Metal‐Organic Framework Nanoparticles in Photodynamic Therapy: Current Status and Perspectives

This feature article covers the recent applications of metal‐organic framework nanoparticles (MOF NPs) in photodynamic therapy (PDT) of cancer. It aims at giving the reader an overview about these two current research fields, i.e., MOF and PDT, and at highlighting the potential synergistic effect that could result from their association. After describing the general photophysics and photochemistry that underlie PDT, the relationship between photosensitizer (PS) properties and PDT requirements is discussed throughout the PSs historical development. This development reveals the advantages of using nanotechnology platforms for the creation of the ideal PS and leads us to define the fourth generation of PSs, which includes NPs built from the PS itself as porphysomes or PS‐based MOF NPs. Especially, the precise spatial control over the PS assembly into well‐defined MOF NPs, which keeps the PS in its monomeric form and prevents PS self‐quenching, appears as a notable feature to solve PS solubility and aggregation issues and therefore improves the PDT efficiency. Finally, we discuss the future perspectives of MOF NPs in PDT and shed light on how promising these nanomaterials are.     

Self‐Mineralized Photothermal Bacteria Hybridizing with Mitochondria‐Targeted Metal–Organic Frameworks for Augmenting Photothermal Tumor Therapy

A photothermal bacterium (PTB) is reported for tumor‐targeted photothermal therapy (PTT) by using facultative anaerobic bacterium Shewanella oneidensis MR‐1 (S. oneidensis MR‐1) to biomineralize palladium nanoparticles (Pd NPs) on its surface without affecting bacterial activity. It is found that PTB possesses superior photothermal property in near infrared (NIR) regions, as well as preferential tumor‐targeting capacity. Zeolitic imidazole frameworks‐90 (ZIF‐90) encapsulating photosensitizer methylene blue (MB) are hybridized on the surface of living PTB to further enhance PTT efficacy. MB‐encapsulated ZIF‐90 (ZIF‐90/MB) can selectively release MB at mitochondria and cause mitochondrial dysfunction by producing singlet oxygen (¹O₂) under light illumination. Mitochondrial dysfunction further contributes to adenosine triphosphate (ATP) synthesis inhibition and heat shock proteins (HSPs) down‐regulated expression. The PTB‐based therapeutic platform of PTB@ZIF‐90/MB demonstrated here will find great potential to overcome the challenges of tumor targeting and tumor heat tolerance in PTT.     

Novel Organic‐Dehydration Membranes Prepared from Zirconium Metal‐Organic Frameworks

Membranes with outstanding performance that are applicable in harsh environments are needed to broaden the current range of organic dehydration applications using pervaporation. Here, well‐intergrown UiO‐66 metal‐organic framework membranes fabricated on prestructured yttria‐stabilized zirconia hollow fibers are reported via controlled solvothermal synthesis. On the basis of the adsorption–diffusion mechanism, the membranes provide a very high flux of up to ca. 6.0 kg m^?2 h^?1 and excellent separation factor (>45 000) for separating water from i ‐butanol (next‐generation biofuel), furfural (promising biochemical), and tetrahydrofuran (typical organic). This performance, in terms of separation factor, is one to two orders of magnitude higher than that of commercially available polymeric and silica membranes with equivalent flux. It is comparable to the performance of commercial zeolite NaA membranes. Additionally, the membrane remains robust during a pervaporation stability test (≈300 h), including exposure to harsh environments (e.g., boiling benzene, boiling water, and sulfuric acid) where some commercial membranes (e.g., zeolite NaA membranes) cannot survive.     

Regulating Uniform Li Plating/Stripping via Dual‐Conductive Metal‐Organic Frameworks for High‐Rate Lithium Metal Batteries

Lithium metal anodes show immense scope for application in high‐energy electronics and electric vehicles. Unfortunately, lithium dendrite growth and volume change leading to short lifespan and safety issues severely limit the feasibility of lithium metal batteries. A rational design of metal–organic framework (MOF)‐modified Li metal anode with optimized Li plating/stripping behavior via one‐step carbonization of ZIF‐67 is proposed. Experimental and theoretical simulation results reveal that carbonized MOFs with uniformly dispersed Co nanoparticles in N‐graphene (Co@N‐G) exhibit an electronic/ionic dual‐conductivity and significantly improved affinity with Li, and so serve as an ideal host for dendrite‐free lithium deposition, consequently leading to uniform lithium plating/stripping during cycling. As a result, the anode delivers highly stable cyclic performance with high coulombic efficiency (CE) at ultrahigh current densities (CE = 91.5% after 130 cycles at 10 mA cm^?2, and CE = 90.4% after 80 cycles at 15 mA cm^?2). Moreover, the practical applicability and functionality of such anodes are demonstrated through assembly of Li‐Co@N‐G/NCM full batteries exhibiting a long cycle life of 100 cycles with a high capacity retention of 92% at 1 C.     

