A highly sensitive near-infrared luminescent metal-organic framework thermometer in the physiological range

Tunable Optical Molecular Thermometers Based on Metallacrowns

The effect of ligands' energy levels on thermal dependence of lanthanide emission was examined to create new molecular nanothermometers. A series of Ln₂Ga₈L₈^'L₈^″ metallacrowns (shorthand Ln₂L₈^'), where Ln = Gd³⁺, Tb³⁺, or Sm³⁺ (H₃L' = salicylhydroxamic acid (H₃shi), 5-methylsalicylhydroxamic acid (H₃mshi), 5-methoxysalicylhydroxamic acid (H₃moshi), and 3-hydroxy-2-naphthohydroxamic acid (H₃nha)) and H₂L″ = isophthalic acid (H₂iph), was synthesized and characterized. Within the series, ligand-centered singlet state (S₁) energy levels ranged from 23,300 to 27,800 cm^-1, while triplet (T₁) energy levels ranged from 18,150 to 21,980 cm^-1. We demonstrated that the difference between T₁ levels and relevant energies of the excited ⁴G_5/2 level of Sm³⁺ (17,800 cm^-1) and ⁵D₄ level of Tb³⁺ (20,400 cm^-1) is the major parameter controlling thermal dependence of the emission intensity via the back energy transfer mechanism. However, when the energy difference between S₁ and T₁ levels is small (below 3760 cm^-1), the S₁ → T₁ intersystem crossing (and its reverse, S₁ ← T₁) mechanism contributes to the thermal behavior of metallacrowns. Both mechanisms affect Ln³⁺-centered room-temperature quantum yields with values ranging from 2.07(6)% to 31.2(2)% for Tb₂L₈^' and from 0.0267(7)% to 2.27(5)% for Sm₂L₈^'. The maximal thermal dependence varies over a wide thermal range (ca. 150-350 K) based on energy gaps between relevant ligand-based and lanthanide-based electronic states. By mixing Tb₂moshi₈^' with Sm₂moshi₈^' in a 1:1 ratio, an optical thermometer with a relative thermal sensitivity larger than 3%/K at 225 K was created. Other temperature ranges are also accessible with this approach.

NIR luminescence thermometers based on Yb-Nd coordination compounds for the 83-393 K temperature range

Multimetallic neodymium-ytterbium-gadolinium compounds with 9-anthracenate and 9-acridinate anions were tested in order to create the first luminescent thermometer for elevated temperatures. High luminescence intensity and high signal resolution were reached thanks to the concentration quenching elimination due to the partial substitution of the emitting ions with Gd³⁺. As a result, NIR emitting materials for luminescence thermometry in the wide temperature range (83-393 K) based on lanthanide coordination compounds (CCs) were obtained. The best thermometric properties among the studied systems were demonstrated by Yb_0.02Nd_0.12Gd_0.86(ant)₃, and its temperature sensitivity reached 1.8% K^-1 in the temperature range of 293-393 K.

Biomedical Applications of Metal-Organic Frameworks for Disease Diagnosis and Drug Delivery: A Review

Metal-organic frameworks (MOFs) are a novel class of porous hybrid organic-inorganic materials that have attracted increasing attention over the past decade. MOFs can be used in chemical engineering, materials science, and chemistry applications. Recently, these structures have been thoroughly studied as promising platforms for biomedical applications. Due to their unique physical and chemical properties, they are regarded as promising candidates for disease diagnosis and drug delivery. Their well-defined structure, high porosity, tunable frameworks, wide range of pore shapes, ultrahigh surface area, relatively low toxicity, and easy chemical functionalization have made them the focus of extensive research. This review highlights the up-to-date progress of MOFs as potential platforms for disease diagnosis and drug delivery for a wide range of diseases such as cancer, diabetes, neurological disorders, and ocular diseases. A brief description of the synthesis methods of MOFs is first presented. Various examples of MOF-based sensors and DDSs are introduced for the different diseases. Finally, the challenges and perspectives are discussed to provide context for the future development of MOFs as efficient platforms for disease diagnosis and drug delivery systems.

