Monitoring of CaCO3 Nanoscale Structuration through Real-Time Liquid Phase Transmission Electron Microscopy and Hyperpolarized NMR.

Calcium carbonate (CaCO3) is one of the most significant biominerals in nature. Living organisms are able to control its biomineralization by means of an organic matrix to tailor a myriad of hybrid functional materials. The soluble organic components are often proteins rich in acidic amino-acids such as l-aspartic acid. While several studies have demonstrated the influence of amino acids on the crystallization of calcium carbonate, nanoscopic insight of their impact on CaCO3 mineralization, in particular at the early stages, is still lacking. Herein, we implement liquid phase-transmission electron microscopy (LP-TEM) in order to visualize in real-time and at the nanoscale the prenucleation stages of CaCO3 formation. We observe that l-aspartic acid favors the formation of individual and aggregated prenucleation clusters which are found stable for several minutes before the transformation into amorphous nanoparticles. Combination with hyperpolarized solid state nuclear magnetic resonance (DNP NMR) and density functional theory (DFT) calculations allow shedding light on the underlying mechanism at the prenucleation stage. The promoting nature of l-aspartic acid with respect to prenucleation clusters is explained by specific interactions with both Ca2+ and carbonates and the stabilization of the Ca2+-CO32-/HCO3- ion pairs favoring the formation and stabilization of the CaCO3 transient precursors. The study of prenucleation stages of mineral formation by the combination of in situ LP-TEM, advanced analytical techniques (including hyperpolarized solid-state NMR), and numerical modeling allows the real-time monitoring of prenucleation species formation and evolution and the comprehension of their relative stability.

A Confinement-Driven Nucleation Mechanism of Metal Oxide Nanoparticles Obtained via Thermal Decomposition in Organic Media.

Thermal decomposition is a very efficient synthesis strategy to obtain nanosized metal oxides with controlled structures and properties. For the iron oxide nanoparticle synthesis, it allows an easy tuning of the nanoparticle's size, shape, and composition, which is often explained by the LaMer theory involving a clear separation between nucleation and growth steps. Here, the events before the nucleation of iron oxide nanocrystals are investigated by combining different complementary in situ characterization techniques. These characterizations are carried out not only on powdered iron stearate precursors but also on a preheated liquid reaction mixture. They reveal a new nucleation mechanism for the thermal decomposition method: instead of a homogeneous nucleation, the nucleation occurs within vesicle-like-nanoreactors confining the reactants. The different steps are: 1) the melting and coalescence of iron stearate particles, leading to "droplet-shaped nanostructures" acting as nanoreactors; 2) the formation of a hitherto unobserved iron stearate crystalline phase within the nucleation temperature range, simultaneously with stearate chains loss and Fe(III) to Fe(II) reduction; 3) the formation of iron oxide nuclei inside the nanoreactors, which are then ejected from them. This mechanism paves the way toward a better mastering of the metal oxide nanoparticles synthesis and the control of their properties.

Supramolecular Assembly of Conjugated Polymers under Vibrational Strong Coupling.

Strong coupling plays a significant role in influencing chemical reactions and tuning material properties by modifying the energy landscapes of the systems. Here we study the effect of vibrational strong coupling (VSC) on supramolecular organization. For this purpose, a rigid-rod conjugated polymer known to form gels was strongly coupled together with its solvent in a microfluidic IR Fabry-Perot cavity. Absorption and fluorescence studies indicate a large modification of the self-assembly under such cooperative VSC. Electron microscopy confirms that in this case, the supramolecular morphology is totally different from that observed in the absence of strong coupling. In addition, the self-assembly kinetics are altered and depend on the solvent vibration under VSC. The results are compared to kinetic isotope effects on the self-assembly to help clarify the role of different parameters under strong coupling. These findings indicate that VSC is a valuable new tool for controlling supramolecular assemblies with broad implications for the molecular and material sciences.

Hydration Properties and Interlayer Organization in Synthetic C-S-H.

