Enhanced Biological Imaging via Aggregation-Induced Emission Active Porous Organic Cages

Aggregation-Induced Enhanced Electrochemiluminescence Resonance Energy Transfer Biosensor for Ultrasensitive Detection of Carcinoembryonic Antigen Based on Donor-Acceptor Organic Nanoparticles

Aggregation-induced electrochemiluminescence (AIECL) combines the merits of aggregation-induced emission (AIE) and electrochemiluminescence (ECL), which has become a research hot spot in recent years. Therefore, we synthesized a novel AIE compound (Z)-3-(4-(2-butyl-1,3-dioxo-2,3-dihydro-1H-benzo[de]isoquinolin-6-yl)phenyl)-2-(4-(1,2,2-triphenylvinyl)phenyl)acrylonitrile (TPENI) with a donor-acceptor (D-A) structure, that is, a simple peripheral modification of 4-(2-butyl-1,3-dioxo-2,3-dihydro-1H-benzo[de]isoquinolin-6-yl) benzaldehyde (NI-CHO) with AIE-active tetraphenylethylene (TPE) to achieve the transition of NI-CHO from aggregation-caused quenching (ACQ) to an AIE molecule. When TPENI was in the aggregated state, the luminescence intensity was significantly enhanced due to the TPE structural unit restricting the free rotation of the intramolecular benzene ring, as well as the π-π stacking interactions of the molecules, which was conducive to the preparation of TPENI NPs as ECL materials. Satisfactorily, we found that the ECL intensity of TPENI NPs was increased by about 4.8-fold compared with that of the molecules dispersed in organic solution, and the stability reached about 1000 s. Based on the excellent ECL properties of TPENI NPs, an "on-off-on" ECL biosensor with a wider detection range (1 fg/mL to 100 ng/mL) and a lower detection limit of 0.20 fg/mL (S/N = 3) was proposed for sensitive analysis of a carcinoembryonic antigen (CEA). Overall, this work provided a new approach to the realization of AIECL and laid the foundation for the application of naphthalimide derivatives in ECL.

Construction of stable porous organic cages: from the perspective of chemical bonds

Porous organic cages (POCs) are constructed from purely organic synthons by covalent linkages with intrinsic cavities and have shown potential applications in many areas. However, the majority of POC synthesis methods reported thus far have relied on dynamically reversible imine linkages, which can be metastable and unstable under humid or harsh chemical conditions. This instability significantly hampers their research prospects and practical applications. Consequently, strategies to enhance the chemical stability of POCs by modifying imine bonds and developing robust covalent linkages are imperative for realizing the full potential of these materials. In this review, we aim to highlight recent advancements in synthesizing chemical-stable POCs through these approaches and their associated applications. Additionally, we propose further strategies for creating stable POCs and discuss future opportunities for practical applications.

Efficient Near-Infrared Fluorophores Based on Cyanostyrene Derivatives for Two-Photon Fluorescence Bioimaging

Organic fluorescent materials with red/near-infrared (NIR) emission are highly promising for use in biotechnology due to their exceptional advantages. However, traditional red/NIR fluorophores often exhibit weak emission at high concentrations or in an aggregated state due to the aggregate-caused quenching effect, which severely limits their applicability in biological imaging. To address this challenge, we developed a series of cyanostyrene derivatives with aggregation-induced emission characteristics, including 2,3-Bis-(4-styryl-phenyl)-but-2-enedinitrile (DPB), 2,3-Bis-{4-[2-(4-methoxy- phenyl)-vinyl]-phenyl}-but-2-enedinitrile (DOB), 2,3-Bis-{4-[2-(4-diphenylamino- phenyl)-vinyl]-phenyl}-but-2-enedinitrile (DTB), and 2,3-Bis-[4-(2-{4-[phenyl- (4-triphenylvinyl-phenyl)-amino]-phenyl}-vinyl)- phenyl]-but-2-enedinitrile (DTTB). Notably, these compounds exhibited intense solid state fluorescence owing to AIE effect, especially DTTB shows NIR emission with high solid state quantum efficiency (712 nm, ΦF=14.2 %). Then we prepared DTTB@PS-PEG NPs nanoparticles by encapsulating DTTB with the amphiphilic polymer polystyrene-polyethylene glycol (PS-PEG). Importantly, DTTB@PS-PEG NPs exhibited highly efficient NIR luminescence (ΦF=28.7 %) and a large two-photon absorption cross-section (1900 GM) under 800 nm laser excitation. The bright two-photon fluorescence of DTTB@PS-PEG indicated that it can be a highly promising candidate for two-photon fluorescence probe. Therefore, this work provides valuable insights for the design of highly efficient and NIR-emitting two-photon fluorescent probes.