Composite Salt in Porous Metal‐Organic Frameworks for Adsorption Heat Transformation

Adsorptive heat transformation systems such as adsorption thermal batteries and chillers can provide space heating and cooling in a more environmental friendly way. However, their use is still hindered by their relatively poor performances and large sizes due to the limited properties of solid adsorbents. Here, the spray‐drying continuous‐flow synthesis of a new type of solid adsorbents that results from combining metal‐organic frameworks (MOFs), such as UiO‐66, and hygroscopic salts, such as CaCl₂ has been reported. These adsorbents, commonly named as composite salt in porous matrix (CSPM) materials, allow improving the water uptake capabilities of MOFs while preventing their dissolution in the water adsorbed; a common characteristic of these salts due to the deliquescence effect. It is anticipated that MOF‐based CSPMs, in which the percentage of salt can be tuned, are promising candidates for thermal batteries and chillers. In these applications, it is showed that a CSPM made of UiO‐66 and CaCl₂ (38% w/w) exhibits a heat storage capacity of 367 kJ kg^?1 , whereas a second CSPM made of UiO‐66 and CaCl₂ (53% w/w) shows a specific cooling power of 631 W kg^?1 and a coefficient of performance of 0.83, comparable to the best solid adsorbents reported so far.     

Porphyrinic Metal–Organic Frameworks Coated Gold Nanorods as a Versatile Nanoplatform for Combined Photodynamic/Photothermal/Chemotherapy of Tumor

In this paper, a simple, but effective method is reported to construct the core?shell gold nanorod@metal–organic frameworks (AuNR@MOFs) as a multifunctional theranostic platform by using functionalized AuNRs as seed crystal for the growth of porphyrinic MOFs on the surface of AuNR. Such a delicate tunable core?shell composite not only possesses the improved drug loading efficiency, near‐infrared light‐trigger drug release, and fluorescence imaging, but also can produce reactive oxygen species as well as photothermal activity to achieve combined cancer therapy. It is further demonstrated that the camptothecin loaded AuNR@MOFs show distinctively synergistic efficiency for damaging the cancer cell in vitro and inhibiting the tumor growth and metastasis in vivo. The development of this high‐performance incorporated nanostructure will provide more perspectives in the design of versatile nanomaterials for biomedical applications.     

Nanoscale Metal‐Organic Frameworks: Synthesis,Biocompatibility, Imaging Applications,and Thermal and Dynamic Therapy of Tumors

Nanoscale metal‐organic frameworks (NMOFs) have attracted increasing attention for biomedical applications due to their large specific surface area, good biocompatibility, adjustable structures, and diverse functions. By choosing appropriate metal ions and ligands, NMOFs can be synthesized and regulated to assist the diagnosis and treatment of cancer, acting as imaging agents, drug carriers, and cancer therapeutic agents. This review summarizes the recent advances of NMOFs in synthesis, biocompatibility, imaging, and applications in cancer therapies. Among these, the term “biocompatibility” is used to outline their various biological characteristics, and it is mainly discussed from the aspects of size and surface properties of NMOFs. The imaging section mainly emphasizes the application advantages of NMOFs as imaging agents in magnetic resonance, computed tomography, and fluorescence imaging. The applications of NMOFs in four cancer therapies, including phototherapy, radiotherapy, microwave therapy, and ultrasonic therapy, are addressed, especially for thermal and dynamic therapy. Finally, the prospects and challenges of NMOFs in imaging and cancer therapies are also discussed.     

