Progress and Trends in AIE-Based Bioprobes: A Brief Overview

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.

AIEgen-Peptide Bioprobes for the Imaging of Organelles

Organelles are important subsystems of cells. The damage and inactivation of organelles are closely related to the occurrence of diseases. Organelles’ functional activity can be observed by fluorescence molecular tools. Nowadays, a series of aggregation-induced emission (AIE) bioprobes with organelles-targeting ability have emerged, showing great potential in visualizing the interactions between probes and different organelles. Among them, AIE luminogen (AIEgen)-based peptide bioprobes have attracted more and more attention from researchers due to their good biocompatibility and photostability and abundant diversity. In this review, we summarize the progress of AIEgen-peptide bioprobes in targeting organelles, including the cell membrane, nucleus, mitochondria, lysosomes and endoplasmic reticulum, in recent years. The structural characteristics and biological applications of these bioprobes are discussed, and the development prospect of this field is forecasted. It is hoped that this review will provide guidance for the development of AIEgen-peptide bioprobes at the organelles level and provide a reference for related biomedical research.

Molecularly engineered AIEgens with enhanced quantum and singlet-oxygen yield for mitochondria-targeted imaging and photodynamic therapy

Luminogens characteristic of aggregation-induced emission (AIEgens) have been extensively exploited for the development of imaging-guided photodynamic therapeutic (PDT) agents. However, intramolecular rotation of donor-acceptor (D-A) type AIEgens favors non-radiative decay of photonic energy which results in unsatisfactory fluorescence quantum and singlet oxygen yields. To address this issue, we developed several molecularly engineered AIEgens with partially "locked" molecular structures enhancing both fluorescence emission and the production of triplet excitons. A triphenylphosphine group was introduced to form a D-A conjugate, improving water solubility and the capacity for mitochondrial localization of the resulting probes. Experimental and theoretical analyses suggest that the much higher quantum and singlet oxygen yield of a structurally "significantly-locked" probe (LOCK-2) than its "partially locked" (LOCK-1) and "unlocked" equivalent (LOCK-0) is a result of suppressed AIE and twisted intramolecular charge transfer. LOCK-2 was also used for the mitochondrial-targeting, fluorescence image-guided PDT of liver cancer cells.

Recent advances of aggregation-induced emission materials for fluorescence image-guided surgery

Real-time intraoperative guidance is essential during various surgical treatment of many diseases. Aggregation-induced emission (AIE) materials have shown great potential for guiding surgeons during complex interventions, with the merits of deep tissue penetration, high quantum yield, high molar absorptivity, low background, good targeting ability and excellent photostability. Herein, we provided insights to design efficient AIE materials regarding three key parameters, i.e., deep-tissue penetration ability, high brightness of AIE luminogens (AIEgens), and precise tumor/other pathology nidus targeting strategies, for realizing better application of fluorescence image-guided surgery. Representative interdisciplinary achievements were outlined for the demonstration of this emerging field. Challenges and future opportunities of AIE materials were briefly discussed. The aim of this review is to provide a comprehensive view of AIE materials for intraoperative guidance for researchers and surgeons, and to inspire more further correlational studies in the new frontiers of image-guided surgery.

A coumarin coupled tetraphenylethylene based multi-targeted AIEgen for cyanide ion and nitro explosive detection, and cellular imaging

A coumarin coupled tetraphenylethylene based AIEgen (TPE-Lac) with an intense greenish-yellow emission has been synthesized and utilized for multipurpose sensing and imaging applications. TPE-Lac acts as a sensitive sensor for the detection of cyanide ions (CN^-) with an immediate turn-off response in the presence of many other interfering cations and anions. The limit of detection (LOD) was as low as 33 nM, which is well below the permissible limit set by the World Health Organization (WHO). Cyanide detection in the solid phase was successfully demonstrated by drop-casting the solution of the TPE-Lac probe on TLC plates and measuring and analysing the fluorescence response by ImageJ analysis. TPE-Lac was further employed in the detection of explosive nitroaromatics in solution and solid phases. Also, TPE-Lac was found suitable as an imaging agent and could easily percolate into live H520 cells giving bright fluorescence from the intra-cellular region. Easy and cost-effective synthesis, fast response and low LODs are some of the advantages of this AIEgen over available molecular probes for the same purpose.

