Revisiting carboxylic group functionalization of silica sol-gel materials.

The carboxylic chemical group is a ubiquitous moiety present in amino acids, a ligand for transition metals, a colloidal stabilizer, and a weak acidic ion-exchanger in polymeric resins and given this property, it is attractive for responsive materials or nanopore-based gating applications. As the number of uses increases, subtle requirements are imposed on this molecular group when anchored to various platforms for the functioning of an integrated chemical system. In this context, silica stands as an inert and multipurpose platform that enables the anchoring of multiple chemical entities combined through several orthogonal synthesis methods on the interface. Surface chemical modification relies on the use of organoalkoxysilanes that must meet the demand of tuned chemical properties; this, in turn, urges for innovative approaches for having an improved, but simple, organic toolbox. Starting from commonly available molecular precursors, several approaches have emerged: hydrosilylation, click thiol-ene additions, the use of carbodiimides or the reaction between cyclic anhydrides and anchored amines. In this review, we analyze the importance of the COOH groups in the area of materials science and the commercial availability of COOH-based silanes and present new approaches for obtaining COOH-based organoalkoxide precursors. Undoubtedly, this will attract widespread interest for the ultimate design of highly integrated chemical platforms.

Photoactive Red Fluorescent SiO2 Nanoparticles Based on Controlled Methylene Blue Aggregation in Reverse Microemulsions.

We present a reverse microemulsion synthesis procedure for incorporating methylene blue (MB), a known FDA-approved type-II red-absorbing photosensitizer and 1O2 generator, into the matrix of hydrophobic-core/hydrophilic-shell SiO2 nanoparticles. Different synthesis conditions were explored with the aim of controlling the entrapped-dye aggregation at high dye loadings in the hydrophobic protective core; minimizing dye aggregation ensured highly efficient photoactive nanoentities for 1O2 production. Monitoring the synthesis in real time using UV-vis absorption allowed tracking of the dye aggregation process. In particular, silica nanoparticles (MB@SiO2 NPs) of ∼50 nm diameter size with a high local entrapped-MB concentration (∼10-2 M, 1000 MB molecules per NP) and a moderate proportion of dye aggregation were obtained. The as-prepared MB@SiO2 NPs showed a high singlet oxygen photogeneration efficiency (ΦΔ = 0.30 ± 0.05), and they can be also considered as red fluorescent probes (ΦF ∼ 0.02, λmax ∼ 650 nm). The distinctive photophysical and photochemical characteristics of the synthesized NPs reveal that the reverse microemulsion synthesis procedure offers an interesting strategy for the development of complex theranostic nano-objects for photodynamic therapy.

Critical Aspects on the Chemical Stability of NaYF4-Based Upconverting Nanoparticles for Biomedical Applications.

This review summarizes essential information about the chemical stability of NaYF4-based upconverting nanoparticles (UCNPs) in aqueous solutions, a crucial aspect for achieving high quality standards for biomedical materials. We present an in-depth analysis of the major experimental evidence and proposed mechanisms that provide a theoretical framework for understanding UCNPs degradation, destabilization, and dissolution under different conditions such as media composition, temperature, particle size, and the synthetic methods employed. The ion release and disintegration of the UCNP crystal structure may trigger cytotoxic events within living organisms and impact on their optical properties, precluding their safe use in biological environments. Also, we present a summary of the characterization techniques' toolbox employed for monitoring and detecting these degradation processes. Closing the existing "information gap" that links UCNP physicochemical properties, such as solubility and chemical stability, with the biological response of living organisms or tissues, is vital for using these nanoparticles as biological tracer probes, theranostic vehicles, or for clinical purposes. The understanding of chemical phenomena at the nanoparticle solid-liquid interface is mandatory to complete the molecular picture of nanosized objects, orienting in a rational manner the efforts of research and development in the early stages of these functional materials.

Light-Induced Polymer Response through Thermoplasmonics Transduction in Highly Monodisperse Core-Shell-Brush Nanosystems.