Tunable Photodynamic Switching of DArE@PAF‐1 for Carbon Capture

A new type of photodynamic carbon capture material with up to 26 wt% CO₂ desorption capacity is synthesized via incorporation of diarylethene (DArE) as guest molecules in porous aromatic framework‐1 (PAF‐1). In these host–guest complexes, the carboxylic acid groups featured in DArE allow multiple noncovalent interactions to exist. DArE loadings ranging from 1 to 50 wt% are incorporated in PAF‐1 and the complexes characterized by UV–vis spectroscopy, FT‐IR spectroscopy, CO₂, and N₂ adsorption. Successful inclusion of DArE in PAF‐1 is indicated by the reduction of pore size distributions and an optimum loading of 5 wt% is determined by comparing the percentage photo­response and CO₂ uptake capacity at 1 bar. Mechanistic studies suggest that photoswitching modulates the binding affinity between DArE and CO₂ toward the host, triggering carbon capture and release. This is the first known example of photodynamic carbon capture and release in a PAF.     

An O2 Self‐Sufficient Biomimetic Nanoplatform for Highly Specific and Efficient Photodynamic Therapy

Conventional oxygen‐dependent photodynamic therapy (PDT) has faced severe challenges because of the non‐specificity of most available photosensitizers (PSs) and the hypoxic nature of tumor tissues. Here, an O₂ self‐sufficient cell‐like biomimetic nanoplatform (CAT‐PS‐ZIF@Mem) consisting of the cancer cell membrane (Mem) and a cytoskeleton‐like porous zeolitic imidazolate framework (ZIF‐8) with the embedded catalase (CAT) protein molecules and Al(III) phthalocyanine chloride tetrasulfonic acid (AlPcS₄, defined as PS) is developed. Because of the immunological response and homologous targeting abilities of the cancer cell membrane, CAT‐PS‐ZIF@Mem is selectively accumulated at the tumor site and taken up effectively by tumor cells after intravenous injection. After the intracellular H₂O₂ penetration into the framework, it is catalyzed by CAT to produce O₂ at the hypoxic tumor site, facilitating the generation of toxic ¹O₂ for highly effective PDT in vivo under near‐infrared irradiation. By integrating the immune escape, cell homologous recognition, and O₂ self‐sufficiency, this cell‐like biomimetic nanoplatform demonstrates highly specific and efficient PDT against hypoxic tumor cells with much reduced side‐effect on normal tissues.     

Hollow Mesoporous Carbon Nanocubes: Rigid‐Interface‐Induced Outward Contraction of Metal‐Organic Frameworks

Novel carbon materials derived from metal‐organic frameworks (MOFs) have attracted much attention, but the commonly inevitable inward contraction during the carbonization process has restricted their structural variety and applications. In this work, a novel rigid‐interface induced outward contraction approach is reported for synthesizing hollow mesoporous carbon nanocubes (HMCNCs) by using ZIF‐8 nanocubes as precursors. HMCNCs exhibit a cubic morphology with the particle sizes slightly larger than ZIF‐8 nanocubes. Due to the unique outward contraction process, uniform carbon nanocubes with a hollow cavity, an outer microporous shell, and an inner mesoporous wall are simultaneously formed with a large pore size (25 nm), high surface area (1085.7 m² g^?1), high porosity (3.77 cm³ g^?1), and high nitrogen content (12.2%). When used as a cathode material for Li–SeS₂ batteries, the HMCNCs deliver a stable capacity of 812.6 mA h g^?1 at 0.2 A g^?1 after 100 cycles and an outstanding rate capability (455.1 mA h g^?1 at 5.0 A g^?1). The findings may pave the way for the construction of distinctive MOF‐derived carbon materials for various applications.     

Synergistic Sonodynamic/Chemotherapeutic Suppression of Hepatocellular Carcinoma by Targeted Biodegradable Mesoporous Nanosonosensitizers

