Aggregation-induced Emission Dots Research Articles

Tetralactam macrocycle based aggregation-induced emission dots for selective detection of Fe3+ in water and drugs

Iron ion (Fe3+) is crucial for both biological organisms and the environment, and iron dyshomeostasis can lead to a variety of diseases and environmental issues. Therefore, the detection of Fe3+ is of significant importance across various fields. For this purpose, through the co-assembly of water-soluble tetralactam macrocycle H and 1,1,2,2-tetraphenylethylene (TPE), we prepared a new type of tetralactam macrocycle based aggregation-induced emission dots (AIE-dots), namely TPE@H. TPE@H exhibitted good water-solubility and allowed the water-insoluble TPE to aggregate and exhibit strong fluorescence emission in water. Furthermore, the fluorescence of TPE@H could be quenched by Fe3+ through the inner filter effect, making TPE@H a potential “turn-off” fluorescent probe for Fe3+ detection. TPE@H exhibited a limit of detection as low as 1 μM with high selectivity, and also retained good detection performance in domestic water, human serum, and even drugs, indicating its great potential for biological and environmental monitoring of Fe3+. This study not only provides a green and efficient method for detecting Fe3+, but also expands the approach for application of water-insoluble dyes in the aqueous environment.

Recent Advances in Fluorescent Nanoparticles for Stimulated Emission Depletion Imaging.

Stimulated emission depletion (STED) microscopy, as a popular super-resolution imaging technique, has been widely used in bio-structure analysis and resolving the dynamics of biological processes beyond the diffraction limit. The performance of STED critically depends on the optical properties of the fluorescent probes. Ideally, the probe should process high brightness and good photostability, and exhibit a sensitive response to the depletion beam. Organic dyes and fluorescent proteins, as the most widely used STED probes, suffer from low brightness and exhibit rapid photobleaching under a high excitation power. Recently, luminescent nanoparticles (NPs) have emerged as promising fluorescent probes in biological imaging due to their high brightness and good photostability. STED imaging using various kinds of NPs, including quantum dots, polymer dots, carbon dots, aggregation-induced emission dots, etc., has been demonstrated. This review will comprehensively review recent advances in fluorescent NP-based STED probes, discuss their advantages and pitfalls, and outline the directions for future development.

Preparation of AIEgen-based near-infrared afterglow luminescence nanoprobes for tumor imaging and image-guided tumor resection.

Fluorescence imaging represents a vital tool in modern biology, oncology and biomedical applications. Afterglow luminescence (AGL), which circumvents the light scattering and tissue autofluorescence interference associated with real-time excitation source, shows remarkably increased imaging sensitivity and depth. Here we present a protocol for the design and synthesis of AGL nanoprobes with an aggregation-induced emission (AIE) effect to simultaneously red shift and amplify the afterglow signal for tumor imaging and image-guided tumor resection. The nanoprobe (AGL AIE dot) is composed of an enol ether format of Schaap's agent and a near-infrared AIE fluorogen (AIEgen) (tetraphenylethylene-phenyl-dicyanomethylene-4H-chromene, TPE-Ph-DCM) to suppress the nonradiative dissipation pathway. Pre-irradiating AGL AIE dots with white light could generate singlet oxygen to convert Schaap's agent to its 1,2-dioxetane format, thus initializing the AGL process. With the aid of AIEgen, the AGL shows simultaneously red shifted emission maximum (from ~540 nm to ~625 nm) and enhanced intensity (by 3.2-fold), facilitating better signal-to-background ratio, imaging sensitivity and depth. Intriguingly, the activated AGL can last for over 10 days. Compared with conventional approaches, our method provides a new solution to concurrently red shift and amplify afterglow signals for better in vivo imaging outcomes. The preparation of AGL AIE dots takes ~2 days, the in vitro characterization takes ~10 days (less than 1 day if not involving afterglow kinetic profile study) and the tumor imaging and image-guided tumor resection takes ~7 days. These procedures can be easily reproduced and amended after standard laboratory training in chemical synthesis and animal handling.

Visualization of tumor-associated neutrophils in malignant ascites of ovarian cancer with aptamer-decorated AIE probes

Neoadjuvant chemotherapy followed by interval debulking surgery is a recommended treatment for advanced-stage ovarian cancer (OC) patients to avoid bowel and spleen resection. Pre-operative chemotherapy requires ascites from OC patients for cytopathological examinations based on hematoxylin & eosin staining to detect tumor cells, whose low ratio make them difficult to be detected in ascites. Sensitive detection of tumor-related immunocytes (TRI) in ascites is not only indicative of underlying malignant ascites, but also could predict chemoresistance and poor overall survival of OC patients. The antibodies can only recognize immunocytes but cannot distinguish TRI. Herein, we identified an aptamer99 (Apt-99) using a fluorescence-activated cell sorting-based aptamer selection strategy, which could target tumor-related neutrophils (TRNs) with high binding affinity. In contrast, FAM-labeled Apt-99 couldn’t distinguish the neutrophils in the smears of other patients’ derived ascites or peritoneal lavages, such as metastatic ovarian cancer from colon carcinoma and myomas of the uterus. LC-MS/MS analysis, and the molecular docking experiments demonstrated that the target molecule of Apt-99 were S100A8&A9 heterodimers. Moreover, Apt-99-labeled aggregation-induced emission dots were facilely prepared and used for specifically visualizing the TRNs in the ascites smears. The findings indicated the diagnostic potential of Apt-99 and the possibility of further clinical trials.

Preparation of AIE Functional Single-Chain Polymer Nanoparticles and Their Application in H2 O2 Detection through Intermolecular Heavy-Atom Effect.

Single-chain polymer nanoparticles (SCNPs) are soft matter constructed by intrachain crosslinks, with promising prospects in detection and catalysis. Herein, a fluorescent core (SCNPs) with aggregation-induced emission (AIE) is prepared, applying for H2 O2 detection through intermolecular heavy-atom effect. In detail, the SCNPs precursors are synthesized by ring-opening copolymerization. Then the SCNPs are prepared by intramolecularly cross-linking via olefin metathesis. Imitating the structure of AIE dots, SCNPs are encapsulated by H2 O2 -responsive polymers. Probably due to the stable secondary structure of SCNPs, the obtained micelles show stable fluorescence performance. Furthermore, as the heavy-atom, tellurium is introduced into the carriers to construct the heavy-atom effect. In this micelle-based system, the SCNPs act as the fluorescent core, and the stimuli-responsive polymer acts as the carrier and the fluorescent switch. The hydrophilicity of the tellurium-containing segment is affected by the concentration of H2 O2 , resulting in a change in the distance from the SCNPs, which ultimately leads to a change in the fluorescence intensity. Furthermore, tellurium is particularly sensitive to H2 O2 , which can detect low concentrations of H2 O2 . The SCNPs are merged with AIE materials, with the hope of exploring new probe designs.

Sonosensitized Aggregation-Induced Emission Dots with Capacities of Immunogenic Cell Death Induction and Multivalent Blocking of Programmed Cell Death-Ligand 1 for Amplified Antitumor Immunotherapy

Sonosensitized Aggregation-Induced Emission Dots with Capacities of Immunogenic Cell Death Induction and Multivalent Blocking of Programmed Cell Death-Ligand 1 for Amplified Antitumor Immunotherapy

Hot-Band-Absorption-Induced Anti-Stokes Fluorescence of Aggregation-Induced Emission Dots and the Influence on the Nonlinear Optical Effect.

Hot-band absorption (HBA)-induced anti-Stokes fluorescence (ASF) with longer-wavelength excitation is one effective pathway to deep penetration and low autofluorescence in intravital fluorescence imaging, raising demands for fluorophores with broad spectra, high absorption, and strong emission. However, typical fluorescent dyes display some emission quenching when their concentration is increased in order to obtain brighter fluorescence. In this work, the HBA-induced ASF of aggregation-induced emission (AIE) dots is reported. BPN-BBTD dots were synthesized and confirmed with a fluorescence enhancement and a considerable ASF intensity. In addition, the mechanism of ASF and the HBA process of BPN-BBTD dots were carefully validated and discussed. To obtain the full advantages of the long-wavelength excitation and the short fluorescence lifetime in deep-tissue bioimaging, a large-depth ASF confocal microscopic imaging of in vivo cerebral vasculature was conducted under the excitation of a 980 nm continuous wave laser after intravenous injection of BPN-BBTD dots. Meanwhile, the 3D structure of the cerebrovascular network was successfully reconstructed.

Bright near-infrared aggregation-induced emission dots for long-term bioimaging in vitro/vivo

Advanced hepatocarcinoma is almost incurable and has caused a huge number of deaths every year. Noninvasive long-term cell tracing is an efficient and important tool to understand genesis, development and evolution of cancer cells. Bright organic luminescent dots (named TNZ2tPPI-Tat NPs) with unique aggregation-induced near-infrared red emission (NIR-AIE), prepared in this contribution, enjoy the advantages of desirable biocompatibility, great water dispersibility, high photoluminescent quantum efficiency (32 %), large Stokes shift (166 nm), anti-background interference and great photostability. Moreover, the thus-obtained AIE-active NPs show ultralong fluorescent bioimaging (7 days) in MHCC97-H cells, and still keep clear fluorescent signals after 5 generations in three hepatic cells (Lo2, MHCC97-H, Hep 3B). In vivo fluorescent imaging demonstrates that TNZ2tPPI-Tat NPs still maintain strong brightness over 26 days, suggest great stability of such bright NPs. Further compare with the counterparts of commercial fluorescent probes such as Cy5 and AF647, such AIE dots enjoy more superior performances in the aspect of fluorescent intensity and long-term bioimaging efficiency, which is promising candidate to serve as noninvasive long-term cell tracker.

Aggregation-induced emission dots assisted non-invasive fluorescence hysterography in near-infrared IIb window

Uterine diseases seriously threaten the physical and mental health of women. The main principle, when clinicians adopt examinations, is to achieve efficient diagnosis without negative effect on the physical function including fertility. Hysterography in near-infrared (NIR) IIb window (1500–1700 nm) presents perceptibly enhanced signal to background ratio (SBR) and higher penetration capability compared with those beyond 1000 nm and 1300 nm, but lays down high requirements for the biosafety of fluorophores at the same time. Assisted by the biologically excretable aggregation-induced emission (AIE) dots, non-invasive NIR-IIb fluorescence hysterography visualized typical Y-shaped uteruses, real-time uterine peristalsis or the uterine lesions (mimetic disease statuses in clinic) in mouse models. Significantly, after intrauterine perfusion, the reproductive capacity was unimpaired via fertility assessment and histological analysis. This work could inspire some new ideas for non-invasive clinical diagnosis of uterine diseases and effectively promote the clinical translation of AIE dots.

Luminescent AIE Dots for Anticancer Photodynamic Therapy.

Photodynamic therapy (PDT) is an emerging effective strategy for cancer treatment. Compared with conventional cancer therapies, such as surgery, chemotherapy, and radiotherapy, PDT has shown great promise as a next-generation cancer therapeutic strategy owing to its many advantages such as non-invasiveness, negligible observed drug resistance, localized treatment, and fewer side effects. One of the key elements in photodynamic therapy is the photosensitizer (PS) which converts photons into active cytotoxic species, namely, reactive oxygen species (ROS). An ideal PS for photodynamic therapy requires the efficient generation of ROS, high stability against photo bleaching, and robust performance in different environments and concentrations. PSs with aggregation-induced emission (AIE) characteristics have drawn significant attention, in that they can overcome the aggregation- caused quenching effect that is commonly seen in the case of fluorescence dyes and provide excellent performance at high concentrations or in their condensed state. Moreover, organic nanomaterials with AIE characteristics, or AIE dots, have played an increasingly significant role in assisting PDT based on its excellent ROS generation efficiency and simultaneous imaging feature. This review summarizes the recent advances on the molecular design of AIE PSs and AIE dots-based probes, as well as their emerging applications for enhanced anticancer PDT theranostics.

One-for-all phototheranostics: Single component AIE dots as multi-modality theranostic agent for fluorescence-photoacoustic imaging-guided synergistic cancer therapy

Construction of single component theranostic agent with one-for-all features to concurrently afford both multi-modality imaging and therapy is an appealing yet significantly challenging task. Herein, a type of luminogens with aggregation-induced emission (AIE) characteristics are tactfully designed and facilely synthesized. These AIE luminogens (AIEgens) exhibit long emission wavelengths, good photostability, remarkable biocompatibility, good reactive oxygen species (ROS) generation performance and excellent photothermal conversion efficiency, which allow them to be powerfully utilized for in vitro and in vivo cancer phototheranostics. The results show that one of the AIEgens is capable of precisely diagnosing solid tumors of mice by means of combined near-infrared-I/II (NIR-I/II) fluorescence-photoacoustic imaging, meanwhile this AIEgen can activate photodynamic and photothermal synergistic therapy (PDT-PTT) upon laser irradiation, resulting in excellent tumor elimination efficacy with only once injection and irradiation. This study thus provides a versatile platform for practical cancer theranostics.

Biologically Excretable Aggregation-Induced Emission Dots for Visualizing Through the Marmosets Intravitally: Horizons in Future Clinical Nanomedicine.

