1743-422X-4-50.

Inactivation of viruses by coherent excitations with a low power visible femtosecond laser

K T Tsen  1 , Shaw-Wei D Tsen, Chih-Long Chang, Chien-Fu Hung, T-C Wu, Juliann G Kiang
Affiliations

Inactivation of viruses by coherent excitations with a low power visible femtosecond laser

K T Tsen et al. Virol J. .

Abstract

Background: Resonant microwave absorption has been proposed in the literature to excite the vibrational states of microorganisms in an attempt to destroy them. But it is extremely difficult to transfer microwave excitation energy to the vibrational energy of microorganisms due to severe absorption of water in this spectral range. We demonstrate for the first time that, by using a visible femtosecond laser, it is effective to inactivate viruses such as bacteriophage M13 through impulsive stimulated Raman scattering.

Results and discussion: By using a very low power (as low as 0.5 nj/pulse) visible femtosecond laser having a wavelength of 425 nm and a pulse width of 100 fs, we show that M13 phages were inactivated when the laser power density was greater than or equal to 50 MW/cm2. The inactivation of M13 phages was determined by plaque counts and had been found to depend on the pulse width as well as power density of the excitation laser.

Conclusion: Our experimental findings lay down the foundation for an innovative new strategy of using a very low power visible femtosecond laser to selectively inactivate viruses and other microorganisms while leaving sensitive materials unharmed by manipulating and controlling with the femtosecond laser system.

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Figures

Figure 1
Figure 1
Experimental setup for the inactivation of M13 bacteriophages. M: mirror; M.O.: lens with extra long focus length; S: sample. The magnification shows the sample area where the laser beam is relatively uniform-focused. The cylindrical volume where the laser beam focuses defines the active volume for the inactivation of M13 bacteriophages through ISRS process.
Figure 2
Figure 2
The three typical assays for a sample with nominally prepared 1 × 103 pfu of M13 bacteriophages (a) without laser irradiation; (b) after laser irradiation for about 10 hours. The extremely few number of plaques observed in the irradiated sample is a manifestation of almost complete inactivation of the M13 bacteriophages in the sample.
Figure 3
Figure 3
The three typical assays for a sample with nominally prepared 5 × 102 pfu of M13 bacteriophages (a) without laser irradiation; (b) after laser irradiation for about 10 hours. The extremely few number of plaques observed in the irradiated sample is indicative of almost complete inactivation of the M13 bacteriophages in the sample.
Figure 4
Figure 4
The number of plaques as a function of the excitation laser power density for a M13 bacteriophage sample with nominally prepared 1.1 × 103 pfu. The sharp cut-off for the number of plaques at around 50 MW/cm2 is indicative of the onset of the inactivation of the M13 bacteriophages.
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References

    1. Ford LH. Estimate of the vibrational frequencies of spherical virus particles. Phys Rev. 2003. E67, 051924-1-051924-3. - PubMed
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    1. Yan Y-X, Gamble EB, Jr, Nelson KA. Impulsive stimulated scattering:General importance in femtosecond laser pulse interactions with matter, and spectroscopic applications. J Chem Phys. 1985;83:5391–5399. doi: 10.1063/1.449708. - DOI
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    1. Tsen KT. Electron velocity overshoot, ballistic electron transport and non-equilibrium phonon dynamics in nanostructure semiconductors. In: Tsen KT, editor. Ultrafast Phenomena in Semiconductors. Springer-Verlag NY; 2001. pp. 191–259.

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