Joachim Allouche

Sol-Gel Biopolymer/Silica Nanocomposites in Biotechnology

Bioencapsulation in silica gels has become a very popular field of research, leading to the design of biosensors and bioreactors. If pure silica gels appear suitable to maintain the biological activity of entrapped enzymes, there are many cases where hybrid materials are necessary to reach the long-term preservation of biomolecular or cellular species and/or to provide new functionalities. This review focuses on the design of such nanocomposite materials combining silica with biopolymers. In the first part, the synthesis and characterization of these bio-hybrid materials are described, emphasizing the importance of the polymer influence on the reactivity of silica precursors. In the second part, the benefits of biopolymer incorporation in silica gels are illustrated in the context of biotechnologi cal devices. As a conclusion, a parallel is drawn between biohybrids and biominerals, opening new perspectives for the design of multi-compone nt biologically-active materials.

Biomimetic core-shell gelatine/silica nanoparticles : a new example of biopolymer-based nanocomposites

Hybrid nanoparticles have great potential for biotechnological and biomedical applications. It was recently proposed that biopolymer/silica nanomaterials could be easily obtained by adapting traditional routes used in pharmaceutical science to design polymer nanoparticles. In this paper, we demonstrate that core–shell gelatine/silica nanoparticles can be obtained using a nano-emulsion route, taking advantage of the thermal gelation properties of the biopolymer and of its strong “biomimetic” affinity for silicates. The formation of the silica coating could be ascertained by SEM, TEM, EDAX, FTIR and DLS/zeta potential measurements. Silica coating was also performed on microparticles, allowing us to investigate in more detail the mechanism of silica deposition on the gelatine surface, which bears some relevance for the understanding of biosilicification processes. Finally, the possible internalization and intracellular degradation of these hybrid nanoparticles by fibroblast cells was demonstrated. A comparison with previously described silica/alginate nanoparticles is provided in the context of drug-delivery system design.

Synthesis of Organic and Bioorganic Nanoparticles: An Overview of the Preparation Methods

Since the emergence of Nanotechnology in the past decades, the development and design of organic and bioorganic nanomaterials has become an important field of research. Such materials find many applications in a wide range of domains such as electronic, photonic, or biotechnology, which contribute to impact our society and our way of life. The improvement of properties and the discovery of new functionalities are key goals that cannot be obtained without a well controlled and a better understanding of the preparation methods which constitute the starting point of the design of a specific organic material. In this context, this chapter gives a general but non-exhaustive overview of the methods of preparation of organic and bioorganic nanoparticles. Some general definitions about organic nanoparticles and description of organic compounds are given before describing the most common methods used divided into two families, the two-step and one-step procedures. The major part of the two-step procedures is based on an emulsification step followed by generation of nanoparticles through different mechanisms such as precipitation, gelation, or polymerization. The one-step procedures are founded on generation of nanoparticles through different techniques such as nanoprecipitation, desolvation, or drying processes without preliminary emulsification step. For each method, the description is supported by several examples and focused on the explanation of the general mechanisms and of the major key parameters involved in the control of the nanoparticles formation. In addition, since emergence and improvement of syntheses are often associated to development of experimental setups, technological aspects are also mentioned.

Sol–gel route to advanced nanoelectrode arrays (NEA) based on titania gold nanocomposites

A simple sol–gel-coating strategy has been used to prepare below 10 nm thin nanostructured oxide (TiO2) membranes on conducting surfaces. Well calibrated (20 nm in diameter) and homogeneously dispersed nanoperforations are embedded into the membranes, altogether forming highly ordered and dense nanoelectrode arrays (NEAs) or patterns. Controlling the deposition conditions and the solution chemistry allowed for the formation of homogeneous membranes on very hydrophobic, and difficult to wet surfaces, such as gold. Calibrated pore size and interpore spacing are controlled through the self-assembly of macromolecular templates with the inorganic precursors upon evaporation. Structures were assessed by AFM and SEM-FEG, while XPS allowed us to estimate surface chemical state and composition. Cyclic voltammetry was used to describe the diffusion regime and the accessibility of the conducting nanosurfaces. We also show, using surface-tension measurement, that the ceramic matrix can be selectively chemically modified, which is an easy method to adjust the surface chemical nature of an electrode without altering its electron-transfer properties. It thus constitutes a novel route to hybrid organic–inorganic nanostructured surfaces with extended multifunctionality.