Molecular Design and Photothermal Application of Thienoisoindigo Dyes with Aggregation-Induced Emission

Organic fluorescent dyes with aggregation-induced emission (AIE) property have an extensive application range, especially in the fields of imaging, labeling, and adjusting microprocesses in aggregated environments. In particular, the thienoisoindigo skeleton, which exhibits an outstanding electron-withdrawing capacity in optoelectronic materials, has been defined as a promising AIE candidate. For instance, by installing AIE blocks or other rotatable groups at two terminal sites, such as various arylamine groups, thienoisoindigo derivatives can be efficiently turned to be functional AIE structures. In this work, a thienoisoindigo derivative with AIE characteristics, namely, TII-TPE, was developed. This AIE system was expanded by linking typical AIE fragments, namely, tetraphenylethene, with the proposed thienoisoindigo derivative, which exhibited typical AIE fluorescence in the 600-850 nm range and maintained high photostability. Then, employing the reported derivative TII-TPA coating thienoisoindigo and triphenylamine as a contrast, aggregated TII-TPE and TII-TPA nanoparticles were prepared and demonstrated photothermal conversion efficiencies of 36.2 and 35.6%, respectively. Moreover, both nanoparticles were evaluated as photothermal therapeutic (PTT) agents in a tumor mouse model, which showed to significantly inhibit tumor growth after four treatment cycles in vivo. This work not only presents an enriched thienoisoindigo system but also provides a pattern for subsequent construction of functional AIE molecules.

Near-Infrared-Emissive AIE Bioconjugates: Recent Advances and Perspectives

Near-infrared (NIR) fluorescence materials have exhibited formidable power in the field of biomedicine, benefiting from their merits of low autofluorescence background, reduced photon scattering, and deeper penetration depth. Fluorophores possessing planar conformation may confront the shortcomings of aggregation-caused quenching effects at the aggregate level. Fortunately, the concept of aggregation-induced emission (AIE) thoroughly reverses this dilemma. AIE bioconjugates referring to the combination of luminogens showing an AIE nature with biomolecules possessing specific functionalities are generated via the covalent conjugation between AIEgens and functional biological species, covering carbohydrates, peptides, proteins, DNA, and so on. This perfect integration breeds unique superiorities containing high brightness, good water solubility, versatile functionalities, and prominent biosafety. In this review, we summarize the recent progresses of NIR-emissive AIE bioconjugates focusing on their design principles and biomedical applications. Furthermore, a brief prospect of the challenges and opportunities of AIE bioconjugates for a wide range of biomedical applications is presented.

Hyperbranched Tetraphenylethylene Derivatives with Low Non-specific Aggregation-Induced Emission for Fluorescence Recognition of Proteins with Hydrophobic Pockets

Proteins play an important role in the physiological process of many organisms, and their abnormal level often indicates the occurrence of some diseases. Therefore, protein analysis has important reference value and clinical significance for early diagnosis and therapy of disease. Using human serum albumin (HSA) as a model protein, a series of super-branched tetraphenylethylene (TPE) derivatives with different branching structures and terminal groups are reported herein for highly sensitive and specific recognition of proteins with hydrophobic cages. Benefiting from the hyperbranched structures, these probes showed much higher critical micelle concentrations (CMCs) than most linear TPE-based amphiphilic molecules since the hyperbranched structure not only improved their solubility but also amplified the steric hindrance effect and electrostatic repulsive force to prevent their aggregation. Dynamic light scattering experiments proved that these probes formed dense aggregates at CMC, and such aggregate structures would lead to a higher background fluorescence noise. Hence, a higher CMC is more conducive to the detection of the target with low backgrounds. Among them, P₃-COOH with -COOH as the terminal unit and a relatively longer branch showed the highest CMC and the best signal to background ratio (S/N). Mechanism studies showed that P₃-COOH was bound to HSA mainly through a hydrophobic force, resulting in a limited P₃-COOH molecular movement and less attack from quenchers in solutions, thus leading to greatly enhanced fluorescence intensity. In addition, P₃-COOH was also applied to the determination of HSA content in actual human serum samples.

