Abstract
BackgroundPrevious work indicated that an ultrashort pulse (USP) 425 nm laser is capable of inactivating murine norovirus (MNV: Virol. J. 11:20), perhaps via an impulsive stimulated Raman scattering (ISRS) mechanism, and does not substantially damage human plasma proteins (PLOS One 9:11). Here, further investigation of virus inactivation by laser light is performed.MethodsIn this study, we evaluate whether inactivation of MNV is specific to the USP wavelength of 425 nm, or if it occurs at other visible wavelengths, using a tunable mode-locked Ti-Sapphire laser that has been frequency doubled to generate femtosecond pulses at wavelengths of 400, 408, 425, 450, 465, and 510 nm. Continuous Wave (CW) lasers are also applied. Singlet oxygen enhancers are used to evaluate the sensitivity of MNV to singlet oxygen and oxygen quenchers are used to evaluate effects on virus inactivation as compared to untreated controls.Results> 3 log10 inactivation of MNV pfu occurs after irradiation with an average power of 150 mW at wavelengths of 408, 425 or 450 nm femtosecond-pulsed light for 3 h. Thus results suggest that the mechanism by which a laser inactivates the virus is not wavelength-specific. Furthermore, we also show that irradiation using a continuous wave (CW) laser of similar power at 408 nm also yields substantial MNV inactivation indicating that inactivation does not require a USP. Use of photosensitizers, riboflavin, rose bengal and methylene blue that generate singlet oxygen substantially improves the efficiency of the inactivation. The results indicate a photochemical mechanism of the laser-induced inactivation where the action of relatively low power blue laser light generates singlet oxygen.ConclusionResults suggest formation of short-lived reactive oxygen species such as singlet oxygen by visible laser light as the cause of virus inactivation rather than via an ISRS mechanism which induces resonant vibrations.
Highlights
Previous work indicated that an ultrashort pulse (USP) 425 nm laser is capable of inactivating murine norovirus
murine norovirus (MNV) inactivation by variable wavelength visible fs light pulses and by continuous wave (CW) Table 1 shows that 400, 408, 425 and 450 nm femtosecond pulse laser light are all capable of nonthermally inactivating MNV, indicating that a discrete wavelength is not required for MNV inactivation
Oxygen dependence Inactivation of MNV by the Ultrashort pulse laser (USPL) with variable wavelengths of blue light (400–450 nm) and by 408 nm CW indicated the inactivation mechanism was not specific to the 425 nm wavelength and, more substantial inactivation was achieved with femtosecond pulse light, was not dependent on light pulses
Summary
Previous work indicated that an ultrashort pulse (USP) 425 nm laser is capable of inactivating murine norovirus It has been shown that blue (405 nm) light can inactivate bacteria via its interactions with porphyrins (5 and 6 carbon multi-ring contain alternating single and double bonds) within the membrane of bacteria [28], and is actively being investigated as a means of disinfection of medical and food surfaces ([2, 17, 19, 27, 39]) Complex compounds such as methylene blue, rose bengal (a.k.a. red food dye 105) and even riboflavin (a.k.a vitamin B2) can function as sensitizers to produce singlet oxygen [15, 24, 50]
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