Nanobody-Based Microfluidic Immunosensor Chip Using Tetraphenylethylene-Derived Covalent Organic Frameworks as Aggregation-Induced Electrochemiluminescence Emitters for the Detection of Thymic Stromal Lymphopoietin

In this letter, a sensitive microfluidic immunosensor chip was developed using tetrakis(4-aminophenyl)ethene (TPE)-derived covalent organic frameworks (T-COF) as aggregation-induced electrochemiluminescence (AIECL) emitters and nanobodies as efficient immune recognition units for the detection of thymic stromal lymphopoietin (TSLP), a novel target of asthma. The internal rotation and vibration of TPE molecules were constrained within the framework structure, forcing nonradiative relaxation to convert into pronounced radiative transitions. A camel-derived nanobody exhibited superior specificity, higher residual activity and epitope recognition postcuring compared to monoclonal antibodies. Benefiting from the affinity between silver ions (Ag+) and cytosine (C), a double-stranded DNA (dsDNA) embedded with Ag+ was modified onto the surface of TSLP. A positive correlation was obtained between the TSLP concentration (1.00 pg/mL to 4.00 ng/mL) and ECL intensity, as Ag+ was confirmed to be an excellent accelerator of the generation of free radical species. We propose that utilizing COF to constrain luminescent molecules and trigger the AIECL phenomenon is another promising method for preparing signal tags to detect low-abundance disease-related markers.

Advancements and Challenges in the Application of Metal-Organic Framework (MOF) Nanocomposites for Tumor Diagnosis and Treatment

Nanoscale metal-organic frameworks (MOFs) offer high biocompatibility, nanomaterial permeability, substantial specific surface area, and well-defined pores. These properties make MOFs valuable in biomedical applications, including biological targeting and drug delivery. They also play a critical role in tumor diagnosis and treatment, including tumor cell targeting, identification, imaging, and therapeutic methods such as drug delivery, photothermal effects, photodynamic therapy, and immunogenic cell death. The diversity of MOFs with different metal centers, organics, and surface modifications underscores their multifaceted contributions to tumor research and treatment. This review is a summary of these roles and mechanisms. The final section of this review summarizes the current state of the field and discusses prospects that may bring MOFs closer to pharmaceutical applications.

Supramolecular cage-mediated cargo transport

A steady stream of material transport based on carriers and channels in living systems plays an extremely important role in normal life activities. Inspired by nature, researchers have extensively applied supramolecular cages in cargo transport because of their unique three-dimensional structures and excellent physicochemical properties. In this review, we will focus on the development of supramolecular cages as carriers and channels for cargo transport in abiotic and biological systems over the past fifteen years. In addition, we will discuss future challenges and potential applications of supramolecular cages in substance transport.

Flaring Inflammation and ER Stress by an Organelle-Specific Fluorescent Cage

The endoplasmic reticulum (ER) plays an important role in protein synthesis and its disruption can cause protein unfolding and misfolding. Accumulation of such proteins leads to ER stress, which ultimately promotes many diseases. Routine screening of ER activity in immune cells can flag serious conditions at early stages, but the current clinically used bio-probes have limitations. Herein, an ER-specific fluorophore based on a biocompatible benzothiadiazole-imine cage (BTD-cage) with excellent photophysical properties is developed. The cage outperforms commercially available ER stains in long-term live cell imaging with no fading or photobleaching over time. The cage is responsive to different levels of ER stress where its fluorescence increases accordingly. Incorporating the bio-probe into an immune disorder model, a 6-, 21-, and 48-fold increase in intensity is shown in THP-1, Raw 246.7, and Jurkat cells, respectively (within 15 min). These results strongly support that this system can be used for rapid visual and selective detection of ER stress. It is envisaged that tailoring molecular interactions and molecular recognition using supramolecular improved fluorophores can expand the library of biological probes for enhanced selectivity and targetability toward cellular organelles.

