AIE based luminescent porous materials as cutting-edge tool for environmental monitoring: State of the art advances and perspectives

Ratiometric responses of AIE/ACQ co-guests functionalized ZIF-8 nano-vehicles: Color-oriented ATP detection and intracellular imaging

In this work, two guests with opposite emission characteristics in aggregated states were rationally selected and delicately incorporated into zeolitic imidazolate framework-8 (ZIF-8) host. The simultaneous presentation aggregation-induced emission (AIE) of 1,1,2,2-Tetra (4-carboxyphenyl) ethylene (H4TCPE) and aggregation-caused quenching (ACQ) of 5-carboxytetramethylrhodamine (5-TAMRA) endowed the as-formed H4TCPE/5-TAMRA@ZIF-8 with dual responsive properties. Upon stimulation with ATP, the coordination environment of H4TCPE/5-TAMRA@ZIF-8 was interrupted, leading to the collapse of ZIF-8 host and the release of guests into their free states. The corresponding quenched blue AIE at 453 nm and recovered red ACQ at 586 nm, as well as the appearance of slight monomer emission (ME) at 409 nm possibly due to weak interaction between H4TCPE and 2-methylimidazole (Hmim), constituted a double-ratiometric sensing strategy for ATP. By plotting the fluorescence intensity ratio of (F409 + F586)/F453 to the concentration of ATP ranging from 0.02-9 mM, a linear relationship was found with the limit of detection as low as 6.09 μM. This along with the good sensitivity and robust reliability of H4TCPE/5-TAMRA@ZIF-8 probe enabled ATP detection in complex biofluids such as artificial serum and cell lysates (2.927 ± 0.565 mM) directly. Moreover, as the unique color-oriented sensing feature is inherited on the test paper, the scarcely reported H4TCPE/5-TAMRA@ZIF-8 test strip was developed. Via the values of R/B, ATP in cell lysates can also be reported (3.1 ± 0.590 mM) easily, which may be even feasible for point-of-care diagnosis of ATP-related diseases in remote areas lacking resources. Meanwhile, as a nano-sized vehicle, H4TCPE/5-TAMRA@ZIF-8 can easily enter cells and report intracellular ATP fluctuations by color-oriented imaging, which offers a more comprehensive and precise insight into cellular metabolism, holds significant potential for applications in bioanalytical research and environmental monitoring.

Respiration Drives Dynamic Metal-Organic Framework for Smart Photoresponse to Volatile Toxic Vapors and Their Photodynamic Sterilization

Using aggregation-induced emission luminous (AIEgens) containing dynamic molecular rotor structures as linkers to construct flexible smart luminescent metal-organic frameworks (MOFs) has become a transformative approach to constructing artificial intelligence color-changing materials. Herein, 4',4″,4'″,4″″-(ethene-1,1,2,2-tetrayl)tetrabiphenyl-4-carboxylic acid (H4TPPE) is selected as a linker, and octahedral Zr6O4(OH)8(H2O)4 cluster are used as secondary building unit (SBU) to construct the first smart luminescent MOF (Zr-TPE-MOF) that can be driven by CH2Cl2 or CH3COOH vapor for respiration. It is worth noting that Zr-TPE-MOF can absorb trace amounts of CH2Cl2 or CH3COOH vapor into the pores through respiration and shows a blue shift of the emission wavelength up to 479 nm and an increase of emission intensity by nearly three times. In addition, the thermochromic behavior of Zr-TPE-MOF is not obvious in the temperature range of 80-350 K, but it has obvious thermofluorochromics behavior in the temperature range of 350-470 K. Zr-TPE-MOF showed highly sensitive and visualized smart photoresponse to the highly toxic Cr2O7 2-, with a detection limit as low as 7.49 µm. Benefiting from the porous framework structure and organic-inorganic hybrid characteristics of Zr-TPE-MOF, it has excellent ROS generation ability and has excellent application prospects in photodynamic sterilization and rapid degradation of colored dyes.

High quantum yield AIE covalent organic frameworks for sensitive pH monitoring, and copper toxicosis Diagnosis&Remission

The luminescence properties of covalent organic frameworks (COFs) have attracted significant attention for biomedical applications. However, conventional fluorescent COFs often suffer from weak fluorescence due to aggregation-caused quenching (ACQ), limiting their utility. Given the critical need for highly efficient and sensitive biosensing tools, herein, we propose an aggregation-induced emission (AIE) COF, named COF-Bpy, with the quantum yield up to 25%. Benefiting from the active nitrogen sites within the bipyridine unit, COF-Bpy demonstrates remarkable pH monitoring capabilities across a wide pH range and displays strong coordination affinity towards Cu2+, achieving satisfactory detection and efficient adsorption of Cu2+. These properties make COF-Bpy superior in cellular pH imaging, and diagnosis&remission of copper toxicosis at both cellular and nematode levels, as it reduces the late apoptotic cells, improves nematode survival and locomotor states. Additionally, the fluorescence quenching mechanism of dynamic quenching with metal-to-ligand charge transfer is clarified. Briefly, this study not only presents a novel strategy for fabrication of AIE-COFs, but also provides a promising avenue for early diagnosis of pH-related diseases, and offers a theranostics for copper toxicosis management.