Water in calcium silicate hydrate (C-S-H) is one of the key parameters driving the macroscopic behavior of cement materials for which water vapor partial pressure has an impact on Young's modulus and the volumic properties. Several samples of C-S-H with a bulk Ca/Si ratio ranging between 0.6 and 1.6 were characterized to study their dehydration/hydration behavior under water-controlled conditions using29Si NMR, water adsorption volumetry, X-ray diffraction, and Fourier-transform near-infrared diffuse reflectance under various water pressures. Coherent with several previous studies, it was observed that an increase in the Ca/Si ratio is due to the progressive omission of Si bridging tetrahedra, with the resulting charge being compensated for by interlayer Ca, and that water conditioning influences the layer-to-layer distance and the achieved NMR spectral resolution. Water desorption experiments exhibit one step toward low relative pressure, accompanied by a decrease in the layer-to-layer distance. When sufficient energy is provided to the system (T ≥ 40 °C under vacuum) to remove the interlayer water, the shrinkage/swelling is partially reversible in our experimental conditions. A change in layer-to-layer distance of less than 3 Å is measured in the C-S-H between the wet and dried states. When the bridging SiO2 tetrahedra are omitted, interlayer Ca interacts with layer O and water interacts with the cations and potentially with the surfaces. This structural organization is interpreted as a mid-plane monolayer of water in the interlayer space, this latter accounting for about 30% of the volume of C-S-H particles.

Quantitative Analysis of the Specific Absorption Rate Dependence on the Magnetic Field Strength in ZnxFe3-xO4 Nanoparticles.

Superparamagnetic ZnxFe3-xO4 magnetic nanoparticles (0 ≤ x < 0.5) with spherical shapes of 16 nm average diameter and different zinc doping level have been successfully synthesized by co-precipitation method. The homogeneous zinc substitution of iron cations into the magnetite crystalline structure has led to an increase in the saturation magnetization of nanoparticles up to 120 Am2/kg for x ~ 0.3. The specific absorption rate (SAR) values increased considerably when x is varied between 0 and 0.3 and then decreased for x ~ 0.5. The SAR values are reduced upon the immobilization of the nanoparticles in a solid matrix being significantly increased by a pre-alignment step in a uniform static magnetic field before immobilization. The SAR values displayed a quadratic dependence on the alternating magnetic field amplitude (H) up to 35 kA/m. Above this value, a clear saturation effect of SAR was observed that was successfully described qualitatively and quantitatively by considering the non-linear field's effects and the magnetic field dependence of both Brown and Neel relaxation times. The Neel relaxation time depends more steeply on H as compared with the Brown relaxation time, and the magnetization relaxation might be dominated by the Neel mechanism, even for nanoparticles with large diameter.

Photon management properties of Yb-doped SnO2 nanoparticles synthesized by the sol-gel technique.

SnO2 is a transparent large band gap semiconductor, particularly interesting for optoelectronic and photovoltaic devices, mainly because its conduction can be easily tuned by doping or by modulating the amount of oxygen vacancies. Besides, rare earth doping was successfully exploited for up conversion properties. Here we report on the functionalization of SnO2 nanoparticles with optically active Yb3+ ions using the sol-gel method, which allows UV to NIR spectral (down) conversion. As starting solutions we used stable non-alkoxide metal-organic compounds, which is rather uncommon. Transmission electron microscopy analysis demonstrated the formation of small well-crystallized nanoparticles while X-ray photoelectron spectroscopy measurements have revealed that the Yb is well inserted in the host matrix and has a 3+ valence state. All nanoparticles present large absorption in the UV-visible range (250 to 550 nm) and a band gap that decreases down to 2.72 eV upon doping. The UV energy converted into NIR on the basis of efficient energy transfer from SnO2 to the Yb3+ ions ranges between 250 and 400 nm. Reference undoped SnO2 nanoparticles with a mean size of 20 nm allow converting UV light into broad visible emission centered at 650 nm. The incorporation of up to 3.5 at% of Yb3+ ions into the SnO2 host matrix results in a spectacular decrease of the nanoparticle size down to 6.6 nm. This allowed also the shift of the photoluminescence to NIR in the 970-1050 nm range. The energy level structure of Yb3+ in SnO2 was successfully determined from the deconvolution of the Yb emission. This emission is significantly enhanced by increasing the doping level. All optical measurements suggest that these nanoparticles can be efficiently used as down-shifting converters.

