Red/NIR-Emissive Benzo[d]imidazole-Cored AIEgens: Facile Molecular Design for Wavelength Extending and In Vivo Tumor Metabolic Imaging

Bright red aggregation-induced emission nanoparticles for multifunctional applications in cancer therapy

Developing multifunctional photosensitizers (PSs) is needed to effectively simplify cancer treatment, but it remains a big challenge. Here, two red-emitting AIE-active, donor-acceptor (D-A) PSs with small ΔE ST and their AIE nanoparticles, are rationally designed and synthesized. The PS1 NPs exhibit bright red-emission with high quantum yield, appropriate 1O2 generation ability and good biocompatibility. More importantly, PS1 NPs can strongly light up the cytoplasm by gently shaking the cells for only 5 s at room temperature, indicating ultrafast staining and mild incubation conditions. In vitro and in vivo cell tracing demonstrate that PS1 NPs can track cells over 14 days, and effectively inhibit tumor growth upon irradiation. To the best of our knowledge, this work is the first example of a PS that integrates image-guided PDT, ultrafast staining and long-term tracing functions, demonstrating the "all-in-one" concept which offers great advantages for potential clinical applications.

Efficient Near-Infrared Photosensitizer with Aggregation-Induced Emission for Imaging-Guided Photodynamic Therapy in Multiple Xenograft Tumor Models

Photodynamic therapy (PDT) strategy has been widely used in tumor treatment, and the reagents for reactive oxygen species (ROS) play a crucial role. Herein, we develop a fluorogen (TTB) containing an electron-accepting benzo[1,2-b:4,5-b']dithiophene 1,1,5,5-tetraoxide core and electron-donating 4,4'-(2,2-diphenylethene-1,1-diyl)bis(N,N-diphenylaniline) groups for image-guided targeting PDT application. TTB exhibits a prominent aggregation-induced emission (AIE) property with strong near-infrared (NIR) fluorescence in aggregates and is capable of efficiently generating ROS of O₂^•- and ¹O₂ under white light irradiation. The nanoparticles (RGD-4R-MPD/TTB NPs) with NIR emission (∼730 nm), high photostability, and low dark cytotoxicity are fabricated by encapsulating TTB within polymeric matrix and then modified with RGD-4R peptide. They show excellent performance in targeting PDT treatment of PC3, HeLa, and SKOV-3 cancer cells in vitro. The investigations on pharmacokinetics, biodistribution, and long-term tracing in vivo reveal that RGD-4R-MPD/TTB NPs can selectively accumulate in tumors for real-time, long-term image-guided PDT treatment. The RGD-4R-MPD/TTB NPs-mediated PDT in multiple xenograft tumor models disclose that the growth of cervical, prostate, and ovarian cancers in mice can be effectively inhibited. These results demonstrate that the reagents employing NIR fluorogen TTB as a photosensitizer could be promising candidates for in vivo image-guided PDT treatments of tumors.

A facile way to obtain near-infrared room-temperature phosphorescent soft materials based on Bodipy dyes

Research on pure organic room-temperature phosphorescent (RTP) materials has made great advances but near-infrared (NIR) RTP emitting materials are still rare. Novel amorphous acrylamide copolymers containing iodine substituted borondipyrromethene (Bodipy) were prepared to obtain strong absorption in the visible region and moderate RTP in the NIR region with much larger Stokes shift than the fluorescence emission of traditional Bodipy dyes. Expensive metals and crystallization were left out to avoid biotoxicity and strict preparation conditions. Monoiodo and diiodo-Bodipy derivatives were both designed to study the substitution effect of iodine atoms. Photophysical properties, phosphorescence quantum yield and lifetime were characterized. Gels with NIR RTP emission were facilely prepared with the incorporation of ureidopyrimidone (UPy) and N,N'-methylenebisacrylamide (MBAA). The mechanical properties of the gels were measured using a rheometer and the results showed that the gels displayed fast self-healing ability due to the strong quadruple hydrogen bonding between UPy moieties.

