Controlled Generation of Singlet Oxygen in Living Cells with Tunable Ratios of the Photochromic Switch in Metal–Organic Frameworks

Synergistic applications of cyclodextrin-based systems and metal-organic frameworks in transdermal drug delivery for skin cancer therapy

This review article explores the innovative field of eco-friendly cyclodextrin-based coordination polymers and metal-organic frameworks (MOFs) for transdermal drug delivery in the case of skin cancer therapy. We critically examine the significant advancements in developing these nanocarriers, with a focus on their unique properties such as biocompatibility, targeted drug release, and enhanced skin permeability. These attributes are instrumental in addressing the limitations inherent in traditional skin cancer treatments and represent a paradigm shift towards more effective and patient-friendly therapeutic approaches. Furthermore, we discuss the challenges faced in optimizing the synthesis process for large-scale production while ensuring environmental sustainability. The review also emphasizes the immense potential for clinical applications of these nanocarriers in skin cancer therapy, highlighting their role in facilitating targeted, controlled drug release which minimizes systemic side effects. Future clinical applications could see these nanocarriers being customized to individual patient profiles, potentially revolutionizing personalized medicine in oncology. With further research and clinical trials, these nanocarriers hold the promise of transforming the landscape of skin cancer treatment. With this study, we aim to provide a comprehensive overview of the current state of research in this field and outline future directions for advancing the development and clinical application of these innovative nanocarriers.

Ratiometric Electrochemiluminescence of Zirconium Metal-Organic Framework as a Single Luminophore for Sensitive Detection of HPV-16 DNA

This study developed a new zirconium metal-organic framework (MOF) luminophore named Zr-DPA@TCPP with dual-emission electrochemiluminescence (ECL) characteristics at a resolved potential. First, Zr-DPA@TCPP with a core-shell structure was effectively synthesized through the self-assembly of 9,10-di(p-carboxyphenyl)anthracene (DPA) and 5,10,15,20-tetra(4-carboxyphenyl)porphyrin (TCPP) as the respective organic ligands and the Zr cluster as the metal node. The reasonable integration of the two organic ligands DPA and TCPP with ECL properties into a single monomer, Zr-DPA@TCPP, successfully exhibited synchronous anodic and cathodic ECL signals. Besides, due to the impressively unique property of ferrocene (Fc), which can quench the anodic ECL but cannot affect the cathodic ECL signal, the ratiometric ECL biosensor was cleverly designed by using the cathode signal as an internal reference. Thus, combined with DNA recycle amplification reactions, the ECL biosensor realized sensitive ratiometric detection of HPV-16 DNA with the linear range of 1 fM-100 pM and the limit of detection (LOD) of 596 aM. The distinctive dual-emission properties of Zr-DPA@TCPP provided a new idea for the development of ECL luminophores and opened up an innovative avenue of fabricating the ratiometric ECL platform.

A versatile nanoplatform based on multivariate porphyrinic metal-organic frameworks for catalytic cascade-enhanced photodynamic therapy

In recent years, the antitumor application of photodynamic therapy (PDT) has gained widespread interest in treating solid tumors. Due to the hypoxic environment in tumors, the major limit of PDT seems to be the source of oxygen. In this work, we attempted to relieve hypoxia and enhance photodynamic therapy, and therefore, designed and assembled a catalytic cascade-enhanced PDT multifunctional nanoplatform. The mentioned platform termed UIO@Ca-Pt is based on porphyrinic metal-organic framework (UIO) combination, which is simultaneously loaded by CaO2 NPs with polydopamine (PDA) and then the Pt raw material to further improve biocompatibility and efficiency. In a tumor microenvironment, CaO2 could react with water to generate calcium hydroxide and hydrogen peroxide, which was further decomposed by Pt nanoparticles to form oxygen, thereby facilitating the generation of cytotoxic singlet oxygen by photosensitizer TCPP under laser irradiation. Both in vitro and in vivo experiment results confirmed the excellent oxygen production capacity and enhanced PDT effect of UIO@Ca-Pt. With guaranteed safety in PDT, the oxygen-supplying strategy might stimulate considerable interest in the development of various metal-organic materials with multifunctionality for tumor diagnosis and therapy.