Synergistic Integration of Aggregation-Induced Emission and FRET Mechanisms in Conjugated Polymers via Molecular Engineering for Ultrasensitive, Rapid, and Discriminative Detection of Perfluoroalkyl Substances

The global contamination of water bodies by persistent organic pollutants (perfluoroalkyl substances (PFAS)) has generated significant societal concern, emphasizing the urgent need for smart strategies for their rapid, ultratrace, and on-site detection. Conjugated polymers (CPs) are exceptional fluorescence sensing materials with signal-amplification properties, yet their performance is often hindered by a conventional aggregation-caused quenching (ACQ) effect. Herein, we present two acceptor-engineered aggregation-induced emission (AIE)-active CPs (FTD-MI and FTD-C8-MI) integrated with efficient Förster resonance energy transfer (FRET) mechanisms for ultralow detection of PFAS. FTD-MI exhibits a turn-off (cyan to dark) fluorescence response, while FTD-C8-MI shows a ratiometric (cyan to red) response to PFAS due to the synergistic effect of AIE and efficient interchain FRET, facilitated by electrostatic and hydrophobic interactions upon binding. Both CPs demonstrate excellent sensitivity at the subnanomolar level toward the most abundant PFAS, perfluorooctanoic acid (PFOA), and perfluorooctanesulfonic acid (PFOS). The sensing mechanism has been thoroughly investigated by both experimental and simulation studies. Additionally, an optical sensor array coupled with machine learning algorithms is established for the discriminative detection of six types of PFAS. Finally, a portable smartphone platform with a custom-designed "app" was developed for real-time, on-site, and semiquantitative analysis of PFAS in actual water samples. Thus, by providing a sensitive, portable, cost-effective, and user-friendly solution, this work offers a powerful tool for monitoring PFAS pollution, ensuring water safety, and reducing risks to public health.

Nanoarchitectonics of a covalent organic supramolecular cage (COSC) for fluorescent visual detection of macrolides

Macrolides, a major group of antibiotic pollutants, have been widely observed in water and sediments. For onsite identification of macrolides in water environments, we designed and synthesized a quadrangular prism-shaped covalent organic supramolecular cage (COSC) via an aldol-amine condensation. Multiple hydrogen bonding sites were introduced into the building blocks to increase host-guest interactions. Meanwhile, by introducing a stimuli-sensitive module, TPE, the fluorescence of the supramolecule changes upon encapsulation of the clarithromycin guest which was a type of macrolides. The cage structure was fully characterized using NMR and high-resolution ESI mass spectrometry. The fluorescence recognition process and detection limitations of the cage for clarithromycin were investigated using NMR, UV-vis, and fluorescence spectroscopy. This study expands the application of precisely designed covalent supramolecular cages for monitoring antibiotic-based environmental pollutants.

Encapsulating Cu NCs with aggregation-induced emission into metal-organic framework ZIF-8 as a novel fluorescent nanoprobe for the highly sensitive detection of felodipine

Fluorescent metal-organic framework nanocomposites (f-MOFs) have been gaining increasing attention in the fields of chemosensors and biosensors due to their unique signal amplification mechanisms and improved selectivity. However, most f-MOFs are constructed by encapsulating fluorescent labelling agents into frameworks via host-guest interactions. The notorious aggregation-caused quenching effect of these fluorescent labelling agents often leads to a decreased fluorescent quantum yield in f-MOFs. Herein, a novel fluorescent nanocomposite, Cu NCs@ZIF-8, was designed and prepared by encapsulating copper nanoclusters (Cu NCs) with aggregation-induced emission (AIE) effects into zeolitic imidazolate framework ZIF-8 through electrostatic attraction. Owing to the AIE effect of Cu NCs and the spatial confinement of ZIF-8, the intramolecular motion of surface ligand hydrolipidic acid (DHLA) in Cu NCs was restricted, resulting in the formation of a highly emissive nanocomposite, Cu NCs@ZIF-8. Intriguingly, the UV-Vis absorption spectrum of felodipine overlaps with the excitation spectrum of Cu NCs@ZIF-8. Therefore, a novel fluorescent nanoprobe based on Cu NCs@ZIF-8 was developed for the highly sensitive detection of felodipine via the inner-filtration effect mechanism. Under optimal detection conditions, the linear response range of Cu NCs@ZIF-8 for felodipine was found to be 1-25 μM, with a detection of limit of 0.09 μM. While determining the labelling-amount percentage in commercially available felodipine tablets, the experimental results validated that the proposed Cu NCs@ZIF-8 nanoprobe exhibits good selectivity and excellent accuracy. This expands the potential applications of fluorescent metal-organic frameworks encapsulated with metal nanoclusters exhibiting AIE properties, positioning them as fluorescent nanoprobes for pharmaceutical quality control.

A near-infrared emitting covalent organic framework with AIE characteristics for light-emitting diodes

By incorporating methyl groups to introduce steric hindrance and utilizing hydroxyl groups to establish intramolecular hydrogen bonds, we synthesized a covalent organic framework (COF) with aggregation-induced emission (AIE) behavior and near-infrared (NIR) luminescence (λem = 657 nm). The integration of the innovative COF with LED chips enabled the fabrication of high-quality red and white organic phosphor-converted light-emitting diodes (LEDs). This work provides a new way to explore COFs to construct low-cost, high-performance, and eco-friendly LED devices.