Nanoparticle-based Cell Trackers for Biomedical Applications

The continuous or real-time tracking of biological processes using biocompatible contrast agents over a certain period of time is vital for precise diagnosis and treatment, such as monitoring tissue regeneration after stem cell transplantation, understanding the genesis, development, invasion and metastasis of cancer and so on. The rationally designed nanoparticles, including aggregation-induced emission (AIE) dots, inorganic quantum dots (QDs), nanodiamonds, superparamagnetic iron oxide nanoparticles (SPIONs), and semiconducting polymer nanoparticles (SPNs), have been explored to meet this urgent need. In this review, the development and application of these nanoparticle-based cell trackers for a variety of imaging technologies, including fluorescence imaging, photoacoustic imaging, magnetic resonance imaging, magnetic particle imaging, positron emission tomography and single photon emission computing tomography are discussed in detail. Moreover, the further therapeutic treatments using multi-functional trackers endowed with photodynamic and photothermal modalities are also introduced to provide a comprehensive perspective in this promising research field.

Precise Molecular Design for High-Performance Luminogens with Aggregation-Induced Emission

Precise design of fluorescent molecules with desired properties has enabled the rapid development of many research fields. Among the different types of optically active materials, luminogens with aggregation-induced emission (AIEgens) have attracted significant interest over the past two decades. The negligible luminescence of AIEgens as a molecular species and high brightness in aggregate states distinguish them from conventional fluorescent dyes, which has galvanized efforts to bring AIEgens to a wide array of multidisciplinary applications. Herein, the useful principles and emerging structure-property relationships for precise molecular design toward AIEgens with desirable properties using concrete examples are revealed. The cutting-edge applications of AIEgens and their excellent performance in enabling new research directions in biomedical theranostics, optoelectronic devices, stimuli-responsive smart materials, and visualization of physical processes are also highlighted.

PVP-coated Sb2Se3 nanorods as nanotheranostic agents for photoacoustic imaging and photothermal therapy in NIR-I bio-windows

Antimony selenide (Sb₂Se₃) as a simple, low toxicity, low-cost p-type semiconductor material with broad absorbance ranging from the UV to the NIR region has many potential applications in photovoltaic, thermoelectric, and phase-change memory devices. Owing to these excellent properties, Sb₂Se₃ nanorods were firstly synthesized with triphenylantimony and dibenzyldiselenide under solvothermal conditions. In order to enhance the biocompatibility of the Sb₂Se₃ nanorods, polyvinylpyrrolidone (PVP) was coated onto the surface of the Sb₂Se₃ nanorods to form PVP-coated Sb₂Se₃ nanorods. The cell viability of PVP-coated Sb₂Se₃ nanorods toward Hep-2 cells was assessed for 24 h using a Cell Counting Kit-8 (CCK-8) assay. The results showed that Hep-2 cells treated with PVP-coated Sb₂Se₃ nanorods were alive at a concentration as high as 100 μg mL⁻¹ in the absence of NIR irradiation. In vivo assessment confirmed that PVP-coated Sb₂Se₃ nanorods exhibited excellent photoacoustic imaging and PTT performance, which yielded complete ablation of tumors after laser irradiation (808 nm or 980 nm) in the NIR-I bio-window.

Herein we reported a biocompatible PVP-coated Sb₂Se₃ nanorods as PTT nanotheranostic agent, which is responsive to the light (808 and 980 nm) in NIR-I bio-windows and effective for photoacoustic imaging and photothermal destruction of cancer cell.

Design of superior phototheranostic agents guided by Jablonski diagrams

This review summarizes how Jablonski diagrams guide the design of advanced organic optical agents and improvement of disease phototheranostic efficacies.

