Zr-Porphyrin Metal-Organic Framework as nanoreactor for boosting the formation of hydrogen clathrates.

We report the first experimental evidence for rapid formation of hydrogen clathrates under mild pressure and temperature conditions within the cavities of a zirconium-metalloporphyrin framework, specifically PCN-222. PCN-222 has been selected for its 1D mesoporous channels, high water-stability, and proper hydrophilic behavior. Firstly, we optimize a microwave (MW)-assisted method for the synthesis of nanosized PCN-222 particles with precise structure control (exceptional homogeneity in morphology and crystalline phase purity), taking advantage of MW in terms of rapid/homogeneous heating, time and energy savings, as well as potential scalability of the synthetic method. Second, we explore the relevance of the large mesoporous 1D open channels within the PCN-222 to promote the nucleation and growth of confined hydrogen clathrates. Experimental results show that PCN-222 drives the nucleation process at a lower pressure than the bulk system (1.35 kbar vs 2 kbar), with fast kinetics (minutes), using pure water, and with a nearly complete water-to-hydrate conversion. Unfortunately, PCN-222 cannot withstand these high pressures, which lead to a significant alteration of the mesoporous structure while the microporous network remains mainly unchanged.

A selenoureido-iminoglycolipid transported by zeolitic-imidazolate framework nanoparticles: a novel antioxidant therapeutic approach.

A selenium-containing metal-organic framework with remarkable antioxidant capacity and ROS-scavenging activity was constructed by a controlled de novo encapsulation approach of a glycoconjugate mimetic, specifically a sp2-iminoglycolipid bearing a selenoureido fragment (DSeU), within a zeolitic-imidazolate framework exoskeleton. Biocompatible and homogeneous nanosized particles of ∼70 nm (DSeU@ZIF8) were obtained, which could be efficiently internalized in cells, overcoming the poor solubility in biological media and limited bioavailability of glycolipids. The ZIF-particle served as nanocarrier for the intracellular delivery of the selenocompound to cells, promoted by the acidic pH inside endosomes/lysosomes. As demonstrated by in vitro studies, the designed DSeU@ZIF8 nanoparticles displayed a high antioxidant activity at low doses; lower intracellular ROS levels were observed upon the uptake of DSeU@ZIF8 by human endothelial cells. Even more interesting was the finding that these DSeU@ZIF8 particles were able to reverse to a certain level the oxidative stress induced in cells by pre-treatment with an oxidizing agent. This possibility of modulating the oxidative stress in living cells may have important implications in the treatment of diverse pathological complications that are generally accompanied with elevated ROS levels.

Enzyme-Responsive Zr-Based Metal-Organic Frameworks for Controlled Drug Delivery: Taking Advantage of Clickable PEG-Phosphate Ligands.

We report for the first time the controlled drug release from a nanoscale Zr-based metal-organic framework (MOF), UiO-66, in the presence of the enzyme alkaline phosphatase (ALP). This unprecedented reactivity was possible thanks to the prior functionalization of the MOF with N3-PEG-PO3 ligands, which were designed for three specific aims: (1) to impart colloidal stability in phosphate-containing media; (2) to endow the MOF with multifunctionality thanks to azide groups for the covalent attachment of an imaging agent by click-chemistry; and (3) to confer stimuli-responsive properties, specifically the selective release of doxorubicin triggered by the enzymatic activity of ALP. Cell studies revealed that the functionalization of the MOF with N3-(PEG)20-PO3 ligands improved their intracellular stability and led to a sustained drug release compared to the bare MOF. More importantly, an enhanced drug release was observed in cells with higher expression of ALP genes (HeLa versus MDA-MB-231 and MCF7), confirming the ALP-responsiveness of the system inside living cells.

Recent progress of metal-organic frameworks as sensors in (bio)analytical fields: towards real-world applications.

The deployment of metal-organic frameworks (MOFs) in a plethora of analytical and bioanalytical applications is a growing research area. Their unique properties such as high but tunable porosity, well-defined channels or pores, and ease of post-synthetic modification to incorporate additional functional units make them ideal candidates for sensing applications. This is possible because the interaction of analytes with a MOF often results in a change in its structure, eventually leading to a modification of the intrinsic physicochemical properties of the MOF which is then transduced into a measurable signal. The high porosity allows for the adsorption of analytes very efficiently, while the tunable pore sizes/nature and/or installation of specific recognition groups allow modulating the affinity towards different classes of compounds, which in turn lead to good sensor sensitivity and selectivity, respectively. Some figures are given to illustrate the potential of MOF-based sensors in the most relevant application fields, and future challenges and opportunities to their possible translation from academia (i.e., laboratory testing of MOF sensing properties) to industry (i.e., real-world analytical sensor devices) are critically discussed.