Synthesis of Au@MOF core-shell hybrids for enhanced photodynamic/photothermal therapy

Photodynamic/photothermal therapy (PDT/PTT) has become a research focus of cancer treatment due to the non-invasiveness, spatio-temporal controllability, and effectiveness of repeated treatment. Here, Au@MOF core-shell hybrids were designed and constructed by the layer-by-layer method, and the thickness of the MOF shell can be adjusted by controlling the coordination reaction between the layers. Au nanorod cores mainly produce the PTT effect due to their strong absorbance at 650 nm. The porphyrin ligand in the MOF shell can convert O₂ into ¹O₂ under light conditions, resulting in a high PDT effect. Moreover, the metal node Fe₃O(OAc)₆(H₂O)₃⁺ cluster of the MOF can catalyze the decomposition of H₂O₂ into O₂ to overcome the hypoxic environment of tumors, which further improves the effect of PDT. The combination of the porphyrin ligand in the MOF structure and Au nanorods has promoted the synergistic effects of PDT/PTT. As expected, the results confirmed that Au@MOF hybrids showed no obvious biotoxicity in both cells and animal experiments, and exhibited good biocompatibility. With the synergistic effects of PDT/PTT, cancer cells could be effectively killed and tumor growth could be inhibited. In addition, the modification of folic acid on the surface of Au@MOF can further enrich the hybrids at the tumor site and enhance the inhibitory effect on tumors. These studies have proved that PDT and PTT can be effectively combined and have greater advantages in enhancing the treatment of tumors.

A MnO2-coated multivariate porphyrinic metal-organic framework for oxygen self-sufficient chemo-photodynamic synergistic therapy

Lately, chemotherapy and photodynamic therapy (PDT) synergistic therapy has become a promising anti-cancer treatment mean. However, the hypoxia in tumor leads to huge impediments to the oxygen-dependentPDT effects. In this work, a multifunctional nanoplatform (TUDMP) based on a multivariable porphyrin-nMOFs core and a manganese dioxide (MnO₂) shell was prepared for relieving tumor hypoxia and enhancing chemo-photodynamic synergistic therapy performance. The obtained TUDMP nanoplatform could effectively catalyze the hydrolysis of hydrogen peroxide to generate oxygen and also lead to consumption of antioxidant GSH, thereby facilitating the production of cytotoxic reactive oxygen species (ROS) by photosensitizer under laser irradiation. More importantly, the decomposition of the MnO₂ shell would further promote the release of the loaded doxorubicin (DOX), and thus an efficient chemo-PDT synergistic therapy was realized. Both in vitro and in vivo experimental results demonstrated the oxygen self-sufficient multifunctional nanoplatform could exhibit significantly enhanced anticancer efficiencies compared with chemotherapy or PDT alone.

Trapping and Releasing of Oxygen in Liquid by Metal-Organic Framework with Light and Heat

Nanoporous materials can adsorb small molecules into their nanospaces. However, the trapping of light gas molecules dissolved in solvents suffers from low concentration and poor adsorption affinity. Here, the reversible trapping and releasing of dissolved oxygen are shown through integrating photosensitization and chemical capturing abilities into a metal-organic framework (MOF), MOMF-1. 9,10-Di(4-pyridyl)anthracene (dpa) ligands in MOMF-1 generates singlet oxygen from triplet oxygen under photoirradiation without additional photosensitizers, and successively reacts with it to produce anthracene endoperoxide, forming MOMF-2, which is proved crystallographically. The reverse reaction also proceeds quantitatively by heating MOMF-2. Moreover, MOMF-1 exhibits excellent water resistance, and completely removes oxygen of ppm order concentrations in water. The new material shown in this report allows controlling of the amount of dissolved oxygen, which can be applicable in various fields relating to numerous oxidation phenomena.

