Innovative label-free microspectroscopy, which can simultaneously collect Brillouin and Raman signals, is used to characterize the viscoelastic properties and chemical composition of living cells with sub-micrometric resolution. The unprecedented statistical accuracy of the data combined with the high-frequency resolution and the high contrast of the recently built experimental setup permits the study of single living cells immersed in their buffer solution by contactless measurements. The Brillouin signal is deconvoluted in the buffer and the cell components, thereby revealing the mechanical heterogeneity inside the cell. In particular, a 20% increase is observed in the elastic modulus passing from the plasmatic membrane to the nucleus as distinguished by comparison with the Raman spectroscopic marker. Brillouin line shape analysis is even more relevant for the comparison of cells under physiological and pathological conditions. Following oncogene expression, cells show an overall reduction in the elastic modulus (15%) and apparent viscosity (50%). In a proof-of-principle experiment, the ability of this spectroscopic technique to characterize subcellular compartments and distinguish cell status was successfully tested. The results strongly support the future application of this technique for fundamental issues in the biomedical field.

Brillouin and Raman scattering spectroscopy are established techniques for the nondestructive contactless and label-free readout of mechanical, chemical and structural properties of condensed matter. Brillouin-Raman investigations currently require separate measurements and a site-matching approach to obtain complementary information from a sample.Here we demonstrate a new concept of fully scanning multimodal micro-spectroscopy for simultaneous detection of Brillouin and Raman light scattering in an exceptionally wide spectral range, from fractions of GHz to hundreds of THz. It yields an unprecedented 150 dB contrast, which is especially important for the analysis of opaque or turbid media such as biomedical samples, and a spatial resolution on sub-cellular scale. We report the first applications of this new multimodal method to a range of systems, from a single cell to the fast reaction kinetics of a curing process, and the mechano-chemical mapping of highly scattering biological samples.

An integrated experimental approach, based on inelastic light-scattering techniques, has been here employed for a multilength scale characterization of networking properties of cyclodextrin nanosponges, a new class of cross-linked polymeric materials built up from natural oligosaccharides cyclodextrins. By using Raman and Brillouin scattering experiments, we performed a detailed inspection of the vibrational dynamics of these polymers over a wide frequency window ranging from gigahertz to terahertz, with the aim of providing physical descriptors correlated to the cross-linking degree and elastic properties of the material. The results seem to suggest that the stiffness of cross-linked polymers can be successfully tuned by acting on the type and the relative amount of the cross-linker during the synthesis of a polymer matrix, predicting and controlling their swelling and entrapment properties. The proposed experimental approach is a useful tool for investigating the structural and physicochemical properties of polymeric network systems.

