Organic Dots Based on AIEgens for Two-Photon Fluorescence Bioimaging

The Application of Nanoparticle-Based Imaging and Phototherapy for Female Reproductive Organs Diseases

Various female reproductive disorders affect millions of women worldwide and bring many troubles to women's daily life. Let alone, gynecological cancer (such as ovarian cancer and cervical cancer) is a severe threat to most women's lives. Endometriosis, pelvic inflammatory disease, and other chronic diseases-induced pain have significantly harmed women's physical and mental health. Despite recent advances in the female reproductive field, the existing challenges are still enormous such as personalization of disease, difficulty in diagnosing early cancers, antibiotic resistance in infectious diseases, etc. To confront such challenges, nanoparticle-based imaging tools and phototherapies that offer minimally invasive detection and treatment of reproductive tract-associated pathologies are indispensable and innovative. Of late, several clinical trials have also been conducted using nanoparticles for the early detection of female reproductive tract infections and cancers, targeted drug delivery, and cellular therapeutics. However, these nanoparticle trials are still nascent due to the body's delicate and complex female reproductive system. The present review comprehensively focuses on emerging nanoparticle-based imaging and phototherapies applications, which hold enormous promise for improved early diagnosis and effective treatments of various female reproductive organ diseases.

Oligo(styryl)benzenes liposomal AIE-dots for bioimaging and phototherapy in an in vitro model of prostate cancer

Whilst the development of advanced organic dots with aggregation-induced emission characteristics (AIE-dots) is being intensively studied, their clinical translation in efficient biotherapeutic devices has yet to be tackled. This study explores the synergistic interplay of oligo(styryl)benzenes (OSBs), potent fluorogens with an increased emission in the aggregate state, and Indocyanine green (ICG) as dual Near Infrared (NIR)-visible fluorescent nanovesicles with efficient reactive oxygen species (ROS) generation capacity for cancer treatment using photodynamic therapy (PDT). The co-loading of OSBs and ICG in different nanovesicles has been thoroughly investigated. The nanovesicles' physicochemical properties were manipulated via molecular engineering by modifying the structural properties of the lipid bilayer and the number of oligo(ethyleneoxide) chains in the OSB structure. Diffusion Ordered Spectroscopy (DOSY) NMR and spectrofluorometric studies revealed key differences in the structure of the vesicles and the arrangement of the OSB and ICG in the bilayer. The in vitro assessment of these OSB-ICG nanovesicles revealed that the formulations can increase the temperature and generate ROS after photoirradiation, showing for the first time their potential as dual photothermal/photodynamic (PTT/PDT) agents in the treatment of prostate cancer. Our study provides an exciting opportunity to extend the range of applications of OSB derivates to potentiate the toxicity of phototherapy in prostate and other types of cancer.

Luminescence Probes in Bio-Applications: From Principle to Practice

Bioanalysis based on optical imaging has gained significant progress in the last few decades. Luminescence probes are capable of detecting, monitoring, and tracing particular biomolecules in complex biological systems to figure out the roles of these molecules in organisms. Considering the rapid development of luminescence probes for bio-applications and their promising future, we have attempted to explore the working principles and recent advances in bio-applications of luminescence probes, in the hope of helping readers gain a detailed understanding of luminescence probes developed in recent years. In this review, we first focus on the current widely used luminescence probes, including fluorescence probes, bioluminescence probes, chemiluminescence probes, afterglow probes, photoacoustic probes, and Cerenkov luminescence probes. The working principles for each type of luminescence probe are concisely described and the bio-application of the luminescence probes is summarized by category, including metal ions detection, secretion detection, imaging, and therapy.