Mimicking the Chemistry of Natural Eumelanin Synthesis: The KE Sequence in Polypeptides and in Proteins Allows for a Specific Control of Nanosized Functional Polydopamine Formation.

The oxidation of dopamine and of other catecholamines leads to the formation of conformal films on the surface of all known materials and to the formation of a precipitate in solution. In some cases, it has been shown that the addition of additives in the dopamine solution, like certain surfactants or polymers, polyelectrolytes, and certain proteins, allows to get polydopamine nanoparticles of controlled size and the concomitant decrease, in an additive/dopamine dependent manner, in film formation on the surface of the reaction beaker. However, the mechanism behind this controlled oxidation and self-assembly of catecholamines is not known. In this article, it is shown that a specific diad of amino acids in proteins, namely KE, allows for specific control in the oxidation-self-assembly of dopamine to obtain polydopamine@protein core-shell nanoparticles which are biocompatible. The interactions between dopamine and the adjacent KE amino acids potentially responsible for the size control of polydopamine aggregates was investigated by molecular dynamics simulations. The obtained core-shell nanoparticles display the biological activity of the protein used to control the self-assembly of PDA. The photon to heat conversion ability of PDA is conserved in the PDA@protein particles.

Spin State As a Probe of Vesicle Self-Assembly.

A novel system of paramagnetic vesicles was designed using ion pairs of iron-containing surfactants. Unilamellar vesicles (diameter ≈ 200 nm) formed spontaneously and were characterized by cryogenic transmission electron microscopy, nanoparticle tracking analysis, and light and small-angle neutron scattering. Moreover, for the first time, it is shown that magnetization measurements can be used to investigate self-assembly of such functionalized systems, giving information on the vesicle compositions and distribution of surfactants between the bilayers and the aqueous bulk.

Enhancement of the Solar Water Splitting Efficiency Mediated by Surface Segregation in Ti-Doped Hematite Nanorods.

Band engineering is employed thoroughly and targets technologically scalable photoanodes for solar water splitting applications. Complex and costly recipes are necessary, often for average performances. Here, we report simple photoanode growth and thermal annealing with effective band engineering results. By comparing Ti-doped hematite photoanodes annealed under nitrogen to photoanodes annealed in air, we found a strongly enhanced photocurrent of more than 200% in the first case. Using electrochemical impedance spectroscopy and synchrotron X-ray spectromicroscopy, we demonstrate that oxidized surface states and increased density of charge carriers are responsible for the enhanced photoelectrochemical (PEC) activity. Surface states are found to be related to the formation of pseudo-brookite clusters by surface Ti segregation. Spectro-ptychography is used for the first time at the Ti L3 absorption edge to isolate Ti chemical coordination arising from pseudo-brookite cluster contribution. Correlated with electron microscopy investigation and density functional theory calculations, the synchrotron spectromicroscopy data unambiguously prove the origin of enhanced PEC activity of N2-annealed Ti-doped hematite nanorods. Finally, we present here a handy and cheap surface engineering method beyond the known oxygen vacancy doping, allowing a net gain in the PEC activity for the hematite-based photoanodes.

Hierarchical superparamagnetic metal-organic framework nanovectors as anti-inflammatory nanomedicines.

Among a plethora of drug nanocarriers, biocompatible nanoscale metal-organic frameworks (nanoMOFs) with a large surface area and an amphiphilic internal microenvironment have emerged as promising drug delivery platforms, mainly for cancer therapy. However, their application in biomedicine still suffers from shortcomings such as a limited chemical and/or colloidal stability and/or toxicity. Here, we report the design of a hierarchically porous nano-object (denoted as USPIO@MIL) combining a benchmark nanoMOF (that is, MIL-100(Fe)) and ultra-small superparamagnetic iron oxide (USPIO) nanoparticles (that is, maghemite) that is synthesized through a one-pot, cost-effective and environmentally friendly protocol. The synergistic coupling of the physico-chemical and functional properties of both nanoparticles confers to these nano-objects valuable features such as high colloidal stability, high biodegradability, low toxicity, high drug loading capacity as well as stimuli-responsive drug release and superparamagnetic properties. This bimodal MIL-100(Fe)/maghemite nanocarrier once loaded with anti-tumoral and anti-inflammatory drugs (doxorubicin and methotrexate) shows high anti-inflammatory and anti-tumoral activities. In addition, the USPIO@MIL nano-object exhibits excellent relaxometric properties and its applicability as an efficient contrast agent for magnetic resonance imaging is herein demonstrated. This highlights the high potential of the maghemite@MOF composite integrating the functions of imaging and therapy as a theranostic anti-inflammatory formulation.

