Enhancing Infrared Light-Matter Interaction for Deterministic and Tunable Nanomachining of Hexagonal Boron Nitride.

Tailoring two-dimensional (2D) materials functionalities is closely intertwined with defect engineering. Conventional methods do not offer the necessary control to locally introduce and study defects in 2D materials, especially in non-vacuum environments. Here, an infrared pulsed laser focused under the metallic tip of an atomic force microscope cantilever is used to create nanoscale defects in hexagonal boron nitride (h-BN) and to subsequently investigate the induced lattice distortions by means of nanoscale infrared (nano-IR) spectroscopy. The effects of incoming light power, exposure time, and environmental conditions on the defected regions are considered. Nano-IR spectra complement the morphology maps by revealing changes in lattice vibrations that distinguish the defects formed under various environments. This work introduces versatile experimental avenues to trigger and probe local reactions that functionalize 2D materials through defect creation with a higher level of precision for applications in sensing, catalysis, optoelectronics, quantum computing, and beyond.

Dual Antioxidant Properties and Organic Radical Stabilization in Cellulose Nanocomposite Films Functionalized by In Situ Polymerization of Coniferyl Alcohol.

A new biobased material based on an original strategy using lignin model compounds as natural grafting additive on a nanocellulose surface through in situ polymerization of coniferyl alcohol by the Fenton reaction at two pH values was investigated. The structural and morphological properties of the materials at the nanoscale were characterized by a combination of analytical methods, including Fourier transform infrared spectroscopy, liquid chromatography combined with mass spectrometry, nuclear molecular resonance spectroscopy, electron paramagnetic resonance spectroscopy, water sorption capacity by dynamic vapor sorption, and atomic force microscopy (topography and indentation modulus measurements). Finally, the usage properties, such as antioxidant properties, were evaluated in solution and the nanostructured casted films by radical 2,2'-diphenyl-1-picrylhydrazyl (DPPH•) scavenging tests. We demonstrate the structure-function relationships of these advanced CNC-lignin films and describe their dual functionalities and characteristics, namely, their antioxidant properties and the presence of persistent phenoxy radicals within the material.

Mechanobiologically induced bone-like nodules: Matrix characterization from micro to nanoscale.

In bone tissue engineering, stem cells are known to form inhomogeneous bone-like nodules on a micrometric scale. Herein, micro- and nano-infrared (IR) micro-spectroscopies were used to decipher the chemical composition of the bone-like nodule. Histological and immunohistochemical analyses revealed a cohesive tissue with bone-markers positive cells surrounded by dense mineralized type-I collagen. Micro-IR gathered complementary information indicating a non-mature collagen at the top and periphery and a mature collagen within the nodule. Atomic force microscopy combined to IR (AFM-IR) analyses showed distinct spectra of "cell" and "collagen" rich areas. In contrast to the "cell" area, spectra of "collagen" area revealed the presence of carbohydrate moieties of collagen and/or the presence of glycoproteins. However, it was not possible to determine the collagen maturity, due to strong bands overlapping and/or possible protein orientation effects. Such findings could help developing protocols to allow a reliable characterization of in vitro generated complex bone tissues.

Quantitative characterization of single-cell adhesion properties by atomic force microscopy using protein-functionalized microbeads.

A method was developed to characterize the adhesion properties of single cells by using protein-functionalized atomic force microscopy (AFM) probes. The quantification by force spectroscopy of the mean detachment force between cells and a gelatin-functionalized colloidal tip reveals differences in cell adhesion properties that are not within reach of a traditional bulk technique, the washing assay. In this latter method, experiments yield semiquantitative and average adhesion properties of a large population of cells. They are also limited to stringent conditions and cannot highlight disparities in adhesion in the subset of adherent cells. In contrast, this AFM-based method allows for a reproducible and quantitative investigation of the adhesive properties of individual cells in common cell culture conditions and allows for the detection of adhesive subpopulations of cells. These characteristics meet the critical requirements of many fields, such as the study of cancer cell migratory abilities.

Real Time and Quantitative Imaging of Lignocellulosic Films Hydrolysis by Atomic Force Microscopy Reveals Lignin Recalcitrance at Nanoscale.

