Ultrafast structural dynamics in electronically excited many-body systems

This thesis reports on results of three different experiments of photo-induced structural dynamics in the condensed phase, investigated by time-resolved pump-probe spectroscopy with femtosecond time-resolution. In the first part, we address the ultrafast dynamics of a quantum solid : crystalline hydrogen. This is accomplished by optical excitation of a dopant molecule, Nitric Oxide (NO), to a large orbital Rydberg state, which leads to a bubble-like expansion of the species surrounding the impurity. The dynamics is directly inferred from the time-resolved data, and compared with the results of molecular dynamics simulations. We report the presence of three time-scales in the structural relaxation mechanism: the first 200 fs are associated with the ultrafast inertial expansion of the first shell of lattice neighbors of NO. During the successive 0.6 ps, as the interactions between the molecules of the first and of the successive shells increase, we observe a progressive slowing-down of the bubble expansion. The third timescale (~ 10 ps) is interpreted as a slow structural re-organization around the impurity center. No differences were observed between the dynamics of normal- and para-hydrogen crystals, justifying the simplified model we use to interpret the data, which ignores all internal degrees of freedom of the host molecules. The molecular dynamics simulations reproduce fairly well the static and dynamic features of the experiment. In line with the measurements, they indicate that the quantum nature of the host medium plays no role in the initial ultrafast expansion of the bubble. In the second part, we present the results of our study on the photo-physics of triangular-shaped silver nanoparticles upon intraband excitation of the conduction electrons. The picosecond dynamics is dominated by periodic shifts of the surface plasmon resonance, associated with the size oscillations of the particles, triggered by impulsive lattice heating by the laser pulse. The oscillation period compares very well with the lowest totally symmetric vibrational frequency of a triangular-plate, which we calculated improving an existing elastodynamic model. We propose an explanation for the unusual phase behavior of the oscillations, based upon the non-spherical shape, and size-inhomogeneity of the sample. Taking into account these effects, we are able to reproduce spectrally and temporally our data. In the last part, we present a comparative study of the ligand dynamics in heme proteins. We studied the photo-induced spectroscopic changes in the ferric CN complexes of Myoglobin and Hemoglobin I upon photo-excitation of the porphyrin ring to a low-lying electronic state (Soret), monitoring the UV-visible region of the Soret band, and the mid-infrared region of the fundamental C=N vibrational stretch. The transient response in the UV-visible spectral region does not depend on the heme pocket environment, and is very similar to that known for ferrous proteins. The infrared data on the MbC=N stretch vibration provides a direct measure for the return of population to the ligated electronic (and vibrational) ground state with a 3 ps time constant. In addition, the CN stretch frequency is sensitive to the excitation of low frequency heme modes, and yields independent information about vibrational cooling, which occurs on the same timescale. The similarity between ferrous and ferric hemes rules out the charge transfer processes commonly invoked to explain the ligand dissociation in the former

Editorial: Use of 3D Models in Drug Development and Precision Medicine - Advances and Outlook

Three-dimensional (3D) in vitro models in the drug development pipeline can help selecting the most promising and safe drug candidates at the pre-clinical stage, prior to clinical trials, reducing and sometimes even replacing animal studies in accordance with the “3Rs (Reduction, Refinement and Replacement) principle”

Frequency Doubling Nanocrystals for Cancer Theranostics

A novel bio-photonics approach based on the nonlinear optical process of second harmonic generation by non-centrosymmetric nanoparticles is presented and demonstrated on malignant human cell lines. The proposed method allows to directly interact with DNA in absence of photosensitizing molecules, to enable independent imaging and therapeutic modalities switching between the two modes of operation by simply tuning the excitation laser wavelength, and to avoid any risk of spontaneous activation by any natural or artificial light source.Comment: 16 pages, 7 figure

Bifeo3 Harmonic Nanoparticle (Bfo-Hnps) Use for the Stem Cell Tracking: Labeling Investigation by Non Linear Microscopy and X-Ray Fluorescence