Reticular Modulation of Piezofluorochromic Behaviors in Organic Molecular Cages by Replacing Non-Luminous Components

Organic piezochromic materials that manifest pressure-stimuli-responses are important in various fields such as data storage and anticounterfeiting. The manipulation of piezofluorochromic behaviors for these materials is promising but remains a great challenge. Herein, a non-luminous components regulated strategy is developed and organic molecular cages (OMCs), a burgeoning class of crystalline organic materials with structural dynamics, are first explored for the design of piezofluorochromic materials with tunable luminescence. A series of OMCs based on aggregation-induced emission (AIE) chromophores, termed Cage 1-3, are synthesized and their piezofluorochromic behaviors are investigated by diamond anvil cell technique. Due to the sufficient voids between its flexible chromophores offered by the OMC structure, Cage 1 exhibits thermofluorochromic and piezofluorochromic properties. Moreover, the piezofluorochromic performance of this OMC could be further promoted by replacing its non-luminous components with improved flexibilities, and a remarkable luminescence peak shift by 150 nm together with a response sensitivity of 13.8 nm GPa-1 was achieved upon hydrostatic compression. The cage structure plays a vital role in facilitating efficient and reversible piezofluorochromic behaviors. This study has shed light on the rational design and exploitation of OMCs as an exceptional platform to accomplish customizable piezofluorochromic behaviors and enlarge their potential applications in pressure-based luminescence.

Pt(II)/Pd(II)-Based Metallosupramolecular Architectures as Light Harvesting Systems and their Applications

The development of artificial light-harvesting systems mimicking the natural photosynthesis method is an ever-growing field of research. Numerous systems such as polymers, metal complexes, POFs, COFs, supramolecular frameworks etc. have been fabricated to accomplish more efficient energy transfer and storage. Among them, the supramolecular coordination complexes (SCCs) formed by non-covalent metal-ligand interaction, have shown the capacity to not only undergo single and multistep energy migration but also to utilize the harvested energy for a wide variety of applications such as photocatalysis, tunable emissive systems, encrypted anti-counterfeiting materials, white light emitters etc. This review sheds light on the light-harvesting behavior of both the 2D metallacycles and 3D metallacages where design ingenuity has been executed to afford energy harvesting by both donor ligands as well as metal acceptors.

Photostable and high-brightness aggregation-induced emission of iridium luminogen achieving reliable and sensitive continuous luminescent quantification of molecular oxygen

Online continuous luminescent oxygen quantification requires both high-brightness luminescence and superior photobleaching resistance of luminogens to afford the requisite level of sensitivity and operational stability, which remains a challenge. Herein, a fluorine-free design strategy of incremental rotors for preparing iridium luminogens with excellent photobleaching resistance and high-brightness aggregation-induced emission (AIE) is presented. The incremental rotors gradually improve the rotational activity of substituents, efficaciously activating the AIE with synchronously improved aggregation-state luminescence efficiency, which is theoretically confirmed by the variations of dipole moments and experimentally verified by the luminescent lifetimes. Moreover, the introduction of triphenylamine significantly improves the photobleaching resistance of iridium luminogens. Subsequently, by optimizing the loading capacity of the iridium luminogen, the improvement of high-brightness AIE on the oxygen sensitivity of ethocel films is successfully observed. Thickness attenuation of ethocel films dramatically shortens the quenching/recovery response to 4.7 s. Importantly, owing to the exceptional photobleaching resistance of the iridium luminogen, distinguished photo-fatigue resistance with operational stability is exhibited by the ethocel film with no luminescence attenuation during 8000 s continuous oxygen quantification.

Single Crystals of Insoluble Porous Salicylimine Cages

Porous organic cages (POCs) are meanwhile an established class of porous materials. Most of them are soluble to a certain extend and thus processable in or from solution. However, a few of larger salicylimine cages were reported to be insoluble in any organic solvents and thus characterized as amorphous materials. These cages were now synthesized as single-crystalline materials to get insight into packing motifs and preferred intermolecular interactions. Furthermore, the pairs of crystalline and amorphous materials for each cage allowed to compare their gas-sorption properties in both morphological states.