Improving Three-Photon Fluorescence of Near-Infrared Quantum Dots for Deep Brain Imaging by Suppressing Biexciton Decay

Three-photon fluorescence microscopy (3PFM) is a promising brain research tool with submicrometer spatial resolution and high imaging depth. However, only limited materials have been developed for 3PFM owing to the rigorous requirement of the three-photon fluorescence (3PF) process. Herein, under the guidance of a band gap engineering strategy, CdTe/CdSe/ZnS quantum dots (QDs) emitting in the near-infrared window are designed for constructing 3PF probes. The formation of type II structure significantly increased the three-photon absorption cross section of QDs and caused the delocalization of electron-hole wave functions. The time-resolved transient absorption spectroscopy confirmed that the decay of biexcitons was significantly suppressed due to the appropriate band gap alignment, which further enhanced the 3PF efficiency of QDs. By utilizing QD-based 3PF probes, high-resolution 3PFM imaging of cerebral vasculature was realized excited by a 1600 nm femtosecond laser, indicating the possibility of deep brain imaging with these 3PF probes.

Semiconducting polymer dots for multifunctional integrated nanomedicine carriers

The expansion applications of semiconducting polymer dots (Pdots) among optical nanomaterial field have long posed a challenge for researchers, promoting their intelligent application in multifunctional nano-imaging systems and integrated nanomedicine carriers for diagnosis and treatment. Despite notable progress, several inadequacies still persist in the field of Pdots, including the development of simplified near-infrared (NIR) optical nanoprobes, elucidation of their inherent biological behavior, and integration of information processing and nanotechnology into biomedical applications. This review aims to comprehensively elucidate the current status of Pdots as a classical nanophotonic material by discussing its advantages and limitations in terms of biocompatibility, adaptability to microenvironments in vivo, etc. Multifunctional integration and surface chemistry play crucial roles in realizing the intelligent application of Pdots. Information visualization based on their optical and physicochemical properties is pivotal for achieving detection, sensing, and labeling probes. Therefore, we have refined the underlying mechanisms and constructed multiple comprehensive original mechanism summaries to establish a benchmark. Additionally, we have explored the cross-linking interactions between Pdots and nanomedicine, potential yet complete biological metabolic pathways, future research directions, and innovative solutions for integrating diagnosis and treatment strategies. This review presents the possible expectations and valuable insights for advancing Pdots, specifically from chemical, medical, and photophysical practitioners' standpoints.

The utilization of nanotechnology in the female reproductive system and related disorders

The health of the reproductive system is intricately linked to female fertility and quality of life. There has been a growing prevalence of reproductive system disorders among women, particularly in younger age groups, resulting in significant adverse effects on their reproductive health. Consequently, there is an urgent need for effective treatment modalities. Nanotechnology, as an advanced discipline, provides innovative avenues for managing and treating diseases of the female reproductive system by enabling precise manipulation and regulation of biological molecules and cells. By utilizing nanodelivery systems, drugs can be administered with pinpoint accuracy, leading to reduced side effects and improved therapeutic efficacy. Moreover, nanomaterial imaging techniques enhance diagnostic precision and sensitivity, aiding in the assessment of disease severity and progression. Furthermore, the implementation of nanobiosensors facilitates early detection and prevention of ailments. This comprehensive review aims to summarize recent applications of nanotechnology in the treatment of female reproductive system diseases. The latest advancements in drug delivery, diagnosis, and treatment approaches will be discussed, with an emphasis on the potential of nanotechnology to improve treatment outcomes and overall quality of life.

The Bioimaging Story of AIEgens

Observations of the micro world, especially the structures of organelles, have been attractive topics since the 17th century. As a powerful detection tool, the fluorescence technique has played a significant role in bioimaging to provide more details and enhance the signal-to-noise ratio compared to that of traditional optical microscopes. The boom of aggregate-induced emission luminogens (AIEgens) in the last two decades has revolutionized the design strategy of luminescent materials for biological applications. This Review summarizes the advantages and recent progress of AIEgens in imaging and tracking. Different imaging strategies of AIEgens including turn-on imaging, stimuli-response sensing, and long-term tracking are presented. NIR AIEgens used for in-depth bioimaging via different methods are also discussed. Finally, we propose several potential development directions for AIEgens in bioimaging.