Smart nanosystems that transduce external stimuli to physical changes are an inspiring challenge in current materials chemistry. Hybrid organic-inorganic materials attract great attention due to the combination of building blocks responsive to specific external solicitations. In this work, we present a sequential method for obtaining an integrated core-shell-brush nanosystem that transduces light irradiation into a particle size change through a thermoplasmonic effect. We first synthesize hybrid monodisperse systems made up of functionalized silica colloids covered with controllable thermoresponsive poly(N-isopropylacrylamide), PNIPAm, brushes, produced through radical photopolymerization. This methodology was successfully transferred to Au@SiO2 nanoparticles, leading to a core-shell-brush architecture, in which the Au core acts as a nanosource of heat; the silica layer, in turn, adapts the metal and polymer interfacial chemistries and can also host a fluorescent dye for bioimaging. Upon green LED irradiation, a light-to-heat conversion process leads to the shrinkage of the external polymer layer, as proven by in situ DLS. Our results demonstrate that modular hybrid nanosystems can be designed and produced with photothermo-physical transduction. These remote-controlled nanosystems present prospective applications in smart carriers, responsive bioscaffolds, or soft robotics.

Mapping the dynamical organization of the cell nucleus through fluorescence correlation spectroscopy.

The hierarchical organization of the cell nucleus into specialized open reservoirs and the nucleoplasm overcrowding impose restrictions to the mobility of biomolecules and their interactions with nuclear targets. These properties determine that many nuclear functions such as transcription, replication, splicing or DNA repair are regulated by complex, dynamical processes that do not follow simple rules. Advanced fluorescence microscopy tools and, in particular, fluorescence correlation spectroscopy (FCS) provide complementary and exquisite information on the dynamics of fluorescent labeled molecules moving through the nuclear space and are helping us to comprehend the complexity of the nuclear structure. Here, we describe how FCS methods can be applied to reveal the dynamical organization of the nucleus in live cells. Specifically, we provide instructions for the preparation of cellular samples with fluorescent tagged proteins and detail how FCS can be easily instrumented in commercial confocal microscopes. In addition, we describe general rules to set the parameters for one and two-color experiments and the required controls for these experiments. Finally, we review the statistical analysis of the FCS data and summarize the use of numerical simulations as a complementary approach that helps us to understand the complex matrix of molecular interactions network within the nucleus.

Diffusion of single dye molecules in hydrated TiO2 mesoporous films.

Mesoporous oxide films are attractive frameworks in technological areas such as catalysis, sensing, environmental protection, and photovoltaics. Herein, we used fluorescence correlation spectroscopy to explore how the pore dimensions of hydrated TiO2 mesoporous calcined films modulate the molecular diffusion. Rhodamine B molecules in mesoporous films follow a Fickian process 2-3 orders slower compared to the probe in water. The mobility increases with the pore and neck radii reaching an approximately constant value for a neck radius >2.8 nm. However, the pore size does not control the dye diffusion at low ionic strength emphasizing the relevance of the probe interactions with the pore walls on dye mobility. In conclusion, our results show that the thermal conditioning of TiO2 mesoporous films provides an exceptional tool for controlling the pore and neck radii on the nanometer scale and has a major impact on molecular diffusion within the mesoporous network.

Chemisorption of lanthanide ions on succinate-functionalized mesoporous silica: An in situ characterization by fluorescence.

Chemisorption of Eu3+ and Tb3+ on SBA-15 functionalized with succinic groups has been studied by in situ steady-state fluorescence measurements. The enhancement of the emission sensitive bands indicates that both ions adsorb forming inner-sphere surface complexes. Adsorption is a fast process that attains equilibrium in about 5min. The variation of the peaks maxima (I592 and I616, for europium, and I490 and I545, for terbium) with the total ion concentration is accounted for by the sum of the contributions due to the adsorbed and free ions. The former contribution is langmuirian. At pH 4.5, the respective adsorption constants are 5×105 and 3×105M-1, and the maximum adsorption capacities are 5.10×10-4 and 5.23×10-4molg-1. The mismatch between the latter values and the number of attached carboxylic groups is discussed. Comparison with other functionalized mesoporous silicas indicates that the anchored succinic groups are very efficient for removing lanthanide ions from aqueous solutions.

