Dual-Color Emissive AIEgen for Specific and Label-Free Double-Stranded DNA Recognition and Single-Nucleotide Polymorphisms Detection

C9-Aryl-substituted berberine derivatives with tunable AIE properties for cell imaging application

Berberine (BBR), a widely used isoquinoline alkaloid derived from natural sources, exhibits aggregation-induced emission (AIE) characteristics and has biological applications such as in selective lipid droplet imaging and photodynamic therapy. However, natural BBR suffers from low fluorescence quantum yield (ΦF) and monotonous emission wavelength. In this paper, a series of C9-position-aryl-substituted berberine derivatives with a D-A structure were designed and synthesized. The electronic effect of the substitution groups can tune the intramolecular charge transfer (ICT) effect of the berberine derivatives, resulting in bluish green to NIR (508-682 nm) luminescence with AIE characteristics and enhanced ΦF up to 36% in the solid state. Interestingly, berberine derivatives containing an amino or a pyridyl group can exhibit fluorescence response to TFA. Cell imaging of the berberine derivatives was conducted using Caco-2 cancer cells, demonstrating their multi-color and efficient wash-free imaging capabilities. This work presents a new strategy for developing novel berberine derivatives with tunable AIE properties for application in biological imaging.

Sensing, Imaging, and Therapeutic Strategies Endowing by Conjugate Polymers for Precision Medicine

Conjugated polymers (CPs) have promising applications in biomedical fields, such as disease monitoring, real-time imaging diagnosis, and disease treatment. As a promising luminescent material with tunable emission, high brightness and excellent stability, CPs are widely used as fluorescent probes in biological detection and imaging. Rational molecular design and structural optimization have broadened absorption/emission range of CPs, which are more conductive for disease diagnosis and precision therapy. This review provides a comprehensive overview of recent advances in the application of CPs, aiming to elucidate their structural and functional relationships. The fluorescence properties of CPs and the mechanism of detection signal amplification are first discussed, followed by an elucidation of their emerging applications in biological detection. Subsequently, CPs-based imaging systems and therapeutic strategies are illustrated systematically. Finally, recent advancements in utilizing CPs as electroactive materials for bioelectronic devices are also investigated. Moreover, the challenges and outlooks of CPs for precision medicine are discussed. Through this systematic review, it is hoped to highlight the frontier progress of CPs and promote new breakthroughs in fundamental research and clinical transformation.

Shining a light on liver health: advancements in fluorescence-enhanced enzyme biosensors for early disease detection

Early detection of liver diseases holds paramount importance in optimizing treatment outcomes and prognosis, thereby significantly enhancing the likelihood of recovery while mitigating the risk of progression to liver cancer. Liver diseases encompass a spectrum of conditions, each potentially manifesting distinct enzymatic profiles. Monitoring these enzymes in situ facilitates timely intervention and therapeutic management. In recent years, the field of biosensor technology has witnessed remarkable advancement, owing to strides in biomedicine and computational sciences. Biosensors have garnered widespread utility across medical and biological domains, spanning the detection of disease biomarkers, drug release tracking, ion imaging, and fluorescence imaging within living organisms. These applications have markedly enhanced imaging resolution and have the potential to refine disease diagnosis accuracy for clinicians. A pivotal aspect in the successful application of this technology lies in the construction of fluorescence probes adept at swiftly and selectively identifying target enzymes by amalgamating liver disease enzymes with fluorescence probe technology. However, research in this niche area remains relatively scarce. Building upon this foundational understanding, the present review delineates the utilization of biosensors in the early diagnosis of liver disease. Serving as a theoretical framework, this review envisages the development of high-performance biosensors tailored for the early detection of liver cancer. Furthermore, it offers insights into the potential of biosensor technology to progress and broaden its practical applications, thus contributing to the advancement of diagnostic methodologies in liver disease management.

Aggregation-Induced Emission-Armored Living Bacteriophage-DNA Nanobioconjugates for Targeting, Imaging, and Efficient Elimination of Intracellular Bacterial Infection

Intracellular bacterial infections bring a considerable risk to human life and health due to their capability to elude immune defenses and exhibit significant drug resistance. As a result, confronting and managing these infections present substantial challenges. In this study, we developed a multifunctional living phage nanoconjugate by integrating aggregation-induced emission luminogen (AIEgen) photosensitizers and nucleic acids onto a bacteriophage framework (forming MS2-DNA-AIEgen bioconjugates). These nanoconjugates can rapidly penetrate mammalian cells and specifically identify intracellular bacteria while concurrently producing a detectable fluorescent signal. By harnessing the photodynamic property of AIEgen photosensitizer and the bacteriophage's inherent targeting and lysis capability, the intracellular bacteria can be effectively eliminated and the activity of the infected cells can be restored. Moreover, our engineered phage nanoconjugates were able to expedite the healing process in bacterially infected wounds observed in diabetic mice models while simultaneously enhancing immune activity within infected cells and in vivo, without displaying noticeable toxicity. We envision that these multifunctional phage nanoconjugates, which utilize AIEgen photosensitizers and spherical nucleic acids, may present a groundbreaking strategy for combating intracellular bacteria and offer powerful avenues for theranostic applications in intracellular bacterial infection-associated diseases.

An efficient extraction method for short single-stranded DNA from agarose gels in aptamer screening

With the rapid advancements in aptamer screening, the efficient extraction of short single-stranded DNA (ssDNA) from agarose gel has become a new requirement. However, the currently available products are primarily designed for double-stranded DNA (dsDNA) and exhibit limited efficacy when applied to the extraction of short ssDNA. In this study, we successfully developed a novel method based on amino-modified silica-coated magnetic particles (ASMPs) for the extraction of short ssDNA from agarose gel. The gel slices containing short ssDNA were subjected to centrifugation in a spin column/centrifugation tube assembly with silica wool, followed by the adsorption using ASMPs. Subsequently, reagents containing phosphate groups were employed to desorb ssDNA from the surface of ASMPs. Through optimization of each step, we realized remarkable efficiency in the extraction of short ssDNA. To assess the efficacy of our method, we utilized it in aptamer screening. The results demonstrated that our method outperformed three commercially available DNA gel extraction products (Q-kit, S-kit, and V-kit). The relative recovery rates of all methods were as follows: M-dNTP (100.00 %) > M-BB (63.38 %) > Q-kit (46.64 %) > S-kit (15.98 %) > V-kit (0.38 %). The results strongly suggest that the developed method holds promise for short ssDNA extraction from agarose gel.