Second Near-Infrared (NIR-II) Window for Imaging-Navigated Modulation of Brain Structure and Function

For a long time, optical imaging of the deep brain with high resolution has been a challenge. Recently, with the advance in second near-infrared (NIR-II) bioimaging techniques and imaging contrast agents, NIR-II window bioimaging has attracted great attention to monitoring deeper biological or pathophysiological processes with high signal-to-noise ratio (SNR) and spatiotemporal resolution. Assisted with NIR-II bioimaging, the modulation of structure and function of brain is promising to be noninvasive and more precise. Herein, in this review, first the advantage of NIR-II light in brain imaging from the interaction between NIR-II and tissue is elaborated. Then, several specific NIR-II bioimaging technologies are introduced, including NIR-II fluorescence imaging, multiphoton fluorescence imaging, and photoacoustic imaging. Furthermore, the corresponding contrast agents are summarized. Next, the application of various NIR-II bioimaging technologies in visualizing the characteristics of cerebrovascular network and monitoring the changes of the pathology signals will be presented. After that, the modulation of brain structure and function based on NIR-II bioimaging will be discussed, including treatment of glioblastoma, guidance of cell transplantation, and neuromodulation. In the end, future perspectives that would help improve the clinical translation of NIR-II light are proposed.

Nanomaterials as multimodal photothermal agents (PTAs) against 'Superbugs'

Superbugs, also known as multidrug-resistant bacteria, have become a lethal and persistent threat due to their unresponsiveness toward conventional antibiotics. The main reason for this is that superbugs can rapidly mutate and restrict any foreign drug/molecule in their vicinity. Herein, nanomaterial-mediated therapies have set their path and shown burgeoning efficiency toward the ablation of superbugs. Notably, treatment modalities like photothermal therapy (PTT) have shown prominence in killing multidrug-resistant bacteria with their ability to generate local heat shock-mediated hyperthermia in such species. However, photothermal treatment has some serious limitations, such as high cost, complexity, and even toxicity to some extent. Hence, it is important to resolve such shortcomings of PTTs as they provide substantial tissue penetration. This is why multimodal PTTs have emerged and taken over this domain of research for the past few years. In this work, we have summarized and critically reviewed such exceptional works of recent times and provided a perspective to enhance their efficiencies. Profoundly, we discuss the design rationales of some novel photothermal agents (PTAs) and shed light on their mechanisms. Finally, challenges for PTT-derived multimodal therapy are presented, and capable synergistic bactericidal prospects are anticipated.

Noncancerous disease-targeting AIEgens

Noncancerous diseases include a wide plethora of medical conditions beyond cancer and are a major cause of mortality around the world. Despite progresses in clinical research, many puzzles about these diseases remain unanswered, and new therapies are continuously being sought. The evolution of bio-nanomedicine has enabled huge advancements in biosensing, diagnosis, bioimaging, and therapeutics. The recent development of aggregation-induced emission luminogens (AIEgens) has provided an impetus to the field of molecular bionanomaterials. Following aggregation, AIEgens show strong emission, overcoming the problems associated with the aggregation-caused quenching (ACQ) effect. They also have other unique properties, including low background interferences, high signal-to-noise ratios, photostability, and excellent biocompatibility, along with activatable aggregation-enhanced theranostic effects, which help them achieve excellent therapeutic effects as an one-for-all multimodal theranostic platform. This review provides a comprehensive overview of the overall progresses in AIEgen-based nanoplatforms for the detection, diagnosis, bioimaging, and bioimaging-guided treatment of noncancerous diseases. In addition, it details future perspectives and the potential clinical applications of these AIEgens in noncancerous diseases are also proposed. This review hopes to motivate further interest in this topic and promote ideation for the further exploration of more advanced AIEgens in a broad range of biomedical and clinical applications in patients with noncancerous diseases.

