A Gadolinium(III) Zeolite-like Metal-Organic-Framework-Based Magnetic Resonance Thermometer

A green approach to encapsulate proteins and enzymes within crystalline lanthanide-based Tb and Gd MOFs

In this work, bovine serum albumin (BSA) and Aspergillus sp. laccase (LC) were encapsulated in situ within two lanthanide-based MOFs (TbBTC and GdBTC) through a green one-pot synthesis (almost neutral aqueous solution, T = 25 °C, and atmospheric pressure) in about 1 h. Pristine MOFs and protein-encapsulated MOFs were characterized through wide angle X-ray scattering, scanning electron microscopy, thermogravimetric analysis, Fourier transform infrared and Raman spectroscopies. The location of immobilized BSA molecules, used as a model protein, was investigated through small angle X-ray scattering. BSA occurs both on the inner and on the outer surface of the MOFs. LC@TbBTC, and LC@GdBTC samples were also characterized in terms of specific activity, kinetic parameters, and storage stability both in water and acetate buffer. The specific activity of LC@TbBTC was almost twice that of LC@GdBTC (10.8 μmol min-1 mg-1vs. 6.6 μmol min-1 mg-1). Both biocatalysts showed similar storage stabilities retaining ∼60% of their initial activity after 7 days and ∼20% after 21 days. LC@TbBTC dispersed in acetate buffer exhibited a higher storage stability than LC@GdBTC. Additionally, terbium-based MOFs showed interesting luminescent properties. Together, these findings suggest that TbBTC and GdBTC are promising supports for the in situ immobilization of proteins and enzymes.

Organizing Photosensitive and Photothermal Single-Sites Uniformly in a Trimetallic Metal-Organic Framework for Efficient Photocatalytic Hydrogen Evolution

Effective combination of the photosensitivity and photothermal property in photocatalyst is vital to achieve the maximum light utilization for superior photocatalytic efficiency. Herein, this work successfully organizes photosensitive Cd-NS single-sites and photothermal Ni-NS single-sites uniformly at a molecular level within a tailored trimetallic metal-organic framework. The optimized Ho6-Cd0.76Ni0.24-NS exhibits a superior photocatalytic hydrogen evolution rate of 40.06 mmol g-1 h-1 under visible-light irradiation and an apparent quantum efficiency of 29.37% at 420 nm without using cocatalysts or photosensitizers. A systematical mechanism study reveals that the uniformly organized photosensitive and photothermal single-sites have synergistic effect, which form ultrashort pathways for efficient transport of photoinduced electrons, suppress the recombination of photogenerated charge carriers, hence promote the hydrogen evolution activity. This work provides a promising approach for organizing dual-functional single-sites uniformly in photocatalyst for high-performance photocatalytic activity.

A Hexanuclear Gadolinium(III)-Based Nanoprobe for Magnetic Resonance Imaging of Tumor Apoptosis

Magnetic resonance imaging (MRI) is instrumental in the noninvasive evaluation of tumor tissues in patients subjected to chemotherapy, thereby yielding essential diagnostic data crucial for the prognosis of tumors and the formulation of therapeutic strategies. Currently, commercially available MRI contrast agents (CAs) predominantly consist of mononuclear gadolinium(III) complexes. Because there is only one Gd(III) atom per molecule, these CAs often require administration in high doses to achieve the desired contrast quality, which inevitably leads to some adverse events. Herein, we develop a six-nuclei, apoptosis-targeting T1 CA, Gd6-ZnDPA nanoprobe, which consists of a hexanuclear gadolinium nanocluster (Gd6) with an apoptosis-targeting group (ZnDPA). The amplification of Gd(III) by the hexanuclear structure generates its high longitudinal relaxivity (44.67 mM-1 s-1, 1T) and low r1/r2 ratio (0.68, 1T). Based on the Solomon-Bloembergen-Morgan (SBM) theory, this notable improvement is primarily ascribed to a long correlation tumbling time (τR). More importantly, the Gd6-ZnDPA nanoprobe shows excellent tumor apoptosis properties with an enhanced MR signal ratio (∼74%) and a long MRI imaging acquisition time window (∼48 h) in 4T1 tumor-bearing mice. This study introduces an experimental gadolinium-based CA for the potential imaging of tumor apoptosis in the context of MRI.

