Ref HAL: hal-04170736_v1
Ref Arxiv: 2306.17640
Ref INSPIRE: 2673548
DOI: 10.1103/PhysRevA.108.062811
Ref. & Cit.: NASA ADS
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We investigate the Casimir-Lifshitz force (CLF) between two identical graphene strip gratings, laid on finite dielectric substrate. By using the scattering matrix (S-matrix) approach derived from the Fourier Modal Method with local basis functions (FMM-LBF), we fully take into account the high-order electromagnetic diffractions, the multiple scattering and the exact 2D feature of the graphene strips. We show that the non-additivity, which is one of the most interesting features of the CLF in general, is significantly high and can be modulated in situ without any change in the actual material geometry, by varying the graphene chemical potential. This study can open the deeper experimental exploration of the non-additive features of CLF with micro- or nano-electromechanical graphene-based systems.

Ref HAL: hal-04165964_v1
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Spinal cord injury (SCI) is a dramatic disease leading to severe motor, sensitive and autonomic impairments. After the injury, the axonal regeneration is partly inhibited by the glial scar, acting as a physical and chemical barrier[1]. The scarring process involves microglia, astrocytes, and extracellular matrix components, such as collagen, composing the fibrotic part of the scar[2]. To investigate the role of collagen and microglia, we used a multimodal label-free imaging approach combining multiphoton and atomic force microscopies. The second harmonic generation signal exhibited by fibrillar collagen-I enables specifically monitoring it as a biomarker of the lesion. An increase in collagen density and the formation of more curved fibers over time after SCI are observed. Whereas 2-photon excitation microscopy (2PEF) showed the appearance and activation of microglia over millimeters in length near the injured area. Nanomechanical investigations revealed a noticeable hardening of the injured area, correlated with collagen fibers’ development. Additionally, we observed that inhibition of microglial proliferation by oral administration of GW2580 decreased the collagen density at the injured area. These observations indicate the concomitance of relevant structural and mechanical modifications during the fibrotic scar evolution.

Ref HAL: hal-04165248_v1
Ref Arxiv: 2212.05582
DOI: 10.1038/s41467-023-39948-7
Ref. & Cit.: NASA ADS
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Abstract Structural defects control the kinetic, thermodynamic and mechanical properties of glasses. For instance, rare quantum tunneling two-level systems (TLS) govern the physics of glasses at very low temperature. Due to their extremely low density, it is very hard to directly identify them in computer simulations. We introduce a machine learning approach to efficiently explore the potential energy landscape of glass models and identify desired classes of defects. We focus in particular on TLS and we design an algorithm that is able to rapidly predict the quantum splitting between any two amorphous configurations produced by classical simulations. This in turn allows us to shift the computational effort towards the collection and identification of a larger number of TLS, rather than the useless characterization of non-tunneling defects which are much more abundant. Finally, we interpret our machine learning model to understand how TLS are identified and characterized, thus giving direct physical insight into their microscopic nature.

Ref HAL: hal-04163438_v1
DOI: 10.1063/5.0155821
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Nucleotides are organic compounds consisting of a phosphate group, a nitrogenous base, namely adenine (A), thymine (T), cytosine (C), or guanine (G), and a sugar, here deoxyribose. The magnitude of the first hyperpolarizability  of these four DNA nucleotides were determined in aqueous solution with the nonlinear optical technique of Hyper Rayleigh Scattering under non resonant conditions at the fundamental wavelength of 800 nm. The smallest value is found to be esu for thymidine-5'-monophosphate and the highest is esu for 2'-guanosine-5'-monophosphate. Polarization resolved studies were also performed to question the symmetry of the first hyperpolarizability tensor and access the ratio of some elements of the first hyperpolarizability tensor.

Ref HAL: hal-04136134_v1
DOI: 10.1021/acs.jpcc.3c01713
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Incoherent Second Harmonic Generation (SHG) from goldnanoparticles,also known as hyper-Rayleigh scattering (HRS), is proposed as a sensingmethod for copper(II) ions. As opposed to colorimetry-based methodsrelying on the shift of the localized surface plasmon resonance withthe copper(II) concentration, which effectively scales with the nanoparticlevolume due to the origin of the absorption phenomenon, SHG relieson the surface origin of the response for sufficiently small nanoparticles.As a result, differences can be expected that could be potentiallyturned into advantages such as improved Limit of Detection and shorterdetection response time. The present study demonstrates that the SHGlight scattered from aqueous suspensions of gold nanoparticles inthe presence of copper(II) ions is indeed sensitive to the copper(II)ion concentration changes. A first approach based on intensity changesshows that there is a competition between the formation of corona-likestructures centered around the gold nanoparticles due to the ionicinteraction between copper(II) ions and the negatively charged citrate-coatednanoparticles on one side and, on the other side, aggregation of nanoparticlesdue to charge screening as the copper(II) bromide concentration increases.The former process dominates at low copper(II) concentrations, whereasaggregation takes over above 1 mM copper(II) concentrations. A figureof merit is thus designed in order to provide a quantitative assessmentof the sensing performance. In a further analysis, a polarizationresolved study of the SHG light scattered from the gold nanoparticlesallows the determination of other figures of merit. The first onebased on the depolarization ratio seems appropriate, as it is basedon the surface origin of the SHG response from gold nanoparticles,whereas the second one, based on the retardation parameter, shouldnot perform better than those derived from colorimetry methods.

Ref HAL: hal-04116979_v1
DOI: 10.1039/D3CP02113K
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Disentangling Second Harmonic Generation (SHG) and Multiphoton Excited Photoluminescence (MEPL) signals in microscopy experiments is not an easy task. Two methods have been so far proposed based either on a time domain or a spectral domain analysis of the collected signals. In this report, a new method based on polarization discrimination is proposed to separate these SHG and MEPL contributions. In order to demonstrate this operation, intensity depth profiles are recorded for an anatase titanium dioxide powder consisting of 22 nm diameter nanoparticles using ultrafast femtosecond laser excitation. Polarization analysis of these intensity depth profiles is therefore performed and demonstrate a polarization angle shift for the SHG intensity contribution as compared to the MEPL one, allowing for the discrimination of the two SHG and MEPL contributions. The fundamental beam is set at two different wavelengths in order to provide a SHG photon energy above and below the anatase TiO 2 band-gap of 3.2 eV, leading to a change in the relative intensity weight and a spectral shift between the SHG and MEPL contributions. This operation further demonstrates the potential of the method when the spectral domain disentangling cannot be performed. SHG profiles are by far narrower than those of MEPL. This study where both SHG and MEPL contributions are observed offers perspectives in photonics of powder materials as the different origin and properties of the two processes can be separated.

Ref HAL: hal-03996959_v1
PMID 36747263
DOI: 10.1186/s12951-023-01797-3
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Abstract Intracellular drug delivery is at the heart of many diagnosis procedures and a key step in gene therapy. Research has been conducted to bypass cell barriers for controlled intracellular drug release and made consistent progress. However, state-of-the-art techniques based on non-viral carriers or physical methods suffer several drawbacks, including limited delivery yield, low throughput or low viability, which are key parameters in therapeutics, diagnostics and drug delivery. Nevertheless, gold nanoparticle (AuNP) mediated photoporation has stood out as a promising approach to permeabilize cell membranes through laser induced Vapour NanoBubble (VNB) generation, allowing the influx of external cargo molecules into cells. However, its use as a transfection technology for the genetic manipulation of therapeutic cells is hindered by the presence of non-degradable gold nanoparticles. Here, we report a new optofluidic method bringing gold nanoparticles in close proximity to cells for photoporation, while avoiding direct contact with cells by taking advantage of hydrodynamic focusing in a multi-flow device. Cells were successfully photoporated with $$\sim {70}{\%}$$ ∼ 70 % efficiency with no significant reduction in cell viability at a throughput ranging from $$10^3$$ 10 3 to $$10^4~\text {cells}~{\hbox {min}^{-1}}$$ 10 4 cells min - 1 . This optofluidic approach provides prospects of translating photoporation from an R &D setting to clinical use for producing genetically engineered therapeutic cells.