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

Double-detecting fluorescent sensor for ATP based on Cu2+ and Zn2+ response of hydrazono-bis-tetraphenylethylene

Although all kinds of sensors with unique detecting ability for one guest were reported, the fluorescence sensor with multiple detecting abilities was seldom presented. This work designed and synthesized a novel AIE fluorescence probe bearing double detecting for ATP based on Cu²⁺ and Zn²⁺ response of hydrazono-bis-tetraphenylethylene (Bis-TPE). Bis-TPE was prepared in 82% yield with simple procedure. It exhibited strong red AIE fluorescence based on the large conjugated electron effect in aqueous media. It showed outstanding selective sensing abilities for Cu²⁺ by strong fluorescence quenching and for Zn²⁺ by red-orange fluorescence change. The sensing mechanism of 1:1 stoichiometric ratios was confirmed by ¹H NMR and MS study. The strong red fluorescence of Bis-TPE + Cu²⁺ system could be recovered by adding ATP. The orange fluorescence of Bis-TPE + Zn²⁺ system could be quenched by adding Cu²⁺ and then was recovered by adding ATP. These double detecting abilities for ATP with the "off-on" red fluorescence in Bis-TPE + Cu²⁺ system and "allochroic-off-on" orange fluorescence in Bis-TPE + Zn²⁺+Cu²⁺ system were successfully applied to test Cu²⁺, Zn²⁺ and ATP in test paper and living cell imaging, displaying the good application prospects for sensing Cu²⁺, Zn²⁺ and double detecting ATP in the complicated environment.

Deep-Red Fluorescent Organic Nanoparticles with High Brightness and Photostability for Super-Resolution in Vitro and in Vivo Imaging Using STED Nanoscopy

To achieve super-resolution imaging in biological research using stimulated emission depletion (STED) nanoscopy, organic luminescent materials and their corresponding fluorescent nanoparticles with high brightness and photostability are of great significance. Herein, donor-acceptor-typed DBTBT-4C8 bearing flexible alkyl chains was developed, not only to afford deep-red emission from 600 to 800 nm but also to obtain high fluorescent brightness with the absolute photoluminescence quantum yields of 25%. After that, well-defined and monodispersed spherical nanoparticles using DBTBT-4C8 with bright emission, excellent biocompatibility, and photostability, which can easily mix with amphipathic block polymers, were then produced for super-resolution in vitro and in vivo imaging using STED nanoscopy. The observations showed that in contrast to confocal microscopy with a full width at half-maximum (FWHM) value of ≈400 nm, superior resolution with a significantly improved FWHM value of only 100 nm was achieved in biomedical cell imaging, which was also used to reconstruct three-dimensional images of stained HeLa cells at an ultrahigh resolution. More importantly, by using the prepared fluorescent organic nanoparticles (FONPs) in STED nanoscopy, in vivo imaging in glass catfish with largely enhanced resolution was also successfully achieved, demonstrating that these developed deep-red FONPs here are highly suitable for super-resolution in vitro and in vivo imaging using STED nanoscopy.

In vivo monitoring of tissue regeneration using a ratiometric lysosomal AIE probe

Tissue regeneration is a crucial self-renewal capability involving many complex biological processes. Although transgenic techniques and fluorescence immunohistochemical staining have promoted our understanding of tissue regeneration, simultaneous quantification and visualization of tissue regeneration processes is not easy to achieve. Herein, we developed a simple and quantitative method for the real-time and non-invasive observation of the process of tissue regeneration. The synthesized ratiometric aggregation-induced-emission (AIE) probe exhibits high selectivity and reversibility for pH responses, good ability to map lysosomal pH both in vitro and in vivo, good biocompatibility and excellent photostability. The caudal fin regeneration of a fish model (medaka larvae) was monitored by tracking the lysosomal pH change. It was found that the mean lysosomal pH is reduced during 24-48 hpa to promote the autophagic activity for cell debris degradation. Our research can quantify the changes in mean lysosomal pH and also exhibit its distribution during the caudal fin regeneration. We believe that the AIE-active lysosomal pH probe can also be potentially used for long-term tracking of various lysosome-involved biological processes, such as tracking the stress responses of tissue, tracking the inflammatory responses, and so on.