Engineering thiol-ene click chemistry for the preparation of a chiral stationary phase based on a [4+6]-type homochiral porous organic cage for enantiomeric separation in normal-phase and reversed-phase high performance liquid chromatography

In this study, a new chiral stationary phase (CSP) was fabricated by covalent bonding of a [4+6]-type homochiral porous organic cage (POC) CC19-R onto thiolated silica via a thiol-ene click reaction. The CC19-R was synthesized via Schiff-base reaction between 2-hydroxybenzene-1,3,5-tricarbaldehyde and (1R, 2R)-(-)-1,2-diaminocyclohexane. The enantioseparation capability of the resulting CC19-R-based CSP was systematically evaluated upon separating various chiral compounds or chiral pharmaceuticals in normal phase HPLC (NP-HPLC) and reversed phase HPLC (RP-HPLC), including alcohols, organic acids, ketones, diols, esters, and amines. Fifteen racemates were enantioseparated in NP-HPLC and 11 racemates in RP-HPLC. Some racemates have been well separated, such as 4-chlorobenzhydrol, cetirizine (in the form of dihydrochloride), 1,2-diphenyl-1,2-ethanediol, and 3-(benzyloxy)propane-1,2-diol whose resolution values reached 3.66, 4.23, 6.50, and 3.50, respectively. When compared with a previously reported chiral POC-based column (NC1-R column), eight racemates were not separated on the NC1-R column in NP-HPLC and five racemates were not separated in RP-HPLC, but were well resolved on this column, revealing that the enantioselectivity and separable range of chiral POCs-type columns could be significantly widened using this fabricated CC19-R column. Moreover, the resolution performance of the CC19-R column was also compared with commercial Chiralpak AD-H [CSP: Amylose tris(3,5-dimethylphenylcarbamate)] and Chiralcel OD-H [CSP: Cellulose tris(3,5-dimethylphenylcarbamate)] columns. The column also can separate some racemates that could not be separated or not well be separated by the two commercial columns, showing its good complementarity to the two commercial columns on chiral separation. In addition, the column also had good stability and reproducibility with the relative standard deviation (n = 5) of the retention time and resolution lower than 1.0% and 1.8%, respectively, after it had undergone multiple injections (100, 200, 300, and 400 times). This work indicated that the features of good resolution ability and simple synthesis methods using with this POC-based CSP provided chiral POCs with potential application prospects in HPLC racemic separation.

Porous Organic Cages

Porous organic cages (POCs) are a relatively new class of low-density crystalline materials that have emerged as a versatile platform for investigating molecular recognition, gas storage and separation, and proton conduction, with potential applications in the fields of porous liquids, highly permeable membranes, heterogeneous catalysis, and microreactors. In common with highly extended porous structures, such as metal-organic frameworks (MOFs), covalent organic frameworks (COFs), and porous organic polymers (POPs), POCs possess all of the advantages of highly specific surface areas, porosities, open pore channels, and tunable structures. In addition, they have discrete molecular structures and exhibit good to excellent solubilities in common solvents, enabling their solution dispersibility and processability─properties that are not readily available in the case of the well-established, insoluble, extended porous frameworks. Here, we present a critical review summarizing in detail recent progress and breakthroughs─especially during the past five years─of all the POCs while taking a close look at their strategic design, precise synthesis, including both irreversible bond-forming chemistry and dynamic covalent chemistry, advanced characterization, and diverse applications. We highlight representative POC examples in an attempt to gain some understanding of their structure-function relationships. We also discuss future challenges and opportunities in the design, synthesis, characterization, and application of POCs. We anticipate that this review will be useful to researchers working in this field when it comes to designing and developing new POCs with desired functions.

Preparation of Chiral Porous Organic Cage Clicked Chiral Stationary Phase for HPLC Enantioseparation

