Aggregation-induced Emission Fluorogen Research Articles

Paper-based fluorescent sensor via aggregation induced emission fluorogen for facile and sensitive visual detection of hydrogen peroxide and glucose

Hydrogen peroxide (H2O2), an important reactive oxygen species (ROS), is related to the oxidative stress in organisms, and plays important roles in a variety of cellular activities as well. So it is of crucial importance to develop sensitive and accurate sensing strategies to detect H2O2 in biological systems. Herein, by taking advantage of the unique emission characteristics of aggregation induced emission (AIE) fluorogens, we proposed a non-enzymatic fluorescence platform for facile and sensitive detection of H2O2, both in solution state using fluorescence spectrometer and on paper-based sensor via visual inspection. Through the reaction between L-cysteine and H2O2, the fluorescence of TPE-M-L, an AIE fluorogen formed between maleimide-functionalized tetraphenylethene (TPE-M) and L-cysteine, is quenched, and highly sensitive non-enzymatic H2O2 assay is readily carried out. The limit of detection (LOD) of 10nM in solution state and 2.5μM on paper-based sensor were obtained for H2O2 detection, which were superior or comparable to those previously reported in literature. Moreover, by integrating glucose oxidase with the AIE fluorogen of TPE-M-L, highly sensitive and selective glucose detection was also conveniently achieved both in solution state and on paper-based sensor by the as-proposed strategy, with the LODs of 50nM in solution state and 10μM via visual observation, much better than those obtained by other fluorescence methods. The as-proposed sensing strategy was also successfully applied to assay glucose in human serum samples. Therefore, the paper-based fluorescence sensor exhibits the advantages of simple fabrication, high sensitivity and portability, and has great potential to be applied in on-site assay of H2O2 and glucose in real samples.

Simultaneous near-infrared and green fluorescence from single conjugated polymer dots with aggregation-induced emission fluorogen for cell imaging.

Near-infrared fluorescent probes are important and interesting for advanced biological and biomedical applications where the fluorescence technology is employed. Herein, we reported high near-infrared (NIR) fluorescent conjugated polymer dots (Pdots) of two polymers (PTPE-DTNT2 and PTPE-DTNT4) with cross-conjugated aggregation-induced emission fluorogen as the side chain. The photoluminescent quantum yields (PLQYs) of Pdots were up to 31.8% with the near-infrared emission peak of 716 nm, which is among the best values of NIR Pdots reported so far. In addition, Pdots possessed a dual-color emission feature. Thus, dual-color cellular imaging with both Pdots was demonstrated in biological applications; to the best of our knowledge, this is the first reported dual-color cellular imaging with Pdots. The NIR Pdots were also applied in in vivo cytotoxicity analysis and microangiography imaging of zebrafish. We anticipate that NIR Pdots with their dual-color feature will find broad applications in multiplexed biological and biomedical fields.

Real-time monitoring of the dissolution kinetics of silver nanoparticles and nanowires in aquatic environments using an aggregation-induced emission fluorogen.

We employed a fluorogenic Ag+ sensor, tetrazole-functionalized tetraphenylethylene derivative 1 (TEZ-TPE-1), to investigate the dissolution kinetics of AgNPs and AgNWs in aquatic environments. Real-time and quantitative monitoring of Ag+ release was achieved by using the proposed method, which agreed well with the conventional ICP-MS detection method.

Hyaluronan-based graft copolymers bearing aggregation-induced emission fluorogens.

In order to develop a technology platform based on two natural compounds from biorenewable resources, a short series of hyaluronan (HA) copolymers grafted with propargylated ferulic acid (HA–FA–Pg) were designed and synthesized to show different grafting degree values and their optical properties were characterized in comparison with reference compounds containing the same ferulate fluorophore. Interestingly, these studies revealed that the ferulate fluorophore was quite sensitive to the restriction of intramolecular motion and its introduction into the rigid HA backbone, as in HA–FA–Pg graft copolymers, led to higher photoluminescence quantum yield values than those obtained with the isolated fluorophore. Thus, the propargyl groups of HA–FA–Pg derivatives were exploited in the coupling with oleic acid through a biocompatible nona(ethylene glycol) spacer as an example of the possible applications of this technology platform. The resulting HA–FA–NEG–OA materials showed self-assembling capabilities in aqueous environment. Furthermore, HA–FA–NEG–OA derivatives have been shown to interact with phospholipid bilayers both in liposomes and living cells, retaining their fluorogenic properties and showing a high degree of cytocompatibility and for this reason they were proposed as potential biocompatible self-assembled aggregates forming new materials for biomedical applications.