Pyrrole-quinazoline derivative as an easily accessible turn-off optical chemosensor for Cu2+ and resultant Cu2+ complex as a turn-on sensor for pyrophosphate in almost neat aqueous solution

A simple chemosensor, 6-(1H-pyrrol-2-yl)-5,6-dihydro-benzo[4,5]imidazo[1,2-c]quinazoline (1), was synthesized via simple nucleophilic addition reaction coupled with Schiff base condensation. The probe 1 is aggregation-induced emission-active and could be used as an on-off fluorescence sensor toward Cu²⁺ in H₂O/CH₃CN (99.5%, v/v) solution. Furthermore, the resultant Cu²⁺ complex selectively responded to pyrophosphate (PPi) among various anions based on fluorescent on-off signal. In addition, the probe could be used for detecting Cu²⁺ and PPi in HeLa cells.

Molecular Engineered Squaraine Nanoprobe for NIR-II/Photoacoustic Imaging and Photothermal Therapy of Metastatic Breast Cancer

Various squaraine dyes have been developed for biological imaging. Nevertheless, squaraine dyes with emission in the second window (NIR-II, 1000-1700 nm) have few reports largely due to the short of a simple and universal design strategy. In this contribution, molecular engineering strategy is explored to develop squaraine dyes with NIR-II emission. First, NIR-I squaraine dye SQ2 is constructed by the ethyl-grafted 1,8-naphtholactam as donor units and square acid as acceptor unit in a donor-acceptor-donor (D-A-D) structure. To red-shift the fluorescence emission into NIR-II window, malonitrile, as a forceful electron-withdrawing group, is introduced to strengthen square acid acceptor. As a result, the fluorescence spectrum of acceptor-engineered squaraine dye SQ1 exhibits a significant red-shift into NIR-II window. To translate NIR-II fluorophores SQ1 into effective theranostic agents, fibronectin-targeting SQ1 nanoprobe was constructed and showed excellent NIR-II imaging performance in angiography and tumor imaging, including lung metastatic foci in deep tissue. Furthermore, SQ1 nanoprobe can be used for photoacoustic imaging and photothermal ablation of tumors. This research demonstrates that the donor-acceptor engineering strategy is feasible and effective to develop NIR-II squaraine dyes.

AIE-active non-conjugated poly(N-vinylcaprolactam) as a fluorescent thermometer for intracellular temperature imaging

Since temperature is one of the most significant physiological parameters that dictate the cellular status of living organisms, accurate intracellular temperature measurement is crucial and a valuable biomarker for the diagnosis and treatment of diseases. Herein, we introduce the foremost example of a non-conjugated polymer as a next generation fluorescent thermometer which is capable of addressing the key shortcomings including toxicity and thermal-induced fluorescence quenching associated with π-π conjugated system-based thermometers developed so far. We revealed, for the first time, the unique photophysical and aggregation-induced emission (AIE) characteristics of well-known thermoresponsive poly(N-vinylcaprolactam) (PNVCL) devoid of any classical fluorophore entity. PNVCL underwent a coil to globular conformational transition in an aqueous medium and appeared to be fluorescent above its lower critical solution temperature (LCST) near body temperature (38 °C). Eventually, this intriguing aspect enabled higher cellular uptake of PNVCL at the LCST boundary. By virtue of the AIE effect, the thermo-induced aggregation phenomenon has been ingeniously utilized to apply PNVCL as a novel fluorescent thermometer for intracellular temperature determination.