Preparation of size-tunable Fe3O4 magnetic nanoporous carbon composites by MOF pyrolysis regulation for magnetic resonance sensing of aflatoxin B1 with excellent anti-matrix effect

Magnetic nanoporous materials represent a new emerging category of magnetic materials for construction of magnetic resonance sensors. In this study, we adopted the metal-organic framework materials, MIL-101(Fe), as the precursor to prepare series nanoporous-carbon-Fe3O4 (NPC-Fe3O4) composites. Results showed that Fe3O4 were uniformly distributed in MIL-101(Fe) and the size of MNP was precisely tuned at different pyrolysis temperatures, conferring the optimal NPC-Fe3O4-450 °C composite with dramatically improved T2 relaxivity. The NPC-Fe3O4-450 °C composite was modified with antibodies and antigens, respectively, for detection of aflatoxin B1 in various food samples with complicated matrix. Range from 0.010 ng mL-1 to 2.0 ng mL-1, extreme low detection limit of 5.0 pg mL-1, and satisfied recoveries were successfully achieved, indicating excellent anti-matrix effect. These findings offer a new dimension to engineer novel magnetic materials with improved relaxivity for simple and easy sensing of food hazards in complicated food matrix without any purification or separation procedures.

The influence of light on the field-induced magnetization dynamics of two Er(III) coordination polymers with different halogen substituents

Photocontrolled magnetic properties are fundamental for the applications of molecular magnets, which have the features of high time and space resolution; however, such magnetic properties are highly challenging to be achieved owing to the weak light-matter interactions. Herein, the influence of in situ light irradiation on the field-induced magnetization dynamics of two Er(III) coordination polymers 1 and 2 with the same coordination skeletons but different halogen substituents was studied. 1 and 2, and their in situ photoexcited products 1a and 2a, display field-induced magnetization dynamics based on Orbach and/or Raman processes. The magnetization dynamics are fine-modulated by the synergetic effect of light irradiation and a ligand substituent, due to the charge re-distribution of the excited states of the ligand.

Modulation of magnetization dynamics of an Er(III) coordination polymer by the conversion of a ligand to a radical using UV light

Light-induced substance conversion is highly promising for creating new radical-based compounds. Herein, we report an Er(III) coordination polymer [Er(CA)(ACA)(DMF)(H₂O)]_n (1) and its Y(III)-diluted analogue 1@Y (H₂CA = 2,5-dichloro-3,6-dihydroxy-p-quinone, HACA = 9-anthracene carboxylic acid) with the light-induced transformation of the ligand to a radical. The χ_MT values of light-transformed products 1a and 1a@Y are higher than those of 1 and 1@Y, respectively, due to the formation of radicals by ultraviolet light irradiation, confirmed by EPR measurement as well. The effective energy barriers for magnetization reversal (U_eff) decrease from 72 K for 1 to 67 K for 1a, and from 117 K for 1@Y to 94 K for 1a@Y. This work not only provides a new light-conversion system but also reveals the nature of photo-induced variation of magnetic properties.

Principles of Design and Synthesis of Metal Derivatives from MOFs

Materials derived from metal-organic frameworks (MOFs) have demonstrated exceptional structural variety and complexity and can be synthesized using low-cost scalable methods. Although the inherent instability and low electrical conductivity of MOFs are largely responsible for their low uptake for catalysis and energy storage, a superior alternative is MOF-derived metal-based derivatives (MDs) as these can retain the complex nanostructures of MOFs while exhibiting stability and electrical conductivities of several orders of magnitude higher. The present work comprehensively reviews MDs in terms of synthesis and their nanostructural design, including oxides, sulfides, phosphides, nitrides, carbides, transition metals, and other minor species. The focal point of the approach is the identification and rationalization of the design parameters that lead to the generation of optimal compositions, structures, nanostructures, and resultant performance parameters. The aim of this approach is to provide an inclusive platform for the strategies to design and process these materials for specific applications. This work is complemented by detailed figures that both summarize the design and processing approaches that have been reported and indicate potential trajectories for development. The work is also supported by comprehensive and up-to-date tabular coverage of the reported studies.

Engineering of metal-organic frameworks (MOFs) for thermometry

Metal-organic frameworks (MOFs ) are excellent candidates for use in chemistry, material sciences and engineering thanks to their interesting qualitative features and potential applications. Quite interestingly, the luminescence of MOFs can be engineered by regulation of the ligand design, metal ion selection and encapsulation of guest molecules within the MOF cavity. Temperature is a very crucial physical parameter and the market share of temperature sensors is rapidly expanding with technology and medicinal advancement. Among the wide variety of available temperature sensors, recently MOFs have emerged as potential temperature sensors with the capacity to precisely measure the temperature. Lanthanide-based thermometry has advantages because of its ratiometric response ability, high quantum yield and photostability, and therefore lanthanide-based MOFs were initially focused on to construct MOF thermometers. As science and technology have gradually changed, it has been observed that with the inclusion of dye, quantum dots, etc. within the MOF cavity, it is possible to develop MOF-based thermometry. This review consolidates the recent advances of MOF-based ratiometric thermometers and their mechanism of energy transfer for determining the temperature (thermal sensitivity and temperature uncertainty). In addition, some fundamental points are also discussed, such as concepts for guiding the design of MOF ratiometric thermometers, thermometric performance and tuning the properties of MOF thermometers.

High-stability spherical lanthanide nanoclusters for magnetic resonance imaging

High-nuclear lanthanide clusters have shown great potential for the administration of high-dose mononuclear gadolinium chelates in magnetic resonance imaging (MRI). The development of high-nuclear lanthanide clusters with excellent solubility and high stability in water or solution has been challenging and is very important for expanding the performance of MRI. We used N-methylbenzimidazole-2-methanol (HL) and LnCl3·6H2O to synthesize two spherical lanthanide clusters, Ln32 (Ln = Ho, Ho32; and Ln = Gd, Gd32), which are highly stable in solution. The 24 ligands L- are all distributed on the periphery of Ln32 and tightly wrap the cluster core, ensuring that the cluster is stable. Notably, Ho32 can remain highly stable when bombarded with different ion source energies in HRESI-MS or immersed in an aqueous solution of different pH values for 24 h. The possible formation mechanism of Ho32 was proposed to be Ho(III), (L)- and H2O → Ho3(L)3/Ho3(L)4 → Ho4(L)4/Ho4(L)5 → Ho6(L)6/Ho6(L)7 → Ho16(L)19 → Ho28(L)15 → Ho32(L)24/Ho32(L)21/Ho32(L)23. To the best of our knowledge, this is the first study of the assembly mechanism of spherical high-nuclear lanthanide clusters. Spherical cluster Gd32, a form of highly aggregated Gd(III), exhibits a high longitudinal relaxation rate (1 T, r1 = 265.87 mM-1·s-1). More notably, compared with the clinically used commercial material Gd-DTPA, Gd32 has a clearer and higher-contrast T1-weighted MRI effect in mice bearing 4T1 tumors. This is the first time that high-nuclear lanthanide clusters with high water stability have been utilized for MRI. High-nuclear Gd clusters containing highly aggregated Gd(III) at the molecular level have higher imaging contrast than traditional Gd chelates; thus, using large doses of traditional gadolinium contrast agents can be avoided.

Recent Advances in Metal-Organic Frameworks for Applications in Magnetic Resonance Imaging

Diagnostics is an important part of medical practice. The information required for diagnosis is typically collected by performing diagnostic tests, some of which include imaging. Magnetic resonance imaging (MRI) is one of the most widely used and effective imaging techniques. To improve the sensitivity and specificity of MRI, contrast agents are used. In this review, the usage of metal-organic frameworks (MOFs) and composite materials based on them as contrast agents for MRI is discussed. MOFs are crystalline porous coordination polymers. Due to their huge design variety and high density of metal ions, they have been studied as a highly promising class of materials for developing MRI contrast agents. This review highlights the most important studies and focuses on the progress of the field over the last five years. The materials are classified based on their design and structural properties into three groups: MRI-active MOFs, composite materials based on MOFs, and MRI-active compounds loaded in MOFs. Moreover, an overview of MOF-based materials for heteronuclear MRI including 129Xe and 19F MRI is given.

Metal-organic frameworks for pharmaceutical and biomedical applications

Metal-organic framework (MOF) materials provide unprecedented opportunities for evaluating valuable compounds for various medical applications. MOFs merged with biomolecules, used as novel biomaterials, have become particularly useful in biological environments. Bio-MOFs can be promising materials in the global to avoid utilization above toxicological substances. Bio-MOFs with crystallin and porosity nature offer flexible structure via bio-linker and metal node variation, which improves their wide applicability in medical science.

Detection of the UV-vis silent biomarker trimethylamine-N-oxide via outer-sphere interactions in a lanthanide metal-organic framework

Trimethylamine-N-oxide (TMAO) is a biomarker of the cardiovascular disease that is one of the leading causes of worldwide death. Facile detection of TMAO can significantly improve the survival rate of this disease by allowing early prevention. However, the UV-vis silent nature of TMAO makes it intricated to be detected by conventional sensing materials or analytical instruments. Here we show a bilanthanide metal-organic framework functionalized by borono group for the recognition of TMAO. Superior sensitivity, selectivity and anti-interference ability were achieved by the inverse emission intensity changes of the two lanthanide centers. The limit of detection is 15.6 μM, covering the clinical urinary concentration range of TMAO. A smartphone application was developed based on the change in R-G-B chromaticity. The sensing mechanism via a well-matched outer-sphere interaction governing the sensing function was studied in detail, providing fundamentals in molecular level for the design of advanced sensing materials for UV-Vis silent molecules.

Designable assembly of atomically precise Al4O4 cubane supported mesoporous heterometallic architectures

Heterometallic cluster-based framework materials are of interest in terms of both their porous structures and multi-metallic reactivity. However, such materials have not yet been extensively investigated because of difficulties in their synthesis and structural characterization. Herein, we reported the designable synthesis of atomically precise heterometallic cluster-based framework compounds and their application as catalysts in aldol reactions. By using the synergistic coordination protocol, we successfully isolated a broad range of compounds with the general formula, [Al₄M₄O₄(L)₁₂(DABCO)₂] (L = carboxylates; DABCO = 1,4-diazabicyclo[2.2.2]-octane; M²⁺ = Co²⁺, Mn²⁺, Zn²⁺, Fe²⁺, Cd²⁺). The basic heterometallic building blocks contain unprecedented main-group γ-alumina moieties and surrounding unsaturated transition metal centers. Interestingly, the porosity and interpenetration of these frameworks can be rationally regulated through the unprecedented strategy of increment of the metal radius in addition to general introduction of sterically bulky groups on the ligand. Furthermore, these porous materials are effective catalysts for aldol reactions. This work provides a catalytic molecular model platform with accurate molecular bonding between the supporters and catalytically active metal ions.

Rare-Earth Doping in Nanostructured Inorganic Materials

Impurity doping is a promising method to impart new properties to various materials. Due to their unique optical, magnetic, and electrical properties, rare-earth ions have been extensively explored as active dopants in inorganic crystal lattices since the 18th century. Rare-earth doping can alter the crystallographic phase, morphology, and size, leading to tunable optical responses of doped nanomaterials. Moreover, rare-earth doping can control the ultimate electronic and catalytic performance of doped nanomaterials in a tunable and scalable manner, enabling significant improvements in energy harvesting and conversion. A better understanding of the critical role of rare-earth doping is a prerequisite for the development of an extensive repertoire of functional nanomaterials for practical applications. In this review, we highlight recent advances in rare-earth doping in inorganic nanomaterials and the associated applications in many fields. This review covers the key criteria for rare-earth doping, including basic electronic structures, lattice environments, and doping strategies, as well as fundamental design principles that enhance the electrical, optical, catalytic, and magnetic properties of the material. We also discuss future research directions and challenges in controlling rare-earth doping for new applications.