The modulation effect of an electron-rich guest on the luminescence of naphthalene diimide-based metal–organic frameworks

A series of host–guest MOF materials were successfully fabricated by virtue of donor–acceptor interactions, which exhibit color-tunable emissions in a wide wavelength range by rational selection of guest molecules.

Fluorescence Thermometer: Intermediation of the Fontal Temperature and Light

The rapid advance of thermal materials and fluorescence spectroscopy has extensively promoted micro-scale fluorescence thermometry development in recent years. Based on the advantages of fast response, high sensitivity, simple operation,...

Near-Infrared Emissive Lanthanide Metal-Organic Frameworks for Targeted Biological Imaging and pH-Controlled Chemotherapy

Near-infrared window II (NIR-II, 1000-1700 nm) imaging displays the advantages in deep-tissue high-contrast imaging in vivo on the strength of the high temporal-spatial resolution and deeper penetration. However, the clinical utility of NIR-II imaging agents is limited by their single function. Herein, for the first time, we report the design of a multifunctional drug delivery system (DDS) assembly, CQ/Nd-MOF@HA nanohybrids, with NIR-II fluorescence (1067 nm), large Stokes shifts, and ultrahigh quantum yield, which combined targeted NIR-II luminescence bioimaging and pH-controlled drug delivery. The nanoscale metal-organic framework (MOF) as a highly promising multifunctional DDS for targeted NIR-II bioimaging and chemotherapy in vitro and in vivo lays the foundation of the MOF-based DDS for further clinical diagnosis and treatment.

The Structure and Property of Two Different Metal-Organic Frameworks Based on N/O-Donor Mixed Ligands

Two different metal-organic frameworks (MOFs) [Cd2(AZN)(HAZN)(btc)(Hbtc)·4H2O]·2H2O (1), and [Zn3(AZN)2(btc)2·4H2O] (2) were synthesized by the reactions of different metal salts with mixed ligands of 1-(4-(1H-imidazol-5-yl)phenyl)-1H-1,2,4-triazole (AZN) and trimesic acid (H3btc). The different metal centers in the reaction condition have important impact on the resulting structures of MOFs 1 and 2. Compound 1 is a one-dimensional (1D) chain structure, while 2 features a three-dimensional (3D) framework with 3-fold interpenetration topology of Point (Schläfli) symbol of (6·82)4(62·82·102). Furthermore, the luminescent properties have been studied for MOFs 1 and 2.

Nanoscale cobalt-based metal-organic framework impairs learning and memory ability without noticeable general toxicity: First in vivo evidence

Metal-organic frameworks (MOFs) exhibit broad potential applications in the environmental, biomedical, catalyst, and energy fields. However, the currently existing data hardly shed light on their health risks before the MOFs' large-scale usage. In this context, we exploratively investigated the in vivo fate and effect of one representative cobalt-based zeolitic imidazolate framework (ZIF-67) at the nano- (60 nm) and submicron- (890 nm) scales. Different from submicron-scale ZIF-67 showing better biosafety, nanoscale particles manifested a neurodegenerative risk at the dose of no general toxicity, evidenced by the impairment of learning and memory ability and disordered function of the neuropeptide signaling pathway in a rat model. The involvement of oxidative damage and inflammatory processes in the neurotoxicity induced by ZIF-67 was discussed as well. These findings not only provide a wake-up call for the prudent applications of MOFs but also provide insight into the better design and safer use of MOFs for broader applications.

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.

Two chiral haloplumbate hybrids with thermochromism luminescence and application potential as luminescent thermometers

Two noncentrosymmetric haloplumbate hybrids, [C6H10(NH3)2][PbCl4] (1) and [C6H10(NH3)2][PbBr4] (2), have been synthesized. Crystals of 1 and 2 belong to the chiral space group P212121. The inorganic parts comprise a one-dimensional chain structure for 1 and a two-dimensional sheet structure for 2. Both compounds exhibit thermochromic luminescence originating from dual emission and have potential applications as self-referencing luminescent thermometers.