A Highly Water-Soluble Aggregation-Induced Emission Luminogen with Anion-π+ Interactions for Targeted NIR Imaging of Cancer Cells and Type I Photodynamic Therapy

The low oxygen dependence of type I photosensitizers (PSs) has made them a popular choice for treating solid tumors. However, the drawbacks of poor water solubility, short emission wavelength, poor stability, and inability to distinguish cancer cells from normal cells limit the application of most type I PSs in clinical therapy. Thereby, developing novel type I PSs for overcoming these problems is an urgent but challenging task. Herein, by utilizing the distinctive structural characteristics of anion-π+ interactions, a highly water-soluble type I PS (DPBC-Br) with aggregation-induced emission (AIE) characteristic and near-infrared (NIR) emission is fabricated for the first time. DPBC-Br displays remarkable water solubility (7.3 mM) and outstanding photobleaching resistance, enabling efficient and precise differentiation between tumor cells and normal cells in a wash-free and long-term tracking manner via NIR-I imaging. Additionally, the superior type I reactive oxygen species (ROS) produced by DPBC-Br provide both specific killing of cancer cells in vitro and inhibition of tumor growth in vivo, with negligible systemic toxicity. This study rationally constructs a highly water-soluble type I PS, which has higher reliability and controllability compared with conventional nanoparticle formulating procedures, offering great potential for clinical cancer treatment.

Aggregation-Induced Emission (AIE), Life and Health

Light has profoundly impacted modern medicine and healthcare, with numerous luminescent agents and imaging techniques currently being used to assess health and treat diseases. As an emerging concept in luminescence, aggregation-induced emission (AIE) has shown great potential in biological applications due to its advantages in terms of brightness, biocompatibility, photostability, and positive correlation with concentration. This review provides a comprehensive summary of AIE luminogens applied in imaging of biological structure and dynamic physiological processes, disease diagnosis and treatment, and detection and monitoring of specific analytes, followed by representative works. Discussions on critical issues and perspectives on future directions are also included. This review aims to stimulate the interest of researchers from different fields, including chemistry, biology, materials science, medicine, etc., thus promoting the development of AIE in the fields of life and health.

Enabling programmable dynamic DNA chemistry using small-molecule DNA binders

The binding of small molecules to the double helical structure of DNA, through either intercalation or minor groove binding, may significantly alter the stability and functionality of DNA, which is a fundamental basis for many therapeutic and sensing applications. Here, we report that small-molecule DNA binders can also be used to program reaction pathways of a dynamic DNA reaction, where DNA strand displacement can be tuned quantitatively according to the affinity, charge, and concentrations of a given DNA binder. The binder-induced nucleic acid strand displacement (BIND) thus enables innovative technologies to accelerate the discovery and characterization of bioactive small molecules. Specifically, we demonstrate the comprehensive characterization of existing and newly discovered DNA binders, where critical parameters for binding affinity and sequence selectivity can be obtained in a single, unbiased molecular platform without the need for any specialized equipment. We also engineer a tandem BIND system as a high-throughput screening assay for discovering DNA binders, through which 8 DNA binders were successfully discovered from a library of 700 compounds.

Multifunctional Nanoprobe Based on Fluorescence Resonance Energy Transfer for Furin Detection and Drug Delivery

Triple-negative breast cancer is particularly difficult to treat because of its high degree of malignancy and poor prognosis. A fluorescence resonance energy transfer (FRET) nanoplatform plays a very important role in disease diagnosis and treatment due to its unique detection performance. Combining the properties of agglomeration-induced emission fluorophore and FRET pair, a FRET nanoprobe (HMSN/DOX/RVRR/PAMAM/TPE) induced by specific cleavage was designed. First, hollow mesoporous silica nanoparticles (HMSNs) were used as drug carriers to load doxorubicin (DOX). HMSN nanopores were coated with the RVRR peptide. Then, polyamylamine/phenylethane (PAMAM/TPE) was combined in the outermost layer. When Furin cut off the RVRR peptide, DOX was released and adhered to PAMAM/TPE. Finally, the TPE/DOX FRET pair was constituted. The overexpression of Furin in the triple-negative breast cancer cell line (MDA-MB-468 cell) can be quantitatively detected by FRET signal generation, so as to monitor cell physiology. In conclusion, the HMSN/DOX/RVRR/PAMAM/TPE nanoprobes were designed to provide a new idea for the quantitative detection of Furin and drug delivery, which is conducive to the early diagnosis and treatment of triple-negative breast cancer.

Multiplexed Nanopore-Based Nucleic Acid Sensing and Bacterial Identification Using DNA Dumbbell Nanoswitches

Multiplexed nucleic acid sensing methods with high specificity are vital for clinical diagnostics and infectious disease control, especially in the postpandemic era. Nanopore sensing techniques have developed in the past two decades, offering versatile tools for biosensing while enabling highly sensitive analyte measurements at the single-molecule level. Here, we establish a nanopore sensor based on DNA dumbbell nanoswitches for multiplexed nucleic acid detection and bacterial identification. The DNA nanotechnology-based sensor switches from an "open" into a "closed" state when a target strand hybridizes to two sequence-specific sensing overhangs. The loop in the DNA pulls two groups of dumbbells together. The change in topology results in an easily recognized peak in the current trace. Simultaneous detection of four different sequences was achieved by assembling four DNA dumbbell nanoswitches on one carrier. The high specificity of the dumbbell nanoswitch was verified by distinguishing single base variants in DNA and RNA targets using four barcoded carriers in multiplexed measurements. By combining multiple dumbbell nanoswitches with barcoded DNA carriers, we identified different bacterial species even with high sequence similarity by detecting strain specific 16S ribosomal RNA (rRNA) fragments.