Fast Detection of Entacapone by a Lanthanide-Organic Framework with Rhombic Channels

Entacapone (ENT) is a powerful catechol-O-methyl transferase inhibitor that is used for the diagnosis and treatment of Parkinson's syndrome, but the amount used must be well controlled to avoid overtreatment and side effect. Fast and selective detection of ENT needs well-matched energy levels and well-designed sensor-ENT interaction which is highly challenging. In this work, a water stable europium-based metal-organic framework (Eu-TDA) was synthesized to detect ENT by luminescence with excellent reusability and selectivity in the presence of main coexisting and interference species of plasma with a limit of detection of 5.01 μM. The experimental results showed that the luminescence of Eu-TDA can be effectively quenched by ENT via well-designed photoinduced electron transfer mechanism and internal filtration effect mechanism in the system.

Photo-induced variation of magnetism in coordination polymers with ligand-based electron transfer

Photo-induced variation of magnetism from ligand-based electron transfer has been extensively studied because of its potential applications in magneto-optical memory devices, light-responsive switches, and high-density information storage materials. In this review, we discussed the progress in the photo-induced variation of magnetism in coordination polymers with ligand-to-metal charge transfer (LMCT), ligand-to-ligand charge transfer (LLCT) and internal ligand charge transfer (ILCT), which provides fundamentals for the rational design of multi-functional materials. We also discussed the design and synthetic strategy of such molecule-based materials and gave views on the current challenges and growth trends in this field.

Solvothermal Preparation of a Lanthanide Metal-Organic Framework for Highly Sensitive Discrimination of Nitrofurantoin and l-Tyrosine

Metal-organic frameworks (MOFs) have been rapidly developed for their broad applications in many different chemistry and materials fields. In this work, a multi-dentate building block 5-(4-(tetrazol-5-yl)phenyl)-isophthalic acid (H₃L) containing tetrazole and carbolxylate moieties was employed for the synthesis of a two-dimensional (2D) lanthanide MOF [La(HL)(DMF)₂(NO₃)] (DMF = N,N-dimethylformamide) (1) under solvothermal condition. The fluorescent sensing application of 1 was investigated. 1 exhibits high sensitivity recognition for antibiotic nitrofurantoin (K_sv: 3.0 × 10³ M⁻¹ and detection limit: 17.0 μM) and amino acid l-tyrosine (K_sv: 1.4 × 10⁴ M⁻¹ and detection limit: 3.6 μM). This work provides a feasible detection platform of 2D MOFs for highly sensitive discrimination of antibiotics and amino acids.

Tailoring the triplet level of isomorphic Eu/Tb mixed MOFs for sensitive temperature sensing

Three different thermo-responsive fluorescent thermometers were constructed by regulating the triplet energy level of organic ligands in isostructural Eu/Tb mixed MOFs. Among them, a quite unusual and rarely reported temperature-dependent fluorescence behavior was observed in LnBDC-NH₂, and Eu_0.01Tb_0.99NDC is effective in the physiological range with the maximum relative sensitivity of 7.32% °C^-1.

Highlights of the development and application of luminescent lanthanide based coordination polymers, MOFs and functional nanomaterials

The development of lanthanide based coordination polymer and metal-organic framework (CPs and MOFs) nanomaterials as novel functional (e.g. luminescent and magnetic) materials has attracted significant attention in recent times. This is in part due to the wide, but yet unique coordination requirements that the f-metal ions possess, as well as their attractive physical properties, which are often transferred to the bulk material. Hence, there is no surprise, that the design, synthesis and characterisation of lanthanide based CP/MOF materials (featuring either 'pure' lanthanides, or a mixture of both f- and d-metal ions) for applications in gas and small molecule absorption, storage, conversion/catalysis, chemical sensing, bio-imaging, drug delivery, etc. has been a prominent feature in the scientific literature. In this review, we give a selected overview of some of the recent developments in the area of Ln CP/MOF based nanomaterials for sensing, optical materials and bio-medicine research, as well as making reference to some more established examples, with the view of introducing, particularly to new researchers to the field, the powerful and attractive features of lanthanide based materials.