Dual-potential electrochemiluminescent film constructed from single AIE luminogens for the sensitive detection of malachite green

Exploiting efficient electrochemiluminescent (ECL) luminogens is crucial for the development of high-performance ECL sensors. Herein, a kind of efficient luminogen (BTPEBT) consisting of benzothiadiazole (BTD) as an electron acceptor and tetraphenylethylene (TPE) as an electron donor was facilely synthesized through a one-step Suzuki reaction. BTPEBT showed typical aggregation-induced emission (AIE) effects with a high solid-state quantum yield of 69.8%. The fabricated solid-state ECL film that is based on single AIE luminogens presented unique dual-potential ECL properties for the first time. The bright ECL of this film could be observed by the naked eye with a satisfactory ECL efficiency of 22.8%. The dense ECL film showed a low electron-transfer resistance, which favors electron transfer among AIE luminogens, electrolytes and the electrode, giving rise to bright ECL emission. The bright ECL film was developed as an ECL sensor for the sensitive and selective detection of malachite green (MG) in a broad linear range from 10^-10 to 10^-5 M. The limit of detection (LOD) was as low as 7.6 × 10^-11 M. Moreover, the ECL sensing platform was further employed to detect MG in a real fish tissue sample with high sensitivity and good specificity. More importantly, the recycled BTPEBT film had good reproducibility for MG detection. The novel dual-potential ECL film constructed from single AIE luminogens provides a promising platform for the sensitive detection of MG in the food industry.

An effective long-wavelength fluorescent sensor for Cu2+ based on dibenzylidenehydrazine-bridged biphenylacrylonitrile

Although numerous fluorescence sensors for Cu²⁺ have been presented, a long-wavelength sensor in aqueous media has rarely been reported as expected due to practical application requirements. In this work, a novel AIE molecule (DHBB) containing two biphenylacrylonitrile units bridged by dibenzylidenehydrazine was prepared. It possessed the merits of long-wavelength emission, good emission in aqueous media, and multiple functional groups for binding Cu²⁺. It exhibited good sensing selectivity for Cu²⁺ among all kinds of tested metal ions. The detection limit was as low as 1.08 × 10^-7 M. The sensing mechanism was clarified as 1:1 stoichiometric ratio based on the binding cooperation of O and N functional groups of DHBB. The selective sensing ability for Cu²⁺ remained stable at pH = 5-9 and was influenced little by other metal ions. The Cu²⁺ sensing ability of DHBB was applied in real samples with 96% recovery rate. The bio-imaging experiment of living cells suggested that DHBB possessed not only good bio-imaging performance but also sensing ability for Cu²⁺ in living environments. This work suggested the good application prospect of DHBB to sense Cu²⁺ in real samples and living environment.

Highly specific esterase activated AIE plus ESIPT probe for sensitive ratiometric detection of carbaryl

Fabrication of facile, sensitive, and accurate pesticide detection strategies plays crucial roles in food safety, environmental protection, and human health. Here, a novel esterase activatable aggregation-induced emission (AIE) plus excited-state intramolecular proton transfer (ESIPT) probe, kaempferol tetraacetate, was designed and synthesized from purified natural kaempferol for ratiometric sensing of carbaryl. Acetate groups are introduced as the esterase reactive sites and AIE plus ESIPT initiator. Kaempferol tetraacetate is an aggregation-caused quenching compound that shows fluorescent (FL) emission at 415 nm. Esterase specifically hydrolyzes kaempferol tetraacetate to kaempferol with AIE plus ESIPT characteristics (distinct FL emission, 530 nm; a large Stokes shift, 165 nm within a short time (8 min). Molecular docking and kinetics performance indicate the high affinity and specific hydrolysis of esterase and kaempferol tetraacetate. Carbaryl inhibits the activity of esterase to efficiently suppress the production of kaempferol. Thus, a facile ratiometric assay strategy is constructed for carbaryl detection. By measuring the FL intensity ratio, the proposed strategy presents high selectivity and reliability with a wide linear range from 0.02 to 2.00 μg L^-1 and a very low limit of detection at 0.007 μg L^-1. Furthermore, appropriate recovery from 93.75% to 108.67% with a relative standard deviation less than 5.66% for real sample analysis indicates good accuracy and precision. All results indicate that the fabricated strategy offers a new way for facile, sensitive, and accurate detection of carbaryl in real complex samples.