Structural Rearrangement in Cyclic Cu(II) Pyridyltriazole Complexes: Oxidation of Dabco to Oxalate and CO2 Conversion to Carbonate

Structural rearrangements in metal-organic supramolecules constructed from the coordination of Cu(II) with m-xpt (m-xylylenebis(pyridyltriazole)) are investigated upon their interaction with 1,4-diazabicyclo[2.2.2]octane (dabco) and carbon dioxide-enriched air. The binuclear [Cu2(m-xpt)2]4+ complexes react with dabco to produce a carbonate-bridged trinuclear complex, [Cu3(m-xpt)3(µ-CO3)]4+, and an oxalate-bridged binuclear complex, [Cu2(m-xpt)2(µ-C2O4)]2+, where carbonate and oxalate likely originate from CO2 and dabco, respectively. The trinuclear complex reassembles the original dimer upon the removal of the carbonate ion. Similarly, polymeric [Cu(o-xpt)(PF6)]n, formed from Cu(I) and o-xpt (o-xylylenebis(pyridyltriazole)) coordination, undergoes oxidation in CO2-enriched air to yield a tetranuclear Cu(II) complex, Cu4(o-xpt)3(μ4-CO3)(μ2-OH)(μ2-OCOCH3)4+. The reaction progress is monitored by UV-Vis spectroscopy, and the major products are characterized by single-crystal X-ray diffraction.

Biological AIE Molecules: Innovations in Synthetic Design and AI-Driven Discovery

Biological aggregation -induced emission (AIE) molecules offer significant advantages over synthetic organic fluorophores, particularly in biocompatibility, environmental sustainability, and emission properties in biological systems. Derived from biomolecules such as peptides, proteins, and nucleic acids, biological AIE molecules hold great promise for applications in biosensing, bioimaging, and target drug delivery. This review explores the design principles, mechanistic insights, and functional properties of biological AIE molecules whiles highlighting the role of artificial intelligence (AI) in accelerating their discovery and optimization. AI-driven approaches, including machine learning and computational modeling, are transforming the identification and synthesis of AIE molecules by enabling precise structural modifications and enhanced fluorescence efficiency. These advancements are paving the way for the integration of AIE molecules in next-generation smart biomedical devices, personalized medicine and sustainable technological applications. Emerging trends, including hybrid biomaterials, Ai-guided molecular engineering, and advanced imaging techniques, are expanding the scope of biological AIE molecules in healthcare and environmental monitoring. The synergy between AI and biological AIE molecules is unlocking new frontiers in biomedical technology, enabling transformative advancements in material science and healthcare applications, and shaping the future of fluorescence- based diagnostics and therapeutics.

Pressure-Modulated Luminescence Enhancement and Quenching in a Hydrogen-Bonded Organic Framework

Light emission in the solid state is central for illumination, sensing, and imaging applications. Unlike luminescence in dilute solutions, where the excited states are unimolecular in nature, intermolecular interaction plays a significant role in the quantum yield of solid-state luminophores, manifested as competing aggregation-caused quenching (ACQ) and aggregation-induced enhancement (AIE). Both effects are extensively studied in various systems; however, it remains unclear how their competition depends on molecular conformation and intermolecular stacking. Here the direct observation of pressure-modulated AIE-ACQ competition in a crystalline hydrogen-bonded organic framework (HOF) is reported. Using in situ spectroscopies and computational modeling, the intramolecular vibration and intermolecular π-π stacking directly responsible for the non-radiative decay of the excited state are identified. The extent of these two contributions is modulated by hydrostatic pressure and guest molecules in the HOF pores. This work demonstrates a physically neat model system to understand and control solid-state luminescence, and a potential material platform for piezoluminescent sensing.

Metal Ion-Based Chemical Coordination Amplification: A Chromophore In Situ Deposition Strategy for Visual Sensitivity-Enhanced Lateral Flow Immunochromatography Assays

Traditional lateral flow immunochromatography assays (LFIAs) have faced low sensitivity for trace detection due to the lack of colorimetric brightness. The current strategies to improve sensitivity commonly have the disadvantages of an uncontrollable enhancement process or high background interference, leading to huge obstacles for signal readout. Herein, an in situ metal ion-based chemical coordination amplification (MICCA) strategy has been reported. Metal ion clusters on metal-organic frameworks could coordinate with chromophores to produce colored complexes for visual signal enhancement. A Zr-based metal AIEgen framework (MAF) loaded with Prussian blue was chosen as the dual-mode signal tag for colorimetric and fluorescent readout. MAF could be employed as a grafting substrate to in situ deposit chromophores through the coordination with Zr4+ clusters and arsenazo III. The process of MICCA was in situ, controllable, and free of background interference. For target cancer biomarker alpha-fetoprotein (AFP), the limit of detection (LOD) by the naked eye was 25 ng/mL, and the LODs of MICCA and fluorescence were 5 ng/mL, which was 5-fold decreased. Significantly, MICCA-LFIA could effectively differentiate between AFP-positive and AFP-negative clinical serum samples. The quantitative results were highly consistent with clinical results (R2 = 0.9927). This work explored the application of metal ion-based chemical coordination reactions in signal amplification strategies and provided ideas for high-sensitivity LFIA development.

