We report a photonic approach for selective inactivation of viruses with a near-infrared subpicosecond laser. We demonstrate that this method can selectively inactivate viral particles ranging from nonpathogenic viruses such as the M13 bacteriophage and the tobacco mosaic virus to pathogenic viruses such as the human papillomavirus and the human immunodeficiency virus (HIV). At the same time, sensitive materials such as human Jurkat T cells, human red blood cells, and mouse dendritic cells remain unharmed. The laser technology targets the global mechanical properties of the viral protein shell, making it relatively insensitive to the local genetic mutation in the target viruses. As a result, the approach can inactivate both the wild and mutated strains of viruses. This intriguing advantage is particularly important in the treatment of diseases involving rapidly mutating viral species such as HIV. Our photonic approach could be used for the disinfection of viral pathogens in blood products and for the treatment of blood-borne viral diseases in the clinic.
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.
We use different theoretical approaches to demonstrate the qualitative and quantitative understanding of coherent electron tunneling transport through several organic molecules. Molecules that we consider are phenylenevinylene oligomer (OPV5), carotene, dithienylethene, and xyxyldithiol. The complex bandstructure technique is useful for molecules that have repeating units, and is used here to make estimates of the conductance and its dependence on molecular length for OPV5 and for carotene (in a charge state). For molecules of a general shape, such as that of the photoswitching dithienylethenes, we use Landauer theory to predict the I-V properties. The same analysis is used to study the conductance of xyxyldithiol molecules that are deformed by stretching as in AFM pulling experiments.
We have experimentally proven the Cerenkov generation of optical phonons by drifting electrons in a semiconductor. We observe an instability of the polar optical phonons in nanoscale semiconductors that occurs when electrons are accelerated to very high velocities by intense electric fields. The instability is observed when the electron drift velocity is larger than the phase velocity of optical phonons and rather resembles a “sonic-boom” for optical phonons. The effect is demonstrated in p-i-n semiconductor nanostructures by suing subpicosecond Raman spectroscopy. We suggest that the observed phenomena will have enormous impact on the carrier dynamics in nanoscale semiconductor devices.
Electric field-induced transient hole transport in an Al0.3Ga0.7As-based p-i-n nanostructure has been studied by picosecond Raman spectroscopy at T=300K. Our experimental results demonstrate that at T=300K, for a 5-ps excitation laser pulse and a hole density of nhapproximately equals 5x1017cm-3, transient hole drift velocity increases from zero to approximately equals (3+/- 0.7)x106cm/sec when the applied electric field intensity increases from E=0 to 15 kV/cm. The transient hole drift velocity then becomes saturated at approximately equals (8+/- 0.8)x106cm/sec for the applied electric field intensity of E>=25 kV/cm and up to 65 kV/cm.
Electric-field-induced non-equilibrium carrier distributions in GaAs-based p-i-n nanostructure semiconductors has been studied by transient Raman spectroscopy on a picosecond time scale and at T approximately equals 80 K. For an injected carrier density of n approximately equals 2.2 X 1018 cm-3 and electric field intensity E equals 25 KV/cm, the drift velocity of electrons as high as Vd equals 2.5 X 107 cm/sec was observed. We demonstrate in this work that time-resolved Raman spectroscopy is a feasible technique to interrogate both ballistic transport and velocity overshoot phenomena in nanostructure semiconductors.
We report a high-resolution resonance Raman study of C60 films. We identify several peaks whose frequencies are in good agreement with the predictions of a first-principles quantum molecular dynamics calculation for an isolated C60 molecule having icosahedral symmetry. On the other hand, the depolarization ratios for most Raman peaks, some fine- structure features observed with high resolution, and the resonance photon energies suggest solid-state effects or the existence of C60 isomers of lower symmetry
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