NIR-II-Excited Intravital Two-Photon Microscopy Distinguishes Deep Cerebral and Tumor Vasculatures with an Ultrabright NIR-I AIE Luminogen

Intravital fluorescence imaging of vasculature morphology and dynamics in the brain and in tumors with large penetration depth and high signal-to-background ratio (SBR) is highly desirable for the study and theranostics of vascular-related diseases and cancers. Herein, a highly bright fluorophore (BTPETQ) with long-wavelength absorption and aggregation-induced near-infrared (NIR) emission (maximum at ≈700 nm) is designed for intravital two-photon fluorescence (2PF) imaging of a mouse brain and tumor vasculatures under NIR-II light (1200 nm) excitation. BTPETQ dots fabricated via nanoprecipitation show uniform size of around 42 nm and a high quantum yield of 19 ± 1% in aqueous media. The 2PF imaging of the mouse brain vasculatures labeled by BTPETQ dots reveals a 3D blood vessel network with an ultradeep depth of 924 µm. In addition, BTPETQ dots show enhanced 2PF in tumor vasculatures due to their unique leaky structures, which facilitates the differentiation of normal blood vessels from tumor vessels with high SBR in deep tumor tissues. Moreover, the extravasation and accumulation of BTPETQ dots in deep tumor (more than 900 µm) is visualized under NIR-II excitation. This study highlights the importance of developing NIR-II light excitable efficient NIR fluorophores for in vivo deep tissue and high contrast tumor imaging.

Barbier Hyperbranching Polymerization-Induced Emission toward Facile Fabrication of White Light-Emitting Diode and Light-Harvesting Film

Luminescent polymers are generally constructed through polymerization of luminescent moieties. Polymerization itself, however, is mainly used for constructing polymer main chain, and the importance of polymerization on luminescence has yet to be explored. Here, we demonstrate a polymerization-induced emission strategy producing luminescent polymers by introducing Barbier reaction to hyperbranching polymerization, which allows luminescent properties to be easily tuned from the traditional type to an aggregation-induced emission type by simply adjusting the monomer structure and the polymerization time. When rotation about the phenyl groups in hyperbranched polytriphenylmethanols (HPTPMs) is hindered, HPTPMs exhibit traditional emission property. When all phenyl groups of HPTPM are rotatable, i.e., p,p',p″-HPTPM, it exhibits interesting aggregation-induced emission property with tunable emission colors from blue to yellow, by just adjusting polymerization time. Further applications of aggregation-induced emission type luminescent polymers are illustrated by the facile fabrication of white light-emitting diode (LED) and light-harvesting film with an antenna effect >14. This Barbier hyperbranching polymerization-induced emission provides a new strategy for the design of luminescent polymers and expands the methodology and functionality library of both hyperbranching polymerization and luminescent polymers.

A Functioning Macroscopic "Rubik's Cube" Assembled via Controllable Dynamic Covalent Interactions

The dynamic behavior of a macroscopic adhered hydrogel stabilized through controllable dynamic covalent interactions is reported. These interactions, involving the cross-linked formation of a hydrogel through reaction of a diacylhydrazine precursor with a tetraformyl partner, increase as a function of time. By using a contact time of 24 h and different compounds with recognized aggregation-induced emission features (AIEgens), it proves possible to create six laminated acylhydrazone hydrogels displaying different fluorescent colors. Blocks of these hydrogels are then adhered into a structure resembling a Rubik's Cube, a trademark of Rubik's Brand Limited, (RC) and allowed to anneal for 1 h. This produces a 3 × 3 × 3 block (RC) wherein the individual fluorescent gel blocks are loosely adhered to one another. As a consequence, the 1 × 3 × 3 layers making up the RC can be rotated either horizontally or vertically to produce new patterns. Ex situ modification of the RC or application of a chemical stimulus can be used to produce new color arrangements. The present RC structure highlights how the temporal features, strong versus weak adhesion, may be exploited to create smart macroscopic structures.