Photophysical and anion sensing properties of a triphenylamine-dioxaborinine trimeric compound

Herein, we report the synthesis and photophysical characterization of the novel tris(4-(2,2-difluoro-6-methyl-2H-1λ³,3,2λ⁴-dioxaborinin-4-yl)phenyl)amine trimeric probe (A2) via the reaction between triphenylamine (1), acetic anhydride, and BF₃·OEt₂ implying the twelve new bond formation in a one-pot manner. This highly fluorescent compound in solution (φ up to 0.91 at 572 nm) and solid state (φ = 0.24 at 571 nm) showed a better solvatofluorochromism than its analog monomeric A1 due to symmetry-broken charge transfer, which is consistent with high solvent dipolarity (SdP) response in Catalán's multiparametric regression. Notably, A2 had a high sensibility and selectivity for CN^- or F^- in solution (LODCN^-/F^- = 0.18/0.70 μM), and CN^- can be discriminated from F^- by the reaction of A2 with 3.0 equiv. of CN^-. In addition, A2 was impregnated on filter paper to prepare test strips that were applied to naked-eye qualitative sensing of CN^- or F^-. Finally, the octupolar system in A2 allows for better action of two-photon excitation cross-section values when compared with that of the dipolar structure in A1. These findings provide further information for the design of new efficient two-photon absorption dyes.

Facile construction of highly luminescent and biocompatible gold nanoclusters by shell rigidification for two-photon pH-edited cytoplasmic and in vivo imaging

Gold nanoclusters (AuNCs), as a novel fluorescent material, have been extensively explored and developed for bioimaging because of their attractive advantages such as ultrasmall size, low toxicity and exceptional two-photon excitation properties. However, it still remains a challenge to produce water-soluble, biocompatible and ultrabright AuNCs. Herein, we report on a novel one-pot synthesis of highly luminescent and biocompatible AuNCs by using polyvinyl pyrrolidone (PVP), a water-soluble polymer, to rigidify the primary stabilizing layer (shell) that is composed of 6-aza-2-thiothymine (ATT) ligands bound to the particle. Such shell-rigidification resulted in a significant enhancement of the fluorescence efficiency, reaching a quantum yield of 39% under the best conditions, about 35-fold increase from the intrinsically weak fluorescence of the AuNCs stabilized by only ATT. The fluorescence enhancement mechanism was systematically characterized, and the results indicate that PVP coating rigidifies the ATT ligand shell through steric hindrance and reduces the nonradiative relaxation of the excited states. The biocompatible PVP-AuNCs were further examined for two-photon cellular and sentinel lymph node (SLN) bioimaging, and we observed pH-dependent cytoplasmic images and intense green fluorescence in SLN and lymphatic vessels.

Assembly of Aggregation-Induced Emission Active Bola-Amphiphilic Macromolecules into Luminescent Nanoparticles Optimized for Two-Photon Microscopy In Vivo

The (Z) and (E)-isomers of an extended tetraphenylethylene-based chromophore with optimized two-photon-induced luminescence properties are separated and functionalized with water-solubilizing pendant polymer groups, promoting their self-assembly in physiological media in the form of small, colloidal stable organic nanoparticles. The two resulting fluorescent suspensions are then evaluated as potential two-photon luminescent contrast agents for intravital epifluorescence and two-photon fluorescence microscopy. Comparisons with previously reported works involving similar fluorophores devoid of polymer side chains illustrate the benefits of later functionalization regarding the control of the self-assembly of the nano-objects and ultimately their biocompatibility toward the imaged organism.

Aggregation-Induced Emission Boosting the Study of Polymer Science

The past one hundred years witness the great development of polymer science. The advancement of polymer science is closely related with the developing of characterization techniques and methods, from viscometry in molecular weight determination to advanced techniques including differential scanning calorimetry, nuclear magnetic resonance and scanning electron microscopy. However, these techniques are normally constrained to tedious sample preparation, high cost, harsh experimental condition, or ex-situ characterization. Fluorescence technology has the merits of high sensitivity and direct visualization. Contrary to conventional aggregation-causing quenching fluorophores, those dyes with aggregation-induced emission characteristic show high emission efficiency in aggregate states. Based on the restriction of intramolecular motions for AIE properties, the AIE materials are very sensitive to the surrounding microenvironments owing to the twisted propeller-like structures and therefore reveal great potentials in polymer's study. The AIE concept has been successfully used in polymer's study and provides us a deeper understanding on polymer structure and properties. In this review, the applications of AIEgens in polymer science for visualizing polymerization, glass transition, dissolution, crystallization, gelation, self-assembly, phase separation, cracking and self-healing were exemplified and summarized. Lastly, the challenges and perspectives in the study of polymer science using AIEgens are addressed. This article is protected by copyright. All rights reserved.