Mitochondria-targeted aggregation-induced emission active near infrared fluorescent probe for real-time imaging

Mitochondria are essential organelles in eukaryotic cells and act as the energy powerhouse and biosynthetic compartment. Fluorescent dyes are widely used powerful molecular tools for analytical sensing and optical imaging. Low photostability, short excitation and emission wavelengths, and aggregation-induced quenching effects restrict the application of traditional commercial mitochondrial fluorescent probes for bioimaging. In this study, using rhodamine as the acceptor and phenothiazine as the donor, we synthesized a novel mitochondrial-targeted near infrared (NIR) fluorescent probe, MIT-PZR. Due to low cytotoxicity, great photostability and high specificity for mitochondria targeting, MIT-PZR has enormous potential for cell imaging. Furthermore, with a sizeable Stokes shift (emission peak at 705 nm), MIT-PZR penetrated tissues providing stable red fluorescence for imaging in vivo. The histological assessment of various tissues after treatment with MIT-PZR indicated that it has good biocompatibility. Thus, MIT-PZR is a promising mitochondrial NIR fluorescent probe for future application in clinical diagnosis and modern biological research.

Rational design of a colorimetric and fluorescence turn-on chemosensor with benzothiazolium moiety for cyanide detection in aqueous solution

A novel colorimetric and fluorescence turn-on chemosensor TBB with benzothiazolium moiety has been explored, which exhibited the high selectivity for cyanide ion (CN^-) in THF-H₂O (2:8, v/v) mixture. The aqueous solution of sensor TBB was scarcely emissive. In the presence of CN^- ion, the nucleophilic addition of CN^- with the benzothiazolium CN bond of TBB produced the new species TBB-CN, consequently resulting in the intense orange-red emission by aggregation-induced emission (AIE) effect. Meanwhile, the color of solution was changed from orange-yellow to light yellow. The sensing mechanism was verified by Mass spectrometry, NMR analysis and DFT calculations.

Zirconium doping level modulation combined with chalconylthiourea organic frameworks induced enhancement of luminescence applied to cell imaging

Derivatives of a zirconium metal–organic framework as the center polymer material with a chalconylthiourea polymer (CT) were applied to cell imaging.

Modular Design of Peptide- or DNA-Modified AIEgen Probes for Biosensing Applications

Fluorophore probes are widely used for bioimaging in cells, tissues, and animals as well as for monitoring of multiple biological processes in complex environments. Such imaging properties allow scientists to make direct visualizations of pathological events and cellular targets. Conventional fluorescent molecules have been developed for several decades and achieved great successes, but their emissions are often weakened or quenched at high concentrations that might suffer from the aggregation-caused quenching (ACQ) effect, which reduces the efficiencies of their applications. In contrast to the ACQ effect, aggregation-induced emission (AIE) luminogens (AIEgens) display much higher fluorescence in aggregated states and possess various advantages such as low background, long-term tracking ability, and strong resistance to photobleaching. Therefore, AIEgens are employed as unique fluorescence molecules and building blocks for biosensing applications in the fields of ions, amino acids, carbohydrates, DNAs/RNAs, peptides/proteins, cellular organelles, cancer cells, bacteria, and so on. Quite a few of the above biosensing missions are accomplished by modular peptide-modified AIEgen probes (MPAPs) or modular DNA-modified AIEgen probes (MDAPs) because of the multiple capabilities of peptide and DNA modules, including solubility, biocompatibility, and recognition. Meanwhile, both electrostatic interactions and coupling reactions could provide efficient methods to construct different MPAPs and MDAPs, finally resulting in a large variety of biosensing probes. Those probes exhibit leading features of detecting nucleic acids or proteins and imaging mass biomolecules. For example, under modular design, peptide modules possessing versatile recognition abilities enable MPAPs to detect numerous targets, such as integrin α_vβ₃, aminopeptidase N, MMP-2, MPO, H₂O₂, and so forth; MDAP could allow the imaging of mRNA in cells and tissue chips, suggesting the diagnostic functions of MDAP in clinical samples. Modular design offers a novel strategy to generate AIEgen-based probes and expedites functional biomacromolecules research. In this vein, here we review the progress on MPAPs and MDAPs in the most recent 10 years and highlight the modular design strategy as well as their advanced biosensing applications including briefly two aspects: (1) detection and (2) imaging. By the use of MPAPs/MDAPs, multiple bioanalytes can be efficiently analyzed at low concentrations and directly visualized through high-contrast and luminous imaging. Compared with MPAPs, the quantities of MDAPs are limited because of the difficult synthesis of long-length DNA strands. In future work, multifunctional of DNA sequences are needed to explore varieties of MDAPs for diverse biosensing purposes. At the end of this Account, some deficiencies and challenges are mentioned for briging more attention to accelerate the development of AIEgen-based probes.

