Studies of inactivation of encephalomyocarditis virus, M13 bacteriophage, and Salmonella typhimurium by using a visible femtosecond laser: insight into the possible inactivation mechanisms

We report experimental results on the inactivation of encephalomyocarditis virus, M13 bacteriophage, and Salmonella typhimurium by a visible femtosecond laser. Our results suggest that inactivation of virus and bacterium by a visible femtosecond laser involves completely different mechanisms. Inactivation of viruses by a visible femtosecond laser involves the breaking of hydrogen∕hydrophobic bonds or the separation of the weak protein links in the protein shell of a viral particle. In contrast, inactivation of bacteria is related to the damage of their DNAs due to irradiation of a visible femtosecond laser. Possible mechanisms for the inactivation of viruses and bacteria are discussed.

Studies of electron-phonon and phonon-phonon interactions in InN using ultrafast Raman spectroscopy

Subpicosecond time-resolved Raman spectroscopy has been employed to investigate electron-phonon interactions and phonon dynamics in InN. The electron-longitudinal optical phonon scattering rate and the decay dynamics of longitudinal optical phonons in InN have been directly measured. Our results indicate that hot-phonon effects can play an important role in the electron relaxation and transport in InN. The carrier dependence of the lifetime of the longitudinal optical phonons has also been measured. The results suggest that more theoretical work is needed to account for the dependence of the lifetime of longitudinal optical phonons on the photoexcited carrier density.

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

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.

Geldanamycin inhibits hemorrhage-induced increases in caspase-3 activity: role of inducible nitric oxide synthase

Hemorrhage has been shown to increase inducible nitric oxide synthase (iNOS) and deplete ATP levels in tissues and geldanamycin limits both processes. Moreover, it is evident that inhibition of iNOS reduces caspase-3 and increases survival. Thus we sought to identify the molecular events responsible for the beneficial effect of geldanamycin. Hemorrhage in mice significantly increased caspase-3 activity and protein while treatment with geldanamycin significantly limited these increases. Similarly, geldanamycin inhibited increases in proteins forming the apoptosome (a complex of caspase-9, cytochrome c, and Apaf-1). Modulation of the expression of iNOS by iNOS gene transfection or siRNA treatment demonstrated that the level of iNOS correlates with caspase-3 activity. Our data indicate that geldanamycin limits caspase-3 expression and protects from organ injury by suppressing iNOS expression and apoptosome formation. Geldanamycin, therefore, may prove useful as an adjuvant in fluids used to treat patients suffering blood loss.

Probing the low-frequency vibrational modes of viruses with Raman scattering--bacteriophage M13 in water

Raman spectroscopy is used to study low-wave-number (</=20 cm(-1)) acoustic vibrations of the M13 phage. A well-defined Raman line is observed at around 8.5 cm(-1). The experimental results are compared with theoretical calculations based on an elastic continuum model and appropriate Raman selection rules derived from a bond polarizability model. The observed Raman mode is shown to belong to one of the Raman-active axial modes of the M13 phage protein coat. It is expected that the detection and characterization of this low-frequency vibrational mode can be used for applications in biomedical nanotechnology such as for monitoring the process of virus functionalization and self-assembly.

Biology of hypoxia

Hypoxia is an often seen problem resulting from conditions such as ischemia, hemorrhage, stroke, premature birth, and other cardiovascular difficulties. To find useful remedies that are capable of ameliorating its casualty is an essential effort. Although the underlying mechanisms of the hypoxia-induce injury and cell death are still not fully understood, it has been shown that hypoxia induces nitric oxide (NO) overproduction and inducible nitric oxide synthase (iNOS) overexpression that play important roles in producing injury including increases in polymorphonuclear neutrophils (PMN) infiltration to injured tissues and leukotriene B4 (LTB4) generation. Moreover, it has been evident that transcription factors responsible for iNOS expression are also altered by hypoxia. Hypoxia also increases intracellular Ca2+ concentration, tumor necrosis factor-alpha, lipid peroxidation, prostaglandin E2 production, activity of caspase-3 and -9, and release of cytochrome c from mitochondria, apoptosis inducible factor, and endonuclease G. However, it has been shown that downregulation of iNOS can limit cell injury caused by hypoxia. In our laboratory, we have found that treatment with either iNOS inhibitors or iNOS siRNA inhibits iNOS expression, reduces lipid peroxidation, apoptosome formation, and cellular caspase-3 activity, preserves cellular ATP levels, and increases cell survival. Therefore, iNOS inhibition may be a novel mechanism for protection from hypoxia-induced injury and cell death.

Observation of the low frequency vibrational modes of bacteriophage M13 in water by Raman spectroscopy

Background

Recently, a technique which departs radically from conventional approaches has been proposed. This novel technique utilizes biological objects such as viruses as nano-templates for the fabrication of nanostructure elements. For example, rod-shaped viruses such as the M13 phage and tobacco mosaic virus have been successfully used as biological templates for the synthesis of semiconductor and metallic nanowires.

Results and discussion

Low wave number (≤ 20 cm^-1) acoustic vibrations of the M13 phage have been studied using Raman spectroscopy. The experimental results are compared with theoretical calculations based on an elastic continuum model and appropriate Raman selection rules derived from a bond polarizability model. The observed Raman mode has been shown to belong to one of the Raman-active axial torsion modes of the M13 phage protein coat.

Conclusion

It is expected that the detection and characterization of this low frequency vibrational mode can be used for applications in nanotechnology such as for monitoring the process of virus functionalization and self-assembly. For example, the differences in Raman spectra can be used to monitor the coating of virus with some other materials and nano-assembly process, such as attaching a carbon nanotube or quantum dots.

Enhancement of band gap emission stimulated by defect loss

Defect radiation has been always considered as the most important loss for an emitter based on band gap emission. Here, we propose a novel approach which goes against this conventional wisdom. Based on the resonance effect between the surface plasmon of metal nanoparticles and defect emission, it is possible to convert the useless defect radiation to the useful excitonic emission with a giant enhancement factor. Through the transfer of the energetic electrons excited by surface plasmon from metal nanoparticles to the conduction band of the emitter, the band gap emission can be greatly enhanced, while the defect emission can be suppressed to noise level.