Fabrication of AIE-active fluorescent polymeric nanoparticles with red emission through a facile catalyst-free amino-yne click polymerization

Fluorescent polymeric nanoparticles (FPNs) as novel probes have attracted more and more attention for biomedical applications owing to their optical properties and multifunctional potential. However, most of FPNs based on conventional organic fluorogens encounter serious aggregation-caused quenching (ACQ) effect. In this work, to overcome these problems, amphiphilic fluorescent copolymers [Poly(PEGY-PhE)] containing aggregation-induced emission (AIE) fluorogens (AIEgens) have been prepared via a facile amino-yne click polymerization under rather mild experimental conditions (catalyst-free and room temperature). The Poly(PEGY-PhE) copolymers can self-assemble into FPNs and be well dispersed in aqueous solution. Fluorescence spectra demonstrate that Poly(PEGY-PhE) FPNs possess strong red fluorescence, excellent photostability and low critical micelle concentration. The biological assays confirm that these AIE-active Poly(PEGY-PhE) FPNs possess low cytotoxicity towards L929 cells and cell dyeing performance. More importantly, this amino-yne click polymerization provides a simple strategy to prepare robust biocompatible fluorescent nanoparticles for biological imaging because of their high efficiency, mild reaction conditions and simple experimental operation procedure.

A multi-functional fluorescent probe with aggregation-induced emission characteristics: Mitochondrial imaging, photodynamic therapy and visualizing therapeutic process in zebrafish model

The combination of fluorescent (FL) probe and photosensitizer (PS) is a powerful tool for monitoring the changes of specific organelles while studying the photodynamic therapy (PDT) processes at the organelle level. It is very valued for biomedical application but remained challenging due to the lack of ideal FL PDT agent. In this work, an aggregation-induced emission (AIE)-active FL probe (AIE-FR-TPP) by conjugation of a far red/near-infrared (FR/NIR) emitting AIE fluorogen with the mitochondria-targeting group, is reported as a multi-functional fluorophore for mitochondrial imaging and PDT. As for bioimaging, AIE-FR-TPP can selectively light up the cellular mitochondria with low working concentration, short staining time and good biocompatibility. As for PDT, the probe can target mitochondria precisely and generate reactive oxygen species (ROS) efficiently both in living cells and zebrafish embryos. Moreover, AIE-FR-TPP is capable of monitoring the morphological changes of mitochondria based on the AIE effect. These results demonstrate that a real-time visual PDT process at the organelle level in living zebrafish embryos is achieved for the first time by using the AIE PS to induce mitochondrial ROS collapse and report the morphological change on site and in time.

Fluorescent Sensors Based on Aggregation-Induced Emission: Recent Advances and Perspectives.

Fluorescent sensors with advantages of excellent sensitivity, rapid response, and easy operation are emerging as powerful tools in environmental monitoring, biological research, and disease diagnosis. However, conventional fluorophores featured with π-planar structures usually suffer from serious self-quenching in the aggregated state, poor photostability, and small Stokes' shift. In contrast to conventional aggregation-caused quenching (ACQ) fluorophores, the newly emerged aggregation-induced emission fluorogens (AIEgens) are featured with high emission efficiency in the aggregated state, which provide unique opportunities for various sensing applications with advantages of high signal-to-noise ratio, strong photostability, and large Stokes' shift. In this review, we will first briefly give an introduction of the AIE concept and the turn-on sensing principles. Then, we will discuss the recent examples of AIE sensors according to types of analytes. Finally, we will give a perspective on the future developments of AIE sensors. We hope this review will inspire more endeavors to devote to this emerging world.

Monitoring Early-Stage Protein Aggregation by an Aggregation-Induced Emission Fluorogen.