Tetrathienylethene-based Positional Isomers with Aggregation-induced Emission Enabling Super Red-shifted Reversible Mechanochromism and Naked-eye Sensing of Hydrazine Vapor

AIE-active positional isomers, TTE-o-PhCHO, TTE-m-PhCHO and TTE-p-PhCHO, tetrathienylethene (TTE) derivates with peripherally attached ortho-/meta-/para-formyl phenyl groups, were designed and synthesized. The formyl substitution position can effectively modulate their photophysical properties, mechanochromism and fluorescent response to hydrazine. TTE-o-PhCHO and TTE-m-PhCHO exhibit remarkable AIE characteristics, and TTE-p-PhCHO possesses aggregation-induced emission enhancement performance. They all exhibit high contrast mechanochromism, and TTE-m-PhCHO shows larger red-shift (164 nm) than TTE-o-PhCHO (104 nm) and TTE-p-PhCHO (125 nm) due to the more twisted molecular conformation and much looser molecular packing. Moreover, TTE-o-PhCHO with a higher contrast color change can be used as ink-free rewritable paper. In addition, TTE-p-PhCHO, as a turn-on fluorescent probe, can selectively detect hydrazine with significant color changes that are visible by the naked eye . Therefore, the position dependence of groups would be an effective method to modulate the molecular arrangement, as well as develop AIE compounds for mechano-stimuli responsive materials, ink-free rewritable papers and chemosensors.

Glutathione-Priming Nanoreactors Enable Fluorophore Core/Shell Transition for Precision Cancer Imaging

In an attempt to develop an imaging probe with ultra-high sensitivity for a broad range of tumors in vivo and inspired by the concept of chemical synthetic nanoreactors, we designed a type of glutathione-priming fluorescent nanoreactor (GPN) with an albumin-coating shell and hydrophobic polymer core containing disulfide bonds, protonatable blocks, and indocyanine green (ICG), a near-infrared fluorophore. The albumin played multiple roles including biocompatible carriers, hydrophilic stabilizer, "receptor" of the fluorophores, and even targeting molecules. The protonation of the hydrophobic core triggered the outside-to-core transport of acidic glutathione (GSH), as well as the core-to-shell transference of ICGs after the disulfide bond cleavage by GSH, which induced strong binding of fluorophores with albumins on the GPN shell, initiating intensive fluorescence signals. As a result, the GPNs demonstrated extremely high response sensitivity and imaging contrast, proper time window, and broad cancer specificity. In fact, an orthogonal activation pattern was found in vitro with an ON/OFF ratio up to 24.7-fold. Furthermore, the nanoprobes specifically amplified the tumor signals in five cancer-bearing mouse models and actualized tumor margin delineation with a contrast up to 20-fold, demonstrating much better imaging efficacy than the other four commercially available probes. Therefore, the GPNs provide a new paradigm in developing high-performance bioresponsive nanoprobes.