Noncancerous disease-targeting AIEgens

Noncancerous diseases include a wide plethora of medical conditions beyond cancer and are a major cause of mortality around the world. Despite progresses in clinical research, many puzzles about these diseases remain unanswered, and new therapies are continuously being sought. The evolution of bio-nanomedicine has enabled huge advancements in biosensing, diagnosis, bioimaging, and therapeutics. The recent development of aggregation-induced emission luminogens (AIEgens) has provided an impetus to the field of molecular bionanomaterials. Following aggregation, AIEgens show strong emission, overcoming the problems associated with the aggregation-caused quenching (ACQ) effect. They also have other unique properties, including low background interferences, high signal-to-noise ratios, photostability, and excellent biocompatibility, along with activatable aggregation-enhanced theranostic effects, which help them achieve excellent therapeutic effects as an one-for-all multimodal theranostic platform. This review provides a comprehensive overview of the overall progresses in AIEgen-based nanoplatforms for the detection, diagnosis, bioimaging, and bioimaging-guided treatment of noncancerous diseases. In addition, it details future perspectives and the potential clinical applications of these AIEgens in noncancerous diseases are also proposed. This review hopes to motivate further interest in this topic and promote ideation for the further exploration of more advanced AIEgens in a broad range of biomedical and clinical applications in patients with noncancerous diseases.

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.

Ligands for Abasic Site-containing DNA and their Use as Fluorescent Probes

Apurinic and apyrimidinic sites, also referred to as abasic or AP sites, are residues of duplex DNA in which one DNA base is removed from a Watson-Crick base pair. They are formed during the enzymatic repair of DNA and offer binding sites for a variety of guest molecules. Specifically, the AP site may bind an appropriate ligand as a substitute for the missing nucleic base, thus stabilizing the abasic site-containing DNA (AP-DNA). Notably, ligands that bind selectively to abasic sites may be employed for analytical and therapeutical purposes. As a result, there is a search for structural features that establish a strong and selective association of a given ligand with the abasic position in DNA. Against this background, this review provides an overview of the different classes of ligands for abasic site-containing DNA (AP-DNA). This review covers covalently binding substrates, namely amine and oxyamine derivatives, as well as ligands that bind to AP-DNA by noncovalent association, as represented by small heterocyclic aromatic compounds, metal-organic complexes, macrocyclic cyclophanes, and intercalator-nucleobase conjugates. As the systematic development of fluorescent probes for AP-DNA has been somewhat neglected so far, this review article contains a survey of the available reports on the fluorimetric response of the ligand upon binding to the AP-DNA. Based on these data, this compilation shall present a perspective for future developments of fluorescent probes for AP-DNA.

Biosensors for the Detection of Enzymes Based on Aggregation-Induced Emission

Enzymes play a critical role in most complex biochemical processes. Some of them can be regarded as biomarkers for disease diagnosis. Taking advantage of aggregation-induced emission (AIE)-based biosensors, a series of fluorogens with AIE characteristics (AIEgens) have been designed and synthesized for the detection and imaging of enzymes. In this work, we summarized the advances in AIEgens-based probes and sensing platforms for the fluorescent detection of enzymes, including proteases, phosphatases, glycosidases, cholinesterases, telomerase and others. The AIEgens involve organic dyes and metal nanoclusters. This work provides valuable references for the design of novel AIE-based sensing platforms.

Ordered heterogeneity in dual-ligand MOF to enable high electrochemiluminescence efficiency for bioassay with DNA triangular prism as signal switch

Herein, the microRNA-141 electrochemiluminescence (ECL) bioassay was developed using the dual-ligand metal-organic framework (d-MOF) with ordered heterogeneity, which simultaneously contained the luminophore ligands (1,1,2,2-tetra(4-carboxylbiphenyl)ethylene, denoted as TCBPE) and the coreactant ligands (1,4-diazabicyclo[2.2.2]octane, denoted as DN₂H₂). The resultant d-MOF revealed significantly enhanced ECL intensity without any exogenous coreactants, which was 3.53 times higher in comparison with that of single-ligand MOF (only TCBPE as ligands) even with the addition of exogenous DN₂H₂. Thanks to the ordered heterogeneity in d-MOF, the intramolecular rotation of TCBPE was restricted via oriented coordination and the spatial location of DN₂H₂ was reasonably arranged due to the framework structure, which could not only enhance the excitation efficiency but also improve the electron-transfer efficiency based on the synergistic enhancement effect between structures and compositions in micro/nano confined space. Based on this, the proposed biosensor employed a novel DNA triangular prism (DNA TP) as signal switch to detect microRNA-141, achieving the low detection limit at the level of 22.9 aM and a broad linear ranging from 100 aM to 100 pM. The precise design of the ordered d-MOFs by co-assembling the luminophore and coreactant ligands holds a promise strategy to achieve ECL MOFs and construct the ECL biosensors in diagnostic analysis.

Fluorescent probes for the detection of disease-associated biomarkers

Fluorescent probes have emerged as indispensable chemical tools to the field of chemical biology and medicine. The ability to detect intracellular species and monitor physiological processes has not only advanced our knowledge in biology but has provided new approaches towards disease diagnosis. In this review, we detail the design criteria and strategies for some recently reported fluorescent probes that can detect a wide range of biologically important species in cells and in vivo. In doing so, we highlight the importance of each biological species and their role in biological systems and for disease progression. We then discuss the current problems and challenges of existing technologies and provide our perspective on the future directions of the research area. Overall, we hope this review will provide inspiration for researchers and prove as useful guide for the development of the next generation of fluorescent probes.