Bioinspired "Intermolecular Pocket" in Soft Molecular Crystal of Porous Organic Cage Exhibiting Reversible Guest Recognition

Porous Organic Cages (POCs) have gathered a lot of attention in sorts of fields. Previous studies often focused on the functionalization of their intrinsic porosity, while the utilization of the extrinsic porosity has been seldom reported. To date, the rational construction of functionalized extrinsic porosity in POCs is a serious challenge, which still relies on trial and error. Inspired by hydrophobic proteins, in the contribution, a POC (namely NKPOC-DS) is obtained with hydrophobic "intermolecular pocket" as extrinsic porosity constructed through the assembly of disulfide bonds with hydrophobic groups, facilitating strong supramolecular interactions as confirmed by Electrostatic Potential (ESP) maps and single-crystal X-ray diffraction analysis. Notably, NKPOC-DS exhibits a unique C2H6-selective "breathing behaviour" due to the presence of softness in its extrinsic porosity, which does not extend to other gases such as C2H4, CH4, CO2, N2, and H2. Such specific recognition of C2H6 thus provides NKPOC-DS with the ability to preferentially adsorb C2H6 from a C2H6/C2H4 mixture. The innovative approach of biomimicry in the design of functional POCs provides new insights into manipulating the packing of cages, paving the way for potential applications in guest recognition and adsorption separations.

Electrophoresis-driven AIE luminogens encapsulated within silica isoporous membrane for acid vapor sensing

Acid vapors emitted by chemical industries pose an increasing threat to public health. The development of a cost-effective sensor for the on-site and real-time monitoring of environmental acid vapor is of great significance. Aggregation-induced emission (AIE) luminogens overcome the aggregation-caused quenching effect and exhibit intense fluorescence when supported in the solid matrices. Silica isoporous membrane (SIM), characterized by vertically ordered nanochannels, holds great promise as a platform for encapsulating AIE luminogens and enabling gas sensing applications. The SIM containing surfactant micelles was prepared on an ITO electrode to obtain the M-SIM/ITO, and Tetrakis(4-carboxyphenyl)ethylene (TCPE) was employed as the investigated AIE luminogen. Upon application of positive potential, the negatively charged TCPE molecules were driven into the vertically ordered nanochannels, resulting in observable AIE fluorescence. By investigating the electrophoresis conditions such as TCPE charge, nanochannel microenvironment, and driving electric field, the AIE mechanism within the nanochannels was elucidated. The fluorescence of TCPE@M-SIM/ITO exhibited high sensitivity towards acid vapor and displayed reversible changes during the absorption and desorption processes. This behavior can be attributed to the SIM's strong absorption capability towards acid vapor as well as the reversible conversion of acid vapor on TCPE aggregates. This work presented an innovative methodology for studying luminophores within an orderly nanoconfined space, leading to a new perspective on the AIE mechanism.

Dynamic Rare-Earth Metal-Organic Frameworks Based on Molecular Rotor Linkers with Efficient Emissions and Ultrasensitive Optical Sensing Performance

4,4',4″-Triphenylamine tricarboxylate (TPA-COOH) with a distinct molecular rotor structure was reacted with rare-earth (RE) metal ions to obtain seven dynamic RE-based luminescent MOFs (RE-LMOFs) (i.e., emission colors in the blue, yellow-green, red, and near-infrared regions and emission peak wavelengths between 400 and 1600 nm) via the effective transfer of absorbed energy from TPA-COOH to the RE metal ions through the antenna effect. Due to the large energy level difference between RE ions, it was rare in the early days to use the same ligand to construct energy-level matching RE-LMOF homologues with multiple RE metal centers. The uncoordinated oxygen atoms on the molecular rotor linkers in RE-LMOFs provide active sites that can specifically capture highly toxic metal ions and strong oxidative pollutants. The limit of detection (LOD) of RE-LMOF for Al(III) ions is far below the maximum concentration of Al(III) ions in drinking water stipulated by the U.S. Environmental Protection Agency (USEPA) and that for H2O2 is much lower than the H2O2 content in cancer cells, showing excellent application potential for diagnosing early cell cancelation.

Optical detection strategies for Ni(II) ion using metal-organic chemosensors: from molecular design to environmental applications

Nickel is an important element utilized in various industrial/metallurgical processes, such as surgical and dental prostheses, Ni-Cd batteries, paint pigments, electroplating, ceramics, computer magnetic tapes, catalysis, and alloy manufacturing. However, its extensive use and associated waste production have led to increased nickel pollution in soils and water bodies, which adversely affects human health, animals and plants. This issue has prompted researchers to develop various optical probes, hereafter luminescent/colorimetric sensors, for the facile, sensitive and selective detection of nickel, particularly in biological and environmental contexts. In recent years, numerous functionalized chemosensors have been reported for imaging Ni2+, both in vivo and in vitro. In this context, metal-based receptors offer clear advantages over conventional organic sensors (viz., organic ligands, polymers, and membranes) in terms of cost, durability, stability, water solubility, recyclability, chemical flexibility and scope. This review highlights recent advancements in the design and fabrication of hybrid receptors (i.e., metal complexes and MOFs) for the specific detection of Ni2+ ions in complex environmental and biological mixtures.

Tetraphenylethene-Based Ni8-Pyrazolate Metal-Organic Framework for Photoredox/Nickel Dual Catalysis of C-S Cross-Coupling

As a prototypical aggregation-induced emission luminogen (AIEgen), the tetraphenylethene (TPE) moiety has been judiciously modified as organic linkers for constructing various functional metal-organic frameworks (MOFs). However, these AIEgen-based MOFs have rarely received research attention in photocatalytic applications due to their limited stability in harsh reaction conditions. In this work, we report a robust Ni8-pyrazolate-based MOF (denoted as TPE4Pz-Ni) under the guidance of reticular chemistry, which is assembled by an AIE-active tetratopic linker of 1,1,2,2-tetrakis(4-(1H-pyrazol-4-yl)phenyl)ethane (H4-TPE4Pz) with a 12-connected Ni8-cluster of [Ni8(OH)4(H2O)2Pz12] (Pz = pyrazolate) in a (4,12)-connected ftw-a topological network. Notably, MOF TPE4Pz-Ni exhibits excellent stability in a wide range of solvents and even in a saturated NaOH solution. Moreover, its luminescent emission is effectively quenched via a ligand-to-metal charge transfer (LMCT) process originating from the TPE-cored linker to the Ni8 cluster, which enables TPE4Pz-Ni to act as an efficient photoredox/nickel dual catalyst for light-mediated C-S cross-coupling reactions between various aryl iodides and thiols.