Aggregation-Induced Emission Luminogens for Activity-Based Sensing

Fluorescent sensing has emerged as a powerful tool for detecting various analytes and visualizing numerous biological processes by virtue of its superb sensitivity, rapidness, excellent temporal resolution, easy operation, and low cost. Of particular interest is activity-based sensing (ABS), a burgeoning sensing approach that is actualized on the basis of dynamic molecular reactivity rather than conventional lock-and-key molecular recognition. ABS has been recognized to possess some distinct advantages, such as high specificity, extraordinary sensitivity, and accurate signal outputs. A majority of ABS sensors are constructed by modifying conventional fluorogens, which are strongly emissive when molecularly dissolved in solvents but experience emission quenching upon aggregate formation or concentration increase. The aggregation-caused quenching (ACQ) phenomenon leads to a limited amount of labeling of the analyte with the sensor and low photobleaching resistance, which could impede practical applications of the ABS protocol. As an anti-ACQ phenomenon, aggregation-induced emission (AIE) provides a straightforward solution to the ACQ problem. Thanks to their intrinsic advantages, including high photobleaching threshold, high signal-to-noise ratio, fluorescence turn-on nature, and large Stokes shift, AIE-active luminogens (AIEgens) represent a class of extraordinary fluorogen alternatives for the ABS protocol. The use of AIEgen-involved ABS can integrate the advantages of AIEgens and ABS, and additionally, the AIE process offers some unique properties to the ABS approach. For instance, in some cases of water-soluble AIEgen-involved ABS, chemical reaction not only leads to a chang in the emission color of the AIEgens but also causes solubility variations, which could result in specific "light-up" signaling. In this Account, the basic concepts and mechanistic insights of the ABS approach involving the AIE principle are briefly summarized, and then we highlight the new breakthroughs, seminal studies, and trends in the area that have been most recently reported by our group. This emerging sensing protocol has been successfully utilized for detecting an array of targets including ions, small molecules, biomacromolecules, and microenvironments, all of which closely relate to human health, medical, and public concerns. These detections are smoothly achieved on the basis of various reactions (e.g., hydrolysis, boronate cleavage, dephosphorylation, addition, cyclization, and rearrangement reactions) through different sensing principles. In these studies, the AIEgen-involved ABS strategy generally shows good biocompatibility, high selectivity, excellent reliability and high signal contrast, strongly indicating its great potential for high-tech innovations in the sensing field, among which bioprobing is of particular interest. With this Account, we hope to spark new ideas and inspire new endeavors in this emerging research area, further promoting state-of-the-art developments in the field of sensing.

Hybrid Azo-fluorophore Organic Nanoparticles as Emissive Turn-on Probes for Cellular Endocytosis

The development of fluorescent organic nanoparticles, serving as bioimaging agents or drug cargos, represents a buoyant field of investigations. Nevertheless, their ulterior fate and structural integrity after cell uptake remain elusive. Toward this aim, we have elaborated original photoactive organic nanoparticles (d_TEM ∼ 35-50 nm wide) with an off-on signal upon cellular internalization. Such nanoparticles are based on the noncovalent association of red-emitting benzothiadiazole (BDZ) derivatives and azo dyes, acting as fluorescence quenchers. Upon varying the azo/BDZ ratio, we found that quantitative emission quenching could be obtained with only a 0.2:1 azo/BDZ ratio and originated from exergonic oxidative and reductive photoinduced electron transfer from the azo units (Δ_elG⁰ = -0.21 and -0.29 eV, respectively). Such results revisited the origin of emission quenching, often confusedly ascribed to Förster resonance energy transfer. A nonlinear and sharp drop of the emission intensity with the increase in the azo unit density n was observed and presents comparable evolution to a n^-1/3 mathematical law. Thorough biological examinations involving cancer cells prove a receptor-independent endocytosis pathway, leading to progressive cell lighting upon nanoparticle accumulation in the late endosomal/lysosomal compartments. Complete emission recovery of the initially quenched azo/BDZ nanosystems could be achieved by using mefloquine, which caused endosomal/lysosomal disruption, and release of their content in the cytoplasm. Such results demonstrate that the dotlike emission from endosomes actually stems from fully dissociated individual dyes and not integer nanoparticles. They conclude on the high spatial confinement promoted by organelles and finally question its severe impact on functional compounds or nanoparticles whose properties are strongly distance dependent.

Fluorescent fibrous mats assembled with self-propagating probes for visual sensing of hydrogen peroxide and choline