Lignocellulosic biomass is considered as a sustainable source of energy and chemicals, but its recalcitrance to bioconversion still limits its use. In this paper, a strategy based on two aspects was developed to improve our knowledge on the lignin recalcitrance to enzymatic hydrolysis. First, lignocellulosic films of cellulose nanofibrils (CNFs) with increasing content of lignin (up to 40%) were prepared. Thanks to in situ real time Atomic Force Microscopy (AFM) measurements during the hydrolysis and by comparison with biochemical assays, the use of such films allows to fully assess the importance of the lignin content and of the arrangement between CNFs and lignin on the hydrolysis efficiency. In a second time, contrary to other studies by AFM which only followed a specific structure during enzymatic processes mostly on simple systems (CNFs or cellulose nanocrystals), a quantitative analysis of in-situ time-lapse measurements was developed. It enables to accurately address lignocellulosic biomass recalcitrance mechanisms mediated by lignin at nanoscale. Such analysis could pave the way for the use of a quantitative criteria to visualize in situ deconstruction of complex lignocellulosic substrates. Coupling the use of lignocellulosic films and dynamical AFM quantitative analysis to follow the evolution of the structure at nanoscale might lead to an effective targeting of new promising bioconversion strategies.

A gentle approach to investigate the influence of LRP-1 silencing on the migratory behavior of breast cancer cells by atomic force microscopy and dynamic cell studies.

The aim of the study was to get more insight into the role of LRP-1 in the mechanism of tumor progression in triple negative breast cancer. Atomic force microscopy, videomicroscopy, confocal microscopy and Rho-GTPAse activity assay were used on MDA-MB-231 and LRP-1-silenced cells. Silencing of LRP-1 in MDA-MB-231 cells was shown to led to a dramatic increase in the Young's modulus in parallel to a spectacular drop in membrane extension dynamics as well as a decrease in the cells migration abilities on both collagen I and fibronectin substrates. These results were perfectly correlated to a corresponding change in cell morphology and spreading capacity as well as in Rho-GTPases activity. By a multi-technique approach, it was demonstrated that LRP-1 played a crucial role in the migration of MDA-MB-231 cells by modulating the membrane extension dynamic. The originality of this AFM investigation lies in the non-invasive aspect of the measurements.

Silicon Wafer Functionalization with a Luminescent Tb(III) Coordination Complex: Synthesis, Characterization, and Application to the Optical Detection of NO in the Gas Phase.

A new luminescent Tb-DOTAGA (1,4,7,10-tetraazacyclododecane-1-glutaric-4,7,10- triacetic acid) complex (TbL) was synthesized and covalently immobilized on a silicon wafer. The grafting process was monitored by means of IR and XPS spectroscopies and the optical properties of the functionalized silicon wafer (TbL@Si) were investigated by fluorescence experiments. A homemade setup was then implemented in order to follow TbL@Si optical properties in the presence of gaseous nitric oxide (NO). The prima facie results indicated that in the presence of NO, the wafer fluorescence was partially quenched. This quenching was reversible as soon as NO was pumped outside the fluorescence cell, which could be interesting for the further development of lanthanide labelled silicon wafers as gas phase sensors.

Langmuir-Blodgett Procedure to Precisely Control the Coverage of Functionalized AFM Cantilevers for SMFS Measurements: Application with Cellulose Nanocrystals.

Atomic force microscopy (AFM) experiments with functionalized tips are currently one of the most powerful tools to locally measure adhesion forces via single-molecule force spectroscopy (SMFS) measurements. The main difficulty is to precisely control the attachment of biomolecules to the cantilever. Different chemistry procedures have been developed including the use of spacer molecules. Even if a process works well for small biomolecules such as antibodies, issues remain regarding nanoparticles or larger objects such as cellulose nanocrystals because it is difficult to precisely control their coverage and homogeneity. In this work, an original procedure based on the Langmuir-Blodgett (LB) technique was implemented for lever functionalization with cellulose nanocrystals and compared with classical chemical strategies. LB shows to be almost 6.0-fold more efficient than chemical procedure in terms of cellulose nanocrystals coverage attachment. Moreover, the LB technology provides advantage of not requiring linker molecules, which could have detrimental effects such as overestimation of the interaction force. The structural characterization and SMFS measurements of lignocellulosic polymers show that this strategy enables the precise control of the lever coverage, which improves the accuracy of the adhesion measurements. Such methodology is expected to strongly impact the AFM tip/tipless functionalization and SMFS measurements in different fields.