Fluorescent Porous Materials Based on Aggregation-induced Emission for Biomedical Applications

Fluorescent porous materials based on aggregation-induced emission (AIE) are growing into a sparkling frontier in biomedical applications. Exploring those materials represents a win-win integration and has recently progressed at a rapid pace, mainly benefiting from intrinsic advantages including tunable pore size and structure, strong guest molecule encapsulation ability, superior biocompatibility, and photophysical outcomes. With the great significance and rapid progress in this area, this review provides an integrated picture on AIE luminogen-based porous materials. It encompasses inorganic, organic, and inorganic-organic porous materials, exploring fundamental concepts and the relationship between AIE performance and material design and highlighting significant breakthroughs and the latest trends in biomedical applications. In addition, some critical challenges and future perspectives in the development of AIE luminogen-based porous materials are also discussed.

Modular Construction of Vinylene-Linked Covalent Organic Frameworks with Tunable Emission for Tumor Visualization

Covalent organic frameworks (COFs) with ordered π structures are very promising in porous light-emitting materials. However, most of these COFs are either poor in luminescence or lack of water-stability. Herein, a series of isostructural D-A vinylene-linked COFs were constructed based a new D2h symmetric linker 1,4-bis(4,6-dimethyl-1,3,5-triazin-2-yl)benzene (TMTA) with high crystallinity, comparative high surface area and excellent chemical/thermal stability. Impressively, their adsorption and luminescence wavelength vary with respect to the density of π-systems in the electron-donating group, which constitute the foundation for molecular engineering the luminescent properties of vinylene-linked COFs. The DFT calculations further established the relationship between the luminescence properties and the donor electronic structure. Moreover, one of representative COF named FZU-203 showed inspiring applications in bioimaging, which may further provide strategic guidance for the use of vinylene-linked COFs as fluorescent nanoprobes in non-invasive medical diagnosis and visualization therapy of tumors.

Anionic Hydrogen-Bonded Frameworks Showing Tautomerism and Colorful Luminescence for the Ultrasensitive Detection of Acetone

Tautomers coexisting in an equilibrium system have significant potential for regulating luminescent properties because of their structural differences. However, separating and stabilizing tautomers at room temperature is a considerable challenge. In this study, it is found that hydrogen-bonded organic frameworks (HOFs) composed of Br- anions can effectively separate and stabilize two proton-transfer tautomers of triarylformamidinium bromide: namely, the nitrogen cation (BA-N) and carbon cation (BA-C). The BA-N crystal consisting of a dense anionic HOF and parallelly aligned organic cations exhibits green thermally activated delayed fluorescence and red room-temperature phosphorescence (RTP). The BA-C crystal contains acetone molecules that induce an antiparallel arrangement of the organic cations to form a loose HOF, producing blue prompt fluorescence and green RTP. Interestingly, switching of the HOFs between BA-N and BA-C can be achieved through the uptake and release of acetone, thereby dynamically adjusting multiple luminescent properties. Consequently, the HOF crystals can be used for the highly sensitive and specific sensing of acetone with a detection limit of 66.74 ppm. This study not only stabilizes tautomeric luminescent materials at room temperature, but also provides a new method for constructing smart HOFs with a sensitive response to a stimulus.

UiOL@AIEgens-assisted lateral flow immunosensor for the ultrasensitive dual-modal point-of-care detection of aflatoxin B1

Aflatoxin B1 (AFB1) contamination in food has attracted worldwide attention. The sensitive detection of AFB1 is vital for ensuring food quality and safety. This study developed an ultrasensitive signal-enhanced lateral flow immunosensor (LFIS) based on the functionalized zirconium metal-organic framework (MOF) of a UiO linker enriched with abundant aggregation-induced emission luminogen (UiOL@AIEgens) probes for the rapid dual-modal point-of-care (POC) determination of AFB1. Using UiO MOFs with numerous active sites as the carrier facilitated abundant AIEgens enrichment on the surface. After coupling with enough anti-AFB1 monoclonal antibodies (mAbs), the green-emissive UiOL@AIEgens-mAbs probes with high specificity and remarkably-enhanced fluorescence responses were obtained to competitively capture target AFB1 in the standard or sample solution and AFB1 antigen immobilized on the test (T) line of the POC LFIS. Under optimum conditions, the LFIS was capable of visual qualitative and smartphone-assisted dual-modal determination of target AFB1 within 7 min. Detection occurred in a range of 0.01-5 ng/mL at an ultra-low detection limit of 0.003 ng/mL, which was 300- and 600-fold lower than traditional immunoassays and the maximum limit set by the European Union, respectively. Moreover, the feasibility and robustness of the LFIS platform were assessed by detecting AFB1 in maize and lotus seed samples with average recoveries of 94.3-109.0%. The developed UiOL@AIEgens-based POC LFIS can be used for ultrasensitive, reliable, on-site detection in food. This study provides a new method for the real-time monitoring of AFB1 and other harmful contaminants in food and more complex matrices.