Highly ordered protein aggregates, termed amyloid fibrils, are associated with a broad range of diseases, many of which are neurodegenerative, for example, Alzheimer's and Parkinson's. The transition from soluble, functional protein into insoluble amyloid fibril occurs via a complex process involving the initial generation of highly dynamic early stage aggregates or prefibrillar species. Amyloid probes, for example, thioflavin T and Congo red, have been used for decades as the gold standard for detecting amyloid fibrils in solution and tissue sections. However, these well-established dyes do not detect the presence of prefibrillar species formed during the early stages of protein aggregation. Prefibillar species have been proposed to play a key role in the cytotoxicity of amyloid fibrils and the pathogenesis of neurodegenerative diseases. Herein, we report a novel fluorescent dye (bis(triphenylphosphonium) tetraphenylethene (TPE-TPP)) with aggregation-induced emission characteristics for monitoring the aggregation process of amyloid fibrils. An increase in TPE-TPP fluorescence intensity is observed only with ordered protein aggregation, such as amyloid fibril formation, and not with stable molten globules states or amorphously aggregating species. Importantly, TPE-TPP can detect the presence of prefibrillar species formed early during fibril formation. TPE-TPP exhibits a distinctive spectral shift in the presence of prefibrillar species, indicating a unique structural feature of these intermediates. Using fluorescence polarization, which reflects the mobility of the emitting entity, the specific oligomeric pathways undertaken by various proteins during fibrillation could be discerned. Furthermore, we demonstrate the broad applicability of TPE-TPP to monitor amyloid fibril aggregation, including under diverse conditions such as at acidic pH and elevated temperature, or in the presence of amyloid inhibitors.

Functional Built-In Template Directed Siliceous Fluorescent Supramolecular Vesicles as Diagnostics.

Functional template directed synthesis of hybrid siliceous fluorescent vesicle (HSFV) is fabricated by using fluorescent vesicle as a built-in template. The template vesicle is the ionic self-assembly of an aggregation-induced emission (AIE) fluorogen. Upon depositing folic acid modified silica shell on its surface, the obtained HSFVs display low cytotoxicity, significant fluorescence, and targeted drug delivery toward cancer cells. Furthermore, the wall-thickness of the HSFVs can be controlled via altered concentration of silica source. This is the first report of HSFV employing the template vesicle as a built-in fluorescent agent, which represents a good example of rational design for an effective diagnostics, and may open up a new avenue for precision medicine.

Aggregation-induced emission: Materials and biomedical applications

Abstract

Chitosan-based cross-linked fluorescent polymer containing aggregation-induced emission fluorogen for cell imaging

A chitosan-based cross-linked fluorescent polymer (Ch-EP3) containing aggregation-induced emission (AIE) fluorogen was prepared through ring-opening polymerization of carboxymethyl chitosan and an AIE monomer with two ethylene oxide groups. 1H NMR, FT-IR, and X-ray photoelectron spectra were conducted to characterize and prove its successful synthesis. The introduction of chitosan component endowed Ch-EP3 with amphiphilic property, and Ch-EP3 could assemble into nanoparticles, which were facilely dispersed in water to form fluorescent polymeric nanoparticles (FPNs). The dynamic light scattering and transmission electron microscopy results indicated the size distribution of the FPNs was 260 ± 12 nm with spherical shape. Fluorescent spectrum of the prepared FPNs demonstrated intense green fluorescence with high fluorescence quantum yield of 35%. The Ch-EP3 FPNs further showed excellent particle stability at highly dilute solution with low critical micelle concentration of 0.063 mg mL−1. The synthesized FPNs also indicated high photostability under UV light irradiation for a period of 60 min. The cytotoxicity evaluation proved high cell viability after incubation of the Ch-EP3 FPNs at different concentrations for a period of 8 h or 24 h, and demonstrated highly biocompatible for cell imaging. Taking advantage of the high-performance Ch-EP3 FPNs, such as, high water dispersibility, good particle stability, and excellent photostability, this work would inspire more approaches to prepare novel cross-linked biocompatible fluorescent polymers for biomedical application.