Hepatocellular carcinoma (HCC) is one of the deadliest malignancies worldwide featured with the poor prognosis and high mortality in affected patients. Given its insensitivity to conventional systemic chemotherapy, the development of novel modalities for HCC management is highly urgent. Sonodynamic therapy (SDT) has gained considerable momentum in cancer therapy. Especially, through synergistic SDT/chemotherapy, SDT would enhance the chemotherapeutic process on inhibiting tumor growth, which holds great potential on combating HCC. In this work, we report on the design/fabrication of targeted biodegradable nanosonosensitizers based on hollow mesoporous organosilica nanoparticles (HMONs), followed by pore‐engineering including covalent anchoring of protoporphyrin (PpIX, HMONs‐PpIX) and conjugation of arginine‐glycine‐aspartic acid in order to specifically targeting HCC cells. Such nanosonosensitizers provide efficient loading and controllable stimuli‐responsive release of chemotherapeutic agents for HCC‐targeting chemotherapy, thus promoting an enhancing chemotherapeutic process via the unique sonotoxicity under ultrasound irradiation. The HMONs matrix with biologically active organic groups in the framework (disulfide bond) are endowed with intrinsic tumor microenvironment‐responsive biodegradability and improved biocompatibility/biosafety. In particular, a synergistic inhibition effect of drug‐loaded HMONs‐PpIX‐arginine‐glycine‐aspartic acid on HCC growth has been systematically demonstrated both in vitro and in vivo (84.7% inhibition rate), which brings insights and meets the versatile therapeutic requirements for HCC management.     

Biocatalytic Metal‐Organic Framework‐Based Artificial Cells

Artificial cells or cell mimics have drawn significant attention in cell biology and material science in the last decade and its development will provide a powerful toolbox for studying the origin of life and pave the way for novel biomedical applications. Artificial cells and their subcompartments are typically constructed from a semipermeable membrane composed of liposomes, polymersomes, hydrogels, or simply aqueous droplets enclosing bioactive molecules to perform cellular‐mimicking activities such as compartmentalization, communication, metabolism, or reproduction. Despite the rapid progress, concerns regarding their physical stability (e.g., thermal or mechanical) and tunability in membrane permeability have significantly hindered artificial cells systems in real‐life applications. In addition, developing a facile and versatile system that can mimic multiple cellular tasks is advantageous. Here, an ultrastable, multifunctional and stimulus‐responsive artificial cell system is reported. Constructed from metal‐phenolic network membranes enclosing enzyme‐containing metal‐organic frameworks as organelles, the bionic cell system can mimic multiple cellular tasks including molecular transport regulation, cell metabolism, communication and programmed degradation, and significantly extends its stability range across various chemical and physical conditions. It is believed that the development of such responsive cell mimics will have significant potentials for studying cellular reactions and have future applications in biosensing and drug delivery.     

Dye Encapsulated Metal‐Organic Framework for Warm‐White LED with High Color‐Rendering Index

A strategy by encapsulating organic dyes into the pores of a luminescent metal‐organic framework (MOF) is developed to achieve white‐light‐emitting phosphor. Both the red‐light emitting dye 4‐(p‐dimethylaminostyryl)‐1‐methylpyridinium ( DSM ) and the green‐light emitting dye acriflavine ( AF ) are encapsulated into a blue‐emitting anionic MOF ZJU‐28 through an ion‐exchange process to yield the MOF?dye composite ZJU‐28?DSM/AF . The emission color of the obtained composite can be easily modulated by simply adjusting the amount and component of dyes. With careful adjustment of the relative concentration of the dyes DSM and AF , the resulting ZJU‐28?DSM/AF (0.02 wt% DSM , 0.06 wt% AF ) exhibits a broadband white emission with ideal CIE coordinates of (0.34, 0.32), high color‐rendering index value of 91, and moderate correlated color temperature value of 5327 K. Such a strategy can be easily expanded to other luminescent MOFs and dyes, thus opening a new perspective for the development of white light emitting materials.     

Luminescent Metal‐Organic Frameworks for Selectively Sensing Nitric Oxide in an Aqueous Solution and in Living Cells

Cu²⁺‐based metal‐organic framework (Cu? TCA ) (H₃ TCA = tricarboxytriphenyl amine) having triphenylamine emitters was assembled and structurally characterized. Cu? TCA features a three‐dimensional porous structure consolidated by the well‐established Cu₂(O₂CR)₄ paddlewheel units with volume of the cavities approximately 4000 nm³. Having paramagnetic Cu²⁺ ions to quench the luminescence of triphenylamine, Cu? TCA only exhibited very weak emission at 430 nm; upon the addition of NO up to 0.1 mM , the luminescence was recovered directly and provided about 700‐fold fluorescent enhancement. The luminescence detection exhibited high selectivity – other reactive species present in biological systems, including H₂O₂, NO₃^?, NO₂^?, ONOO^?, ClO^? and ¹O₂, did not interfere with the NO detection. The brightness of the emission of Cu? TCA also led to its successful application in the biological imaging of NO in living cells. As a comparison, lanthanide metal‐organic framework Eu? TCA having triphenylamine emitters and characteristic europium emitters was also assembled. Eu? TCA exhibited ratiometric fluorescent responses towards NO with the europium luminescence maintained as the internal standard and the triphenylamine emission exhibited more than 1000‐fold enhancement.     

