Nanoindentation based on atomic force microscopy (AFM) can measure the elasticity of biomaterials and cells with high spatial resolution and sensitivity, but relating the data to quantitative mechanical properties depends on information on the local contact, which is unclear in most cases. Here, we demonstrate nonlocal deformation sensing on biorelevant soft matters upon AFM indentation by using nitrogen-vacancy centers in nano-diamonds, providing data for studying both the elasticity and capillarity without requiring detailed knowledge about the local contact. Using fixed HeLa cells for demonstration, we show that the apparent elastic moduli of the cells would have been overestimated if the capillarity was not considered. In addition, we observe that both the elastic moduli and the surface tensions are reduced after depolymerization of the actin cytoskeleton in cells. This work demonstrates that the nanodiamond sensing of nonlocal deformation with nanometer precision is particularly suitable for studying mechanics of soft biorelevant materials.

The mechanics of biological tissuesmainly proceeds from the cell cortex rheology.A direct, explicit link between cortex rheology and tissue rheology remains lacking, yet would be instrumental in understanding how modulations of cortical mechanics may impact tissue mechanical behaviour.Using an ordered geometry built on 3D hexagonal, incompressible cells,we build a mapping relatingthe cortical rheology to the monolayer tissue rheology.Our approach shows that the tissue low frequency elastic modulusis proportional to the rest tension of the cortex,as expected from the physics of liquid foamsas well as of tensegrity structures.A fractional visco-contractile cortex rheologyis predicted to yield a high-frequency fractional visco-elastic monolayer rheology, where such a fractional behaviour has been recently observed experimentally at each scale separately.In particular cases, the mapping may be inverted, allowing toderive from a given tissue rheology the underlying cortex rheology. Interestingly, applying the same approach to a 2D hexagonal tiling fails,which suggests that the 2D character of planar cell cortex-based models may be unsuitable to account for realistic monolayer rheologies.We provide quantitative predictions, amenable to experimental tests through standard perturbation assays ofcortex constituents, and hope to foster new, challenging mechanicalexperiments on cell monolayers.

The key parameter controlling the glass transition of colloidal suspensions is ϕ, the fraction of the sample volume occupied by the particles. Unfortunately, changing ϕ by varying an external parameter, e.g. temperature T as in molecular glass formers, is not possible, unless one uses thermosensitive colloidal particles, like the popular poly(Nisopropylacrylamide) (PNiPAM) microgels. These however have several drawbacks, including high deformability, osmotic deswelling and interpenetration, which complicate their use as a model system to study the colloidal glass transition. Here, we propose a new system consisting of a colloidal suspension of non-deformable spherical silica nanoparticles, in which PNiPAM hydrogel spheres of ∼ 100 − 200 µm size are suspended. These non-colloidal 'mesogels' allow for controlling the sample volume effectively available to the silica nanoparticles and hence their ϕ, thanks to the T-induced change in mesogels volume. Using optical microscopy, we first show that the mesogels retain their ability to change size with T when suspended in Ludox suspensions, similarly as in water. We then show that their size is independent of the sample thermal history, such that a well-defined, reversible relationship between T and ϕ may be established. Finally, we use space-resolved dynamic light scattering to demonstrate that, upon varying T , our system exhibits a broad range of dynamical behaviors across the glass transition and beyond, comparable with those exhibited by a series of distinct silica nanoparticle suspensions of various ϕ.

Carotenoids are conjugated linear molecules built from the repetition of terpene units, which display a large structural diversity in nature. They may, in particular, contain several types of side or end groups, which tune their functional properties, such as absorption position and photochemistry. We report here a detailed experimental study of the absorption and vibrational properties of allene-containing carotenoids, together with an extensive modeling of these experimental data. Our calculations can satisfactorily explain the electronic properties of vaucheriaxanthin, where the allene group introduces the equivalent of one CC double bond into the conjugated CC chain. The position of the electronic absorption of fucoxanthin and butanoyloxyfucoxanthin requires long-range corrections to be found correctly on the red side of that of vaucheriaxanthin; however, these corrections tend to overestimate the effect of the conjugated and nonconjugated CO groups in these molecules. We show that the resonance Raman spectra of these carotenoids are largely perturbed by the presence of the allene group, with the two major Raman contributions split into two components. These perturbations are satisfactorily explained by modeling, through a gain in the Raman intensity of the CC antisymmetric stretching mode, induced by the presence of the allene group in the carotenoid CC chain.

Aggregation of amyloid β peptides is known to be one of the main processes responsible for Alzheimer’s disease. The resulting dementia is believed to be due in part to the formation of potentially toxic oligomers. However, the study of such intermediates and the understanding of how they form are very challenging because they are heterogeneous and transient in nature. Unfortunately, few techniques can quantify, in real time, the proportion and the size of the different soluble species during the aggregation process. In a previous work (Deleanu et al. Anal. Chem. 2021, 93, 6523−6533), we showed the potential of Taylor dispersion analysis (TDA) in amyloid speciation during the aggregation process of Aβ (1−40) and Aβ (1−42). The current work aims at exploring in detail the aggregation of amyloid Aβ (1− 40):Aβ (1−42) peptide mixtures with different proportions of each peptide (1:0, 3:1, 1:1, 1:3, and 0:1) using TDA and atomic force microscopy (AFM). TDA allowed for monitoring the kinetics of the amyloid assembly and quantifying the transient intermediates. Complementarily, AFM allowed the formation of insoluble fibrils to be visualized. Together, the two techniques enabled us to study the influence of the peptide ratios on the kinetics and the formation of potentially toxic oligomeric species.

We report on two selective functionalization strategies to create a chemical contrast between the active rib waveguides and the passive surrounding areas of a chalcogenide-based optical sensing system. In such configuration, the analyte could be concentrated on the waveguides and interact with the evanescent field, producing a stronger optical signature. The rib waveguides are obtained by photolithography and subsequent ion beam etching of amorphous Ge-Se-Te thin films that allow residual resist to remain above the waveguides. The first functionalization strategy consists in the reuse of the resist as a mask during the following surface modification process. It allows the functionalization of all areas around the waveguides. The second strategy consists of depositing a new sacrificial metal layer, leading to a perfect negative functionalization contrast, modifying only the waveguides. For the two strategies developed, three precursors were used. The use of a silylated fluorescein derivative allowed the validation of the protocols, with the observation of a fluorescence contrast between the functionalized and non-functionalized areas. The use of tetraethoxysilane as a hydrophilic precursor and the mixture of tetraethoxysilane and octyl-trimethoxysilane as a hydrophobic precursor created a clear contrast in wettability between the rib waveguides and the surrounding areas. A spore deposition was performed on functionalized components according to the two proposed strategies, with the two hydrophilic/hydrophobic precursors. The spore immobilization rate was increased by making the waveguides more hydrophobic, as well as by making the areas surrounding the guides more hydrophilic, demonstrating the effectiveness of our two strategies.