N-Formylation modifies membrane damage associated with PSMα3 interfacial fibrillation.

The virulence of Staphylococcus aureus, a multi-drug resistant pathogen, notably depends on the expression of the phenol soluble modulins α3 (PSMα3) peptides, able to self-assemble into amyloid-like cross-α fibrils. Despite remarkable advances evidencing the crucial, yet insufficient, role of fibrils in PSMα3 cytotoxic activities towards host cells, the relationship between its molecular structures, assembly propensities, and modes of action remains an open intriguing problem. In this study, combining atomic force microscopy (AFM) imaging and infrared spectroscopy, we first demonstrated in vitro that the charge provided by the N-terminal capping of PSMα3 alters its interactions with model membranes of controlled lipid composition without compromising its fibrillation kinetics or morphology. N-formylation eventually dictates PSMα3-membrane binding via electrostatic interactions with the lipid head groups. Furthermore, PSMα3 insertion within the lipid bilayer is favoured by hydrophobic interactions with the lipid acyl chains only in the fluid phase of membranes and not in the gel-like ordered domains. Strikingly, our real-time AFM imaging emphasizes how intermediate protofibrillar entities, formed along PSMα3 self-assembly and promoted at the membrane interface, likely disrupt membrane integrity via peptide accumulation and subsequent membrane thinning in a peptide concentration and lipid-dependent manner. Overall, our multiscale and multimodal approach sheds new light on the key roles of N-formylation and intermediate self-assembling entities, rather than mature fibrils, in dictating deleterious interactions of PSMα3 with membrane lipids, likely underscoring its ultimate cellular toxicity in vivo, and in turn S. aureus pathogenesis.

Modeling progression of fluorescent probes in bioinspired lignocellulosic assemblies.

Progression of enzymes in lignocellulosic biomass is a crucial parameter in biorefinery processes, and it appears to be one of the limiting factors in optimizing lignocellulose degradation. In order to assay the importance of the chemical and structural features of the substrate matrix on enzyme mobility, we have designed bioinspired model assemblies of secondary plant cell walls, which have been used to measure the mobility of fluorescent probes while modifying different parameters (probe size, water content, polysaccharide concentration). The results were used to construct a model of probe mobility and to rank the parameters in order of importance. Water content and probe size were shown to have the greatest effect. Although these assemblies are simplified templates of the plant cell walls, our strategy paves the way for proposing new approaches for optimizing biomass saccharification, such as selecting enzymes with suitable properties.

Characterizations of Ohmic and Schottky-behaving contacts of a single ZnO nanowire.

Current-voltage and Kelvin probe force microscopy (KPFM) measurements were performed on single ZnO nanowires. Measurements are shown to be strongly correlated with the contact behavior, either Ohmic or diode-like. The ZnO nanowires were obtained by metallo-organic chemical vapor deposition (MOCVD) and contacted using electronic-beam lithography. Depending on the contact geometry, good quality Ohmic contacts (linear I-V behavior) or non-linear (diode-like) contacts were obtained. Current-voltage and KPFM measurements on both types of contacted ZnO nanowires were performed in order to investigate their behavior. A clear correlation could be established between the I-V curve, the electrical potential profile along the device and the nanowire geometry. Some arguments supporting this behavior are given based on technological issues and on depletion region extension. This work will help to better understand the electrical behavior of Ohmic contacts on single ZnO nanowires, for future applications in nanoscale field-effect transistors and nano-photodetectors.

Electrodeposition of silicon nanotubes at room temperature using ionic liquid.