A silica supported tricarbocyanine based pH nanosensor with a large Stokes shift and a near infrared fluorescence response: performance in vitro and in live cells.

We report the synthesis of a near-infrared (NIR) fluorescent pH probe with a remarkable Stokes shift (∼135 nm) based on a tricarbocyanine (Cy-PIP). The fluorescent molecule was anchored to SiO2 nanoparticles (Cy-PIP@SiO2) and is capable of monitoring pH changes within the physiological range (pH 6-8). The Cy-PIP@SiO2 nanoparticles were successfully internalized by HeLa cells as shown by fluorescence confocal microscopy, while flow cytometry revealed pH fluctuations during the endocytic pathway.

Glyco-nano-oncology: Novel therapeutic opportunities by combining small and sweet.

Recent efforts toward defining the molecular features of the tumor microenvironment have revealed dramatic changes in the expression of glycan-related genes including glycosyltransferases and glycosidases. These changes affect glycosylation of proteins and lipids not only in cancer cells themselves, but also in cancer associated-stromal, endothelial and immune cells. These glycan alterations including increased frequency of ß1,6-branched N-glycans and bisecting N-glycans, overexpression of tumor-associated mucins, preferred expression of T, Tn and sialyl-Tn antigen and altered surface sialylation, may contribute to tumor progression by masking or unmasking specific ligands for endogenous lectins, including members of the C-type lectin, siglec and galectin families. Differential expression of glycans or glycan-binding proteins could be capitalized for the identification of novel biomarkers and might provide novel opportunities for therapeutic intervention. This review focuses on the biological relevance of lectin-glycan interactions in the tumor microenvironment (mainly illustrated by the immunosuppressive and pro-angiogenic activities of galectin-1) and the design of functionalized nanoparticles for pharmacological delivery of multimeric glycans, lectins or selective inhibitors of lectin-glycan interactions with antitumor activity.

Wired enzymes in mesoporous materials: A benchmark for fabricating biofuel cells.

Evolution of fuel cells using metallic inorganic catalysts has led to the development of biofuel cells with potential applications in implantable devices. However, the main disadvantages in real world applications of enzymatic biofuel cells are short lifetime and low power density. Many efforts have been devoted to immobilize redox enzymes on surfaces to allow efficient electrical communication with electrodes and to provide an adequate habitat for biochemical activity. In this context, nanocavities of mesoporous materials offer a tailored environment for protein immobilization. Mesostructured platforms with high surface area and stability have been developed to enhance mass transport, charge transfer from biocatalysts to electrodes and enzyme stability, leading to biofuel cells with improved power density (up to 602 µW cm(-2) at physiological conditions) and overall performance (high stability after 30 h of continuous operation and after 10 days of storage). This review discusses recent developments using mesoporous materials as novel platforms for effective electronic charge transfer in the context of current and emerging technologies in enzymatic fuel cell research, emphasizing their practical implications and potential improvements leading to a major impact on medical science and portable electronics.

Simple thiol-ene click chemistry modification of SBA-15 silica pores with carboxylic acids.

A straightforward approach for anchoring tailored carboxylic groups in mesoporous SiO2 colloidal materials is presented. The thiol-ene photochemical reaction between vinyltrimethoxysilane precursors and various thiocarboxylic acids which has, click chemistry features (i.e. high conversion yields, insensitivity to oxygen, mild reaction conditions), results in carboxylated silane precursors that can be readily used as surface modifiers. The carboxylic groups of acetic, undecanoic and succinic acid were immobilized on the silica mesopore walls of SBA-15 powders employing the synthesized silane precursors. Post-grafting has been confirmed through infrared spectrometry (FTIR), energy dispersive X-ray spectroscopy (EDS), elemental analysis (EA) and zeta potential measurements. Detailed field-emission gun scanning electron microscopy (FESEM) images and small angle X-ray scattering (SAXS) data revealed parallel mesopores and ordered mesostructures. It is shown that the immobilized COOH groups are chemically accessible for acid-base reactions as well as copper adsorption. Immobilization of easily synthesized tailored carboxylic modified alkoxide precursors within mesoporous systems provides a unique chemical nanoenvironment within these ordered frameworks.