A New Cationic Fluorescent Probe for HSO3- Based on Bisulfite Induced Aggregation Self-Assembly

In comparison with the numerous studies that have centered on developing molecular frameworks for the functionalization of fluorescent materials, less research has addressed the influence of the side chains, despite such appendages contributing significantly to the properties and applications of fluorescent materials. In this work, a new series of cationic fluorescent probes with AIE characteristics have been developed, which exhibit unique sensitivity for charge-diffusion anions, namely HSO₃⁻, via the interactions of ions and the cooperation of the controllable hydrophobicity. The impact of the alkyl chain length attached at the cationic probes suggested that the fluorescent intensity and sensitivity of the probes could be partially enhanced by adjusting their aggregation tendency through the action of the hydrophobic effect under aqueous conditions. DLS and SEM images indicated that different particle sizes and new morphologies of the probes were formed in the anion-recognition-triggered self-assembly process, which could be attributed to the composite effect of electrostatic actions, Van der Waals forces and π-π stacking.

An effective dual sensor for Cu2+ and Zn2+ with long-wavelength fluorescence in aqueous media based on biphenylacrylonitrile Schiff-base

Although some sensors for Cu²⁺ and Zn²⁺ had been reported, the sensor with long-wavelength emission in aqueous media for in-situ detecting Cu²⁺ and Zn²⁺ was always expected. Herein, a biphenylacrylonitrile Schiff-base (OPBS) with large aromatic conjugated system was designed and synthesized in yield of 82%. OPBS possessed excellent long-wavelength fluorescence at 550-750 nm in aqueous media, which selectively response to sense Cu²⁺ with quenched fluorescence and Zn²⁺ with chromotropic fluorescence from red to yellow. The detection of Cu²⁺ and Zn²⁺ were realized without mutual interference in their coexistence system by means of the assistance of ATP. The detection limits were 2.3 × 10^-7 M for Cu²⁺ and 1.8 × 10^-6 M for Zn²⁺, respectively. The sensing mechanism was elucidated by binding MS spectra, fluorescence Job's plot and ¹H NMR spectra. Moreover, OPBS exhibited good bioimaging performance and the in-situ sensing abilities for Cu²⁺ and Zn²⁺ in living cells, suggesting the application potential for detecting Cu²⁺ and Zn²⁺ in both vitro assay and vivo environment.

Upper Critical Solution Temperature Polyvalent Scaffolds Aggregate and Exterminate Bacteria

Specific recognition and strong affinities of bacteria receptors with the host cell glycoconjugates pave the way to control the bacteria aggregation and kill bacteria. Herein, using aggregation-induced emission (AIE) molecules decorated upper critical solution temperature (UCST) polyvalent scaffold (PATC-GlcN), an approach toward visualizing bacteria aggregation and controlling bacteria-polyvalent scaffolds affinities under temperature stimulus is described. Polyvalent scaffolds with diblocks, one UCST block PATC of polyacrylamides showing a sharp UCST transition and typical AIE behavior, the second bacteria recognition block GlcN of hydrophilic glucosamine modified polyacrylamide, are prepared through a reversible addition and fragmentation chain transfer polymerization. Aggregated chain conformation of polyvalent scaffolds at temperature below UCST induces the aggregation of E. coli ATCC8739, because of the high density of glucosamine moieties, whereas beyond UCST, the hydrophilic state of the scaffolds dissociates the bacteria aggregation. The sweet-talking of bacteria toward the polyvalent scaffolds can be visualized by the fluorescent imaging technique, simultaneously. Due to the specific recognition of polyvalent scaffolds with bacteria, the photothermal agent IR780 loaded PATC-GlcN shows the targeted killing ability toward E. coli ATCC8739 in vitro and in vivo under NIR radiation.