Incorporating zeolitic-imidazolate framework-8 nanoparticles into kidney scaffolds: a first step towards innovative renal therapies.

We demonstrate for the first time the potential of zeolitic-imidazolate framework-8 nanoparticles to be incorporated within a renal scaffold while retaining their ability to remove uremic toxins (mainly hydrophobic toxins like p-cresol) under flow conditions. This work may pave the way for the future development of novel adsorbents for dialysis and/or artificial kidneys.

Plasmonic-Assisted Thermocyclizations in Living Cells Using Metal-Organic Framework Based Nanoreactors.

We describe a microporous plasmonic nanoreactor to carry out designed near-infrared (NIR)-driven photothermal cyclizations inside living cells. As a proof of concept, we chose an intramolecular cyclization that is based on the nucleophilic attack of a pyridine onto an electrophilic carbon, a process that requires high activation energies and is typically achieved in bulk solution by heating at ∼90 °C. The core-shell nanoreactor (NR) has been designed to include a gold nanostar core, which is embedded within a metal-organic framework (MOF) based on a polymer-stabilized zeolitic imidazole framework-8 (ZIF-8). Once accumulated inside living cells, the MOF-based cloak of NRs allows an efficient diffusion of reactants into the plasmonic chamber, where they undergo the transformation upon near-IR illumination. The photothermal-driven reaction enables the intracellular generation of cyclic fluorescent products that can be tracked using fluorescence microscopy. The strategy may find different type of applications, such as for the spatio-temporal activation of prodrugs.

In Vitro Cellular Uptake Studies of Self-Assembled Fluorinated Nanoparticles Labelled with Antibodies.

Nanoparticles (NPs) functionalized with antibodies (Abs) on their surface are used in a wide range of bioapplications. Whereas the attachment of antibodies to single NPs to trigger the internalization in cells via receptor-mediated endocytosis has been widely studied, the conjugation of antibodies to larger NP assemblies has been much less explored. Taking into account that NP assemblies may be advantageous for some specific applications, the possibility of incorporating targeting ligands is quite important. Herein, we performed the effective conjugation of antibodies onto a fluorescent NP assembly, which consisted of fluorinated Quantum Dots (QD) self-assembled through fluorine-fluorine hydrophobic interactions. Cellular uptake studies by confocal microscopy and flow cytometry revealed that the NP assembly underwent the same uptake procedure as individual NPs; that is, the antibodies retained their targeting ability once attached to the nanoassembly, and the NP assembly preserved its intrinsic properties (i.e., fluorescence in the case of QD nanoassembly).

Exploiting the Potential of Biosilica from Rice Husk as Porous Support for Catalytically Active Iron Oxide Nanoparticles.

Biomass-derived materials are put forward as eco-friendly alternatives to design heterogeneous catalysts. To contribute in this field, we explored the potential of mesoporous biogenic silica (RH-Silica) obtained from lignocellulosic waste, in particular from rice husk, as an inorganic support to prepare heterogenized iron oxide-based catalysts. Mechanochemistry, considered as a green and sustainable technique, was employed to synthetize iron oxide nanoparticles in pure hematite phase onto the biosilica (α-Fe2O3/RH-Silica), making this material a good candidate to perform catalyzed organic reactions. The obtained material was characterized by different techniques, and its catalytic activity was tested in the selective oxidation of styrene under microwave irradiation. α-Fe2O3/RH-Silica displayed a good catalytic performance, achieving a conversion of 45% under optimized conditions, and more importantly, with a total selectivity to benzaldehyde. Furthermore, a good reusability was achieved without decreasing its activity after multiple catalytic cycles. This work represents a good example of using sustainable approaches and green materials as alternatives to conventional methods in the production of high-added value products.

Rapid, Effective, and Versatile Extraction of Gluten in Food with Application on Different Immunological Methods.