Superb reliability and biocompatibility equip aggregation-induced emission (AIE) dots with tremendous potential for fluorescence bioimaging. However, there is still a chronic lack of design instructions of excretable and bright AIE emitters. Here, a kind of PEGylated AIE (OTPA-BBT) dots with strong absorption and extremely high second near-infrared region (NIR-II) PLQY of 13.6% is designed, and a long-aliphatic-chain design blueprint contributing to their excretion from an animal's body is proposed. Assisted by the OTPA-BBT dots with bright fluorescence beyond 1100nm and even 1500nm (NIR-IIb), large-depth cerebral vasculature (beyond 600µm) as well as real-time blood flow are monitored through a thinned skull, and noninvasive NIR-IIb imaging with rich high-spatial-frequency information gives a precise presentation of gastrointestinal tract in marmosets. Importantly, after intravenous or oral administration, the definite excretion of OTPA-BBT dots from the body is demonstrated, which provides influential evidence of biosafety.

Organic Dots with Large π-Conjugated Planar for Cholangiography beyond 1500 nm in Rabbits: A Non-Radioactive Strategy.

Iatrogenic extrahepatic bile duct injury remains a dreaded complication while performing cholecystectomy. Although X-ray based cholangiography could reduce the incidence of biliary tract injuries, the deficiencies including radiation damage and expertise dependence hamper its further clinical application. The effective strategy for intraoperative cholangiography is still urgently required. Herein, a fluorescence-based imaging approach for cholangiography in the near-infrared IIb window (1500-1700 nm) using TT3-oCB, a bright aggregation-induced emission luminogen with large π-conjugated planar unit, is reported. In phantom studies, TT3-oCB nanoparticles exhibit high near-infrared IIb emission and show better image clarity at varying penetrating depths. When intrabiliary injected into the gallbladder or the common bile duct of the rabbit, TT3-oCB nanoparticles enable the real-time imaging of the biliary structure with deep penetrating capability and high signal-to-background ratio. Moreover, the tiny iatrogenic biliary injuries and the gallstones in established disease models could be precisely diagnosed by TT3-oCB nanoparticle assisted near-infrared IIb imaging. In summary, we reported a feasible application for aggregation-induced emission dots as biliary contrast agent and realized high-quality cholangiography in the near-infrared IIb window with precise diagnostic ability and nonradioactive damage, which could possibly be applied for intraoperative diagnosis.

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

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

NIR-II Excitation and NIR-I Emission Based Two-photon Fluorescence Lifetime Microscopic Imaging Using Aggregation-induced Emission Dots

Near-infrared(NIR) lights are powerful tools to conduct deep-tissue imaging since NIR-I wavelengths hold less photon absorption and NIR-II wavelengths serve low photon scattering in the biological tissues compared with visible lights. Two-photon fluorescence lifetime microscopy(2PFLM) can utilize NIR-II excitation and NIR-I emission at the same time with the assistance of a well-designed fluorescent agent. Aggregation induced emission(AIE) dyes are famous for unique optical properties and could serve a large two-photon absorption(2PA) cross-section as aggregated dots. Herein, we report two-photon fluorescence lifetime microscopic imaging with NIR-II excitation and NIR-I emission using a novel deep-red AIE dye. The AIE-gens held a 2PA cross-section as large as 1.61×104 GM at 1040 nm. Prepared AIE dots had a two-photon fluorescence peak at 790 nm and a stable lifetime of 2.2 ns under the excitation of 1040 nm femtosecond laser. The brain vessels of a living mouse were vividly reconstructed with the two-photon fluorescence lifetime information obtained by our home-made 2PFLM system. Abundant vessels as small as 3.17 µm were still observed with a nice signal-background ratio at the depth of 750 µm. Our work will inspire more insight into the improvement of the working wavelength of fluorescent agents and traditional 2PFLM.

Small Molecular Prodrug Amphiphile Self-Assembled AIE Dots for Cancer Theranostics.

A simple and facile one-step method was developed to construct a small molecular prodrug amphiphile self-assembled organic dots CPPG with aggregation-induced emission (AIE) characteristics. Diphenylalanine peptide (FF), which is the essential moiety of the self-assembling peptide-drug conjugate and as its core recognition motifs for molecular self-assembly. In addition, the D-glucose transported protein (GLUT), which is one of the important nutrient transporters and is overexpressed in cancer cells. The conjugation of glycosyl further endues the nanoparticle with good biocompatibility and tumor-targeting ability. Taking advantages of both the cancer cell-targeting capability of small molecular prodrug amphiphile CPPG and the AIE aggregates with strong emission, the prepared CPPG AIE dots can target cancer cells specifically and inhibit the proliferation of cancer cells with good biocompatibility and photostability. Based on the general approach, types of universal organic fluorescent nanoprobes could be facilely constructed for imaging applications and biological therapeutics, which possess the properties of specific recognition and high brightness.