In Situ Visualization of Reversible Diels-Alder Reactions with Self-Reporting Aggregation-Induced Emission Luminogens

The dynamic reversible Diels-Alder (DA) reactions play essential roles in both academic and applied fields. Currently, in situ visualization and direct monitoring of the formation and cleavage of covalent bonds in DA reactions are hampered by finite compatibility and expensive precise instruments, especially limited in solid reactions. We herein report a fluorescence system capable of in situ visualization by naked eyes and monitoring DA/retro-DA reactions. With the fluorescence quenching effect, the synthesized TPEMI could work as an innovative self-indicator for both DA termination and retro-DA occurrence. The fluorescence increases during DA reactions, and the mechanism is investigated to establish qualitative and quantitative relations. Besides rapid screening of reaction conditions and monitoring of DA exchange processes, the TPEMI fluorescence system can visualize heterogeneous and solid-state reactions with the AIE character. The TPEMI platform is expected to offer novel insights into reversible DA processes and dynamic covalent chemistry.

Dark to bright fluorescence state by inter-connecting fluorophores: concentration-dependent blue to NIR emission and live cell imaging applications

Interconnected AIEgens produced concentration dependent tunable emission from blue to NIR.

Mechanochemical synthesis of an AIE-TICT-ESIPT active orange-emissive chemodosimeter for selective detection of hydrogen peroxide in aqueous media and living cells, and solid-phase quantitation using a smartphone

We report herein the design and mechanochemical synthesis of a chemodosimeter, benzothiazole-derived unsymmetrical azine protected by 4-bromomethylphenylboronic acid (BTPAB), an orange aggregation-induced emission (AIE), for the selective detection of H2O2 in a turn-on manner.

An aggregation-induced emission-active bis-heteroleptic ruthenium(ii) complex of thiophenyl substituted phenanthroline for the selective “turn-off” detection of picric acid

A bis-heteroleptic Ru(ii) polypyridine complex-based AIEgen has been developed for the selective detection of nitroaromatic explosive picric acid in aqueous media.

Tunning Intermolecular Interaction of Peptide-Conjugated AIEgen in Nano-Confined Space for Quantitative Detection of Tumor Marker Secreted from Cells

Determining the expression level of biomarkers is crucial for disease diagnosis. However, the low abundance of biomarkers in the early stage makes the detection extremely difficult by traditional aggregation-induced emission (AIE)-based fluorescent probes. Here, by tuning the intermolecular interaction, a two steps-based MP/NPs-SLIPS sensing system is designed for ultrasensitive detection of the tumor marker matrix metalloproteinase-2 (MMP-2). During the sensing process, aggregation of AIE residual could be intensified through the electrostatic absorption by negatively charged nanoparticles (NPs), as well as the confined space formed by the self-assembly of NPs to photonic crystals (PCs) on slippery lubricant-infused porous substrates (SLIPS). The fluorescent signals obviously increased with a strengthened aggregation degree, which contributes to improved sensitivity. Thus, the limit of detection is decreased to 3.7 ng/mL for MP/NPs-SLIPS sensing system, which could be used for detecting the MMP-2 secreted by tumor cells directly. This strategy also demonstrated its potential applications as high-throughput detection devices and will be of significance for the ultrasensitive analysis of biomarkers.

Aggregation-Induced Emission Luminogens with Photoresponsive Behaviors for Biomedical Applications

Fluorescent biomedical materials can visualize subcellular structures and therapy processes in vivo. The aggregation-induced emission (AIE) phenomenon helps suppress the quenching effect in the aggregated state suffered by conventional fluorescent materials, thereby contributing to design strategies for fluorescent biomedical materials. Photoresponsive biomedical materials have attracted attention because of the inherent advantages of light; i.e., remote control, high spatial and temporal resolution, and environmentally friendly characteristics, and their combination with AIE facilitates development of fluorescent molecules with efficient photochemical reactions upon light irradiation. In this review, organic compounds with AIE features for biomedical applications and design strategies for photoresponsive AIE luminogens (AIEgens) are first summarized briefly. Applications are then reviewed, with the employment of photoresponsive and AIE-active molecules for photoactivation imaging, super-resolution imaging, light-induced drug delivery, photodynamic therapy with photochromic behavior, and bacterial targeting and killing being discussed at length. Finally, the future outlook for AIEgens is considered with the aim of stimulating innovative work for further development of this field.