3D analysis of the morphology and spatial distribution of nitrogen in nitrogen-doped carbon nanotubes by energy-filtered transmission electron microscopy tomography.

We present here the application of the energy-filtered transmission electron microscopy (EFTEM) in the tomographic mode to determine the precise 3D distribution of nitrogen within nitrogen-doped carbon nanotubes (N-CNTs). Several tilt series of energy-filtered images were acquired on the K ionization edges of carbon and nitrogen on a multiwalled N-CNT containing a high amount of nitrogen. Two tilt series of carbon and nitrogen 2D maps were then calculated from the corresponding energy-filtered images by using a proper extraction procedure of the chemical signals. Applying iterative reconstruction algorithms provided two spatially correlated C and N elemental-selective volumes, which were then simultaneously analyzed with the shape-sensitive reconstruction deduced from Zero-Loss recordings. With respect to the previous findings, crucial information obtained by analyzing the 3D chemical maps was that, among the two different kind of arches formed in these nanotubes (transversal or rounded ones depending on their morphology), the transversal arches contain more nitrogen than do the round ones. In addition, a detailed analysis of the shape-sensitive volume allowed the observation of an unexpected change in morphology along the tube axis: close to the round arches (with less N), the tube is roughly cylindrical, whereas near the transversal ones (with more N), its shape changes to a prism. This relatively new technique is very powerful in the material science because it combines the ability of the classical electron tomography to solve 3D structures and the chemical selectivity of the EFTEM imaging.

Engineering siderophore production in Pseudomonas to improve asbestos weathering.

Iron plays a key role in microbial metabolism and bacteria have developed multiple siderophore-driven mechanisms due to its poor bioavailability for organisms in the environment. Iron-bearing minerals generally serve as a nutrient source to sustain bacterial growth after bioweathering. Siderophores are high-affinity ferric iron chelators, of which the biosynthesis is tightly regulated by the presence of iron. Pyoverdine-producing Pseudomonas have shown their ability to extract iron and magnesium from asbestos waste as nutrients. However, such bioweathering is rapidly limited due to repression of the pyoverdine pathway and the low bacterial requirement for iron. We developed a metabolically engineered strain of Pseudomonas aeruginosa for which pyoverdine production was no longer repressed by iron as a proof of concept. We compared siderophore-promoted dissolution of flocking asbestos waste by this optimized strain to that by the wild-type strain. Interestingly, pyoverdine production by the optimized strain was seven times higher in the presence of asbestos waste and the dissolution of magnesium and iron from the chrysotile fibres contained in flocking asbestos waste was significantly enhanced. This innovative mineral weathering process contributes to remove toxic iron from the asbestos fibres and may contribute to the development of an eco-friendly method to manage asbestos waste.

In situ liquid transmission electron microscopy reveals self-assembly-driven nucleation in radiolytic synthesis of iron oxide nanoparticles in organic media.

We have investigated the early stages of the formation of iron oxide nanoparticles from iron stearate precursors in the presence of sodium stearate in an organic solvent by in situ liquid phase transmission electron microscopy (IL-TEM). Before nucleation, we have evidenced the spontaneous formation of vesicular assemblies made of iron polycation-based precursors sandwiched between stearate layers. Nucleation of iron oxide nanoparticles occurs within the walls of the vesicles, which subsequently collapse upon the consumption of the iron precursors and the growth of the nanoparticles. We then evidenced that fine control of the electron dose, and therefore of the local concentration of reactive iron species in the vicinity of the nuclei, enables controlling crystal growth and selecting the morphology of the resulting iron oxide nanoparticles. Such a direct observation of the nucleation process templated by vesicular assemblies in a hydrophobic organic solvent sheds new light on the formation process of metal oxide nanoparticles and therefore opens ways for the synthesis of inorganic colloidal systems with tunable shape and size.