Aggregation-Induced Emission (AIE) in Super-resolution Imaging: Cationic AIE Luminogens (AIEgens) for Tunable Organelle-Specific Imaging and Dynamic Tracking in Nanometer Scale

Organelle-specific imaging and dynamic tracking in ultrahigh resolution is essential for understanding their functions in biological research, but this remains a challenge. Therefore, a facile strategy by utilizing anion-π⁺ interactions is proposed here to construct an aggregation-induced emission luminogen (AIEgen) of DTPAP-P, not only restricting the intramolecular motions but also blocking their strong π-π interactions. DTPAP-P exhibits a high photoluminescence quantum yield (PLQY) of 35.04% in solids, favorable photostability and biocompatibility, indicating its potential application in super-resolution imaging (SRI) via stimulated emission depletion (STED) nanoscopy. It is also observed that this cationic DTPAP-P can specifically target to mitochondria or nucleus dependent on the cell status, resulting in tunable organelle-specific imaging in nanometer scale. In live cells, mitochondria-specific imaging and their dynamic monitoring (fission and fusion) can be obtained in ultrahigh resolution with a full-width-at-half-maximum (fwhm) value of only 165 nm by STED nanoscopy. This is about one-sixth of the fwhm value in confocal microscopy (1028 nm). However, a migration process occurs for fixed cells from mitochondria to nucleus under light activation (405 nm), leading to nucleus-targeted super-resolution imaging (fwhm= 184 nm). These findings indicate that tunable organelle-specific imaging and dynamic tracking by a single AIEgen at a superior resolution can be achieved in our case here via STED nanoscopy, thus providing an efficient method to further understand organelle's functions and roles in biological research.

A Nuclear-Targeted AIE Photosensitizer for Enzyme Inhibition and Photosensitization in Cancer Cell Ablation

The nucleus is considered the ideal target for anti-tumor therapy because DNA and some enzymes in the nucleus are the main causes of cell canceration and malignant proliferation. However, nuclear target drugs with good biosafety and high efficiency in cancer treatment are rare. Herein, a nuclear-targeted material MeTPAE with aggregation-induced emission (AIE) characteristics was developed based on a triphenylamine structure skeleton. MeTPAE can not only interact with histone deacetylases (HDACs) to inhibit cell proliferation but also damage telomere and nucleic acids precisely through photodynamic treatment (PDT). The cocktail strategy of MeTPAE caused obvious cell cycle arrest and showed excellent PDT anti-tumor activity, which offered new opportunities for the effective treatment of malignant tumors.

DNA-Templated Modulation in the Photophysical Properties of a Fluorescent Molecular Rotor Auramine O by Varying the DNA Composition

This work delineates an integrative approach combining spectroscopic and computational studies to decipher the association-induced fluorescence properties of a fluorescent molecular rotor, viz., auramine O (AuO), after interacting with 20-mer duplex DNA having diverse well-matched base pairs. While exploring the scarcely explored sequence-dependent interaction mechanism of AuO and DNA, we observed that DNA could act as a conducive scaffold to the formation of AuO dimer through noncovalent interactions at lower molecular density. The photophysical properties of AuO depend on the nucleotide compositions as described from sequence-dependent shifting in the emission and absorption maxima. Furthermore, we explored such DNA base pair-dependent fluorescence spectral characteristics of AuO toward discriminating the thermodynamically most stable single nucleotide mismatch in a 20-mer sequence. Our results are interesting and could be useful in developing analogues with further enhanced emission properties toward mismatched DNA sequences.

Molecular Probes, Chemosensors, and Nanosensors for Optical Detection of Biorelevant Molecules and Ions in Aqueous Media and Biofluids

Synthetic molecular probes, chemosensors, and nanosensors used in combination with innovative assay protocols hold great potential for the development of robust, low-cost, and fast-responding sensors that are applicable in biofluids (urine, blood, and saliva). Particularly, the development of sensors for metabolites, neurotransmitters, drugs, and inorganic ions is highly desirable due to a lack of suitable biosensors. In addition, the monitoring and analysis of metabolic and signaling networks in cells and organisms by optical probes and chemosensors is becoming increasingly important in molecular biology and medicine. Thus, new perspectives for personalized diagnostics, theranostics, and biochemical/medical research will be unlocked when standing limitations of artificial binders and receptors are overcome. In this review, we survey synthetic sensing systems that have promising (future) application potential for the detection of small molecules, cations, and anions in aqueous media and biofluids. Special attention was given to sensing systems that provide a readily measurable optical signal through dynamic covalent chemistry, supramolecular host-guest interactions, or nanoparticles featuring plasmonic effects. This review shall also enable the reader to evaluate the current performance of molecular probes, chemosensors, and nanosensors in terms of sensitivity and selectivity with respect to practical requirement, and thereby inspiring new ideas for the development of further advanced systems.

Bringing Inherent Charges into Aggregation-Induced Emission Research

Charged organic molecules, such as DNA, RNA, proteins, and polysaccharides, are ubiquitous and indispensable in natural living systems, which possess specific biological functions to interact with oppositely charged species via electrostatic attraction. The molecules with inherent charges typically differentiate themselves from the neutral ones with unique attributes (e.g., ionic interactions and high polarity), thereby playing a pivotal role in a broad spectrum of areas, including supramolecular chemistry, structural biology, and materials science. It is thus of great importance to explore and develop various charged organic systems for biomimicry and the creation of functional materials. In 2001, our group reported a peculiar luminogen that exhibited weak emission in solution but had significantly enhanced emission in aggregates, and we, for the first time, coined this phenomenon as aggregation-induced emission (AIE). The AIE concept significantly changes the cognition of the scientific community toward classic photophysical phenomena. Since the discovery of this unusual luminescence phenomenon, AIE luminogens (AIEgens) have attracted extensive attention from researchers in a plethora of disciplines because of their high brightness in aggregates, large Stokes shift, excellent photostability, and good biocompatibility. In the past 10 years, our laboratory has expended a great amount of effort to bring inherent charges into AIE research and acquired fruitful achievements.In this Account, we summarize the progress of charged AIE systems primarily made by our laboratory. We start with a brief introduction to charged AIEgens and then discuss their design strategies from molecular and topological perspectives, respectively. Next, we review the unique properties of charged AIEgens, including D-A interactions, anion-π⁺ interactions, and intermolecular electrostatic interactions, with an emphasis on how they differentiate themselves from the neutral analogs. On the one hand, positively charged AIEgens exhibit unique photophysical properties by forming typical donor-acceptor structures to manipulate the emission wavelength or initiate ultralong persistent luminescence. On the other hand, positively charged AIEgens exhibit unique physiochemical properties, such as an adjustable targeting capability toward biological targets and a strong capability for the generation of reactive oxygen species. Furthermore, we showcase the applications of charged AIEgens in imaging and diagnosis, photodynamic therapy, gas separation, and solar desalination. Finally, we conclude this Account with a summary and some perspectives regarding the existing challenges and future directions. We hope that this Account can spark new ideas and inspire scientists from different disciplines to explore this nascent yet promising research area.