Recent Advances in the Development and Applications of Conjugated Polymer dots

Conjugated polymer dots or semiconducting polymer nanoparticles (Pdots) are nanoparticles prepared based on organic polymers. Pdots have the advantages of lower cost, simple preparation process, good biocompatibility, excellent stability, easy...

Photoactivatable Biomedical Materials Based on Luminogens with Aggregation-Induced Emission (AIE) Characteristics

Fluorescence probes with aggregation-induced emission (AIE) property are fascinating and vital in biological fields due to their bright fluorescence in the solid state. In contrast, traditional AIE materials are obscured by the off-target effects and lack of spatial and temporal control. Photoactivatable materials with AIE characteristics, whose physicochemical behaviors can be remotely activated by light, provide great potential in biochemical information acquisition with high spatial and temporal resolution. By using AIE-featured photoactivatable fluorescence probes, accurate analysis of the targets of interest is possible. For example, where, when, and to what extent a process is started or stopped by manipulating the non-invasive light accurately. Thus, many researchers are enthusiastic about developing AIE-featured photoactivatable materials and mainly focus on developing novel molecules by rational molecular structure design, and exploring advanced applications by appropriate molecular functionalization. In this review, the recent achievements of photoactivatable materials with AIE characteristics from the aspects involving inherent mechanism of photoactivity, molecular design strategy, and the corresponding applications in biological fields, are summarized. The biological applications are highlighted and discussed, including photoactivatable bioimaging, diagnosis, and photo-controlled therapy. Finally, the challenges and prospects of the AIE-featured photoactivatable materials are also outlined and discussed.

Functionalization of Silk by AIEgens through Facile Bioconjugation: Full-Color Fluorescence and Long-Term Bioimaging

Silkworm silk is a promising natural biopolymer for textile and biomedical applications for its remarkable flexibility, excellent biocompatibility and controllable biodegradability. The functionalization of silks makes them more versatile for flexible displays and visible bioscaffolds. However, fluorescent silks are normally fabricated through unstable physical absorption or complicated chemical reactions under harsh conditions. Herein, we developed a simple strategy for preparing fluorescent silks. Five aggregation-induced emission luminogens (AIEgens) with activated alkynes were synthesized by rational molecular design, and then reacted with silk fibers through facile metal-free click bioconjugation. The resulting conjugates show bright full-color emissions and high stability. A white light-emitting silk was fabricated by simultaneous bioconjugation with red-, green- and blue-emissive AIEgens. The red-emissive AIEgen-functionalized silks were successfully applied for long-term cell tracking and two-photon bioimaging, demonstrating great potential for tissue engineering and bioscaffold monitoring.

A benzothiazole-based near-infrared fluorescent probe for sensing SO2 derivatives and viscosity in HeLa cells

The unbalanced metabolism of sulfur dioxide can cause various diseases, such as neurological disorders and lung cancer. Until now, some researches revealed that the normal function of lysosomes would be disrupted by its abnormal viscosity. As a signal molecule, sulfur dioxide (SO₂) plays an important role in lysosome metabolism. However, the connection of metabolism between the SO₂ and viscosity in lysosomes is still unknown. Herein, we developed a benzothiazole-based near-infrared (NIR) fluorescent probe (Triph-SZ), which can monitor the SO₂ derivatives and respond to the change of viscosity in lysosomes through two-photon imaging. Triph-SZ present high sensitivity and selectivity fluorescence response with the addition of SO₂ derivatives based on the nucleophilic addition, and it also exhibits a sensitive fluorescence enhancement to environmental viscosity, which allows Triph-SZ to be employed to monitor the level of HSO₃^- and viscosity changes in lysosomes by the two-photon fluorescence lifetime imaging microscopy.