[Ga3+ 8 Sm3+ 2 , Ga3+ 8 Tb3+ 2 ] Metallacrowns are Highly Promising Ratiometric Luminescent Molecular Nanothermometers Operating at Physiologically Relevant Temperatures

Nanothermometry is the study of temperature at the submicron scale with a broad range of potential applications, such as cellular studies or electronics. Molecular luminescent-based nanothermometers offer a non-contact means to record these temperatures with high spatial resolution and thermal sensitivity. A luminescent-based molecular thermometer comprised of visible-emitting Ga³⁺ /Tb³⁺ and Ga³⁺ /Sm³⁺ metallacrowns (MCs) achieved remarkable relative thermal sensitivity associated with very low temperature uncertainty of S_r =1.9 % K^-1 and δT<0.045 K, respectively, at 328 K, as an aqueous suspension of polystyrene nanobeads loaded with the corresponding MCs. To date, they are the ratiometric molecular nanothermometers offering the highest level of sensitivity in the physiologically relevant temperature range.

808 nm-Light-Excited Near-Infrared Luminescent Lanthanide Metal-Organic Frameworks for Highly Sensitive Physiological Temperature Sensing

Ongoing demand for accurate self-calibrated noninvasive thermometers for micro-/nano-scale applications, particular biomedical diagnosis, is driving the development of temperature sensors. Here a new type of lanthanide metal-organic framework having near-infrared absorption and near-infrared emission features is presented, and it is based on efficient Nd³⁺ -to-Yb³⁺ energy transfer in 808 nm photoexcitation. The results show that the ratiometric parameter of Nd_0.5 Yb_0.5 TPTC (TPTC= 1,1':4',1''-terphenyl]-3,3'',5,5''-tetracarboxylic acid) can deliver good exponential-type luminescence response to temperature in the physiological regime (293-328 K) with high relative sensitivity and accurate temperature resolution, as well as good biocompatibility and chemical stability. Such lanthanide-based materials are especially useful in biomedical applications.

Near-infrared-emissive metal–organic frameworks

We describe the recent progress in near-infrared-emissive metal–organic frameworks, and especially highlight their appealing applications in bio-imaging, sensing and barcoding.

Synergistic Effect between Different Coordination Geometries of Lanthanides and Various Coordination Modes of 2-Picolinic Acid Ligands Tuning Three Types of Rare 3d-4f Heterometallic Tungstoantimonates

Three types of N-heterocyclic aromatic acid decorated 3d-4f heterometallic Keggin-type tungstoantimonates: Na₄[Ln(H₂O)₅]₂[Fe₄(H₂O)₂(pic)₄(B-β-SbW₉O₃₃)₂]·26H₂O [Ln³⁺ = La³⁺ (1), Pr³⁺ (2), Nd³⁺ (3), Sm³⁺ (4), Eu³⁺ (5)], Na₆H₄[Fe₂W₄O₉(H₂O)₂(Hpic)₄ (B-β-SbW₉O₃₃)₂][Ln(H₂O)₈]₂[Fe₄W₂O₇(H₂O)₄(pic)₂(Hpic)₂(B-β-SbW₉O₃₃)₂]·38H₂O [Ln³⁺ = Gd³⁺ (6), Dy³⁺ (7)], and Na₂H₂{[Ln(H₂O)₆]₂[Fe₄(H₂O)₂(Hpic)₂(pic)₂(B-β-SbW₉O₃₃)₂]}₂·44H₂O [Ln³⁺ = Ho³⁺ (8), Er³⁺ (9), Hpic = 2-picolinic acid] have been prepared. 1-5 comprise a quadripic-inserted Krebs-type [Fe₄(H₂O)₂(pic)₄(B-β-SbW₉O₃₃)₂]^10- moiety supported by two [Ln(H₂O)₅]³⁺ groups on both sides where it can be considered that four pic ligands replace eight aqua ligands located on the original Krebs-type [Fe₄(H₂O)₁₀(B-β-SbW₉O₃₃)₂]^10- fragment to form the [Fe₄(H₂O)₂(pic)₄(B-β-SbW₉O₃₃)₂]^10- moiety. Remarkably, the quadripic-inserted subunits are further concatenated through the coordination role of the pic ligands to create a 3-D heterometallic framework. In contrast, the molecular units of 6-7 contain two kinds of non-Krebs-type quadripic-inserted [Fe₂W₄O₉(H₂O)₂(Hpic)₄(B-β-SbW₉O₃₃)₂]^6- and {[Ln(H₂O)₈]₂[Fe₄W₂O₇(H₂O)₄(pic)₂(Hpic)₂(B-β-SbW₉O₃₃)₂]}^4- moieties. The molecular units of 8-9 contain two identical quadripic-inserted Krebs-type {[Ln(H₂O)₆]₂[Fe₄(H₂O)₂(Hpic)₂(pic)₂(B-β-SbW₉O₃₃)₂]}^2- moieties, and both display a 1-D heterometallic double chain. For all we know, 1-9 stand for the first 3d-4f heterometallic tungstoantimonate hybrids functionalized by pic ligands. Particularly, the solid-state NIR photoluminescence (PL) spectrum in the range of 800-1450 nm of 3 and the solid-state visible PL spectra in the range of 500-750 nm of 4, 5, 7, and 8 at room temperature display the featured fluorescence emission bands stemming from Ln³⁺ cations. In the PL emission procedures of 5 and 7, energy transfer from [B-β-SbW₉O₃₃]^9- fragments and pic ligands to Ln³⁺ ions has been observed. Additionally, the correlated color temperatures of 4, 5, 7, and 8 are indexed to 2731, 2020, 4557, and 1685 K, respectively.