Silver nanoparticle-mesoporous oxide nanocomposite thin films: a platform for spatially homogeneous SERS-active substrates with enhanced stability.

We introduce a nanoparticle-mesoporous oxide thin film composite (NP-MOTF) as low-cost and straightforward sensing platforms for surface-enhanced Raman Spectroscopy (SERS). Titania, zirconia, and silica mesoporous matrices templated with Pluronics F-127 were synthesized via evaporation-induced self-assembly and loaded with homogeneously dispersed Ag nanoparticles by soft reduction or photoreduction. Both methods give rise to uniform and reproducible Raman signals using 4-mercaptopyridine as a probe molecule. Details on stability and reproducibility of the Raman enhancement are discussed. Extensions in the design of these composite structures were explored including detection of nonthiolated molecules, such as rhodamine 6-G or salicylic acid, patterning techniques for locating the enhancement regions and bilayered mesoporous structures to provide additional control on the environment, and potential size-selective filtration. These inorganic oxide-metal composites stand as extremely simple, reproducible, and versatile platforms for Raman spectroscopy analysis.

When size does matter: organelle size influences the properties of transport mediated by molecular motors.

BACKGROUND: Organelle transport is driven by the action of molecular motors. In this work, we studied the dynamics of organelles of different sizes with the aim of understanding the complex relation between organelle motion and microenvironment. METHODS: We used single particle tracking to obtain trajectories of melanosomes (pigmented organelles in Xenopus laevis melanophores). In response to certain hormones, melanosomes disperse in the cytoplasm or aggregate in the perinuclear region by the combined action of microtubule and actin motors. RESULTS AND CONCLUSIONS: Melanosome trajectories followed an anomalous diffusion model in which the anomalous diffusion exponent (α) provided information regarding the trajectories' topography and thus of the processes causing it. During aggregation, the directionality of big organelles was higher than that of small organelles and did not depend on the presence of either actin or intermediate filaments (IF). Depolymerization of IF significantly reduced α values of small organelles during aggregation but slightly affect their directionality during dispersion. GENERAL SIGNIFICANCE: Our results could be interpreted considering that the number of copies of active motors increases with organelle size. Transport of big organelles was not influenced by actin or IF during aggregation showing that these organelles are moved processively by the collective action of dynein motors. Also, we found that intermediate filaments enhance the directionality of small organelles suggesting that this network keeps organelles close to the tracks allowing their efficient reattachment. The higher directionality of small organelles during dispersion could be explained considering the better performance of kinesin-2 vs. dynein at the single molecule level.

Temperature response of luminescent tris(bipyridine)ruthenium(II)-doped silica nanoparticles.

Nanoparticle-based temperature imaging is an emerging field of advanced applications. Herein, the sensitivity of the phosphorescence of tris(bipyridine)ruthenium(II)-doped silica nanoparticles towards temperature is studied. 130 nm size particles were prepared by a modification of Stöber's method, that allows the incorporation of Ru[(bpy)(3)](2+) into the outer particle shell. The entrapped Ru[(bpy)(3)](2+) retains its photophysical properties, yet the emission of the particles is not affected by the presence of O(2), neither by anionic quenchers; quenching by MV(2+), on the other hand, is strongly dependent on pH. Between 20 and 60°C, the steady-state emission of the particles decreases linearly with increasing temperature. The slope of the straight line diminishes slightly on thermal cycling, but soon stabilizes. Fluorescence measurements by scanning confocal microscopy indicate that the silica nanoparticles doped with Ru[(bpy)(3)](2+) can indeed be employed to probe thermal processes in micro-environments.

ATP and Mg2+ promote the reversible oligomerization and aggregation of chloroplast 2-Cys peroxiredoxin.