A light-up near-infrared probe with aggregation-induced emission characteristics for highly sensitive detection of alkaline phosphatase

Developing activatable near-infrared (NIR) probes to specifically monitor and visualize the activities of cancer-related enzymes is highly significant yet challenging in early cancer diagnosis. Taking advantage of the unique photophysical characteristics of aggregation-induced emission (AIE) fluorophores, here we design and synthesize a novel activatable probe QMTP by conjugating an AIE fluorophore quinolone-malononitrile to a hydrophilic phosphate-modified phenol group. The probe was initially non-fluorescent in aqueous solution due to its good water solubility, but was readily activated to generate a strong NIR fluorescence upon treatment with alkaline phosphatase (ALP), which enables specific detection of ALP activity. Furthermore, we have employed QMTP to monitor and spatially map the activity of endogenous ALP both in cancer cells and in drug-treated zebrafish larvae. The experimental results reveal that the QMTP probe has great specificity and sensitivity for ALP detection. We thus believe that our work offers a promising tool for accurate detection of ALP-associated diseases in preclinical applications.

Functionalized Acrylonitriles with Aggregation-Induced Emission: Structure Tuning by Simple Reaction-Condition Variation, Efficient Red Emission, and Two-Photon Bioimaging

Acrylonitriles with aggregation-induced emission (AIE) characteristics have been found to show promising applications in two-photon biomedical imaging. Generally, elaborate synthetic efforts are required to achieve different acrylonitriles with distinct functionalities. In this work, we first reported the synthesis of two different group-functionalized AIE-active acrylonitriles (TPAT-AN-XF and 2TPAT-AN) obtained simply by mixing the same reactants at different temperatures using a facile and transition metal-free synthetic method. These two AIE luminogens (AIEgens) exhibit unique properties such as bright red emission in the solid state, large Stokes shift, and large two-photon absorption cross section. Water-soluble nanoparticles (NPs) of 2TPAT-AN were prepared by a nanoprecipitation method. In vitro imaging data show that 2TPAT-AN NPs can selectively stain lysosome in live cells. Besides one-photon imaging, remarkable two-photon imaging of live tumor tissues can be achieved with high resolution and deep tissue penetration. 2TPAT-AN NPs show high biocompatibility and are successfully utilized in in vivo long-term imaging of mouse tumors with a high signal-to-noise ratio. Thus, the present work is anticipated to shed light on the preparation of a library of AIE-active functionalized acrylonitriles with intriguing properties for biomedical applications.

Near-Infrared Organic Fluorescent Nanoparticles for Long-term Monitoring and Photodynamic Therapy of Cancer

Photodynamic therapy (PDT), which utilizes reactive oxygen species to ablate tumor, has attracted much attention in recent years. Photosensitizers with near-infrared (NIR) fluorescence as well as efficient ROS generation ability have been used for precise diagnosis and simultaneous treatment of cancer. However, photosensitizers frequently suffer from low ROS generation ability and NIR fluorescence quenching in aqueous media due to the aggregation.

Methods: We prepare an effective AIE active NIR emissive photosensitizer containing rhodanine as electron acceptor and triphenylvinylthiophene as electron donor is prepared, and encapsulate the corresponding photosensitizer into Pluronic F127 to fabricate NIR organic fluorescent nanoparticles. We then evaluate the NIR fluorescence bioimaging and photodynamic therapy ability of TPVTR dots in vitro and in vivo.

Results: The yielded organic fluorescent nanoparticles exhibit effective ROS generation ability, bright NIR emission, high photostability, and good biocompatibility. Both in vitro and in vivo experiments confirm that NIR organic fluorescent nanoparticles demonstrate good performances in long-term tracing and photodynamic ablation of tumor.

Conclusion: In summary, the synthesized organic fluorescent nanoparticles, TPVTR dots, showed great potentials in long-term cell tracing and photodynamic therapy of tumor. Our study highlights the efficient strategy for developing promising near-infrared organic fluorescent nanoparticles in advancing the field of bioimaging and further image-guide clinical applications.