A unique self-reporting photosensitizer enabling simultaneous photodynamic therapy and real-time monitoring of phototheranostic process in a dynamic dual-color mode

Phototheranostics has attracted great interest in cancer therapy. Small-molecule self-reporting photosensitizers, one kind of idea agent in phototheranostics, enables simultaneous photodynamic therapy (PDT) and feedback of therapeutic efficacy. However, previous such photosensitizers exclusively employed the change of single emission to monitor cell death, which can be disturbed by variations in photosensitizer concentration and the excitation intensity. Herein, we report a unique self-reporting photosensitizer TPA-3PyA+ constructed from a twisted triphenylamine unit (TPA), three benzene ring units and three cyanovinyl-pyridinium units (PyA) for PDT and its real-time monitoring in a dynamic dual-color mode. TPA-3PyA+ possesses a rotatable electron donor-π bridge-electron acceptor framework and exhibits high singlet oxygen quantum yield (124%) and a twisted intramolecular charge transfer (TICT) effect. TPA-3PyA+ not only enables effective staining of cancer cells with dual-color fluorescence due to the TICT effect but also shows excellent PDT performance. The simultaneous change in emission color, intensity and intracellular location of TPA-3PyA+ during cell death allows it to self-report cell death. Moreover, the change of dual-emission color allows distinguishing living and dead cells and effectively avoids interference in previous single-emission self-reporting photosensitizers. This work highlights the great potential of a self-reporting photosensitizer with dual-color emissions for efficient feedback of theranostics.

Aggregation induced emission molecules for detection of nucleic acids

Aggregation-induced emission (AIE) is an ingenious concept in the field of luminescent molecules. AIE is the energy released in an excited state that in turn is converted into light irrespective of being in either liquid phase or solid phase. Aggregation or crystallization of AIE molecules impedes the free movement of molecules and it resultantly becomes highly fluorescent. It is currently being used for several applications including sensing, diagnostic, protein, DNA or RNA detection, cells and cell organelles imaging. AIEs are highly sensitive and specific for binding with target molecules. In this chapter, we underline different AIE molecules for detection of nucleic acids.

Off-On Squalene Epoxidase-Specific Fluorescent Probe for Fast Imaging in Living Cells

SQLE (squalene epoxidase) is a cell membrane-bound enzyme. It is a target of fungicides and may become a new target for cancer therapy. Therefore, monitoring the content and distribution of the key enzyme in living cells is very challenging. To achieve this goal, tetraphenyl ethylene-Ter (TPE-Ter) was first designed as a new fluorescent probe to SQLE based on its active cavity. Spectral experiments discovered that SQLE/TPE-Ter shows stronger emission with fast response time and low interference from other analytes. Molecular dynamics simulation clearly confirmed the complex structure of SQLE/TPE-Ter, and the key residues contribute to restriction of TPE-Ter single-molecular motion in the cavity. TPE-Ter-specific response to SQLE is successfully demonstrated in living cells such as LO2, HepG2, and fungi. Imaging of TPE-Ter-treated fungi indicates that it can be used to rapidly assess antifungal drug susceptibility (30 min at least). The present work provides a powerful tool to detect content and distribution of SQLE in living cells.

Dual-Emissive Tris-Heteroleptic Ruthenium Complexes: Tuning the DNA-Triggered Ratiometric Emission Response by Ancillary Ligands

Three tris-heteroleptic mononuclear Ru(II) complexes with dual fluorescence and phosphorescence-[Ru(dpma)(bpy)(phen)]²⁺ (1²⁺), [Ru(dpma)(bpy)(dppz)]²⁺ (2²⁺), and [Ru(dpma)(phen)(dppz)]²⁺ (3²⁺)-have been designed and used as ratiometric light-response probes for DNA, where dpma is di(pyrid-2-yl)(methyl)-amine, bpy is 2,2'-bipyridine, phen is 1,10-phenanthroline, and dppz is dipyridophenazine, respectively. Single crystals of complex 2(PF₆)₂ have been obtained and studied by X-ray analysis. The interactions of these complexes with different DNAs are investigated by means of spectroscopic methods, viscosity measurements, and molecular modeling. In the presence of calf thymus DNA, complexes 2(PF₆)₂ and 3(PF₆)₂ show the emergence of a new lower-energy phosphorescence emission band; meanwhile, the higher-energy fluorescence emission band is essentially unchanged, functioning as an intrinsic internal reference. These two complexes exhibit stronger preference for calf thymus DNA over single-strand DNA (d(A)₁₆ and d(C)₁₆). In contrast, no binding interaction between 1(PF₆)₂ and calf thymus DNA is observed. The intrinsic binding constants (K_b) of 2(PF₆)₂ and 3(PF₆)₂ with calf thymus DNA are determined to be (1.4 ± 0.4) × 10⁵ and (9.5 ± 0.15) × 10⁴ M^-1, respectively. In addition, these spectroscopic results are compared with those of the prototype complex [Ru(bpy)₂(dppz)]²⁺ (4²⁺), and density functional theory and time-dependent density functional theory calculations are employed to elucidate these experimental findings.