Nanoscale Metal-Organic Frameworks for Therapeutic, Imaging, and Sensing Applications

Nanotechnology has played an important role in drug delivery and biomedical imaging over the past two decades. In particular, nanoscale metal-organic frameworks (nMOFs) are emerging as an important class of biomedically relevant nanomaterials due to their high porosity, multifunctionality, and biocompatibility. The high porosity of nMOFs allows for the encapsulation of exceptionally high payloads of therapeutic and/or imaging cargoes while the building blocks-both ligands and the secondary building units (SBUs)-can be utilized to load drugs and/or imaging agents via covalent attachment. The ligands and SBUs of nMOFs can also be functionalized for surface passivation or active targeting at overexpressed biomarkers. The metal ions or metal clusters on nMOFs also render them viable candidates as contrast agents for magnetic resonance imaging, computed tomography, or other imaging modalities. This review article summarizes recent progress on nMOF designs and their exploration in biomedical areas. First, the therapeutic applications of nMOFs, based on four distinct drug loading strategies, are discussed, followed by a summary of nMOF designs for imaging and biosensing. The review is concluded by exploring the fundamental challenges facing nMOF-based therapeutic, imaging, and biosensing agents. This review hopefully can stimulate interdisciplinary research at the intersection of MOFs and biomedicine.

Near-Infrared Ratiometric Luminescent Thermometer Based on a New Lanthanide Silicate

A new lanthanide silicate system, Na₂ K[Ln₃ Si₆ O₁₈ ] (Ln=Lu, Yb/ Er, Lu/Eu, or Lu/Yb/Er), comprising microcrystals embedded in an amorphous siliceous matrix, obtained by sintering at 1373 K a Na₃ K[Ln₂ Si₆ O₁₇ ]⋅3 H₂ O nano-crystalline precursor, is reported. The crystal structure of these lanthanide silicates was solved from high-resolution synchrotron power X-ray diffraction data collected at 110 K, and further supported by ²⁹ Si MAS NMR and Eu³⁺ luminescence. The materials crystallize in the Pī triclinic centrosymmetric space group, exhibiting a dense framework consisting of hexameric [Si₆ O₁₈ ]^12- cyclosilicate units, and chains of two distinct {LnO₆ } octahedra. Na₂ K[(Lu_0.75 Yb_0.20 Er_0.05 )₃ Si₆ O₁₈ ] is the first example of a lanthanide silicate operative as a near-infrared ratiometric luminescent thermometer, with good sensitivity at cryogenic temperatures (<100 K). Upon excitation at 903 nm, the ratio between the ² F_7/2 →² F_5/2 (Yb³⁺ ) and ⁴ I_13/2 →⁴ I_15/2 (Er³⁺ ) emissions was used for sensing temperature in the 12-450 K range, reaching a maximum thermal sensitivity of 2.6 % K^-1 at 26.8 K.