Challenges remain in the facile, rapid and sensitive detection of substances at ultralow levels. In the current study, visual sensors of hydrogen peroxide (H2O2) and choline are developed via the integration of an ultrafine fibrous substrate and self-propagating and aggregation-induced emission (AIE) probes. Self-immolative probes (SIPs) composed of phenylboronic acid triggers and choline units are grafted on electrospun polyethylene terephthalate (PET) fibers, followed by electrostatic adsorption of tetraphenylethene derivatives (TPE-SO3) to obtain fluorescent PET-Ch/TPE fibers. Choline oxidase (ChOX) is immobilized on polystyrene-co-maleic anhydride (PSMA) fibers to obtain PSMA-ChOX, followed by assembly into PET-Ch/TPE@PSMA-ChOX composite mats. The presence of H2O2 initiates the cleavage of phenylboronic acid triggers in SIPs to release choline and choline/TPE complexes from PET-Ch/TPE fibers. The released choline is oxidized by PSMA-ChOX fibers to generate H2O2 that then activates a cascade of self-propagating reactions until the release of all choline/TPE complexes, leading to the alleviation of AIE effect and gradual fluorescence fading of fibrous mats. Thus, the hydrogen peroxide and choline concentrations can be read out from the fluorescence fading time of fibrous mats with a detection limit of 0.5 μM H2O2 within 30 min, providing potential self-test devices for a real-time, naked-eye and sensitive detection of bioactive substances.

Rejuvenated Photodynamic Therapy for Bacterial Infections

The emergence of multidrug resistant bacterial strains has hastened the exploration of advanced microbicides and antibacterial techniques. Photodynamic antibacterial therapy (PDAT), an old-fashioned technique, has been rejuvenated to combat "superbugs" and biofilm-associated infections owing to its excellent characteristics of noninvasiveness and broad antibacterial spectrum. More importantly, bacteria are less likely to produce drug resistance to PDAT because it does not require specific targeting interaction between photosensitizers (PSs) and bacteria. This review mainly focuses on recent developments and future prospects of PDAT. The mechanisms of PDAT against bacteria and biofilms are briefly introduced. In addition to classical macrocyclic PSs, several innovative PSs, including non-self-quenching PSs, conjugated polymer-based PSs, and nano-PSs, are summarized in detail. Numerous multifunctional PDAT systems such as in situ light-activated PDAT, stimuli-responsive PDAT, oxygen self-enriching enhanced PDAT, and PDAT-based multimodal therapy are highlighted to overcome the inherent defects of PDAT in vivo (e.g., limited penetration depth of light and hypoxic environment of infectious sites).

Assembly of 1H-isoindole derivatives by selective carbon-nitrogen triple bond activation: access to aggregation-induced emission fluorophores for lipid droplet imaging

A method of selectively activating carbon–nitrogen triple bonds has been developed to access 1H-isoindole AIE fluorophores for lipid droplet imaging.

A novel strategy has been established to assemble a series of single (Z)- or (E)-1H-isoindole derivatives through selectively and sequentially activating carbon–nitrogen triple bonds in a multicomponent system containing various nucleophilic and electrophilic sites. The reaction provides efficient access to structurally unique fluorophores with aggregation-induced emission characteristics. These new fluorophores show fluorescence wavelengths and efficiencies that can be modulated and have excellent potential to specifically light up lipid droplets (LDs) in living cells with bright fluorescence, low cytotoxicity and better photostability than commercially available LD-specific dyes.

Synthesis of an efficient far-red/near-infrared luminogen with AIE characteristics for in vivo bioimaging applications

A selenium-containing FR/NIR AIE luminogen with efficient solid-state emission is reported. Its AIE dots exhibit high brightness, large Stokes shift, good biocompatibility and satisfactory photostability, making them the first selenium-containing FR/NIR nanoprobes with AIE characteristics for in vivo bioimaging applications with high contrast and a high penetration depth.

Peptide-modulated self-assembly as a versatile strategy for tumor supramolecular nanotheranostics

Advances in supramolecular self-assembly have promoted the development of theranostics, the combination of both therapeutic and diagnostic functions in a single nanoplatform, which is closely associated with antitumor applications and has shown promising potential in personalized medicine. Peptide-modulated self-assembly serves as a versatile strategy for tumor supramolecular nanotheranostics possessing controllability, programmability, functionality and biosafety, thus promoting the translation of nanotheranostics from bench to bedside. In this review, we will focus on the self-assembly of peptide-photosensitizers and peptide-drugs as well as multicomponent cooperative self-assembly for the fabrication of nanotheranostics that integrate diagnosis and therapeutics for antitumor applications. Emphasis will be placed on building block design, interaction strategies and the potential relationships between their structures and properties, aiming to increase understanding of the critical role of peptide-modulated self-assembly in advancing antitumor supramolecular nanotheranostics.