Aggregation‐Induced Emission for Highly Selective and Sensitive Fluorescent Biosensing and Cell Imaging

ABSTRACTFluorescent bioprobes are powerful analytical tools for studying biological activities in living systems. Fluorogens with aggregation‐induced emission (AIE) characteristics have recently emerged as a new class of fluorescent bioprobes for biosensing and cell imaging. As discovered by Tang, AIE fluorogens are nearly nonemissive in molecular states with their intermolecular rotations being not restricted whereas their fluorescence is turned on by binding with certain biomolecules, leading to highly selective turn‐on fluorescent probes for specific biomolecules and fluorescent cell imaging with a high signal‐to‐background noise ratio. By introducing the AIE characteristics into polymeric materials, AIE polymers could possess a good solubility and biocompatibility, excellent structural diversity, and ease for functionalization useful for efficient biosensing and cell imaging. Herein, we highlight a few recently published articles on small and macromolecular AIE molecules to provide a fundamental understanding of the AIE mechanism and illustrate the working principle for AIE based biosensing and cell imaging. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 653–659

Quantitative evaluation and in vivo visualization of mercury ion bioaccumulation in rotifers by novel aggregation-induced emission fluorogen nanoparticles

In this study, a specifically-designed AIEgen was used to quantitatively evaluate the bioaccumulation of Hg2+and visualize Hg2+kineticsin vivowithin the rotifer for the first time.

P-Quaterphenylene as an Aggregation-Induced Emission Fluorogen in Supramolecular Organogels and Fluorescent Sensors.

Two dumbbell-shaped organogelators with a p-quaterphenylene core were synthesized, and their self-assembly properties were investigated. These low-molecular-weight gelators could form self-supporting gels in many apolar organic solvents with an H-type aggregation form through a synergic effect of π-π stacking, intermolecular translation-related hydrogen bonding, and van der Waals forces. In comparison to the p-terphenylene-cored gelator, the extended π-conjugated segment improved the gelation efficiency significantly with enhanced gelation rate. Additionally, these p-quaterphenylene-centered gelators exhibited strong fluorescence emission induced by aggregation, which not only provided an in situ method to optically monitor the gelation process, but also endowed these self-assemblies with substantial applications in sensing explosives.

Nanocrystallization: A Unique Approach to Yield Bright Organic Nanocrystals for Biological Applications.

A new bottom-up nanocrystallization method is developed to fabricate highly fluorescent organic nanocrystals in aqueous media using an aggregation-induced emission fluorogen (AIEgen) as an example. The nanocrystallization strategy leads to the fabrication of uniform nanocrystals of 110 ± 10 nm size in aqueous media, which shows over 400% increase in brightness as compared to the amorphous nanoaggregates.

Theranostic hyaluronic acid prodrug micelles with aggregation-induced emission characteristics for targeted drug delivery

Theranostic hyaluronic acid (HA) prodrug micelles with pH-responsive drug release and aggregation-induced emission (AIE) properties were prepared by chemical graft of biomimetic phosphorylcholine (PC), anticancer drug doxorubicin (DOX) and AIE fluorogen tetraphenylene (TPE) to the HA backbone. DOX was conjugated to the HA backbone by a hydrazone bond which can be hydrolyzed under acidic environment and result in pH-triggered smart release of DOX. The TPE units with typical AIE characteristics were applied for real time drug tracking in cancer cells. The HA-based prodrugs could self-assemble into micelles in aqueous solution as confirmed by the dynamic light scattering (DLS) and transmission electron microscopy (TEM). The intracellular distribution of HA prodrug micelles could be clearly observed by fluorescence microscopy based on the strong fluorescence of TPE. Moreover, after treated with the micelles, stronger fluorescence of TPE in CD44 overexpressed MDA-MB-231 cancer cells was observed, compared to the CD44 negative cell line, NIH3T3 cells, suggesting efficient cell uptake of HA prodrug micelles by receptor-mediated endocytosis. The cell viability results indicated that the prodrug micelles could inhibit the proliferation of the cancer cells effectively. Such pH-triggered theranostic drug delivery system with AIE features can provide a new platform for targeted and image-guided cancer therapy.

Aggregation Induced Emission Fluorogens Based Nanotheranostics for Targeted and Imaging-Guided Chemo-Photothermal Combination Therapy.