Multi-responsive luminescent sensor based on three dimensional lanthanide metal–organic framework

A novel multi-functional luminescent MOF was synthesized, which shows excellent recyclable luminescent sensing for acetone, Fe³⁺, Cr₂O₇²⁻ and 4-NP.

Characterization and study of luminescence enhancement behaviour of alginate-based hydrogels

Luminescence enhanced composites were fabricated via introducing 5-sulfosalicylic acid molecules into a Tb(iii)-based system to avoid being quenched by water.

Photonic functional metal–organic frameworks

The recent progress in photonic MOFs for luminescence sensing, white-light emission, photocatalysis, nonlinear optics, lasing devices, and biomedicine is summarized.

Synthesis, structure and temperature sensing of a lanthanide-organic framework constructed from a pyridine-containing tetracarboxylic acid ligand

A high sensitive, thermostable mixed lanthanide metal–organic framework, Eu_0.19Tb_0.81PDDI, was developed as a self-calibrated thermometer effective in the high temperature range of 313 to 473 K.

XEOL spectroscopy of lanthanides in aqueous solution

As part of an ongoing study of the electronic interactions between solute and solvent molecules, a method for X-ray excited optical luminescence (XEOL) analysis of aqueous solutions was developed at the double-crystal monochromator beamline (DCM) of the Canadian Synchrotron Radiation Facility (CSRF). It was tested using a series of solutions containing lanthanide ions. The samples were contained in a sample holder for liquids with a 3 μm Mylar window separating them from the vacuum (≤3 × 10−6 torr, 1 torr = 133.3224 Pa) in the solid state absorption chamber of the DCM beamline. Terbium, samarium, and dysprosium have 4 intense and narrow luminescence peaks between 450 and 700 nm, well separated from the luminescence peak of the Mylar window between 300 and 425 nm. The intensity of the rare earth (RE3+) luminescence peaks was lower for the solutions than for solid RECl3·6H2O. In part, this was caused by the lower RE3+ concentration in the solutions than in the solid. In addition, the solvent (water) acts as a quencher. The disorder and the molecular motion in the solution increase the availability of nonradiative de-excitation pathways. A high concentration of SO42− in the solution enhanced the luminescence intensity, probably by inhibiting some nonradiative de-excitation pathways. This study has shown that it is in principle possible to investigate the luminescence of aqueous solutions with XEOL spectroscopy. Furthermore, it is possible to use this technique as a quantitative analytical tool for concentrated luminescent solutions and to study the shielding effects of anions in the solution that increase the luminescence intensity.

Multifunctional, Tunable Metal-Organic Framework Materials Platform for Bioimaging Applications

Herein, we describe a novel multifunctional metal-organic framework (MOF) materials platform that displays both porosity and tunable emission properties as a function of the metal identity (Eu, Nd, and tuned compositions of Nd/Yb). Their emission collectively spans the deep red to near-infrared (NIR) spectral region (∼614-1350 nm), which is highly relevant for in vivo bioimaging. These new materials meet important prerequisites as relevant to biological processes: they are minimally toxic to living cells and retain structural integrity in water and phosphate-buffered saline. To assess their viability as optical bioimaging agents, we successfully synthesized the nanoscale Eu analog as a proof-of-concept system in this series. In vitro studies show that it is cell-permeable in individual RAW 264.7 mouse macrophage and HeLa human cervical cancer tissue culture cells. The efficient discrimination between the Eu emission and cell autofluorescence was achieved with hyperspectral confocal fluorescence microscopy, used here for the first time to characterize MOF materials. Importantly, this is the first report that documents the long-term conservation of the intrinsic emission in live cells of a fluorophore-based MOF to date (up to 48 h). This finding, in conjunction with the materials' very low toxicity, validates the biocompatibility in these systems and qualifies them as promising for use in long-term tracking and biodistribution studies.

Metal–organic frameworks: functional luminescent and photonic materials for sensing applications

This review summarizes the diverse routes to derive sensing applications from suitably functionalized and crystal-engineered metal–organic framework (MOF) materials, either by fluorometric responses, or based on photonic crystal-based signal transduction.