We have investigated the factors that affect the virucidal activity of methylene blue (MB) photosensitization. The M13 bacteriophage was more rapidly inactivated at higher temperatures (6° < 24° < 38°). Rate constants for inactivation were 0.072, 0.139 and 0.260 (log 10 inactivation)/(J/cm 2 ) at 6°, 24° and 38°, respectively. On the other hand, dye penetration into virus particles, which was monitored by the fluorescence of YOYO- 1, was unchanged with incubation temperature. These data suggest that temperature dependency of M13 inactivation was due to factors other than dye permeability. The pH of the virus suspension also affected the rate of M13 inactivation by MB. The M13 bacteriophage was inactivated faster in basic suspensions and slower in acidic suspensions compared with neutral buffers. These results suggest that temperature and pH are factors that influence the extent of MB photosensitization, and hence, the control of these factors will be necessary for MB phototreatment of plasma products in transfusion medicine.
H. Abe, S. J. Wagner, M. Kuwabara, N. Kamo, K. Ikebuchi, S. Sekiguchi, "Factors Affecting M13 Bacteriophage Inactivation by Methylene Blue Photosensitization," Photochem Photobiol,65, 873 (97).