Multifunctional metal-organic framework heterostructures for enhanced cancer therapy

Metal-organic frameworks (MOFs) are an emerging class of molecular crystalline materials built from metal ions or clusters bridged by organic linkers. By taking advantage of their synthetic tunability and structural regularity, MOFs can hierarchically integrate nanoparticles and/or biomolecules into a single framework to enable multifunctions. The MOF-protected heterostructures not only enhance the catalytic capacity of nanoparticle components but also retain the biological activity of biomolecules in an intracellular microenvironment. Therefore, the multifunctional MOF heterostructures have great advantages over single components in cancer therapy. In this review, we comprehensively summarize the general principle of the design and functional modulation of nanoscaled MOF heterostructures, and biomedical applications in enhanced therapy within the last five years. The functions of MOF heterostructures with a controlled size can be regulated by designing various functional ligands and in situ growth/postmodification of nanoparticles and/or biomolecules. The advances in the application of multifunctional MOF heterostructures are also explored for enhanced cancer therapies involving photodynamic therapy, photothermal therapy, chemotherapy, radiotherapy, immunotherapy, and theranostics. The remaining challenges and future opportunities in this field, in terms of precisely localized assembly, maximizing composite properties, and processing new techniques, are also presented. The introduction of multiple components into one crystalline MOF provides a promising approach to design all-in-one theranostics in clinical treatments.

Coordination-Assembled Water-Soluble Anionic Lanthanide Organic Polyhedra for Luminescent Labeling and Magnetic Resonance Imaging

Lanthanide-containing functional complexes have found a variety of applications in materials science and biomedicine because of their unique electroptical and magnetic properties. However, the poor stability and solubility in water of multicomponent lanthanide organic assemblies significantly limit their practical applications. We report here a series of water-stable anionic Ln_2nL_3n-type (n = 2, 3, 4, and 5) lanthanide organic polyhedra (LOPs) constructed by deprotonation self-assembly of three fully conjugated ligands (H₄L¹ and H₄L^2a/b) featuring a 2,6-pyridine bitetrazolate chelating moiety. The outcomes of the LOPs formation reactions were found to be very sensitive toward the reaction conditions including base, metal source, solvents, and concentrations as characterized by a combination of NMR, high-resolution ESI-MS and X-ray crystallography. Ligands H₄L^2a/b manifested an excellent sensitization toward lanthanide ions (Ln = Eu^III and Tb^III), with high luminescent quantum yields for Tb₈L^2a₁₂ (Φ = 11.2% in water) and Eu₈L^2b₁₂ (Φ = 76.8% in DMSO) measured in polar solvents. Furthermore, due to the giant molecular weight and rigidity of the polyhedral skeleton, Gd₈L^2b₁₂ showed a very high longitudinal relaxivity (r₁) of 400.53 mM^-1S^-1. The performance of Gd₈L^2b₁₂ as potential magnetic resonance imaging contrast agents (CAs) in vivo was evaluated with much longer retention time in the tumor sites compared with the commercial Gd^III-based CAs. Dual-modal imaging potential has also been demonstrated with the mixed Eu/Gd LOPs. Our results not only provide a new design route toward water-stable multinuclear lanthanide organic assemblies but also offer potential candidates of supramolecular-edifices for bioimaging and drug delivery.

Fabrication of a multifunctional magnetic-fluorescent material for medical applications

Multifunctional biocompatible materials have evoked considerable interest in the field of medical applications. Here we report the thermal decomposition preparation of homogeneous fluorescent-magnetic particles with a composite structure containing CoFe2O4 nanoparticles as nucleation seeds for fluorescent Gd2-xO3:Eux. The composite exhibited a wide range of fluorescence transitions in the whole visible spectrum, displaying 18 different emission peaks when excited at a 250 nm wavelength. Moreover, at low temperature the peaks of the composite were wider than the peaks of the fluorescent material, which may be attributed to a set of new energy levels due to a combination of Stark splitting with the magnetic field of CoFe2O4. Because this material is intended to be used for biomedical applications, the potential toxicity of the composite was tested using an invertebrate hemocyte cell model. The cells showed slight morphological and biochemical changes upon exposure to the composite; however, there was no increase in cell death at concentrations of up to 40 ppm. In addition, the material could be tracked by its fluorescence inside the cells, when excited at a more bio-friendly and less energetic wavelength of 405 nm. Furthermore, MRI showed T1 and T2 dual contrast with relaxivity values in the range of most reported materials.