2-Cys peroxiredoxins (2-Cys Prxs) are ubiquitous peroxidases with important roles in cellular antioxidant defense and hydrogen peroxide-mediated signaling. Post-translational modifications of conserved cysteines cause the transition from low to high molecular weight oligomers, triggering the functional change from peroxidase to molecular chaperone. However, it remains unclear how non-covalent interactions of 2-Cys Prx with metabolites modulate the quaternary structure. Here, we disclose that ATP and Mg(2+) (ATP/Mg) promote the self-polymerization of chloroplast 2-Cys Prx (polypeptide 23.5 kDa) into soluble higher order assemblies (>2 MDa) that proceed to insoluble aggregates beyond 5 mM ATP. Remarkably, the withdrawal of ATP or Mg(2+) brings soluble oligomers and insoluble aggregates back to the native conformation without compromising the associated functions. As confirmed by transmission electron microscopy, ATP/Mg drive the toroid-like decamers (diameter 13 nm) to the formation of large sphere-like particles (diameter ∼30 nm). Circular dichroism studies on ATP-labeled 2-Cys Prx reveal that ATP/Mg enhance the proportion of ß-sheets with the concurrent decrease in the content of α-helices. In line with this observation, the formation of insoluble aggregates is strongly prevented by 2,2,2-trifluoroethanol, a cosolvent employed to induce α-helical conformations. We further find that the response of self-polymerization to ATP/Mg departs abruptly from that of the associated peroxidase and chaperone activities when two highly conserved residues, Arg(129) and Arg(152), are mutated. Collectively, our data uncover that non-covalent interactions of ATP/Mg with 2-Cys Prx modulate dynamically the quaternary structure, thereby coupling the non-redox chemistry of cell energy with redox transformations at cysteine residues.

Mesoporous ZnS nanorattles: programmed size selected access to encapsulated enzymes.

A size selective nanorattle was formed by encapsulating soybean peroxidase (SBP) within a ZnS mesoporous hollow sphere. Once encapsulated within the mesoporous hollow sphere, the SBP remained active against molecules smaller than the 3 nm diameter of the mesopores in the shell wall, while molecules larger than the mesopores, which could not pass into the hollow sphere, did not interact with the SBP. Specifically, encapsulated SBP catalyzed the oxidation of Amplex Ultra-Red, a small fluorogen, in the presence of hydrogen peroxide, encapsulated SBP was deactivated by sodium azide, and no reaction was observed between encapsulated SBP and a greater than 3 nm diameter protease.

Double direct templating of periodically nanostructured ZnS hollow microspheres.

We introduce a "double direct templating" method for obtaining hollow microspheres with periodically nanostructured walls. Silica or polystyrene colloids are dispersed in a self-assembled hexagonal lyotropic liquid crystal containing precursors for ZnS. The semiconductor ZnS mineralizes on the surface of the colloid, expressing a pore morphology that is a copy of the structure of the liquid crystal. After etching of the sacrificial colloids, hollow capsules with templated and uniform mesoporous shells are obtained.

Wiring enzymes in nanostructures built with electrostatically self-assembled thin films.

The construction of electrostatically self-assembled intelligent nanostructures on electrodes with redox enzyme layers and redox polymer molecular wires defined in space allowed the analysis of redox charge transport from the redox enzyme to the electrode along nanometric distances. Recent results on the electrical connection of enzymes to electrodes and perspectives of generating electrical signals from molecular recognition in integrated enzyme electrodes are discussed.

Supramolecular multilayer structures of wired redox enzyme electrodes.

Supramolecular multilayer structures comprised of glucose oxidase (GOx), and Os complex derivatised poly(allylamine) (PAH-Os) have been built by alternate layer-by-layer (LBL) electrostatic adsorption in a self-assembly process. The resulting modified electrodes with integrated mediator were tested as reagentless glucose biosensors. The enzyme kinetic parameters and the surface concentration of "wired" enzyme GammaE have been obtained by analysis of the catalytic current dependence on glucose concentrations for the ping-pong mechanism of glucose oxidation. An average osmium volume concentration was estimated by integration of the redox charge in the absence of glucose and the ellipsometric thickness. The total enzyme surface concentration was measured with a quartz crystal microbalance (QCM) during each adsoption step and the fraction of "wired" enzyme and the bimolecular rate constant for FADH2 oxidation by the redox polymer for the different multilayers. The catalytic current increases with the number of LBL layers because the increase in the enzyme loading while the efficiency of enzyme FADH2 oxidation by the Os redox polymer, except for the first dipping cycle remains almost constant at about 2 x 10(4) M(-1) S(-1).