One of the main concerns in gluten analysis is to achieve efficient extraction of gluten proteins. Conventional ethanol-based extraction solutions are inefficient and, because of this, it is necessary to use reducing agents or acids for proper solubilization. The extraction recommended by CODEX Standard 118-1979 (revised 2008) utilizes Cocktail solution (patent WO 02/092633 A1). However, it is harmful with a disgusting odor and is not compatible with some immunological techniques. Here, the versatility and extraction capacity of a new Universal Gluten Extraction Solution (UGES) (patent ES 2 392 412 A1) were evaluated using different methodological conditions, food matrices, and various immunological methods. UGES includes safer compounds for both the user and the environment, and it displayed similar extraction efficiency to that of the extraction method recommended for sandwich enzyme-linked immunosorbent assay (ELISA). The extraction time was significantly reduced from 100 to 40 min, depending on the type of the sample. Furthermore, unlike the currently used solution, UGES is compatible with competitive ELISA.

Core-Shell Palladium/MOF Platforms as Diffusion-Controlled Nanoreactors in Living Cells and Tissue Models.

Translating the potential of transition metal catalysis to biological and living environments promises to have a profound impact in chemical biology and biomedicine. A major challenge in the field is the creation of metal-based catalysts that remain active over time. Here, we demonstrate that embedding a reactive metallic core within a microporous metal-organic framework-based cloak preserves the catalytic site from passivation and deactivation, while allowing a suitable diffusion of the reactants. Specifically, we report the fabrication of nanoreactors composed of a palladium nanocube core and a nanometric imidazolate framework, which behave as robust, long-lasting nanoreactors capable of removing propargylic groups from phenol-derived pro-fluorophores in biological milieu and inside living cells. These heterogeneous catalysts can be reused within the same cells, promoting the chemical transformation of recurrent batches of reactants. We also report the assembly of tissue-like 3D spheroids containing the nanoreactors and demonstrate that they can perform the reactions in a repeated manner.

Toward Diffusion Measurements of Colloidal Nanoparticles in Biological Environments by Nuclear Magnetic Resonance.

Protein corona formation on the surface of nanoparticles (NPs) is observed in situ by measuring diffusion coefficients of the NPs under the presence of proteins with a 19 F nuclear magnetic resonance (NMR) based methodology. Formation of a protein corona reduces the diffusion coefficient of the NPs, based on an increase in their effective hydrodynamic radii. With this methodology it is demonstrated that the apparent dissociation constant of protein-NP complexes may vary over at least nine orders of magnitude for different types of proteins, in line with the Vroman effect. Using this methodology, the interaction between one type of protein and one type of nanoparticle can be studied quantitatively. Due to the NMR-based detection, this methodology has no interference by absorption/scattering effects, by which optical detection schemes are affected. By using the potential of the NMR chemical shift, the detection of multiple 19 F signals simultaneously opens the possibility to study the diffusion of several NPs at the same time. The 19 F labeling of the NPs has negligible effect on their acute toxicity and moderate effect on NPs uptake by cells.

Nanoscale metal-organic frameworks as key players in the context of drug delivery: evolution toward theranostic platforms.

Metal-organic frameworks (MOFs) have emerged as one of the most fascinating libraries of porous materials with a huge potential in very diverse application areas. In particular, the bioanalytical and biomedical fields have evolved tremendously due to the emergence of these hybrid inorganic-organic MOF-based materials. This is because these materials possess a series of key properties essential for bioapplications, such as minimal toxicity to living cells, intrinsic biodegradability, and possibility of synthesizing with nanoscale sizes. Additional properties of MOFs such as ultra-large surface-to-volume ratios, tunable pore size, high drug loading capacity, tunable structure and chemical composition, and potential for multiple postsynthetic modification make them ideal candidates for drug delivery. This review highlights recent research progress on MOF-based drug delivery systems (DDS), pointing out the evolution of these systems toward the development of theranostic nanoplatforms. Rather than a comprehensive review, representative recent examples are selected to illustrate such an evolution, and a critical discussion of the advantages and limitations of the different DDS types is given. Finally, the remaining challenges and future opportunities in this field are presented, highlighting that overcoming the current issues will pave the way toward the elusive dream of "personalized medicine." Graphical Abstract.

Triple-Labeling of Polymer-Coated Quantum Dots and Adsorbed Proteins for Tracing their Fate in Cell Cultures.