New insights into micro/nanoscale combined probes (nanoAuger, μXPS) to characterize Ag/Au@SiO2 core–shell assemblies

This work has examined the elemental distribution and local morphology at the nanoscale of core@shell Ag/Au@SiO2 particles. The characterization of such complex metal/insulator materials becomes more efficient when using an initial cross-section method of preparation of the core@shell nanoparticles (ion milling cross polisher). The originality of this route of preparation allows one to obtain undamaged, well-defined and planar layers of cross-cut nano-objects. Once combined with high-resolution techniques of characterization (XPS, Auger and SEM), the process appears as a powerful way to minimize charging effects and enhance the outcoming electron signal (potentially affected by the topography of the material) during analysis. SEM experiments have unambiguously revealed the hollow-morphology of the metal core, while Auger spectroscopy observations showed chemical heterogeneity within the particles (as silver and gold are randomly found in the core ring). To our knowledge, this is the first time that Auger nano probe spectroscopy has been used and successfully optimized for the study of some complex metal/inorganic interfaces at such a high degree of resolution (≈12 nm). Complementarily, XPS Au 4f and Ag 3d peaks were finally detected attesting the possibility of access to the whole chemistry of such nanostructured assemblies.

Design of Magnetic Gelatine/Silica Nanocomposites by Nanoemulsification: Encapsulation versus in Situ Growth of Iron Oxide Colloids

The design of magnetic nanoparticles by incorporation of iron oxide colloids within gelatine/silica hybrid nanoparticles has been performed for the first time through a nanoemulsion route using the encapsulation of pre-formed magnetite nanocrystals and the in situ precipitation of ferrous/ferric ions. The first method leads to bi-continuous hybrid nanocomposites containing a limited amount of well-dispersed magnetite colloids. In contrast, the second approach allows the formation of gelatine-silica core-shell nanostructures incorporating larger amounts of agglomerated iron oxide colloids. Both magnetic nanocomposites exhibit similar superparamagnetic behaviors. Whereas nanocomposites obtained via an in situ approach show a strong tendency to aggregate in solution, the encapsulation route allows further surface modification of the magnetic nanocomposites, leading to quaternary gold/iron oxide/silica/gelatine nanoparticles. Hence, such a first-time rational combination of nano-emulsion, nanocrystallization and sol-gel chemistry allows the elaboration of multi-component functional nanomaterials. This constitutes a step forward in the design of more complex bio-nanoplatforms.

Thermoresponsive gold nanoshell@mesoporous silica nano-assemblies: an XPS/NMR survey

This work provides a detailed study on the physico-chemical characterization of a mechanized silver-gold alloy@mesoporous silica shell/pseudorotaxane nano-assembly using two main complementary techniques: XPS and NMR (liquid- and solid-state). The pseudorotaxane nanovalve is composed of a stalk (N-(6-aminohexyl)-aminomethyltriethoxysilane)/macrocycle (cucurbit[6]uril (CB6)) complex anchored to the silica shell leading to a silica/nanovalve hybrid organic-inorganic interface that has been fully characterized. The stalk introduction in the silica network was clearly demonstrated by XPS measurements, with the Si 2p peak shifting to lower energy after grafting, and through the analysis of the C 1s and N 1s core peaks, which indicated the presence of CB6 on the nanoparticle surface. For the first time, the complex formation on nanoparticles was proved by high speed (1)H MAS NMR experiments. However, these solid state NMR analyses have shown that the majority of the stalk does not interact with the CB6 macrocycle when formulated in powder after removing the solvent. This can be related to the large number of possible organizations and interactions between the stalk, the CB6 and the silica surface. These results highlight the importance of using a combination of adapted and complementary highly sensitive surface and volume characterization techniques to design tailor-made hybrid hierarchical structured nano-assemblies with controlled and efficient properties for potential biological purposes.