3D multiscale analysis of the hierarchical porosity in Coscinodiscus sp. diatoms using a combination of tomographic techniques.

A full 3D analysis of the hierarchical porosity in Coscinodiscus sp. diatom structures was carried out by using a multiscale approach that combines three advanced volumetric imaging techniques with resolutions and fields of view covering all the porous characteristics of such complex architectures: electron tomography, "slice and view" approach that uses a dual-beam microscope (FIB-SEM), and array tomography consisting of serial imaging of ultrathin specimen sections. This multiscale approach allowed the whole porosity network to be quantified and provided an unprecedented structural insight into these natural nanostructured materials with internal organization ranging from micrometer to nanometer. The analysed species is made of several nested layers with different pore sizes, shapes and connectivities and characterized by the presence of interconnected pores structured in various ways. The first evidence of the presence of a nanometric porosity made of ellipsoidal pores in the siliceous diatom frustules is also provided.

Biodeterioration of asbestos cement by siderophore-producing Pseudomonas.

Since the ban on the use of asbestos due to its carcinogenic properties, the removal of asbestos cement, representing the major asbestos-containing waste, has proven to be a challenge in most industrial countries. Asbestos-containing products are mainly disposed of in landfills and have remained untreated. Bioremediation involving bacteria previously reported the ability of Pseudomonas aeruginosa to release iron from flocking asbestos waste through a siderophore-driven mechanism. We examined the involvement of siderophore-producing Pseudomonas in the biodeterioration of asbestos cement. Iron and magnesium solubilization were evaluated by specific siderophore-producing mutants. The absence of one of the two siderophores affected iron extraction, whereas equivalent dissolution as that of the control was observed in the absence of siderophore. Both pyoverdine and pyochelin biosynthesis was repressed in the presence of asbestos cement, suggesting iron bioavailability from the waste. We compared the efficiency of various pyoverdines to scavenge iron from asbestos cement waste that revealed the efficiency of all pyoverdines. Pyoverdines were efficient in iron removal extracted continuously, with no evident extraction limit, in long-term weathering experiments with these pyoverdines. The optimization of pyoverdine-asbestos weathering may allow the development of a bioremediation process to avoid the disposal of such waste in landfills.

Mercury cyclic porosimetry: Measuring pore-size distributions corrected for both pore-space accessivity and contact-angle hysteresis.

We propose a set of simple formulae for interpreting "mercury cyclic porosimetry" measurements where multiple intrusion-extrusion cycles are carried out. By employing two parameters α∈[0,1] and κ∈[0,1], our theory quantitatively breaks down any hysteresis observed in cyclic porosimetry data into contributions due to connectivity effects and contact-angle hysteresis, respectively. In particular, the parameter α, called "pore-space accessivity", characterizes any serial connectivity between different-size pores. It has long been recognized that the standard method for determining the pore-size distribution (PSD) from mercury intrusion data based on the capillary bundle assumption overestimates the fraction of smaller pores; that corresponds to the α→1 limit of our model. In contrast, for materials with α<1, our theory predicts a broadened PSD shifted toward larger radii, thus representing a simple way of rectifying PSDs for connectivity effects. The proposed model also establishes mercury cyclic porosimetry as a standard experimental procedure for measuring α, which can then be used in continuum models of porous media where connectivity effects play a significant role, such as in multiphase flow.

Gold labelling of a green fluorescent protein (GFP)-tag inside cells using recombinant nanobodies conjugated to 2.4 nm thiolate-coated gold nanoparticles.

Advances in microscopy technology have prompted efforts to improve the reagents required to recognize specific molecules within the intracellular environment. For high-resolution electron microscopy, conjugation of selective binders originating from the immune response arsenal to gold nanoparticles (AuNPs) as contrasting agents is the method of choice to obtain labeling tools. However, conjugation of the minimal sized 15 kDa nanobody (Nb) to AuNPs remains challenging in comparison to the conjugation of 150 kDa IgG to AuNPs. Herein, effective Nb-AuNP assemblies are built using the selective and almost irreversible non-covalent associations between two peptide sequences deriving from a p53 heterotetramer domain variant. The 15 kDa GFP-binding Nb is fused to one dimerizing motif to obtain a recombinant Nb dimer with improved avidity for GFP while the other complementing dimerizing motif is equipped with thiols and grafted to a 2.4 nm substituted thiobenzoate-coordinated AuNP via thiolate exchange. After pegylation, the modified AuNPs are able to non-covalently anchor Nb dimers and the subsequent complexes demonstrate the ability to form immunogold label GFP-protein fusions within various subcellular locations. These tools open an avenue for precise localization of targets at high resolution by electron microscopy.

