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Register a new userStimulated low-frequency Raman scattering in albumin
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Added by
Nikolay Tcherniega V.
Publication date
2019
fields
Physics
and research's language is
English
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Stimulated low-frequency Raman scattering can give essential information about the elastic properties of different nanoparticles systems, in particular, biological nanostructures. In the present study, low-frequency vibrational modes in human and bovine serum albumin were for the first time investigated using stimulated low-frequency Raman scattering. Stimulated low-frequency Raman scattering frequency shifts, corresponding to acoustic eigenfrequencies of the sample, were registered by Fabri-Perot interferometers. Conversion efficiency, threshold and set of eigenfrequencies were also measured. Stimulated low-frequency Raman scattering can be applied for biological objects identification and impact on them.
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Laser pulses interaction with tobacco mosaic virus (TMV) in Tris-HCl pH7.5 buffer and in water has been investigated. 20 ns ruby laser pulses have been used for excitation. Spectrum of the light passing through the sample was registered with the help of Fabri-Perot interferometer. In the case of TMV in water we observed in the spectrum only one line of the exciting laser light, for TMV in Tris-HCl pH7.5 buffer second line appeared, corresponding to the stimulated low-frequency Raman scattering (SLFRS) on the breathing radial mode of TMV. SLFRS frequency shift by 2 cm-1, (60 GHz), conversion efficiency and threshold are measured for the first time to the best of our knowledge.
A simple physical mechanism of stimulated light scattering on nanoscale objects in water suspension similar to Langmuir waves mechanism in plasma is proposed. The proposed mechanism is based on a dipole interaction between the light wave and the non-compensated electrical charge that inevitably exists on a nanoscale object (a virus or a nanoparticle) in water environment. The experimental data for tobacco mosaic virus and polystyrene nanospheres are presented to support the suggested physical mechanism. It has been demonstrated that stimulated amplification spectral line frequencies observed experimentally are well explained by the suggested mechanism. In particular, the absence of lower frequency lines and the generation lines shift when changing the pH are due to ion friction appearing in the ionic solution environment. The selection rules observed experimentally also confirm the dipole interaction type. It has been shown that microwave radiation on nanoscale object acoustic vibrations frequency should appear under such scattering conditions. We demonstrate that such conditions also allow for local selective heating of nanoscale objects by dozens to hundreds degrees K. This effect is controlled by the optical irradiation parameters and can be used for affecting selectively certain types of viruses.
Stimulated Raman scattering (SRS) in plasma in a non-eigenmode regime is studied theoretically and numerically. Different from normal SRS with the eigen electrostatic mode excited, the non-eigenmode SRS is developed at plasma density $n_e>0.25n_c$ when the laser amplitude is larger than a certain threshold. To satisfy the phase-matching conditions of frequency and wavenumber, the excited electrostatic mode has a constant frequency around half of the incident light frequency $omega_0/2$, which is no longer the eigenmode of electron plasma wave $omega_{pe}$. Both the scattered light and the electrostatic wave are trapped in plasma with their group velocities being zero. Super hot electrons are produced by the non-eigen electrostatic wave. Our theoretical model is validated by particle-in-cell simulations. The SRS driven in this non-eigenmode regime may play a considerable role in the experiments of laser plasma interactions as long as the laser intensity is higher than $10^{15}$W/cm$^2$.
The interaction between ultrashort light pulses and non-absorbing materials is dominated by Impulsive Stimulated Raman Scattering (ISRS). The description of ISRS in the context of pump&probe experiments is based on effective classical models describing the interaction between the phonon and pulsed electromagnetic fields. Here we report a theoretical description of ISRS where we do not make any semi-classical approximation and we treat both photonic and phononic degrees of freedom at the quantum level. The results of the quantum model are compared with semiclassical results and validated by means of spectrally resolved pump&probe measurements on $alpha$-quartz.
Rapid antimicrobial susceptibility testing (AST) is urgently needed for treating infections with correct antibiotics and slowing down the emergence of antibiotic-resistant bacteria. Here, we report a phenotypic platform that rapidly produces AST results by femtosecond stimulated Raman scattering imaging of deuterium oxide (D2O) metabolism. Metabolic incorporation of D2O into biomass in a single bacterium is probed in as short as 10 minutes after culture in 70% D2O medium, the fastest among current technologies. Single-cell metabolism inactivation concentration (SC-MIC) is obtained in less than 2.5 hours from colony to results. The SC-MIC results of 37 sets of samples, which include 8 major bacterial species and 14 different antibiotics often encountered in clinic, are validated by standard minimal inhibitory concentration blindly measured via broth microdilution. Towards clinical translation, SRS imaging of D2O metabolic incorporation and SC-MIC determination after 1-h antibiotics treatment and 30-minutes mixture of D2O and antibiotics incubation of bacteria in urine or whole blood is demonstrated.
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