Adjustable luminescence copper nanoclusters nanoswitch based on competitive coordination of samarium ions for cascade detection of adenosine triphosphate and acid phosphatase activity

Benefit from the strong coordination property, lanthanide metal ions have been used as competitive reagents to modulate the fluorescence changes of the system. However, lanthanide metal ions as inducers for aggregation-induced emission enhancement in nanosystems is rare. Herein, we report a "turn on-off-on" fluorescent switch for cascade detection of acid phosphatase (ACP) and adenosine triphosphate (ATP) based on the competitive coordination of samarium ions (Sm3+). Novel copper nanoclusters (CuNCs) with long wavelength emission (614 nm) stabilized by glutathione (GSH) and glycylglycine (Gly-Gly) have been confirmed to have AIE property. With the continuous aggregation of GSH/Gly-Gly CuNCs under the induction of Sm3+, the fluorescence of the system increased to achieve the "turn-on" process. The coordinated behaviour between Sm3+ and GSH/Gly-Gly CuNCs is discussed. Due to the strong metal coordination ability of ATP, the Sm3+ coordinated with the GSH/Gly-Gly CuNCs is competed out, resulting in the fluorescence "turn-off" process of the system. As the substrate of enzymatic hydrolysis of ACP, with the continuous hydrolysis of ATP by ACP, Sm3+ coordinates with GSH/Gly-Gly CuNCs again, which leads to the AIE effect and realize the fluorescence "turn-on" process of the system. This strategy results in ATP linear range of 0.508 ~ 120.0 μM with a detection limit of 0.508 μM (S/N = 3) and ACP linear range of 0.011 ~ 30.0 U·L-1 with a detection limit of 0.011 U·L-1 (S/N = 3). Application to biologic samples was successful.

Linkages Make a Difference in the Photoluminescence of Covalent Organic Frameworks

Covalent organic frameworks (COFs) with structural designability and tunability of photophysical properties enable them to be a promising class of organic luminescent materials by incorporating well-designed fluorescent units directly into the periodic skeletons. The photophysical properties of COFs are mainly affected by the structural features, which determine the conjugation degree, charge delocalization ability, and exciton dynamics of COFs. To understand the relationship between COF structures and their photophysical properties, two COFs with the same pyrene chromophore units but different linkages (imine or vinylene) were designed and synthesized. Interestingly, different linkages endow COFs with huge differences in solid-state photoluminescence quantum yield (PLQY) for imine- and vinylene-linked pyrene-based COFs, which possess PLQY values of 0.34 % and 15.43 %, respectively. The femtosecond-transient absorption spectra and time-dependent density functional theory reveal the different charge-transfer pathways in imine- and vinylene-linked COFs, which influence the exciton relaxation way and fluorescence intensity. In addition, an effective white-light device was obtained by coating the vinylene-linked COF on a light-emitting diode strip.

Luminescence and Palladium: The Odd Couple

The synthesis, photophysical properties, and applications of highly fluorescent and phosphorescent palladium complexes are reviewed, covering the period 2018–2022. Despite the fact that the Pd atom appears closely related with an efficient quenching of the fluorescence of different molecules, different synthetic strategies have been recently optimized to achieve the preservation and even the amplification of the luminescent properties of several fluorophores after Pd incorporation. Beyond classical methodologies such as orthopalladation or the use of highly emissive ligands as porphyrins and related systems (for instance, biladiene), new concepts such as AIE (Aggregation Induced Emission) in metallacages or in coordination-driven supramolecular compounds (CDS) by restriction of intramolecular motions (RIM), or complexes showing TADF (Thermally Activated Delayed Fluorescence), are here described and analysed. Without pretending to be comprehensive, selected examples of applications in areas such as the fabrication of lighting devices, biological markers, photodynamic therapy, or oxygen sensing are also here reported.

As Fiber Meets with AIE: Opening a Wonderland for Smart Flexible Materials

Aggregation-induced emission luminogens (AIEgens) have recently been developed at a tremendous pace in the area of organic luminescent materials by virtue of their superior properties. However, the practical applications of AIEgens still face the challenge of transforming AIEgens from molecules into materials. Till now, many AIEgens have been integrated into fiber, endowing the fiber with prominent fluorescence and/or photosensitizing capacities. AIEgens and fiber complement each other for making progress in flexible smart materials, in which the utilization of AIEgens creates new application possibilities for fiber, and the fiber provides an excellent carrier for AIEgens towards realizing the conversion from molecule to materials and an ideal platform to research the aggregate state of AIEgens in mesoscale and macroscale. This review begins with a brief summary of the recent advances related to some typical AIEgens with various functions and the technology for the fabrication of AIEgen-functionalized fiber. The most representative applications are then highlighted by focusing on energy conversion, personal protective equipment, biomedical, sensor, and fluorescence-related fields. Finally, the challenges, opportunities, and tendencies in future development are discussed in detail. This review hopes to inspire innovation in AIEgens and fiber from the view of mesoscale and macroscale.