Sequential Ag+/biothiol and synchronous Ag+/Hg2+ biosensing with zwitterionic Cu2+-based metal-organic frameworks

Zwitterionic metal-organic frameworks (MOFs) of {[Cu(Cbdcp)(Dps)(H₂O)₃]·6H₂O}_n (MOF 1) and [Cu₄(Dcbb)₄(Dps)₂(H₂O)₂]_n (MOF 2) (H₃CbdcpBr = N-(4-carboxybenzyl)-(3,5-dicarboxyl)pyridinium bromide; H₂DcbbBr = 1-(3,5-dicarboxybenzyl)-4,4'-bipyridinium bromide; Dps = 4,4'-dipyridyl sulfide) quench the fluorescence of cytosine-rich DNA tagged with 5-carboxytetramethylrhodamine (TAMRA, emission at 582 nm, denoted as C-rich P-DNA-1) and yield the corresponding P-DNA-1@MOF hybrids. Exposure of these hybrids to Ag⁺ results in the release of the P-DNA-1 strands from the MOF surfaces as double-stranded, hairpin-like C-Ag^I-C (ds-DNA-1@Ag⁺) with the restoration of TAMRA fluorescence. The ds-DNA-1@Ag⁺ formed on the surface of 1 can subsequently sense biothiols cysteine (Cys), glutathione (GSH), and homocysteine (Hcy) due to the stronger affinity of mercapto groups for Ag⁺ that serves to unfold the ds-DNA-1@Ag⁺ duplex, reforming P-DNA-1, which is re-adsorbed by MOF 1 accompanied by quenching of TAMRA emission. Meanwhile, MOF 2 is also capable of co-loading a thymine-rich probe DNA tagged with 5-carboxyfluorescein (FAM, emission at 518 nm, denoted as T-rich P-DNA-2) to achieve synchronous sensing of Ag⁺ and Hg²⁺, resulting from the simultaneous yet specific ds-DNA-1@Ag⁺ and T-Hg^II-T duplex (ds-DNA-2@Hg²⁺) formation, as well as the distinctive emission wavelengths of TAMRA and FAM. Detection limits are as low as 5.3 nM (Ag⁺), 14.2 nM (Cys), 13.5 nM (GSH), and 9.1 nM (Hcy) for MOF 1, and 7.5 nM (Ag⁺) and 2.6 nM (Hg²⁺) for MOF 2, respectively. The sequential sensing of Ag⁺ and biothiols by MOF 1, and the synchronous sensing of Ag⁺ and Hg²⁺ by MOF 2 are rapid and specific, even in the presence of other mono- and divalent metal cations or other biothiols at much higher concentrations. Molecular simulation studies provide insights regarding the molecular interactions that underpin these sensing processes.

Metal-Organic Frameworks for Biomedical Applications

Metal-organic frameworks (MOFs) are an interesting and useful class of coordination polymers, constructed from metal ion/cluster nodes and functional organic ligands through coordination bonds, and have attracted extensive research interest during the past decades. Due to the unique features of diverse compositions, facile synthesis, easy surface functionalization, high surface areas, adjustable porosity, and tunable biocompatibility, MOFs have been widely used in hydrogen/methane storage, catalysis, biological imaging and sensing, drug delivery, desalination, gas separation, magnetic and electronic devices, nonlinear optics, water vapor capture, etc. Notably, with the rapid development of synthetic methods and surface functionalization strategies, smart MOF-based nanocomposites with advanced bio-related properties have been designed and fabricated to meet the growing demands of MOF materials for biomedical applications. This work outlines the synthesis and functionalization and the recent advances of MOFs in biomedical fields, including cargo (drugs, nucleic acids, proteins, and dyes) delivery for cancer therapy, bioimaging, antimicrobial, biosensing, and biocatalysis. The prospects and challenges in the field of MOF-based biomedical materials are also discussed.

A water-stable terbium metal–organic framework as a highly sensitive fluorescent sensor for nitrite

A terbium metal–organic framework was synthesized for highly sensitive nitrite detection. The mechanism of the quenching process was also studied in detail.