Sub‐10 nm Aggregation‐Induced Emission Quantum Dots Assembled by Microfluidics for Enhanced Tumor Targeting and Reduced Retention in the Liver

AbstractA robust platform is developed to assemble sub‐10 nm organic aggregation‐induced emission (AIE) particles using four different AIE luminogens (AIEgens) with emissions from green to the second near‐infrared window (NIR‐II). They are called AIE quantum dots (QDs) to distinguish from typical AIE dots which are larger than 25 nm. Compared with AIE dots that are larger than 25 nm, AIE QDs allow more efficient cellular uptake and imaging without surface modification of any membrane‐penetrating peptides or other targeting molecules. NIR‐II AIEgens, which have nearly no background fluorescence from organisms, are used to demonstrate that AIE QDs can achieve high contrast at the tumor as small as 80 mm3 and evade the liver more efficiently than AIE dots. AIE QDs hold a good promise for sensitive and precise diagnosis of the latent solid tumor in clinical medicine with much lower off‐targeting to the liver than AIE dots.

Sub-10 nm Aggregation-Induced Emission Quantum Dots Assembled by Microfluidics for Enhanced Tumor Targeting and Reduced Retention in the Liver.

A robust platform is developed to assemble sub-10 nm organic aggregation-induced emission (AIE) particles using four different AIE luminogens (AIEgens) with emissions from green to the second near-infrared window (NIR-II). They are called AIE quantum dots (QDs) to distinguish from typical AIE dots which are larger than 25 nm. Compared with AIE dots that are larger than 25 nm, AIE QDs allow more efficient cellular uptake and imaging without surface modification of any membrane-penetrating peptides or other targeting molecules. NIR-II AIEgens, which have nearly no background fluorescence from organisms, are used to demonstrate that AIE QDs can achieve high contrast at the tumor as small as 80 mm3 and evade the liver more efficiently than AIE dots. AIE QDs hold a good promise for sensitive and precise diagnosis of the latent solid tumor in clinical medicine with much lower off-targeting to the liver than AIE dots.

Near-Infrared AIE Dots with Chemiluminescence for Deep-Tissue Imaging.

Near-infrared (NIR) chemiluminescence (CL) emission is highly favorable for deep-tissue imaging, but chemically conjugated NIR CL emitters with the aggregation-induced emission (AIE) property for biotechnology are seldom reported. Herein, an AIE-active NIR CL emitter, TBL, is synthesized by conjugating luminol unit with electron-accepting benzothiadiazole and an electron-donating triphenylamine, and subsequently TBL dots are prepared by using F127 as the surfactant. The CL emission of TBL dots can last continuously for over 60 min and can be employed for quantitative (in vitro) and qualitative (in vivo) detection of 1 O2 . Strikingly, the NIR CL emission can penetrate through tissues with a total thickness of over 3 cm, exhibiting significantly better performance than NIR fluorescence emission and blue CL emission. Moreover, the successful differentiation of tumor and normal tissues by TBL-based CL imaging in vivo also paves the way for CL-guided cancer diagnosis and surgery.

Highly stable and bright AIE dots for NIR-II deciphering of living rats

Abstract The emerging second near-infrared (NIR-II) fluorescence imaging has shown great promise for in vivo imaging of small animals such as mice, yet the onward movement to large-size animals such as rats is still undeveloped. In this work, for the first time, we report comprehensive NIR-II deciphering of brain blood vasculature and main organs of living rats based on aggregation-induced emission (AIE) dots. The AIE dots possess simultaneously high brightness, excellent stability with various treatments, and good biocompatibility. Thanks to the long emission range and high brightness, in vivo NIR-II fluorescence microscopic imaging with the AIE dots beyond 1200 nm allows for visualizing rat brain vasculature with high spatial resolution (∼4 μm) and deep penetration (700 μm), representing the highest penetration depth and best resolution of rat brain imaging yet achieved in the field. The NIR-II AIE dots also enable the detection of tiny vascular blockage in real time at the early stage of cerebral thrombosis. Furthermore, in vivo non-invasive monitoring of rat’s gastrointestinal tract and bladder in a high-contrast manner helps to better understand the digestive system and excretory processes. This work will inspire new insights into the development of advanced NIR-II technique for large animal imaging, rendering great promise for real applications.