Colloidal CdSe/ZnS quantum dots were water solubilized by overcoating with an amphiphilic polymer. Human serum albumin (HSA) as a model protein was either adsorbed or chemically linked to the surface of the polymer-coated quantum dots. As the quantum dots are intrinsically fluorescent, and as the polymer coating and the HSA were fluorescent labeled, the final nanoparticle had three differently fluorescent components: the quantum dot core, the polymer shell, and the human serum albumin corona. Cells were incubated with these hybrid nanoparticles, and after removal of non-internalized nanoparticles, exocytosis of the three components of the nanoparticles was observed individually by flow cytometry and confocal microscopy. The data indicate that HSA is partly transported with the underlying polymer-coated quantum dots into cells. Upon desorption of proteins, those initially adsorbed to the quantum dots remain longer inside cells compared to free proteins. Part of the polymer shell is released from the quantum dots by enzymatic degradation, which is on a slower time scale than protein desorption. Data are quantitatively analyzed, and experimental pitfalls, such as the impact of cell proliferation and fluorescence quenching, are discussed.

Aqueous Stable Gold Nanostar/ZIF-8 Nanocomposites for Light-Triggered Release of Active Cargo Inside Living Cells.

A plasmonic core-shell gold nanostar/zeolitic-imidazolate-framework-8 (ZIF-8) nanocomposite was developed for the thermoplasmonic-driven release of encapsulated active molecules inside living cells. The nanocomposites were loaded, as a proof of concept, with bisbenzimide molecules as functional cargo and wrapped with an amphiphilic polymer that prevents ZIF-8 degradation and bisbenzimide leaking in aqueous media or inside living cells. The demonstrated molecule-release mechanism relies on the use of near-IR light coupled to the plasmonic absorption of the core gold nanostars, which creates local temperature gradients and thus, bisbenzimide thermodiffusion. Confocal microscopy and surface-enhanced Raman spectroscopy (SERS) were used to demonstrate bisbenzimide loading/leaking and near-IR-triggered cargo release inside cells, thereby leading to DNA staining.

Fluorinated CdSe/ZnS quantum dots: Interactions with cell membrane.

Fluorescent inorganic quantum dots are highly promising for biomedical applications as sensing and imaging agents. However, the low internalization of the quantum dots, as well as for most of the nanoparticles, by living cells is a critical issue which should be solved for success in translational research. In order to increase the internalization rate of inorganic CdSe/ZnS quantum dots, they were functionalized with a fluorinated organic ligand. The fluorinated quantum dots displayed an enhanced surface activity, leading to a significant cell uptake as demonstrated by in vitro experiments with HeLa cells. We combined the experimental and computational results of Langmuir monolayers of the DPPC phospholipid as a model cell membrane with in vitro experiments for analyzing the mechanism of internalization of the fluorinated CdSe/ZnS quantum dots. Surface pressure-molecular area isotherms suggested that the physical state of the DPPC molecules was greatly affected by the quantum dots. UV-vis reflection spectroscopy and Brewster Angle Microscopy as in situ experimental techniques further confirmed the significant surface concentration of quantum dots. The disruption of the ordering of the DPPC molecules was assessed. Computer simulations offered detailed insights in the interaction between the quantum dots and the phospholipid, pointing to a significant modification of the physical state of the hydrophobic region of the phospholipid molecules. This phenomenon appeared as the most relevant step in the internalization mechanism of the fluorinated quantum dots by cells. Thus, this work sheds light on the role of fluorine on the surface of inorganic nanoparticles for enhancing their cellular uptake.

Surface-Active Fluorinated Quantum Dots for Enhanced Cellular Uptake.

Fluorescent nanoparticles, such as quantum dots, hold great potential for biomedical applications, mainly sensing and bioimaging. However, the inefficient cell uptake of some nanoparticles hampers their application in clinical practice. Here, the effect of the modification of the quantum dot surface with fluorinated ligands to increase their surface activity and, thus, enhance their cellular uptake was explored.

Study of Fluorinated Quantum Dots-Protein Interactions at the Oil/Water Interface by Interfacial Surface Tension Changes.