Design of gold nanoshells via a gelatin-mediated self-assembly of gold nanoparticles on silica cores

A gelatin-mediated self-assembly of gold nanoparticles on silica particles has been performed during gold ion reduction using ascorbic acid as reductant and PVP as stabilizer. Gold nanoshells with near infrared photothermal properties have been successfully designed.

Gold and silver quantification from gold-silver nanoshells in HaCaT cells

A method to determine total gold (Au) and/or silver (Ag) elemental concentrations from gold nanoparticles, Au-Ag nanoshells (NS) and silica coated Au-Ag nanoshells was developed, evaluated and validated. Samples were mineralized in a mixture of concentrated aqua regia and hydrofluoric acid at 65 °C for 4 h. Mineralized solutions were diluted and standard solutions were prepared in aqua regia 5%. ICP-MS analysis was performed with or without the use of a reaction cell (CRC). For the determination of elemental concentrations of nanopowders and test suspensions, the average recovery was 99 ± 2% and 101 ± 2% for gold and silver respectively. The repeatability was evaluated by the Relative Standard Deviation (RSD). The overall analytical RSD was ≤4% (n = 3) and the RSD associated to ICP-MS analysis was ≤2% (n = 10). The limits of detection were 0.005 and 0.002 μg(element) L-1 (analyzed solution), and the limits of quantitation 0.017 and 0.005 μg(element) L-1 (analyzed solution), for 197Au and 109Ag respectively. The Ag/Au mass ratios of the NS in the different samples considered were all equal to (0.93 ± 0.04). From this information, the average thickness of gold and silver layers in the nanoshells was deduced, being 7.5 ± 0.5 and 23 ± 3 nm respectively. Finally, the developed method was successfully applied to in vitro studies to evaluate NS cellular uptake in HaCaT keratinocyte cells confirming the method robustness toward biological medium. Experiments in cell culture medium gave coherent concentrations, 70-100% of uncoated or silica-coated NS being recovered, distributed between the culture medium and the cells (internalized). The analytical repeatability (over the whole procedure, or that of the ICP-MS analysis only) remains in the same order of magnitude as in test suspensions. Minimum concentrations less than or equal to 1 μg(element) g-1(suspension) were determined with the same accuracy.

Morphology and Surface Reactivity Relationship in the Li1+xMn2–xO4 Spinel with x = 0.05 and 0.10: A Combined First-Principle and Experimental Study

This article focuses on the surface reactivity of two spinel samples with different stoichiometries and crystal morphologies, namely Li1+xMn2-xO4 with x = 0.05 and 0.10. LiMn2O4 compounds are good candidates as positive electrode of high-power lithium-ion batteries for portable devices. The samples were investigated using both experimental and theoretical approaches. On the experimental point of view, they were characterized in depth from X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy (XPS) analyses. Then, the reactivity was investigated through the adsorption of (SO2) gaseous probes, in controlled conditions, followed by XPS characterization. First-principle calculations were conducted simultaneously to investigate the electronic properties and the reactivity of relevant surfaces of an ideal LiMn2O4 material. The results allow us to conclude that the reactivity of the samples is dominated by an acido-basic reactivity and the formation of sulfite species. Nonetheless, on the x = 0.05 sample, both sulfite and sulfate species are obtained, the later, in lesser extent, corresponding to a redox reactivity. Combining experimental and theoretical results, this redox reactivity could be associated with the presence of a larger quantity of Mn4+ cations on the last surface layers of the material linked to a specific surface orientation.