Nanotheranostics for biomedical imaging-guided cancer therapy have attracted increasing interest due to their capabilities of both precise tumor diagnosis and high therapeutic efficacy. Among the diverse imaging models, fluorescence imaging have been extensively researched for their high sensitivity, simple operation, and low cost. In this work, aggregation induced emission (AIE) fluorogens based targeted nanotheranostics are facilely fabricated via paclitaxel (PTX) induced assembly of proteins for the first time. Thanks to the unique fluorescence property of AIE fluorogens PhENH2 , the prepared theranostic nanoplatforms can emit bright fluorescence even after being incorporated with the photothermal therapy agent polypyrrole (PPy), which will often decrease or quench the emission of common fluorescence dyes. The target moiety of cyclic arginine-glycine-aspartic acid (cRGD) endows the nanotheranostics with outstanding targeting ability, which can further facilitate the targeted imaging and cancer treatment. As revealed by the in vitro and in vivo experiments, the prepared nanotheranostics human serum albumin-PhENH2 -PPy-PTX-cRGD shows impressive performance in the targeted fluorescence imaging even after intravenous injection for 48 h, and their combined chemo-photothermal therapy is also very effective. These results indicate that AIE fluorogens based nanotheranostics would find a promising prospect in further improved multimodal imaging and imaging guided cancer treatment.

Real‐Time Imaging of Cell Behaviors in Living Organisms by a Mitochondria‐Targeting AIE Fluorogen

Visualizing behaviors of cell populations within living multicellular organisms in real time is of great value to life science but challenging due to the lack of ideal probes. In this work, a biocompatible fluorogen, azide‐functionalized tetraphenylethene pyridinium (TPE‐PyN3), is reported for noninvasive imaging and sensing within living systems. TPE‐PyN3 exhibits unique aggregation‐induced emission (AIE) attributes and high affinity to mitochondria, enabling it to achieve specific mitochondrial imaging and long‐term cellular observing with excellent photostability both in vitro and in vivo. The high membrane penetrability of TPE‐PyN3 allows all of the cells within the living zebrafish embryos to be morphologically visualized and reconstructed in 3D. Moreover, TPE‐PyN3 is capable of indicating cell apoptosis because of its sensitivity to the change of mitochondrial membrane potential. The findings presented here provide a simple and noninvasive tool for studying behaviors of cell populations in vivo for the first time by a small‐molecule AIE probe.

Organic Dots Based on AIEgens for Two-Photon Fluorescence Bioimaging.

Two-photon fluorescence imaging technique is a powerful bioanalytical approach in terms of high photostability, low photodamage, high spatiotemporal resolution. Recently, fluorescent organic dots comprised of organic emissive cores and a polymeric matrix are emerging as promising contrast reagents for two-photon fluorescence imaging, owing to their numerous merits of high and tunable fluorescence, good biocompatibility, strong photobleaching resistance, and multiple surface functionality. The emissive core is crucial for organic dots to get high brightness but many conventional chromophores often encounter a severe problem of fluorescence quenching when they form aggregates. To solve this problem, fluorogens featuring aggregation-induced emission (AIE) can fluoresce strongly in aggregates, and thus become ideal candidates for fluorescent organic dots. In addition, two-photon absorption property of the dots can be readily improved by just increase loading contents of AIE fluorogen (AIEgen). Hence, organic dots based on AIEgens have exhibited excellent performances in two-photon fluorescence in vitro cellular imaging, and in vivo vascular architecture visualization of mouse skin, muscle, brain and skull bone. In view of the rapid advances in this important research field, here, we highlight representative fluorescent organic dots with an emissive core of AIEgen aggregate, and discuss their great potential in bioimaging applications.

Gelation process visualized by aggregation-induced emission fluorogens.

Alkaline-urea aqueous solvent system provides a novel and important approach for the utilization of polysaccharide. As one of the most important polysaccharide, chitosan can be well dissolved in this solvent system, and the resultant hydrogel material possesses unique and excellent properties. Thus the sound understanding of the gelation process is fundamentally important. However, current study of the gelation process is still limited due to the absence of direct observation and the lack of attention on the entire process. Here we show the entire gelation process of chitosan LiOH-urea aqueous system by aggregation-induced emission fluorescent imaging. Accompanied by other pseudo in situ investigations, we propose the mechanism of gelation process, focusing on the formation of junction points including hydrogen bonds and crystalline.