Understanding the interaction of nanoparticles with proteins and how this interaction modifies the nanoparticles’ surface is crucial before their use for biomedical applications. Since fluorinated materials are emerging as potential imaging probes and delivery vehicles, their interaction with proteins of biological interest must be studied in order to be able to predict their performance in real scenarios. It is known that fluorinated planar surfaces may repel the unspecific adsorption of proteins but little is known regarding the same process on fluorinated nanoparticles due to the scarce examples in the literature. In this context, the aim of this work is to propose a simple and fast methodology to study fluorinated nanoparticle-protein interactions based on interfacial surface tension (IFT) measurements. This technique is particularly interesting for fluorinated nanoparticles due to their increased hydrophobicity. Our study is based on the determination of IFT variations due to the interaction of quantum dots of ca. 5 nm inorganic core/shell diameter coated with fluorinated ligands (QD_F) with several proteins at the oil/water interface. Based on the results, we conclude that the presence of QD_F do not disrupt protein spontaneous film formation at the oil/water interface. Even if at very low concentrations of proteins the film formation in the presence of QD_F shows a slower rate, the final interfacial tension reached is similar to that obtained in the absence of QD_F. The differential behaviour of the studied proteins (bovine serum albumin, fibrinogen and apotransferrin) has been discussed on the basis of the adsorption affinity of each protein towards DCM/water interface and their different sizes. Additionally, it has been clearly demonstrated that the proposed methodology can serve as a complementary technique to other reported direct and indirect methods for the evaluation of nanoparticle-protein interactions at low protein concentrations.

Taking Advantage of Hydrophobic Fluorine Interactions for Self-Assembled Quantum Dots as a Delivery Platform for Enzymes.

Self-assembly of nanoparticles provides unique opportunities as nanoplatforms for controlled delivery. By exploiting the important role of noncovalent hydrophobic interactions in the engineering of stable assemblies, nanoassemblies were formed by the self-assembly of fluorinated quantum dots in aqueous medium through fluorine-fluorine interactions. These nanoassemblies encapsulated different enzymes (laccase and α-galactosidase) with encapsulation efficiencies of ≥74 %. Importantly, the encapsulated enzymes maintained their catalytic activity, following Michaelis-Menten kinetics. Under an acidic environment the nanoassemblies were slowly disassembled, thus allowing the release of encapsulated enzymes. The effective release of the assayed enzymes demonstrated the feasibility of this nanoplatform to be used in pH-mediated enzyme delivery. In addition, the as-synthesized nanoassemblies, having a diameter of about 50 nm, presented high colloidal stability and fluorescence emission, which make them a promising multifunctional nanoplatform.

Cyclodextrin-modified nanodiamond for the sensitive fluorometric determination of doxorubicin in urine based on its differential affinity towards ß/γ-cyclodextrins.

The manuscript reports on the preparation of ß-cyclodextrin-modified nanodiamonds (ßCD-ND) for the extraction and preconcentration of the fluorescent anticancer drug doxorubicin (DOX) from biological samples. The inclusion of DOX into the cavities of ß- and γ-cyclodextrin (CD) confirms their utility for selective extraction and elution of the drug based on its good fit to the cyclodextrin cavity. Although both larger cyclodextrins (ßCD and γCD) accommodate DOX, DOX clearly prefers the bigger γCD cavities. Dispersive micro solid-phase extraction using ßCD-ND as sorbent enables the inclusion complexation of DOX. The elution of DOX from ßCD-ND cavities occurs with a basic solution of γCD containing 10% acetonitrile owing to the preferential affinity (i.e. optimal fit) of DOX into the larger γCD cavity. DOX is quantified by monitoring its intrinsic fluorescence (exc/em = 475/595 nm). The method can determine DOX in urine with a limit of detection of 18 ng·mL-1. Recoveries (93.2% and 94.0%) and precision (RSDs of 5.9% and 4.7%) at 100 and 400 ng·mL-1 DOX levels in urine are satisfactory. The matrix effect is negligible even when working with undiluted urine samples. Graphical abstract Nanodiamonds functionalized with ß-cyclodextrin (ßCD-ND) were used as sorbent for the determination of nanomolar levels of doxorubicin (DOX). It is based on host:guest interactions ruled by different stabilities of DOX within cyclodextrin (CD) cavity-size: ßCD/γCD.

In situ detection of the protein corona in complex environments.

Colloidal nanoparticles (NPs) are a versatile potential platform for in vivo nanomedicine. Inside blood circulation, NPs may undergo drastic changes, such as by formation of a protein corona. The in vivo corona cannot be completely emulated by the corona formed in blood. Thus, in situ detection in complex media, and ultimately in vivo, is required. Here we present a methodology for determining protein corona formation in complex media. NPs are labeled with 19F and their diffusion coefficient measured using 19F diffusion-ordered nuclear magnetic resonance (NMR) spectroscopy. 19F diffusion NMR measurements of hydrodynamic radii allow for in situ characterization of NPs in complex environments by quantification of protein adsorption to the surface of NPs, as determined by increase in hydrodynamic radius. The methodology is not optics based, and thus can be used in turbid environments, as in the presence of cells.