Porphyrin-Based Metal-Organic Frameworks for Biomedical Applications

Porphyrins and porphyrin derivatives have been widely explored for various applications owing to their excellent photophysical and electrochemical properties. However, inherent shortcomings, such as instability and self-quenching under physiological conditions, limit their biomedical applications. In recent years, metal-organic frameworks (MOFs) have received increasing attention. The construction of porphyrin-based MOFs by introducing porphyrin molecules into MOFs or using porphyrins as organic linkers to form MOFs can combine the unique features of porphyrins and MOFs as well as overcome the limitations of porphyrins. This Review summarizes important synthesis strategies for porphyrin-based MOFs including porphyrin@MOFs, porphyrinic MOFs, and composite porphyrinic MOFs, and highlights recent achievements and progress in the development of porphyrin-based MOFs for biomedical applications in tumor therapy and biosensing. Finally, the challenges and prospects presented by this class of emerging materials for biomedical applications are discussed.

Effective Singlet Oxygen Generation in Silica-Coated CsPbBr3 Quantum Dots through Energy Transfer for Photocatalysis

Here, silica-coated CsPbBr₃ quantum dots (QDs) were demonstrated to be effective photosensitizers for the generation of singlet oxygen (¹ O₂ ). The silica encapsulation improved the stability of the perovskite QDs while also preserving an excellent light-harvesting capability in the visible-light region. The appropriate exciton binding energy and dark exciton generation characteristics of perovskite QDs may be responsible for the energy transfer. The high oxidizability of ¹ O₂ makes the material attractive for application in decomposition of organic dyes such as methyl orange. This work provides new insight for designing excellent perovskite-based photocatalysts.

Visible-light harvesting pyrene-based MOFs as efficient ROS generators

The utilization of reactive oxygen species (ROS) in organic transformations is of great interest due to their superior oxidative abilities under mild conditions. Recently, metal-organic frameworks (MOFs) have been developed as photosensitizers to transfer molecular oxygen to ROS for photochemical synthesis. However, visible-light responsive MOFs for oxygen activation remains scarce. Now we design and synthesize two porous MOFs, namely, PCN-822(M) (M = Zr, Hf), which are constructed by a 4,5,9,10-(K-region) substituted pyrene-based ligand, 4,4',4'',4'''-((2,7-di-tert-butylpyrene-4,5,9,10-tetrayl)tetrakis(ethyne-2,1-diyl))-tetrabenzoate (BPETB4-). With the extended π-conjugated pyrene moieties isolated on the struts, the derived MOFs are highly responsive to visible light, possessing a broad-band adsorption from 225-650 nm. As a result, the MOFs can be applied as efficient ROS generators under visible-light irradiation, and the hafnium-based MOF, PCN-822(Hf), can promote the oxidation of amines to imines by activating molecular oxygen via synergistic photo-induced energy and charge transfer.

Synthesis of Functionalized Azobiphenyl- and Azoterphenyl- Ditopic Linkers: Modular Building Blocks for Photoresponsive Smart Materials

Modular synthesis of structurally diverse functionalized azobiphenyls and azoterphenyls for the realization of optically switchable materials has been described. The corresponding synthesis of azobiphenyls and azoterphenyls by stepwise Mills/Suzuki-Miyaura cross-coupling reaction, proceeds with high yields and provides facile access to a library of functionalized building blocks. The synthetic methods described herein allow combining several distinct functional groups within a single unit, each intended for a specific task, such as 1) the -N=N- azobenzene core as a photoswitchable moiety, 2) aryls and heteroaryls, functionalized with carboxylic acids or pyridine at its peripheries, as coordinating moieties and 3) varying substitution, size and length of the backbone for adaptability to specific applications. These specifically designed azobiphenyls and azoterphenyls provide modular bricks, potentially useful for the assembly of a variety of polymers, molecular containers and coordination networks, offering a high degree of molecular functionality. Once integrated into materials, the azobenzene system, as a side group on the organic linker backbone, can be exploited for remotely controlling the structural, mechanical or physical properties, thus being applicable for a broad variety of 'smart' applications.

Structural Transformation in Metal-Organic Frameworks for Reversible Binding of Oxygen

Polycyclic aromatic derivatives can trap ¹ O₂ to form endoperoxides (EPOs) for O₂ storage and as sources of reactive oxygen species. However, these materials suffer from structural amorphism, which limit both practical applications and fundamental studies on their structural optimization for O₂ capture and release. Metal-organic frameworks (MOFs) offer advantages in O₂ binding, such as clear structure-performance relationships and precise controllability. Herein, we report the reversible binding of O₂ is realized via the chemical transformation between anthracene-based and the corresponding EPO-based MOF. It is shown that anthracene-based MOF, the framework featuring linkers with polycyclic aromatic structure, can rapidly trap ¹ O₂ to form EPOs and can be restored upon UV irradiation or heating to release O₂ . Furthermore, we confirm that photosensitizer-incorporated anthracene-based MOF are promising candidates for reversible O₂ carriers controlled by switching Vis/UV irradiation.