Electrodeposition inside an insulated nanoporous template using Room Temperature Ionic Liquids (RTILs) has recently been demonstrated as a promising alternative technique for synthesizing silicon nanowires due to low cost ambient growth conditions. An improvement of the method is shown here to produce Si nanotubes. A fine adjustment of electro-chemical parameters influencing ionic diffusion inside the nanopores of the template is demonstrated to preferably lead to the growth of Si nanotubes at the expense of Si nanowires. This study shows that electrodeposition in RTILs is a competitive process to grow high surface to volume ratio nanostructures at low cost and over a large scale. It also indicates a new prospect for the technique to grow and control nanostructures such as radial core-shell nanowires.

Dynamized ultra-low dilution of Ruta graveolens disrupts plasma membrane organization and decreases migration of melanoma cancer cell.

Cutaneous melanoma is a cancer with a very poor prognosis mainly because of metastatic dissemination and therefore a deregulation of cell migration. Current therapies can benefit from complementary medicines as supportive care in oncology. In our study, we show that a dynamized ultra-low dilution of Ruta Graveolens leads to an in vitro inhibition of migration on fibronectin of B16F10 melanoma cells, as well as a decrease in metastatic dissemination in vivo. These effects appear to be due to a disruption of plasma membrane organization, with a change in cell and membrane stiffness, associated with a disorganization of the actin cytoskeleton and a modification of the lipid composition of the plasma membrane. Together, these results demonstrate, in in vitro and in vivo models of cutaneous melanoma, an anti-cancer and anti-metastatic activity of ultra-low dynamized dilution of Ruta graveolens and reinforce its interest as complementary medicine in oncology.

Influence of Surface Chemistry of Fiber and Lignocellulosic Materials on Adhesion Properties with Polybutylene Succinate at Nanoscale.

The production of bio-based composites with enhanced characteristics constitutes a strategic action to minimize the use of fossil fuel resources. The mechanical performances of these materials are related to the specific properties of their components, as well as to the quality of the interface between the matrix and the fibers. In a previous research study, it was shown that the polarity of the matrix played a key role in the mechanisms of fiber breakage during processing, as well as on the final properties of the composite. However, some key questions remained unanswered, and new investigations were necessary to improve the knowledge of the interactions between a lignocellulosic material and a polar matrix. In this work, for the first time, atomic force microscopy based on force spectroscopy measurements was carried out using functionalized tips to characterize the intermolecular interactions at the single molecule level, taking place between poly(butylene succinate) and four different plant fibers. The efficiency of the tip functionalization was checked out by scanning electron microscopy and energy-dispersive X-ray spectroscopy, whereas the fibers chemistry was characterized by Fourier-transform infrared spectroscopy. Larger interactions at the nanoscale level were found between the matrix and hypolignified fibers compared to lignified ones, as in control experiments on single lignocellulosic polymer films. These results could significantly aid in the design of the most appropriate composite composition depending on its final use.

Locally strained hexagonal boron nitride nanosheets quantified by nanoscale infrared spectroscopy.

Defect engineering in two-dimensional materials expands the realm of their applications in catalysis, nanoelectronics, sensing, and beyond. As limited tools are available to explore nanoscale functional properties in non-vacuum environments, theoretical modeling provides some invaluable insight into the effect of local deformations to deepen the understanding of experimental signals acquired by nanoscale chemical imaging. We demonstrate the controlled creation of nanoscale strained defects in hexagonal boron nitride (h-BN) using atomic force microscopy and infrared (IR) light under an inert environment. Nanoscale IR spectroscopy reveals the broadening of the in-plane phonon (E1u) mode of h-BN during defect formation while density functional theory-based calculations and molecular dynamics provide quantification of the tensile and compressive strain in the deformation.

WITHDRAWN: Aptamer-based nanotrains and nanoflowers as quinine delivery systems.

This article has been withdrawn: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been withdrawn at the request of the author, editor and publisher. The publisher regrets that an error occurred during the publication of this paper, which was intended to be published in International Journal of Pharmaceutics: X (not International Journal of Pharmaceutics). This error bears no reflection on the scientific content of this article or its authors. The publisher apologizes to the readers for this unfortunate error.

Aptamer-based nanotrains and nanoflowers as quinine delivery systems.