Interfering with Lactate‐Fueled Respiration for Enhanced Photodynamic Tumor Therapy by a Porphyrinic MOF Nanoplatform

Lactate is a prominent energy substrate for oxidative tumor cells. Interfering with the lactate‐fueled respiration of oxidative tumor cells would be a promising therapeutic strategy for cancer treatment. In this study, α‐cyano‐4‐hydroxycinnamate (CHC) is incorporated into a porous Zr (IV)‐based porphyrinic metal‐organic framework (PZM) nanoparticle, to reduce the lactate uptake by inhibiting the expression of lactate‐proton symporter, monocarboxylate transporter 1 (MCT1) in tumor cells, thus transform lactate‐fueled aerobic respiration to anaerobic glycolysis. The alteration in energy supply can also decrease the oxygen consumption in tumor cells, which would facilitate the photodynamic therapy (PDT) in cancer treatment. Moreover, hyaluronic acid (HA) is coated on the surface of PZM nanoparticles for CD44‐targeting and hyaluronidase‐induced intracellular drug releasing. Both in vitro and in vivo studies confirmed good biocompatibility and enhanced PDT efficacy of the HA‐coated PZM nanoparticles (CHC‐PZM@HA) in tumor cells. The CHC‐PZM@HA platform will provide a new perspective in cancer therapy.     

Metal‐Organic Frameworks Derived Nanotube of Nickel–Cobalt Bimetal Phosphides as Highly Efficient Electrocatalysts for Overall Water Splitting

The design of highly efficient, stable, and noble‐metal‐free bifunctional electrocatalysts for overall water splitting is critical but challenging. Herein, a facile and controllable synthesis strategy for nickel–cobalt bimetal phosphide nanotubes as highly efficient electrocatalysts for overall water splitting via low‐temperature phosphorization from a bimetallic metal‐organic framework (MOF‐74) precursor is reported. By optimizing the molar ratio of Co/Ni atoms in MOF‐74, a series of Cox Niy P catalysts are synthesized, and the obtained Co4Ni1P has a rare form of nanotubes that possess similar morphology to the MOF precursor and exhibit perfect dispersal of the active sites. The nanotubes show remarkable hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalytic performance in an alkaline electrolyte, affording a current density of 10 mA cm^?2 at overpotentials of 129 mV for HER and 245 mV for OER, respectively. An electrolyzer with Co4Ni1P nanotubes as both the cathode and anode catalyst in alkaline solutions achieves a current density of 10 mA cm^?2 at a voltage of 1.59 V, which is comparable to the integrated Pt/C and RuO₂ counterparts and ranks among the best of the metal‐phosphide electrocatalysts reported to date.     

Functional Defective Metal‐Organic Coordinated Network of Mesostructured Nanoframes for Enhanced Electrocatalysis

Although defects are traditionally perceived as undesired feature, the prevalence of tenacious low‐coordinated defects can instead give rise to desirable functionalities. Here, a spontaneous etching of mesostructured crystal, cyanide‐bridged cobalt‐iron (CN‐CoFe) organometallic hybrid into atomically crafted open framework that is populated with erosion‐tolerant high surface energy defects is presented. Unprecedently, the distinct mechanistic etching pathway dictated by the mesostructured assembly, bulk defects, and strong intercoordinated cyanide‐bridged hybrid mediates not only formation of excess low‐coordinated defects but also more importantly stabilizes them against prevailing dissolution and migration issues. Clearly, the heteropolynuclear cyanide bonded inorganic mesostructured clusters sanction the restructuring of a new breed of stable organometallic polymorph with 3D accessible structure enclosed by electrochemical active atomic stepped edges and high index facets. The exceptional electrocatalysis performance supports the assertion that defective mesostructured polymorph offers a new material paradigm to synthetically tailor the elementary building block constituents toward functional materials.