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.

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.

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.

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.

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.