A Continuous Add-On Probe Reveals the Nonlinear Enlargement of Mitochondria in Light-Activated Oncosis

Oncosis, depending on DNA damage and mitochondrial swelling, is an important approach for treating cancer and other diseases. However, little is known about the behavior of mitochondria during oncosis, due to the lack of probes for in situ visual illumination of the mitochondrial membrane and mtDNA. Herein, a mitochondrial lipid and mtDNA dual-labeled probe, MitoMN, and a continuous add-on assay, are designed to image the dynamic process of mitochondria in conditions that are unobservable with current mitochondrial probes. Meanwhile, the MitoMN can induce oncosis in a light-activated manner, which results in the enlargement of mitochondria and the death of cancer cells. Using structured illumination microscopy (SIM), MitoMN-stained mitochondria with a dual-color response reveals, for the first time, how swelled mitochondria interacts and fuses with each other for a nonlinear enlargement to accelerate oncosis into an irreversible stage. With this sign of irreversible oncosis revealed by MitoMN, oncosis can be segregated into three stages, including before oncosis, initial oncosis, and accelerated oncosis.

Stimuli-Responsive AIEgens

The unique advantages and the exciting application prospects of AIEgens have triggered booming developments in this area in recent years. Among them, stimuli-responsive AIEgens have received particular attention and impressive progress, and they have been demonstrated to show tremendous potential in many fields from physical chemistry to materials science and to biology and medicine. Here, the recent achievements of stimuli-responsive AIEgens in terms of seven most representative types of stimuli including force, light, polarity, temperature, electricity, ion, and pH, are summarized. Based on typical examples, it is illustrated how each type of systems realize the desired stimuli-responsive performance for various applications. The key work principles behind them are ultimately deciphered and figured out to offer new insights and guidelines for the design and engineering of the next-generation stimuli-responsive luminescent materials for more broad applications.

Real-Time Visualization and Monitoring of Physiological Dynamics by Aggregation-Induced Emission Luminogens (AIEgens)

Physiological dynamics in living cells and tissues are crucial for maintenance and regulation of their normal activities and functionalities. Tiny fluctuations in physiological microenvironments can leverage significant influences on cell growth, metabolism, differentiation, and apoptosis as well as disease evolution. Fluorescence imaging based on aggregation-induced emission luminogens (AIEgens) exhibits superior advantages in real-time sensing and monitoring of the physiological dynamics in living systems, including its unique properties such as high sensitivity and rapid response, flexible molecular design, and versatile nano- to mesostructural fabrication. The introduction of canonic AIEgens with long-wavelength, near-infrared, or microwave emission, persistent luminescence, and diversified excitation source (e.g., chemo- or bioluminescence) offers researchers a tool to evaluate the resulting molecules with excellent performance in response to subtle fluctuations in bioactivities with broader dimensionalities and deeper hierarchies.

Long-Term Dynamic Imaging of Cellular Processes Using an AIE Lipid Order Probe in the Dual-Color Mode

Lipid order in the cytoplasm membrane of eukaryotic cells undergoes dynamic changes in almost all cellular processes. Dynamically monitoring these changes is of essential biological significance and remains challenging. This work provides the first aggregation-induced emission probe, TPNPDA-C15, with highly three-dimensional specificity to cell membranes for fluorescent imaging of lipid order of live cells. TPNPDA-C15 displays red fluorescence enhancement with the viscosity increase while emits yellow fluorescence when aggregates form. Imaging analyses of giant unilamellar vesicles and live cells under osmotic shock by the probe demonstrate its sensitive response to the degree of phospholipids packing on artificial and cell membranes. Taking advantage of its superior low photocytotoxicity and high photostability, TPNPDA-C15 is further applied for long-term dynamic imaging of entire live cell physiological processes including apoptosis, ferroptosis, and mitosis in the dual-color mode. With the analysis of fluorescence signal changes in the two fluorescence channels, TPNPDA-C15 serves as a robust fluorescent probe for the imaging study of cellular dynamics.

Selective, pH-Dependent Colorimetric and Fluorimetric Detection of Quadruplex DNA with 4-Dimethylamino(phenyl)-Substituted Berberine Derivatives

The 9- and 12-dimethylaminophenyl-substituted berberine derivatives 3 a and 3 b were readily synthesized by Suzuki-Miyaura reactions and shown to be useful fluorescent probes for the optical detection of quadruplex DNA (G4-DNA). Their association with the nucleic acids was investigated by spectrometric titrations, CD and LD spectroscopy, and with DNA-melting analysis. Both ligands bind to duplex DNA by intercalation and to G4-DNA by terminal π stacking. At neutral conditions, they bind with higher affinity (Kb =105 -106  M-1 ) to representative quadruplex forming oligonucleotides 22AG, c-myc, c-kit, and a2, than to duplex calf thymus (ct) DNA (Kb =5-7×104  M-1 ). At pH 5, however, the affinity of 3 a towards G4-DNA 22AG is higher (Kb =1.2×106  M-1 ), whereas the binding constant towards ct DNA is lower (Kb =3.9×103  M-1 ) than under neutral conditions. Notably, the association of the ligand with DNA results in characteristic changes of the absorption and emission properties under specific conditions, which may be used for optical DNA detection. Other than the parent berberine, the ligands do not show a noticeable increase of their very low intrinsic emission intensity upon association with DNA at neutral conditions. In contrast, a fluorescence light-up effect was observed upon association to duplex (Φfl =0.01) and quadruplex DNA (Φfl =0.04) at pH 5. This fluorimetric response to G4-DNA association in combination with the distinct, red-shifted absorption under these conditions provides a simple and conclusive optical detection of G4-DNA at lower pH.