Practicable Applications of Aggregation-Induced Emission with Biomedical Perspective

Considerable efforts have been made into developing aggregation-induced emission fluorogens (AIEgens)-containing nano-therapeutic systems due to the excellent properties of AIEgens. Compared to other fluorescent molecules, AIEgens have advantages including low background, high signal-to-noise ratio, good sensitivity, and resistance to photobleaching, in addition to being exempt from concentration quenching or aggregation-caused quenching effects. The present review outlines the major developments in the biomedical applications of AIEgens-containing systems. From a literature survey, the recent AIE works are reviewed and the reasons why AIEgens are chosen in various biomedical applications are highlighted. The research activities on AIEgens-containing systems are increasing rapidly, therefore, the present review is timely.

Fundamentals and exploration of aggregation-induced emission molecules for amyloid protein aggregation

The past decade has witnessed the growing interest and advances in aggregation-induced emission (AIE) molecules as driven by their unique fluorescence/optical properties in particular sensing applications including biomolecule sensing/detection, environmental/health monitoring, cell imaging/tracking, and disease analysis/diagnosis. In sharp contrast to conventional aggregation-caused quenching (ACQ) fluorophores, AIE molecules possess intrinsic advantages for the study of disease-related protein aggregates, but such studies are still at an infant stage with much less scientific exploration. This outlook mainly aims to provide the first systematic summary of AIE-based molecules for amyloid protein aggregates associated with neurodegenerative diseases. Despite a limited number of studies on AIE-amyloid systems, we will survey recent and important developments of AIE molecules for different amyloid protein aggregates of Aβ (associated with Alzheimer's disease), insulin (associated with type 2 diabetes), (α-syn, associated with Parkinson's disease), and HEWL (associated with familial lysozyme systemic amyloidosis) with a particular focus on the working principle and structural design of four types of AIE-based molecules. Finally, we will provide our views on current challenges and future directions in this emerging area. Our goal is to inspire more researchers and investment in this emerging but less explored subject, so as to advance our fundamental understanding and practical design/usages of AIE molecules for disease-related protein aggregates.

Anti-cancer adjuvant drug screening via epithelial-mesenchymal transition-related aptamer probe

Epithelial-mesenchymal transition (EMT) is implicated in the pathological processes of cancer metastasis and drug resistance. Anti-cancer drugs may also potentially lead to EMT, resulting in their reduced therapeutic effect. Therefore, the combination of these anti-cancer drugs with anti-EMT agents has been promoted in clinic. Screening anti-EMT drugs and evaluation of EMT process are highly dependent on EMT biomarkers on cell membrane. At present, the detection of EMT biomarker is mainly by Western blot method, which is time-consuming and complicated. In this work, for effectively screening anti-EMT drugs by evaluation of the EMT process, a type of aptamer probe based on aggregation-induced emission (AIE) was designed. The aptamer SYL3C was employed to target the EMT biomarker EpCAM on cell membrane. Two fluorophores, FAM and tetraphenylethene (TPE, an AIE dye), were modified at the two ends of SYL3C, respectively. This aptamer probe (TPE-SYL3C-FAM) can monitor the EpCAM expression, which can be recovered by anti-EMT drugs. By observation of the change in TPE emission intensity, the anti-EMT effect of drugs can be evaluated. The FAM emission was used as internal reference to reduce environmental interferences. This probe can be potentially used to screen anti-EMT agents as anti-cancer adjuvant drugs with high throughput.