Self-Assembly Mitochondria-Targeting Donor-Acceptor Type Theranostic Nanosphere Activates ROS Storm for Multimodal Cancer Therapy

The rational design of cancer theranostics with natural diagnostic information and therapeutic behavior has been considered to be a big challenge, since common theranostics from photothermal and photodynamic therapy need to be activated with external stimuli of photoirradiation to enable the chemotherapeutic effects. In this contribution, we have designed and synthesized a series of simple theranostic agents, TPA-N-n (n = 4, 8, 12), which could accumulate at the tumor site over 48 h and indicate superior antiproliferative performance in vivo. TPA-N-n was constructed with electron donor triphenylamine-acceptor benzothiadiazole-mitochondria-targeting moiety pyridinium. Complex TPA-N-8 indicated the best cytotoxicity to cancerous HeLa cells, with an IC₅₀ value of 4.3 μM, and could self-assemble to a nanosphere with a size of 161.2 nm in the DMSO/PBS solution. It is worth noting that TPA-N-8 could accumulate in the mitochondria and produce major ROS species O₂•^- and OH• as well as small amounts of ¹O₂ without photoirradiation. Oxidative DNA damage is initiated due to the imbalance of intracellular redox homeostasis from the significant ROS storm. Multimodal synergistic therapy for HeLa cells was activated, as the PINK1-mediated mitophagy from the damaged mitochondria and DNA damage responsive (DDR) induced necroptosis and autophagy. This work not only provided a successful D-A type theranostic agent with superior anticancer performance from multimodal synergistic therapy but also further demonstrated the high efficacy of a mitochondria-targeting strategy for cancer treatment.

Aggregation-Induced Emission-Active Nanostructures: Beyond Biomedical Applications

The discovery of aggregation-induced emission (AIE) phenomenon in 2001 has had a significant impact on materials development across different research disciplines. AIE-active materials have been widely exploited for various applications in optoelectronics, sensing, biomedical, and stimuli-responsive systems, etc. This is made possible by integrating AIE features with other fields of science and engineering, such as nanoscience and nanotechnology. AIE has been extensively employed, particularly for biomedical applications, such as biosensing, bioimaging, and theranostics. However, development of AIE-based nanotechnology for other applications is comparatively less, although there have been increasing research activities in recent years. Given the significance and potential of the marriage between AIE hallmark and nanotechnology in AIE-active materials development, this review article summarizes and showcases the latest research efforts in AIE-based nanomaterials, including nanomaterials synthesis and their nonbiomedical applications, such as sensing, optoelectronics, functional coatings, and stimuli-responsive systems. A perspective on the outlook of AIE-based nanostructured materials and relevant nanotechnology for nonbiomedical applications will be provided, giving an insight into how to design AIE-active nanostructures as well as their applications beyond the biomedical domain.

Conjugated Aggregation-Induced Fluorescent Materials for Biofluorescent Probes: A Review

The common fluorescent conjugated materials present weak or quenching luminescent phenomena in the solid or aggregate state (ACQ), which limits their applications in medicine and biology. In the last two decades, certain materials, named aggregation-induced emission (AIE) fluorescent materials, have exhibited strong luminescent properties in the aggregate state, which can overcome the ACQ phenomenon. Due to their intrinsic properties, the AIE materials have been successfully used in biolabeling, where they can not only detect the species of ions and their concentrations in organisms, but can also monitor the organisms' physiological activity. In addition, these kinds of materials often present non-biological toxicity. Thus, AIE materials have become some of the most popular biofluorescent probe materials and are attracting more and more attention. This field is still in its early infancy, and several open challenges urgently need to be addressed, such as the materials' biocompatibility, metabolism, and so on. Designing a high-performance AIE material for biofluorescent probes is still challenging. In this review, based on the molecular design concept, various AIE materials with functional groups in the biofluorescent probes are introduced, including tetrastyrene materials, distilbene anthracene materials, triphenylamine materials, and hexaphenylsilole materials. In addition, according to the molecular system design strategy, the donor-acceptor (D-A) system and hydrogen-bonding AIE materials used as biofluorescent probes are reviewed. Finally, the biofluorescent probe design concept and potential evolution trends are discussed. The final goal is to outline a theoretical scaffold for the design of high-performance AIE biofluorescent probes that can at the same time further the development of the applications of AIE-based biofluorescent probes.

MXene-based aptasensor for the detection of aflatoxin in food and agricultural products

The detection of toxins that contaminate food needs highly sensitive and selective techniques to prevent substantial monitory loss. In this regard, various nanostructured material-enabled biosensors, have recently been developed to improve the detection of food toxins among them aflatoxin is the prevalent one. The biosensor-based detection of aflatoxin is quick, cheaper, and needs less skilled personnel, therefore overcoming the shortcomings of conventional techniques such as LC/MS-MS, HPLC, and ELISA assays. 2D MXenes manifest as an efficient material for biosensing due to their desirable biocompatibility, magnificent mechanical strength, easiness of surface functionalization, and tuneable optical and electronic features. Contrary to this, aptamers as biorecognition elements (BREs) possess high selectivity, sensitivity, and ease of synthesis when compared to conventional BREs. In this review, we explored the most cutting-edge aptamer-based MXene-enabled biosensing technologies for the detection of the most poisonous mycotoxins (i.e., Aflatoxins) in food and environmental matrices. The discussion begins with the synthesis processes and surface functionalization/modification of MXenes. Computational approaches for designing aptasensors and advanced data analysis based on artificial intelligence and machine learning with special emphasis over Internet-of-Thing integrated biosensing devices has been presented. Besides, the advantages of aptasensors over conventional methods along with their limitations have been briefed. Their benefits, drawbacks, and future potential are discussed concerning their analytical performance, utility, and on-site adaptability. Additionally, next-generation MXene-enabled biosensing technologies that provide end users with simple handling and improved sensitivity and selectivity have been emphasized. Owing to massive applicability, economic/commercial potential of MXene in current and future perspective have been highlighted. Finally, the existing difficulties are scrutinized and a roadmap for developing sophisticated biosensing technologies to detect toxins in various samples in the future is projected.