We report measurements of the sound attenuation coefficient in vitreous silica, for sound waves of wavelength between 50 and 80 nm, performed with the new inelastic UV light scattering technique. These data indicate that in silica glass a crossover between a temperature-dependent (at low frequency) and a temperature-independent (at high frequency) acoustic attenuation mechanism occurs at Q 0:15 nm ÿ1 . The absence of any signature in the static structure factor at this Q value suggests that the observed crossover should be associated with local elastic constant fluctuations. DOI: 10.1103/PhysRevLett.97.035501 PACS numbers: 61.43.Fs, 63.50.+x The sound attenuation in disordered materials and its frequency and wavelength dependence are the result of the interplay between two physical mechanisms: one is due to the anharmonicity of the interparticle interactions, and the other to the structural disorder.The anharmonic attenuation of an acoustic sound wave, identified by its wavelength , frequency , and wave vector Q 2 = , is characterized by a specific, temperature-dependent, relaxation time r [1]. At low frequency (! r < 1) this process dominates the sound absorption through mechanisms such as, e.g., the Akhiezer mechanism [2,3]. Accordingly, the sound attenuation coefficient, as measured by the broadening ÿ of the Brillouin peak in the dynamic structure factor S Q; ! , scales as ! 2 and Q 2 . At high frequency ÿ! r > 1, i.e., Q > Q r 1=v r , where v is the sound velocity, the anharmonic attenuation becomes frequency independent [1][2][3].The sound attenuation associated with topological disorder gives rise to a steeper Q dependence of ÿ Q . If Rayleigh scattering is responsible for this attenuation, ÿ / Q 4 is expected for wavelengths larger than the typical defects size 2 =Q R . For Q > Q R , when the Rayleigh scattering regime is abandoned, one expects that ÿ Q is no longer / Q 4 . Experimentally, for Q larger than 1 nm ÿ1 , all glasses studied so far show ÿ / Q x , with x very close to 2 [4,5].This scenario can be summarized by a three-regime behavior of ÿ Q : (i) at low Q, ÿ Q is determined by anharmonic processes, and ÿ Q / Q 2 up to a first (temperature-dependent) crossover Q r 1=v r ; (ii) an intermediate regime, where the Q dependence of ÿ Q is determined by the system dependent strengths of anharmonicity and structural disorder processes; (iii) a high-Q regime, where ÿ Q is determined by the topological disorder and ÿ Q / Q 2 with a temperature-independent coefficient. This picture is highly debated because it critically depends on the location of Q r and Q R in different glasses. In densified v-SiO 2 , for example, the crossover Q R has been hypothesized to be around 2 nm ÿ1 [6].In the most studied case of vitreous silica, similarly to what happens in many other glasses, both Q r and Q R belong to a Q region which is not directly accessed by traditional scattering probes. In the case of v-SiO 2 , clear evidence is reported for the low-and high-Q quadratic behaviors of ÿ Q , using Brillouin light scat...

Raman-scattering measurements are used to follow the modification of the vibrational density of states in a reactive epoxy-amine mixture during isothermal polymerization. Combining them with Brillouin light and inelastic x-ray scattering measurements, we analyze the variations of the boson peak and of the Debye level while the system changes from liquid to glass upon increasing the number of covalent bonds among the constituent molecules. The shift and intensity variation of the boson peak are explained by the modification of the elastic properties throughout the reaction, and a master curve for the boson peak can therefore be obtained. Surprisingly, bond-induced modifications of the structure do not affect this master curve.

The dynamic structure factor, S(Q, ω), of vitreous silica, has been measured by inelastic X-ray scattering in the exchanged wavevector (Q) region Q=4÷16.5 nm −1 and up to energies ω=115 meV in the Stokes side. The unprecedented statistical accuracy in such an extended energy range allows to accurately determine the longitudinal current spectra, and the energies of the vibrational excitations. The simultaneous observation of two excitations in the acoustic region, and the persistence of propagating sound waves up to Q values comparable with the (pseudo-)Brillouin zone edge, allow to observe a positive dispersion in the generalized sound velocity that, around Q≈5 nm −1 , varies from ≈6500 to ≈9000 m/s: this phenomenon was never experimentally observed in a glass.

Raman, Brillouin light, and x-ray scattering measurements have been carried out to characterize the low-frequency vibrational dynamics of the SiO(2) glass as function of its density. The obtained results demonstrate that while the distribution of the low-frequency states in the boson peak range is conserved under densification, these modes do not shift as a function of density as the acoustic modes do. The clear difference between the behavior of the vibrational states in the Boson peak range and that of the acoustic modes, could be explained considering the contribution of specific nonacoustic modes (tetrahedra rotation

The study of the effects of the density variations on the vibrational dynamics in vitreous silica is presented. A detailed analysis of the dynamical structure factor, as well as of the current spectra, allows the identification of a flattened transverse branch which is highly sensitive to the density variations. The experimental variations on the intensity and position of the Boson Peak (BP) in v-SiO2 as a function of density are reproduced and interpreted as being due to the shift and disappearance of the latter band. The BP itself is found to correspond to the lower energy tail of the excess states due to the piling up of vibrational modes at energies corresponding to the flattening of the transverse branch.