Porous organic cages (POCs) are a new subclass of porous materials, which are constructed from discrete cage molecules with permanent cavities via weak intermolecular forces. In this study, a novel chiral stationary phase (CSP) has been prepared by chemically binding a [4 + 6]-type chiral POC (C120H96N12O4) with thiol-functionalized silica gel using a thiol-ene click reaction and applied to HPLC separations. The column packed with this CSP presented good separation capability for chiral compounds and positional isomers. Thirteen racemates have been enantioseparated on this column, including alcohols, diols, ketones, amines, epoxides, and organic acids. Upon comparison with a previously reported chiral POC NC1-R-based column, commercial Chiralpak AD-H, and Chiralcel OD-H columns, this column is complementary to these three columns in terms of its enantiomeric separation; and can also separate some racemic compounds that cannot be separated by the three columns. In addition, eight positional isomers (iodoaniline, bromoaniline, chloroaniline, dibromobenzene, dichlorobenzene, toluidine, nitrobromobenzene, and nitroaniline) have also been separated. The influences of the injection weight and column temperature on separation have been explored. After the column has undergone multiple injections, the relative standard deviations (RSDs) for the retention time and selectivity were below 1.0 and 1.5%, respectively, indicating the good reproducibility and stability of the column for separation. This work demonstrates that POCs are promising materials for HPLC separation.

Enzyme coordination conferring stable monodispersity of diverse metal–organic frameworks for photothermal/starvation therapy

The agglomeration of metal-organic frameworks (MOFs) has long been a problem, and achieving stable monodispersity in water remains a great challenge. This paper reports a universal strategy that functionalizes MOFs by using an endogenous bioenzyme namely glucose oxidase (GOx), to achieve stable water monodispersity, and integrates it as a highly efficient nanoplatform for cancer synergistic therapy. Phenolic hydroxyl groups in GOx chain confers robust coordination interactions with MOFs, which not only endows stable monodispersion in water, but also provides many reactive sites for further modification. Silver nanoparticles are uniformly deposited onto MOFs@GOx to achieve high conversion efficiency from near-infrared light to heat, resulting in an effective starvation and photothermal synergistic therapy model. In vitro and in vivo experiments confirm excellent therapeutic effect at very low doses without using any chemotherapeutics. In addition, the nanoplatform generates large amounts of reactive oxygen species, induces heavy cell apoptosis, and demonstrates the first experimental example to effectively inhibit cancer migration. Our universal strategy enables stable monodispersity of various MOFs via GOx functionalization and establishes a non-invasive platform for efficient cancer synergistic therapy.

Porous Framework Materials for Bioimaging and Cancer Therapy

Cancer remains one of the most pressing diseases in the world. Traditional treatments, including surgery, chemotherapy, and radiotherapy still show certain limitations. Recently, numerous cancer treatments have been proposed in combination with novel materials, such as photothermal therapy, chemodynamic therapy, immunotherapy, and a combination of therapeutic approaches. These new methods have shown significant advantages in reducing side effects and synergistically enhancing anti-cancer efficacy. In addition to the above approaches, early diagnosis and in situ monitoring of lesion areas are also important for reducing side effects and improving the success rate of cancer therapy. This depends on the decent use of bioimaging technology. In this review, we mainly summarize the recent advances in porous framework materials for bioimaging and cancer therapy. In addition, we present future challenges relating to bioimaging and cancer therapy based on porous framework materials.

Conformationally Confined Emissive Cationic Macrocycle with Photocontrolled Organelle-Specific Translocation

The optimization of molecular conformation and aggregation modes is of great significance in creation of new luminescent materials for biochemical research and medical diagnostics. Herein, a highly emissive macrocycle (1) is reported, which is constructed by the cyclization reaction of triphenylamine with benzyl bromide and exhibits very distinctive photophysical performance both in aqueous solution and the solid state. Structural analysis reveals that the 1 can form self-interpenetrated complex and emit bright yellow fluorescence in the crystal lattice. The distorted yet symmetrical structure can endow 1 with unique two-photon absorption property upon excitation by near-infrared light. Also, 1 can be utilized as an efficient photosensitizer to produce singlet oxygen (1 O2 ) both in inanimate milieu and under cellular environment. More intriguingly, due to the strong association of 1 with negatively charged biomacromolecules, organelle-specific migration is achieved from lysosome to nucleus during the 1 O2 -induced cell apoptosis process. To be envisaged, this conformationally confined cationic macrocycle with photocontrolled lysosome-to-nucleus translocation may provide a feasible approach for in situ identifying different biospecies and monitoring physiological events at subcellular level.

Recent advances in the applications of porous organic cages

Porous organic cages (POCs) have emerged as a new sub-class of porous materials that stand out by virtue of their tunability, modularity, and processibility. Similar to other porous materials such...