Second near-infrared (NIR-II) imaging: a novel diagnostic technique for brain diseases

Imaging in the second near-infrared II (NIR-II) window, a kind of biomedical imaging technology with characteristics of high sensitivity, high resolution, and real-time imaging, is commonly used in the diagnosis of brain diseases. Compared with the conventional visible light (400-750 nm) and NIR-I (750-900 nm) imaging, the NIR-II has a longer wavelength of 1000-1700 nm. Notably, the superiorities of NIR-II can minimize the light scattering and autofluorescence of biological tissue with the depth of brain tissue penetration up to 7.4 mm. Herein, we summarized the main principles of NIR-II in animal models of traumatic brain injury, cerebrovascular visualization, brain tumor, inflammation, and stroke. Simultaneously, we encapsulated the in vivo process of NIR-II probes and their in vivo and in vitro toxic effects. We further dissected its limitations and following optimization measures.

3D-Printed, Portable, Fluorescent-Sensing Platform for Smartphone-Capable Detection of Organophosphorus Residue Using Reaction-Based Aggregation Induced Emission Luminogens

Development of an easy-to-use, low-cost, household device can help the consumer quickly identify an organophosphorus (OP) residue concentration level. In this work, we demonstrate a 3D-printed, portable, fluorescent-sensing platform for smartphone-capable detection of OPs in vegetables. For development of the proposed device, we utilize the smartphone for capturing the strong thiol-activated fluorescence, which was produced by hydrolysis of OPs in the presence of alkali. The thiol-responsive AIEgen (maleimide-functionalized tetraphenylethylene) was non-emissive in both solution and the solid state but could be readily lighted up by the click addition of thiol to its MI pendant. An android application "Detection" has been developed on the basis of the gray value to analyze the different concentration levels of OPs in vegetable samples. The gray value was linearly related with the concentration of five kinds of organophosphorus residue, ranging from 0 to 20 μg/mL. It was also applied for determination of OPs residue in the leaves of cowpea, celery, and Chinese cabbage. Different from acetylcholinesterase enzyme-based sensors for poor stability under high temperature, the proposed method was a direct detection method for OPs and can be used for rapid monitoring of OPs residue concentration levels before LC-MS analysis.

Rational design of pyrrole derivatives with aggregation-induced phosphorescence characteristics for time-resolved and two-photon luminescence imaging

Pure organic room-temperature phosphorescent (RTP) materials have been suggested to be promising bioimaging materials due to their good biocompatibility and long emission lifetime. Herein, we report a class of RTP materials. These materials are developed through the simple introduction of an aromatic carbonyl to a tetraphenylpyrrole molecule and also exhibit aggregation-induced emission (AIE) properties. These molecules show non-emission in solution and purely phosphorescent emission in the aggregated state, which are desirable properties for biological imaging. Highly crystalline nanoparticles can be easily fabricated with a long emission lifetime (20 μs), which eliminate background fluorescence interference from cells and tissues. The prepared nanoparticles demonstrate two-photon absorption characteristics and can be excited by near infrared (NIR) light, making them promising materials for deep-tissue optical imaging. This integrated aggregation-induced phosphorescence (AIP) strategy diversifies the existing pool of bioimaging agents to inspire the development of bioprobes in the future.

An effective fluorescent sensor for ClO- in aqueous media based on thiophene-cyanostilbene Schiff-base

Although some reports on sensing ClO^- had been presented, the ClO^- sensor with high selectivity and sensitivity in aqueous media was still expected. Herein, an effective fluorescent sensor for ClO^- in aqueous media was designed and synthesized by simple procedure based on cyanostilbene derivative (TCS). TCS exhibited strong fluorescence in aqueous media, which could be selectively quenched by ClO^- among various species. The detection limit was as low as 3.2 × 10^-8 M. The sensing mechanism of the oxidation of sulfur in thiophene unit was confirmed by the FT-IR spectrum, fluorescence Job's plot, ¹H NMR spectrum and MS spectrum. This sensor was successfully applied on detecting ClO^- in real sample and living-cell imaging, suggesting its potential application for sensing ClO^- in both vitro assay and vivo environment.