Application of Nanotechnology for Sensitive Detection of Low-Abundance Single-Nucleotide Variations in Genomic DNA: A Review

Single-nucleotide polymorphisms (SNPs) are the simplest and most common type of DNA variations in the human genome. This class of attractive genetic markers, along with point mutations, have been associated with the risk of developing a wide range of diseases, including cancer, cardiovascular diseases, autoimmune diseases, and neurodegenerative diseases. Several existing methods to detect SNPs and mutations in body fluids have faced limitations. Therefore, there is a need to focus on developing noninvasive future polymerase chain reaction (PCR)-free tools to detect low-abundant SNPs in such specimens. The detection of small concentrations of SNPs in the presence of a large background of wild-type genes is the biggest hurdle. Hence, the screening and detection of SNPs need efficient and straightforward strategies. Suitable amplification methods are being explored to avoid high-throughput settings and laborious efforts. Therefore, currently, DNA sensing methods are being explored for the ultrasensitive detection of SNPs based on the concept of nanotechnology. Owing to their small size and improved surface area, nanomaterials hold the extensive capacity to be used as biosensors in the genotyping and highly sensitive recognition of single-base mismatch in the presence of incomparable wild-type DNA fragments. Different nanomaterials have been combined with imaging and sensing techniques and amplification methods to facilitate the less time-consuming and easy detection of SNPs in different diseases. This review aims to highlight some of the most recent findings on the aspects of nanotechnology-based SNP sensing methods used for the specific and ultrasensitive detection of low-concentration SNPs and rare mutations.

Recent progress of nanotechnology-based theranostic systems in cancer treatments

Theranostics that integrates therapy and diagnosis in one system to achieve accurate cancer diagnosis and treatment has attracted tremendous interest, and has been recognized as a potential breakthrough in overcoming the challenges of conventional oncotherapy. Nanoparticles are ideal candidates as carriers for theranostic agents, which is attributed to their extraordinary physicochemical properties, including nanoscale sizes, functional properties, prolonged blood circulation, active or passive tumor targeting, specific cellular uptake, and in some cases, excellent optical properties that ideally meet the needs of phototherapy and imaging at the same time. Overall, with the development of nanotechnology, theranostics has become a reality, and is now in the transition stage of "bench to bedside." In this review, we summarize recent progress on nanotechnology-based theranostics, i.e., nanotheranostics, that has greatly assisted traditional therapies, and has provided therapeutic strategies emerging in recent decades, as well as "cocktail" theranostics mixing various treatment modalities.

Differentiating a Least-Stable Single Nucleotide Mismatch in DNA Via Metal Ion-Mediated Base Pairing and Using Thioflavin T as an Extrinsic Fluorophore

Monitoring the DNA dynamics in solution has great potential to develop new nucleic acid-based sensors and devices. With spectroscopic approaches, both at the ensemble average and single-molecule resolution, this study is directed to differentiate a single nucleotide mismatch (SNM) via a metal ion-stabilized mismatched base-pairing (C-Ag⁺-C/C-Cu²⁺-T) (C = cytosine, T = thymine) and site-selective extrinsic fluorophore, specifically, Thioflavin T (ThT). This is the first approach of its kind where dynamic quantities like molecular diffusion coefficients and diffusion times have been utilized to distinguish the least-stable SNM (CC & CT) formed by the most discriminating nucleobase, specifically, cytosine in a 20-mer duplex DNA. Additionally, this work also quantifies metal ions (Ag⁺ and Cu²⁺) at lower concentrations using fluorescence correlation spectroscopy. Our results can provide greater molecular-level insights into the mismatch-dependent metal-DNA interactions and also illuminate ThT as a new fluorophore to monitor the dynamics involved in DNA-metal composites.

The Promise of Aggregation-Induced Emission Luminogens for Detecting COVID-19

The long-term pandemic of coronavirus disease 2019 (COVID-19) requires sensitive and accurate diagnostic assays to detect severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus and SARS-CoV-2 antibodies in infected individuals. Currently, RNA of SARS-CoV-2 virus is mainly detected by reverse transcription-polymerase chain reaction (RT-PCR)-based nucleic acid assays, while SARS-CoV-2 antigen and antibody are identified by immunological assays. Both nucleic acid assays and immunological assays rely on the luminescence signals of specific luminescence probes for qualitative and quantitative detection. The exploration of novel luminescence probes will play a crucial role in improving the detection sensitivity of the assays. As innate probes, aggregation-induced emission (AIE) luminogens (AIEgens) exhibit negligible luminescence in the free state but enhanced luminescence in the aggregated or restricted states. Moreover, AIEgen-based nanoparticles (AIE dots) offer efficient luminescence, good biocompatibility and water solubility, and superior photostability. Both AIEgens and AIE dots have been widely used for high-performance detection of biomolecules and small molecules, chemical/biological imaging, and medical therapeutics. In this review, the availability of AIEgens and AIE dots in nucleic acid assays and immunological assays are enumerated and discussed. By building a bridge between AIE materials and COVID-19, we hope to inspire researchers to use AIE materials as a powerful weapon against COVID-19.

Lighting up forensic science by aggregation-induced emission: A review

Forensic science requires a fast, sensitive, and anti-interfering imaging tool for on-site investigation and bio-analysis. The aggregation-induced emission (AIE) phenomenon exhibits remarkable luminescence properties (large Stokes shift, diverse molecular structures, and high photo-stability), which can provide a viable solution for on-site analysis, while at the same time overcoming the problem of aggregation-caused quenching (ACQ). Based on the outstanding performance in chemical analysis and bio-sensing, AIE materials have great prospects in the field of forensic science. Therefore, the application of AIE in forensic science has been summarized for the first time in this article. After a brief introduction to the concept and development of AIE, its applications in the determination of toxic or hazardous substances, based on data on poisoning deaths, has been summarized. Subsequently, besides the bio-imaging function, other applications of AIE in analyzing markers related to forensic genetics, forensic pathology, (focusing on the corpse) and clinical forensics (focusing on the living) have been discussed. In addition, applications of AIE molecules in criminal investigations, including recognition of fingerprints and blood stains, detection of explosives and chemical warfare agents, and anti-counterfeiting have also been presented. It is hoped that this review will light up the future of forensic science by stimulating more research work on the suitability of AIE materials in advancing forensic science.