In this study, we designed aptamer-based self-assemblies for the delivery of quinine. Two different architectures were designed by hybridizing quinine binding aptamers and aptamers targeting Plasmodium falciparum lactate dehydrogenase (PfLDH): nanotrains and nanoflowers. Nanotrains consisted in controlled assembly of quinine binding aptamers through base-pairing linkers. Nanoflowers were larger assemblies obtained by Rolling Cycle Amplification of a quinine binding aptamer template. Self-assembly was confirmed by PAGE, AFM and cryoSEM. The nanotrains preserved their affinity for quinine and exhibited a higher drug selectivity than nanoflowers. Both demonstrated serum stability, hemocompatibility, low cytotoxicity or caspase activity but nanotrains were better tolerated than nanoflowers in the presence of quinine. Flanked with locomotive aptamers, the nanotrains maintained their targeting ability to the protein PfLDH as analyzed by EMSA and SPR experiments. To summarize, nanoflowers were large assemblies with high drug loading ability, but their gelating and aggregating properties prevent from precise characterization and impaired the cell viability in the presence of quinine. On the other hand, nanotrains were assembled in a selective way. They retain their affinity and specificity for the drug quinine, and their safety profile as well as their targeting ability hold promise for their use as drug delivery systems.

The impact of lipid polyunsaturation on the physical and mechanical properties of lipid membranes.

The lipid composition of cellular membranes and the balance between the different lipid components can be impacted by aging, certain pathologies, specific diets and other factors. This is the case in a subgroup of individuals with psychiatric disorders, such as schizophrenia, where cell membranes of patients have been shown to be deprived in polyunsaturated fatty acids (PUFAs), not only in brain areas where the target receptors are expressed but also in peripheral tissues. This PUFA deprivation thus represents a biomarker of such disorders that might impact not only the interaction of antipsychotic medications with these membranes but also the activation and signaling of the targeted receptors embedded in the lipid membrane. Therefore, it is crucial to understand how PUFAs levels alterations modulate the different physical properties of membranes. In this paper, several biophysical approaches were combined (Laurdan fluorescence spectroscopy, atomic force microscopy, differential scanning calorimetry, molecular modeling) to characterize membrane properties such as fluidity, elasticity and thickness in PUFA-enriched cell membranes and lipid model systems reflecting the PUFA imbalance observed in some diseases. The impact of both the number of unsaturations and their position along the chain on the above properties was investigated. Briefly, data revealed that PUFA presence in membranes increases membrane fluidity, elasticity and flexibility and decreases its thickness and order parameter. Both the level of unsaturation and their position affect these membrane properties.

Comparative efficiency of energy transfer from CdSe-ZnS quantum dots or nanorods to organic dye molecules.

Fluorescence resonance energy transfer (FRET) in conjugates of CdSe-ZnS semiconductor nanocrystals of different shapes (FRET donors) and an Alexa Fluor organic dye (FRET acceptors) is examined. The dye molecules are chemically conjugated with quantum dots (QDs) or nanorods (NRs) in dimethyl sulfoxide colloidal solutions, and FRET efficiency in the purified conjugates is measured. The FRET from NR to a single dye molecule is less efficient than that of the QD-dye conjugates and this effect is explained in terms of distance-limited energy-transfer rate in the case of a point-like acceptor and extended donor dipoles. However, the larger surface area of NRs allows for many more dye acceptors to be bound, and the total FRET efficiency in NR-dye conjugates approaches those of QD-dye conjugates.

Hydrogels incorporating GdDOTA: towards highly efficient dual T1/T2 MRI contrast agents.

Do not tumble dry: Gadolinium-DOTA encapsulated into polysaccharide nanoparticles (GdDOTA NPs) exhibited high relaxivity (r(1) =101.7 s(-1) mM(-1) per Gd(3+) ion at 37 °C and 20 MHz). This high relaxation rate is due to efficient Gd loading, reduced tumbling of the Gd complex, and the hydrogel nature of the nanoparticles. The efficacy of the nanoparticles as a T(1)/T(2) dual-mode contrast agent was studied in C6 cells.