Dual-Color 2D Lead-Organic Framework with Two-Fold Interlocking Structures for the Detection of Nitrofuran Antibiotics and 2,6-Dichloro-4-nitroaniline

The misuse of organic pollutants such as nitrofuran antibiotics (NFAs) and 2,6-dichloro-4-nitroaniline (DCN) has become a hot topic of global concern, and developing rapid, efficient, and accurate techniques for detecting NFAs and pesticides in water is a major challenge. Here, we designed a novel lead-based anion 2D metal-organic framework (MOF){[(CH₃)₂NH₂]₂[Pb(TCBPE)(H₂O)₂]}_n (F3) with interlocking structures, in which TCBPE stands for 1,1,2,2-tetra(4-carboxylbiphenyl)ethylene. Powder X-ray diffraction and thermogravimetric analysis revealed that F3 has excellent chemical and solvent stability. It is worth noting that F3 has a grinding discoloration effect. The solvent-protected grinding approach achieved F3B with a high quantum yield (QY = 73.77%) and blue fluorescence, while the direct grinding method produced F3Y with a high quantum yield (QY = 37.27%) and yellow-green fluorescence. Importantly, F3B can detect NFAs in water rapidly and sensitively while remaining unaffected by other antibiotics. F3Y can identify DCN in water quickly and selectively while remaining unchanged by other pesticides. F3B demonstrated high selectivity and rapid response to NFAs at a limit of detection (LOD) as low as 0.26 μM, while F3Y indicated high selectivity and responded quickly to DCN in water at an LOD as low as 0.14 μM. The method was successfully applied to detect NFAs in actual water samples of the fish tanks and ponds as well as the pesticide DCN in soil samples. The recovery rates were 97.0-105.15% and 102.2-106.48%, and the relative standard deviations were 0.63-1.45% and 0.29-1.69%, respectively. In addition, F3B and F3Y can be made into fluorescent test papers for the visual detection of NFAs and DCN, respectively. Combined with experiments and density functional theory calculations, the mechanism of fluorescence quenching of MOFs by target analytes was also revealed.

Stimuli-Responsive Electrospun Fluorescent Fibers Augmented with Aggregation-Induced Emission (AIE) for Smart Applications

This review addresses the latest advancements in the integration of aggregation-induced emission (AIE) materials with polymer electrospinning, to accomplish fine-scale electrospun fibers with tunable photophysical and photochemical properties. Micro- and nanoscale fibers augmented with AIE dyes (termed AIEgens) are bespoke composite systems that can overcome the limitation posed by aggregation-caused quenching, a critical deficiency of conventional luminescent materials. This review comprises three parts. First, the reader is exposed to the basic concepts of AIE and the fundamental mechanisms underpinning the restriction of intermolecular motions. This is followed by an introduction to electrospinning techniques pertinent to AIE-based fibers, and the core parameters for controlling fiber architecture and resultant properties. Second, exemplars are drawn from latest research to demonstrate how electrospun nanofibers and porous films incorporating modified AIEgens (especially tetraphenylethylene and triphenylamine derivatives) can yield enhanced photostability, photothermal properties, photoefficiency (quantum yield), and improved device sensitivity. Advanced applications are drawn from several promising sectors, encompassing optoelectronics, drug delivery and biology, chemosensors and mechanochromic sensors, and innovative photothermal devices, among others. Finally, the outstanding challenges together with potential opportunities in the nascent field of electrospun AIE-active fibers are presented, for stimulating frontier research and explorations in this exciting field.

An Overview of the Design of Metal-Organic Frameworks-Based Fluorescent Chemosensors and Biosensors

Taking advantage of high porosity, large surface area, tunable nanostructures and ease of functionalization, metal-organic frameworks (MOFs) have been popularly applied in different fields, including adsorption and separation, heterogeneous catalysis, drug delivery, light harvesting, and chemical/biological sensing. The abundant active sites for specific recognition and adjustable optical and electrical characteristics allow for the design of various sensing platforms with MOFs as promising candidates. In this review, we systematically introduce the recent advancements of MOFs-based fluorescent chemosensors and biosensors, mainly focusing on the sensing mechanisms and analytes, including inorganic ions, small organic molecules and biomarkers (e.g., small biomolecules, nucleic acids, proteins, enzymes, and tumor cells). This review may provide valuable references for the development of novel MOFs-based sensing platforms to meet the requirements of environment monitoring and clinical diagnosis.

Bis-Pyridine-Based Organogel with AIE Effect and Sensing Performance towards Hg2

A novel gelator (1) based on a bis-pyridine derivative was designed and synthesized, which could form stable gels in methanol, ethanol, acetonitrile, ethyl acetate, DMF/H₂O (4/1, v/v) and DMSO/H₂O (4/1, v/v). The self-assembly process of gelator 1 was studied by field emission scanning electron microscopy (FESEM), UV–vis absorption spectroscopy, fluorescence emission spectroscopy, Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction and a water contact angle experiment. Gelator 1 exhibited obvious AIE behavior. On the base of its AIE, the gel of 1 could detect Hg²⁺, which resulted in fluorescence quenching and a gel–sol transition. ¹H NMR titration experiments with Hg²⁺ revealed that the metal coordination interaction induced the fluorescence quenching and the breakdown of the noncovalent interaction in the gel system. This research provides a new molecular mode for designing a functional self-assembly gel system.