Bimodal Fluorescence-Magnetic Resonance Contrast Agent for Apoptosis Imaging

Effective cancer therapy largely depends on inducing apoptosis in cancer cells via chemotherapy and/or radiation. Monitoring apoptosis in real-time provides invaluable information for evaluating cancer therapy response and screening preclinical anticancer drugs. In this work, we describe the design, synthesis, characterization, and in vitro evaluation of caspase probe 1 (CP1), a bimodal fluorescence-magnetic resonance (FL-MR) probe that exhibits simultaneous FL-MR turn-on response to caspase-3/7. Both caspases exist as inactive zymogens in normal cells but are activated during apoptosis and are unique biomarkers for this process. CP1 has three distinct components: a DOTA-Gd(III) chelate that provides the MR signal enhancement, tetraphenylethylene as the aggregation induced emission luminogen (AIEgen), and DEVD peptide which is a substrate for caspase-3/7. In response to caspase-3/7, the water-soluble peptide DEVD is cleaved and the remaining Gd(III)-AIEgen (Gad-AIE) conjugate aggregates leading to increased FL-MR signals. CP1 exhibited sensitive and selective dual FL-MR turn-on response to caspase-3/7 in vitro and was successfully tested by fluorescence imaging of apoptotic cells. Remarkably, we were able to use the FL response of CP1 to quantify the exact concentrations of inactive and active agents and accurately predict the MR signal in vitro. We have demonstrated that the aggregation-driven FL-MR probe design is a unique method for MR signal quantification. This probe design platform can be adapted for a variety of different imaging targets, opening new and exciting avenues for multimodal molecular imaging.

Rational design and synthesis of yellow-light emitting triazole fluorophores with AIE and mechanochromic properties

Previously, we reported that N-2-aryl triazoles (NATs) exhibited good fluorescence activity in the UV/blue light range. In an effort to achieve biocompetitive NAT fluorophores with green/yellow emission, a new class of 4-keto-2-(4'-N,N-diphenyl)-phenyl triazoles were designed and synthesized. Herein, we present our study on these novel fluorophores which demonstrated excellent luminescence emission both in solution (Φ up to 96%) and in the solid state (Φ up to 43%). Furthermore, these new compounds showed aggregation-induced emission (AIE) properties and reversible mechanochromic luminescence properties, which suggested their potential applications in chemical and materials science.

Photostable pH-Sensitive Near-Infrared Aggregation-Induced Emission Luminogen for Long-Term Mitochondrial Tracking

Mitochondria are crucial in the process of oxidative metabolism and apoptosis. Their morphology is greatly associated with the development of certain diseases. For specific and long-term imaging of mitochondrial morphology, we synthesized a new mitochondria-targeted near-infrared (NIR) fluorescent probe (TPE-Xan-In) by incorporating TPE with a NIR merocyanine skeleton (Xan-In). TPE-Xan-In displayed both absorption (660 nm) and emission peaks (743 nm) in the NIR region. Moreover, it showed aggregation-induced emission properties at neutral pH and specifically illuminated mitochondria with good biocompatibility, superior photostability, and high tolerance to mitochondrial membrane potential changes. With a pH-responsive unit, hydroxyl xanthene (Xan), the probe exhibited a pH-sensitive fluorescence emission in the range of pH 4.0-7.0, which indicated its potential in long-term tracking of pH and morphology changes of mitochondria in the biomedical research studies.