A pillar[5]arene-based fluorescent sensor for sensitive detection of L-Met through a dual-site collaborative mechanism

L-Methionine (L-Met) is one of the essential amino acids in human health, efficiently detect L-Met is a significant issue. Herein, a concept "dual-site collaborative recognition" had been successfully introduced into the design and achieved high selective and sensitive recognition of L-Met. In order to realize the "dual-site collaborative recognition", we rationally designed and synthesized an ester functionalized pillar[5]arene-based fluorescent sensor (SP5). And it shows blue Aggregation-induced emission (AIE) fluorescence. In the SP5, the pillar[5]arene group act as C-H···π interactions site, and ester group serve as multi hydrogen bonding acceptor. Interestingly, the SP5 exhibited high selectivity and sensitivity (2.84 × 10^-8 M) towards L-Met based on the collaboration of electron-rich cavernous pillar[5]arene group and ester group through C-H···π and H-bond interactions, respectively. This "dual-site collaborative recognition" mechanism has been investigated by ¹H NMR, ESI-MS and theoretical calculation including frontier orbital (HOMO and LUMO), electrostatic potential (ESP) and the noncovalent interaction (NCI). These theoretical calculations not only support the proposed host-guest recognition mechanism, but also provided visualized information on the "dual-site collaborative recognition" mode. Furthermore, the concept "dual-site collaborative recognition" is an effective strategy for easily detecting biological molecules.

Instrument-free and visual detection of organophosphorus pesticide using a smartphone by coupling aggregation-induced emission nanoparticle and two-dimension MnO2 nanoflake

Given the importance of food safety, it is highly desirable to develop a convenient, low-cost, and practical sensor for organophosphorus pesticides (OPs) detection. Here, a fluorescent paper analytical device (FPAD) based on aggregation-induced emission (AIE) nanoparticles (PTDNPs-0.10) and two-dimension MnO₂ nanoflakes (2D-MnNFs) was developed for instrument-free and naked-eye analysis of OPs. PTDNP-MnNFs composites were obtained through 2D-MnNFs and PTDNPs-0.10 by electrostatic interaction and the fluorescence emission of PTDNPs-0.10 was quenched through fluorescence resonance energy transfer (FRET). When acetylcholinesterase (AChE) was present, acetylthiocholine (ATCh) was catalytically hydrolyzed into thiocholine, which reduced MnO₂ of PTDNP-MnNFs into Mn²⁺, subsequently blocking the FRET and enhancing the fluorescence. Upon the addition of OP, AChE activity was depressed and thus the FRET between 2D-MnNFs and PTDNPs-0.10 was not affected, resulting in a slight change in fluorescence. On the basis of the variation in fluorescence intensity, highly sensitive detection of OP was readily achieved with a detection limit of 0.027 ng/mL; on the basis of the variation in brightness of FPAD, instrument-free and visual detection of OP was realized using a smartphone with a detection limit of 0.73 ng/mL. The application of FPAD has significantly simplified the detection procedure and decreased the test cost, supplying a new approach for on-site detection of OPs.

Aggregate Science: From Structures to Properties

Molecular science entails the study of structures and properties of materials at the level of single molecules or small interacting complexes of molecules. Moving beyond single molecules and well-defined complexes, aggregates (i.e., irregular clusters of many molecules) serve as a particularly useful form of materials that often display modified or wholly new properties compared to their molecular components. Some unique structures and phenomena such as polymorphic aggregates, aggregation-induced symmetry breaking, and cluster excitons are only identified in aggregates, as a few examples of their exotic features. Here, by virtue of the flourishing research on aggregation-induced emission, the concept of "aggregate science" is put forward to fill the gaps between molecules and aggregates. Structures and properties on the aggregate scale are also systematically summarized. The structure-property relationships established for aggregates are expected to contribute to new materials and technological development. Ultimately, aggregate science may become an interdisciplinary research field and serves as a general platform for academic research.

An aggregation-induced emission fluorogen/DNA probe carrying an endosome escaping pass for tracking reduced thiol compounds in cells

The fluorescent nanoprobes for reduced thiol compounds (represented by glutathione, GSH) are constructed based on the aggregation-induced emission (AIE) luminescence mechanism and endosome escape technology. First, a DNA sequence was designed with the decoration of biotin at the 5'-end, disulfide bound in the internal portion, and amino at the 3'-end. The aptamer of the MCF-7 cell was also one of the most important structures in our DNA sequence for the selectivity of MCF-7 cells. We modified streptavidin-modified magnetic beads (MB) with biotin-modified influenza virus hemagglutinin peptide (HA) and biotin-DNA-amino to form MB/DNA/HA. Carboxyl-modified tetraphenylethylene (TPE), an iconic AIE fluorogen, was bonded with amino-modified DNA by covalent interactions (TPE/DNA). Then, the TPE molecule was attached on the outer layer of MB via biotin-modified TPE/DNA to form MB/DNA/HA/TPE. Compared with traditional AIE/biomolecule conjugates, the nanoprobe had an enhanced endosome escape function, due to the assembly of HA. This construction made the intracellular fluorescence response more accurate. In the presence of reduced thiol compounds (take GSH, for example), the disulfide bond on the DNA was reduced by thiol-disulfide exchange reactions and the TPE molecule was released into the solution. The shedding TPE molecule was more hydrophobic than TPE/DNA and the conversion of TPE/DNA to shedding TPE could lead to the aggregation of the TPE fluorogen. Thus, its fluorescence was enhanced. Under the optimized condition, the fluorescence intensity increased with the increase in concentration of GSH' ranging from 1.0 × 10^-9 M to 1.0 × 10^-5 M' and the detection limit was 1.0 × 10^-9 M. The relative standard deviation (RSD) was calculated to be 3.6%. The recovery in cell homogenate was from 94.5 to 102.7%. The nanoprobe provided a way for the detection of reduced thiol compounds in MCF-7 cells. We envision that, in the near future, our strategy of DNA-instructed AIE could be widely applied for biosensing and bioimaging in vitro and even in vivo with dramatically enhanced sensitivity. Graphical Abstract.

A two-photon AIE fluorophore as a photosensitizer for highly efficient mitochondria-targeted photodynamic therapy

Nowadays, photodynamic therapy (PDT) has become an effective method for cancer therapy.