Solvent switching smart metal–organic framework as a catalyst of reduction and condensation

The organization of a Zn-based metal–organic framework (MOF) as the first solvent switching catalyst has been achieved via in situ ligand incorporation.

A CuO-functionalized NMOF probe with a tunable excitation wavelength for selective detection and imaging of H2S in living cells

Recently, fluorescent nanoscale metal-organic frameworks (NMOFs) have been proven to be useful probes for the detection and imaging of active biomolecules in living cells. However, the excitation wavelengths of these NMOF fluorescence probes are mostly in the ultraviolet region, which unavoidably results in reduced cell activity, limited tissue penetration depth and inevitable biological background interference. Herein, to solve this problem, a CuO functionalized NMOF probe with a tunable excitation wavelength based on Förster resonance energy transfer (FRET) for selective detection and imaging of the third important gaseous signaling molecule hydrogen sulfide (H2S) in living cells as an example is presented. In the energy transfer system, NMOF confines the luminophore organic dye thiazole orange within its intrinsic porous matrix as the energy donor, in which the excitation wavelength of the NMOF can be tuned simply from UV to Vis through the choice of dye molecules, and the H2S-responding site copper oxide nanoparticle (CuO NP) is the acceptor. After the surface functionalization of CuO NPs onto the NMOF, the fluorescence of the NMOF can be efficiently quenched based on the FRET. When H2S appeared, the fluorescence of the nanoprobe is recovered due to the interruption of FRET. This facile yet powerful strategy not only provides an instantaneous fluorescence probe for selective H2S detection in living cells but also offers a valuable approach for using porous NMOFs to sense other biological species.

Spiropyran in nanoassemblies as a photosensitizer for photoswitchable ROS generation in living cells

Reversibly controlled generation of singlet oxygen from photosensitizing nanosystems has the benefits of selective cell killing and controllable effect time, but is a challenging option for photodynamic therapies. We report a strategy for integrating photochromic spiropyrans into biocompatible cationic polymers, which involved assembling nucleic acids into functional nanoparticles without introducing additional photosensitizers and imaging agents. We found that spiropyran-containing nanoparticles have photoswitching properties for both fluorescence (with a quantum yield of up to 0.27) and singlet oxygen generation (with a quantum yield of up to 0.22) in aqueous solutions and cells, and demonstrated that spiropyrans in nanoassemblies featuring aggregation-induced enhanced photosensitization and emission could be potentially applied in photodynamic therapy studies on tumor cells.

Controllable Photodynamic Therapy Implemented by Regulating Singlet Oxygen Efficiency

With singlet oxygen (1O2) as the active agent, photodynamic therapy (PDT) is a promising technique for the treatment of various tumors and cancers. But it is hampered by the poor selectivity of most traditional photosensitizers (PS). In this review, we present a summary of controllable PDT implemented by regulating singlet oxygen efficiency. Herein, various controllable PDT strategies based on different initiating conditions (such as pH, light, H2O2 and so on) have been summarized and introduced. More importantly, the action mechanisms of controllable PDT strategies, such as photoinduced electron transfer (PET), fluorescence resonance energy transfer (FRET), intramolecular charge transfer (ICT) and some physical/chemical means (e.g. captivity and release), are described as a key point in the article. This review provide a general overview of designing novel PS or strategies for effective and controllable PDT.

A core–shell metal–organic-framework (MOF)-based smart nanocomposite for efficient NIR/H2O2-responsive photodynamic therapy against hypoxic tumor cells

In this work, core–shell MOF-based smart nanocomposite UCNPs/MB@ZIF-8@catalase has been constructed for bio-imaging and efficient NIR/H₂O₂-responsive photodynamic therapy against hypoxic tumor cells.