Aggregation-Induced Emission Luminogens with the Capability of Wide Color Tuning, Mitochondrial and Bacterial Imaging, and Photodynamic Anticancer and Antibacterial Therapy

Recently, luminogens with the aggregation-induced emission characteristic (AIEgens) have received much attention in the field of bioimaging and therapeutic applications. However, the development of AIEgens that are derived from the simple core skeleton with emission color tuning for imaging and therapy is still a formidable challenge. To address this constraint, we present a series of cationic AIEgens based on cyanopyridinium salts (CP1-CP5). The AIEgens can be facilely prepared by varying the aromatic electron donor while fixing the cyanopyridinium group as the electron acceptor within a single benzene ring. The obtained AIEgens possess wide color tunability, large Stokes shifts, and bright emission in the condensed state. Due to their good biocompatibility and cationic nature, these AIEgens can be utilized for multiple-color imaging of intracellular mitochondria as well as Gram-negative and Gram-positive bacteria. Importantly, these AIEgens exhibit remarkable structure-dependent singlet-oxygen generation ability under white light illumination (25 mW cm^-2), and CP4 was optimized to serve as an excellent photosensitizer for photodynamic anticancer and antibacterial therapy.

Aggregation-Induced Emission for Visualization in Materials Science

Fluorescent imaging techniques have attracted much attention as a powerful tool to realize the visualization of structural and morphological evolution of various materials. However, the traditional fluorescent dyes usually suffered from aggregation-caused quenching, which severely limits the visualization results. In contrast, aggregation-induced emission (AIE) molecules with high quantum yields in the condensed state showed great opportunities for imaging techniques. In this feature article, recent progresses in visualization with AIE molecules are discussed. Assembly processes including crystallization, gelation process, and dissipative assembly have been observed. To better study information obtained regarding the processes, visualization during reactions, phase transitions, and molecular motions are successfully presented. Based on these successes, AIE molecules were further applied for phase recognition, macro-dispersion evaluation, and damage detection. Finally, we also present the outlook and perspectives, in our opinion, for the development of visualization by AIE molecules.

Electroluminochromic Materials: From Molecules to Polymers

Electroluminochromism is an interesting property found in certain classes of molecules and polymers whose photoluminescence can be modulated through the application of an external electrical bias. Unlike electrochromic materials, electroluminochromic counterparts and their applications are comparatively fewer in quantity and are less established. Nonetheless, there prevails an increasing interest in this class of electro-active materials due to their potential applications in optoelectronics, such as smart-displays, and chemical and biological sensing. This review seeks to showcase the different classes of electroluminochromic materials with focus on (i) organic molecules, (ii) transition metal complexes, and (iii) organic polymers. The mechanisms and electroluminochromic performance of these classes of materials are summarized. This review should allow scientists to have a better and deeper understanding of materials design strategies and, more importantly, structure-property relationships and, thus, develops electroluminochromic materials with desired performance in the future.

Selective red-emission detection for mercuric ions in aqueous solution and cells using a fluorescent probe based on an unnatural peptide receptor

The selective ratiometric red-emission detection of Hg²⁺ions in aqueous buffered solutions and live cells is still a significant challenge.

Aggregation-induced emission and polymorphism/shape/size-dependent emission behaviours of fenamates for potential drug evaluation

Aggregation-induced emission and polymorphism/shape/size-dependent emission behaviors were found coexisting in fenamates, which provides a novel approach toward future drug evaluation.

A water-soluble AIE-gen for organic-solvent-free detection and wash-free imaging of Al3+ ions and subsequent sensing of F− ions and DNA tracking

A water-soluble TPE-based AIEgen (TPE-diBuS) was developed for organic-solvent-free detection of Al³⁺ ions and its wash-free cell imaging. The TPE-diBuS-Al ensemble was used for the detection of F⁻ ions and DNA tracking.

A review on graphene-based nanocomposites for electrochemical and fluorescent biosensors

Biosensors with high sensitivity, selectivity and a low limit of detection, reaching nano/picomolar concentrations of biomolecules, are important to the medical sciences and healthcare industry for evaluating physiological and metabolic parameters.

Tetraphenylethene decorated with disulfide-functionalized hyperbranched poly(amido amine)s as metal/organic solvent-free turn-on AIE probes for biothiol determination

Novel hyperbranched poly(amido amine)s AIE probes were developed for organic solvent-free biothiol sensing.

Positive charge-dependent cell targeted staining and DNA detection

Fluorescence probes containing pyridinium compounds and different negative ions with the applications of specific tracing of different cell organelles and DNA detection!