Aggregation induced emission (AIE) materials for mitochondria imaging

Mitochondria are energy producing organelle of the eukaryotic cells. The main activities of mitochondria monitored by various marker molecules are autophagy detection, estimation of Reactive Oxygen Species (ROS), mitochondrial death and Photodynamic therapy in cancer cells. Due to the advantages of specificity and sensitivity, aggregation induced emission (AIE) is now popular for the mitochondria labeling. In this chapter, we would like to discuss three major types of AIEgens probe used in mitochondrial staining. There are three different types of AIEgens available for mitochondrial detection and sensing based on their different structural motifs. The first type of AIEgens is tetraphenylethene (TPE) based molecules. Due to simple engineering architecture, TPE based AIEgens are widely employed in bioimaging applications. AIEgen such as triphenylphosphine (TPP), and triphenylamine (TPA) are also employed as a novel building block. These are successfully used as exceptional lipid droplet (LD)-specific bio probes in cell imaging, assurance of cell combination, and photodynamic cancer cell removal. The third group is the miscellaneous AIEgens probe involved in mitochondria imaging.

Fluorogenic Biosensors Constructed via Aggregation-Induced Emission based on Enzyme-Catalyzed Coupling Reactions for Detection of Hydrogen Peroxide

Hydrogen peroxide (H2O2) is a main reactive oxygen by-product produced in the metabolism of organisms and a common biomarker of oxidative stress. Aggregation-induced emission (AIE) probes for H2O2 have been proposed. Such AIEgens mostly use benzeneboronic acid as a recognition group. Recently, a strategy involving enzyme-catalyzed polymerization of AIE compounds shows great potential in AIEgens design. We herein modify the AIE motif, tetraphenylethene (TPE) with o-phenylenediamine (TPE-TAF), which can be oxidated by H2O2 in HRP to form an intramolecular phenazine structure. Compared with a similar approach, the proposed strategy is simple and the TPE-TAF showed a sensitive "turn-on" fluorescence with H2O2. The detection limit (LOD) is 3.39 μM and the probe is highly specific against H2O2. We further verified the reaction mechanism of the enzyme-catalyzed coupling reaction. The probe is a promising candidate as a stable and safe fluorescent substrate in H2O2 sensing.

Imaging, Identification and Inhibition of Microorganisms Using AIEgens

Microorganisms, including bacteria, viruses and fungi, are ubiquitous in nature. Some are extremely beneficial to life on Earth, whereas some cause diseases and disrupt normal human physiology. Pathogenic microorganisms can also undergo mutations and develop resistance to antimicrobial agents, which complicates diagnostic and therapeutic regimens. This calls for continuing efforts to develop new strategies and tools that can provide fast, sensitive and accurate diagnosis, as well as effective treatment of ever-evolving infectious diseases. Aggregation-induced emission luminogens (AIEgens) have shown promise in imaging, identification and inhibition of various microbial species. Compared to conventional organic fluorophores, AIEgens can offer improved photostability, and have found utilities in imaging microorganisms. AIEgens have been shown to detect microbial viability and differentiate among different microbial strains. Theranostic AIEgens that integrate imaging and killing of microbes have also been developed. This review highlights examples in the literature where AIEgens have been employed as molecular probes in the imaging, discrimination and killing of bacteria, viruses and fungi.

Aggregation-induced fluorescence probe for hypochlorite imaging in mitochondria of living cells and zebrafish

Hypochlorite is an important active oxygen species formed in living organisms, and rapid and highly sensitive detection of trace hypochlorite is of great significance for understanding the mechanism of diseases caused by abnormal hypochlorite concentrations at an early stage. Although aggregation-induced emission (AIE) probes are highly important for analyte de-tection in living organisms, there is a lack of AIE probes for hypochlorite detection. In this study, two AIE probes based on benzothiazole derivatives (BTD-1 and BTD-2) were designed and synthesized. Both probes exhibited good AIE charac-teristics and allowed different visual detection for hypochlorite. Additionally, the two probes could be used to detect endogenous hypochlorite in mitochondria and were successfully applied for in vivo hypochlorite imaging in zebrafish.