Versatile template-directed synthesis of gold nanocages with a predefined number of windows.

Highly symmetrical gold nanocages can be produced with a controllable number of circular windows of either 2, 3, 4, 6 or 12 via an original fabrication route. The synthetic pathway includes three main stages: the synthesis of silica/polystyrene multipod templates, the regioselective seeded growth of a gold shell on the unmasked part of the silica surface and the development of gold nanocages by dissolving/etching the templates. Electron microscopy and tomography provide evidence of the symmetrical features of the as-obtained nanostructures. The optical properties of nanocages with 4 and 12 windows were measured at the single particle level by spatial modulation spectroscopy and correlated with numerical simulations based on finite-element modeling. The new multi-step synthesis approach reported here also allows the synthesis of rattle-like nanostructures through filling of the nanocages with a guest nano-object. With the potential to adjust the chemical composition, size and geometry of both the guest particle and the host cage, it opens new routes towards the fabrication of hollow nanostructures of high interest for a variety of applications including sensing devices, catalytic reactors and biomedicine.

Efficiency of pyoverdines in iron removal from flocking asbestos waste: An innovative bacterial bioremediation strategy.

The use of asbestos-containing products has been banned in many countries since the beginning of the 80's due to its carcinogenic properties. However, asbestos is widely present in private and public buildings, resulting in the need to process a vast amount of asbestos-containing waste. Among the current technologies for the destruction of asbestos fibers, biodegradation by fungi, lichens, and, more recently, bacteria has been described. We previously reported the involvement of the bacterial siderophore pyoverdine in the release of iron from the two asbestos groups, serpentines and amphiboles. Among the large diversity encountered in the pyoverdine family, we examined whether these siderophores can alter flocking asbestos waste as well. All the tested pyoverdines were efficient in chrysotile-gypsum and amosite-gypsum weathering, although some exhibited higher iron dissolution. Iron was solubilized by pyoverdines from Pseudomonas aeruginosa and mandelii in a time-dependent manner from chrysotile-gypsum within 24 h. Renewal of pyoverdine-containing supernatant every 24 or 96 h allowed iron removal from chrysotile-gypsum at each cycle, until a limit was reached after 42 days of total incubation. Moreover, the dissolution was concentration-dependent, as demonstrated for the pyoverdine of P. mandelii. Pyoverdine-asbestos weathering could therefore become an innovative method to reduce anthropogenic waste.

Iron removal from raw asbestos by siderophores-producing Pseudomonas.

Asbestos, mineral present in soil, are highly toxic due to the presence of iron. Microbes-mineral interactions occur naturally through various processes leading to their alteration. We examined the effect of siderophore-producing Pseudomonas with a particular focus on the role of pyoverdine and pyochelin on raw asbestos fibers such as amosite, crocidolite and chrysotile. We compared the efficiency of pyoverdine to the iron chelating agent EDTA in the release of iron from raw asbestos fibers. Pyoverdine was able to extract iron from all the tested raw asbestos with the higher efficiency observed for chrysotile and crocidolite. When asbestos were grinded, the iron removal was more important for all types. We monitored the effect of bacterial growth and siderophores containing bacterial supernatant on raw asbestos dissolution by solution chemistry analysis and transmission electron microscopy. The siderophore-containing supernatant allowed a higher iron solubilisation than the one obtained after bacterial growth. Moreover, the iron dissolution was faster with pyoverdine-containing supernatant than pyochelin-containing supernatant, with approximately the same iron level for the maximum extraction with a delay of 48 h. Our study clearly showed the involvement of bacterial siderophores, pyoverdine and pyochelin on chrysotile, crocidolite and amosite fibers weathering.