Duchenne Muscular Dystrophy is the most common form of degenerative muscle disease; currently, there is no effective treatment. In 2011, our group showed that an adult stem cell population (MuStem) isolated from healthy dog skeletal muscle induces long-term muscle repair and striking clinical efficacy after its systemic delivery in clinically relevant dystrophic dog. During last years, our group isolated the human counterparts (hMuStem) [1]. To achieve the full therapeutic potential of the hMuStem cells, their homing process, survival and engraftment post-transplantation must be clearly understood. BiFeO3 harmonic nanoparticles (BFO-HNPs) were used as probes for the hMuStem cell tracking [2]. We demonstrate the possibility of identifying <100 nm BFO-HNPs in depth of muscle tissue at more than 1 mm from the surface by multiphoton microscopy. Based on this successful assessment, we monitor over 14 days any modification on proliferation and morphology features of the hMuStem cells upon exposure to BFO-HNPs revealing their high biocompatibility. To complete these studies, the stability of BFO-HNPs was followed in the labeled hMuStem cells by investigation of Bi and Fe X-ray fluorescence mapping on both Nanoscopium (Soleil, Gif-sur-Yvette, France) and ID16B (ESRF, Grenoble, France) beamlines. In this work, correlation between non-linear microscopy and X-Ray fluorescence was done. Bi and Fe X-Ray fluorescence allowed us to localize with high resolution the BFO-HNPs in the labeled hMuStem cells and the variation of Bi/Fe ratio was analyzed to detect possible dissociation of the nanoparticles in the labeled cells

Time-Resolved Visible and Infrared Study of the Cyano Complexes of Myoglobin and of Hemoglobin I from Lucina pectinata

AbstractThe dynamics of the ferric CN complexes of the heme proteins Myoglobin and Hemoglobin I from the clam Lucina pectinata upon Soret band excitation is monitored using infrared and broad band visible pump-probe spectroscopy. The transient response in the UV-vis spectral region does not depend on the heme pocket environment and is very similar to that known for ferrous proteins. The main feature is an instantaneous, broad, short-lived absorption signal that develops into a narrower red-shifted Soret band. Significant transient absorption is also observed in the 360–390nm range. At all probe wavelengths the signal decays to zero with a longest time constant of 3.6ps. The infrared data on MbCN reveal a bleaching of the C≡N stretch vibration of the heme-bound ligand, and the formation of a five-times weaker transient absorption band, 28cm−1 lower in energy, within the time resolution of the experiment. The MbC≡N stretch vibration provides a direct measure for the return of population to the ligated electronic (and vibrational) ground state with a 3–4ps time constant. In addition, the CN-stretch frequency is sensitive to the excitation of low frequency heme modes, and yields independent information about vibrational cooling, which occurs on the same timescale

Simultaneous Multi-Harmonic Imaging of Nanoparticles in Tissues for Increased Selectivity

We investigate the use of Bismuth Ferrite (BFO) nanoparticles for tumor tissue labelling in combination with infrared multi-photon excitation at 1250 nm. We report the efficient and simultaneous generation of second and third harmonic by the nanoparticles. On this basis, we set up a novel imaging protocol based on the co-localization of the two harmonic signals and demonstrate its benefits in terms of increased selectivity against endogenous background sources in tissue samples. Finally, we discuss the use of BFO nanoparticles as mapping reference structures for correlative light-electron microscopy.Comment: 19 pages, 6 figure

Circadian Clocks in Mouse and Human CD4+ T Cells

Though it has been shown that immunological functions of CD4+ T cells are time of day-dependent, the underlying molecular mechanisms remain largely obscure. To address the question whether T cells themselves harbor a functional clock driving circadian rhythms of immune function, we analyzed clock gene expression by qPCR in unstimulated CD4+ T cells and immune responses of PMA/ionomycin stimulated CD4+ T cells by FACS analysis purified from blood of healthy subjects at different time points throughout the day. Molecular clock as well as immune function was further analyzed in unstimulated T cells which were cultured in serum-free medium with circadian clock reporter systems. We found robust rhythms of clock gene expression as well as, after stimulation, IL-2, IL-4, IFN-γ production and CD40L expression in freshly isolated CD4+ T cells. Further analysis of IFN-γ and CD40L in cultivated T cells revealed that these parameters remain rhythmic in vitro. Moreover, circadian luciferase reporter activity in CD4+ T cells and in thymic sections from PER2::LUCIFERASE reporter mice suggest that endogenous T cell clock rhythms are self-sustained under constant culture conditions. Microarray analysis of stimulated CD4+ T cell cultures revealed regulation of the NF-κB pathway as a candidate mechanism mediating circadian immune responses. Collectively, these data demonstrate for the first time that CD4+ T cell responses are regulated by an intrinsic cellular circadian oscillator capable of driving rhythmic CD4+ T cell immune responses

Nonlinear Nanomedecine: Harmonic Nanoparticles toward Targeted Diagnosis and Therapy

Harmonic nanoparticles were first introduced in 2006 as biomarkers for nonlinear imaging. This review provides a general explanation of the physical mechanism at the basis of this novel approach, highlighting its benefits and the complementarity to fluorescent/luminescent labels. A series of application examples from the very recent literature are reported, ranging from in vitro cell monitoring to the first proofs of in vivo imaging and rare event detection in physiological fluids