Recent Advances in Two-Photon AIEgens and Their Application in Biological Systems

Two-photon fluorescence imaging technology has the advantages of high light stability, little light damage, and high spatiotemporal resolution, which make it a powerful biological analysis method. However, due to the high concentration or aggregation state of traditional organic light-emitting molecules, the fluorescence intensity is easily reduced or disappears completely, and is not conducive to optimal application. The concept of aggregation-induced emission (AIE) provides a solution to the problem of aggregation-induced luminescence quenching (ACQ), and realizes the high fluorescence quantum yield of luminescent molecules in the aggregation state. In addition, two-photon absorption properties can readily be improved just by increasing the loading content of AIE fluorogen (AIEgen). Therefore, the design and preparation of two-photon fluorescence probes based on AIEgen to achieve high-efficiency fluorescence imaging in vitro/in vivo has become a major research hotspot. This review aims to summarize representative two-photon AIEgens based on triphenylamine, tetraphenylethene, quinoline, naphthalene and other new structures from the past five years, and discuss their great potential in bioimaging applications.

A lysosomal targeted NIR photosensitizer for photodynamic therapy and two-photon fluorescence imaging

A lysosome-targeting NIR photosensitizer has been developed for two-photon fluorescence imaging and imaging-guided photodynamic therapy via lysosomal-damage-mediated apoptosis.

Fluorescent AIE-Active Materials for Two-Photon Bioimaging Applications

Fluorescence imaging has been widely used as a powerful tool for in situ and real-time visualization of important analytes and biological events in live samples with remarkably high selectivity, sensitivity, and spatial resolution. Compared with one-photon fluorescence imaging, two-photon fluorescence imaging exhibits predominant advantages of minimal photodamage to samples, deep tissue penetration, and outstanding resolution. Recently, the aggregation-induced emission (AIE) materials have become a preferred choice in two-photon fluorescence biological imaging because of its unique bright fluorescence in solid and aggregate states and strong resistance to photobleaching. In this review, we will exclusively summarize the applications of AIE-active materials in two-photon fluorescence imaging with some representative examples from four aspects: fluorescence detection, in vitro cell imaging, ex vivo tissue imaging, and in vivo vascular imaging. In addition, the current challenges and future development directions of AIE-active materials for two-photon bioimaging are briefly discussed.

Nanoparticles of Organic Electronic Materials for Biomedical Applications

Organic electronic materials play important roles in modern electronic devices such as light-emitting diodes, solar cells, and transistors. Upon interaction with light, these optically active materials can undergo different photophysical and photochemical pathways, providing unique opportunities for optimization of light emission via radiative decay, heat generation via nonradiative decay, and singlet oxygen production or phosphorescence emission via intersystem crossing, all of which open alternative opportunities for their applications in sensing, imaging, and therapy. In this Perspective, we discuss all of the pathways that determine the optical properties of high-performance organic electronic materials, focusing on the optimization of each pathway for photogeneration and relaxation of electronic excited states. We also examine nanoparticle (NP) fabrication techniques tailored to macromolecules and small molecules to render them into NPs with optimized size and distribution for biomedical applications and endow organic electronic materials with water dispersibility and biocompatibility. Lastly, we illustrate the in vitro and in vivo applications of some representative organic electronic materials after optimization of each relaxation pathway.

Biomass-Based Polymer Nanoparticles With Aggregation-Induced Fluorescence Emission for Cell Imaging and Detection of Fe3+ Ions

Polymeric nanoparticles, which show aggregation-induced luminescence emission, have been successfully prepared from larch bark, a natural renewable biomass resource, in a simple, rapid ultrasonic fragmentation method. The structure, element, particle size and molecular weight distribution of larch bark extracts (LBE) were studied by FTIR, XPS, TEM, XRD and linear mode mass spectrometry, respectively. LBE was found containing large numbers of aromatic rings, displaying an average particle size of about 4.5 nm and mainly presenting tetramers proanthocyanidins. High concentration, poor solvent, low temperature and high viscosity restricted the rotation and vibration of the aromatic rings in LBE, leading to the formation of J-aggregates and enhancing the aggregation-induced fluorescence emission. LBE possessed good resistance to photobleaching under ultraviolet light (200 mW/m²). Cytotoxicity experiments for 24 h and flow cytometry experiments for 3 days proved that even the concentrations of LBE as high as 1 mg/mL displayed non-toxic to MG-63 cells. