Gold nanoparticles are widely used in sensing, notably in colorimetry-based methods, where a color change is associated to the Surface Plasmon Resonance peak shift due to a binding event or an environment modification in the vicinity of the nanoparticles. In this work, we explore the sensitivity of the Second Harmonic response from gold nanoparticles of two different diameters as this response stems principally from the nanoparticle surface at small sizes as opposed to the whole volume of the nanoparticle at larger sizes. The origin of this response is therefore different from that involved in the colorimetric response, the latter being of volume origin. Upon addition of Glycerol to an aqueous solution of nanoparticles, Surface Plasmon Resonance peak shifts are first observed but they cannot fully explain the Second Harmonic intensity changes recorded. Hence, in order to gain further insights into the origin of the changes observed in the experimental data, polarization-resolved Second Harmonic measurements are performed. A mechanism where first a modification of the first hyperpolarizability of the nanoparticles due to the presence of glycerol occurs followed by nanoparticle aggregation is then proposed. The potential alternative use of this nonlinear optical method of Second Harmonic scattering for sensing purposes is then discussed in light of a figure of merit proposed to describe the sensing sensitivity observed.

Securing communications over long distances requires bright single photon sources emitting in the telecom band in a well-defined spatial and polarization mode. First, we report our efforts to obtain single photon emission and a Gaussian far-field radiation pattern in the telecom O-band from single quantum dot-nanowires (QD-NWs) monolithically grown on silicon. The InAs/InP QD-NWs were grown on silicon (111) substrates by Vapor-Liquid-Solid assisted solid-source Molecular Beam Epitaxy using In-Au droplets as a catalyst in-situ deposited at 500°C [1]. Low QD-NW density was obtained by a careful control of the In/Au catalyst flux ratio to achieve density <1 NW/μm² [2]. The growth conditions have been tuned (Fig 1.a) to optimize the source brightness and reduce the far-field divergence. The control of the nanowire geometry allows us to demonstrate a Gaussian far field emission profile with an emission angle θ≈30° (Fig 1.c) from a single QD at room temperature in the telecom O-band and the observation of single photon emission with g2(0) = 0.05 (Fig 1.b) at cryogenic temperature [3]. Secondly, we have optimized the growth procedure to achieve InAs/InP QD NWs with an elongated top-view cross-section. Polarization-resolved photoluminescence measurements have revealed a significant influence of the asymmetric shaped NWs on the InAs QD emission polarization with the photons being mainly polarized parallel to the NW long cross section axis [4]. A degree of linear polarization (DLP) up to 91% is obtained, being at the state of the art for the reported DLP values from QD-NWs.\\References:[1] A. Mavel et al, Journal of Crystal Growth, 458 (2017) 96.[2] A. Jaffal et al, Nanotechnology, 31 (2020) 354003.[3] A. Jaffal et al, Nanoscale, 11 (2019) 21847-21855.[4] A. Jaffal et al, Nanoscale, 13 (2021) 16952–16958.

Biomechanical characterization of a fibrinogen–blood hydrogel for human dental pulp regeneration.

Spinal cord injury is a dramatic disease leading to severe motor, sensitive and autonomic impairments. After injury the axonal regeneration is partly inhibited by the glial scar, acting as a physical and chemical barrier. The scarring process involves microglia, astrocytes and extracellular matrix components, such as collagen, con- structing the fibrotic component of the scar. To investigate the role of collagen, we used a multimodal label-free imaging approach combining multiphoton and atomic force microscopy. The second harmonic generation signal exhibited by fibrillar collagen enabled to specifically monitor it as a biomarker of the lesion. An increase in collagen density and the formation of more tortuous fibers over time after injury are observed. Nano-mechanical investigations revealed a noticeable hardening of the injured area, correlated with collagen fibers' formation. These observations indicate the concomitance of important structural and mechanical modifications during the fibrotic scar evolution.

Random granular media may exhibit characteristics more often related to ordered media. In the present work, this feature is observed in the polarized Second Harmonic Generation (SHG) response from reduced iron-doped lithium niobate (LN:Fe) powders, an effect that is not expected due to multiple scattering. Besides, this subsisting order property of the powders can be further controlled using magnetic induction to tailor the SHG response. The samples where characterized employing X-Ray Diffraction (XRD) and confocal Raman Spectroscopy. Their SHG response both in the absence and the presence of an external static magnetic field was then studied as the fundamental beam focus was translated from air into the powder. The SHG intensity polarization state was then studied as a function of the linear polarization of the fundamental beam for different fundamental beam focus depths. These results demonstrate that the SHG properties from LN:Fe powders can be modified through post-thermal treatment in a reducing atmosphere in view of photonic applications.

Concentrated colloidal suspensions and emulsions are amorphous soft solids, widespread in technological and industrial applications and studied as model systems in physics and materials sciences. They are easily fluidized by applying mechanical stress, undergoing a yielding transition that still lacks a unified description. Here we investigate yielding in three classes of repulsive soft solids and find that at the microscopic level, yielding consists of a transition between two distinct dynamical states. We rationalize this by proposing a lattice model with dynamical coupling between neighbouring sites, leading to a unified state diagram for yielding. Employing the analogy with van der Waals phase diagram for real gases, we show that distance from a critical point plays a major role in the emergence of first-order-like versus second-order-like features in yielding, thereby reconciling previously contrasting observations on the nature of the transition.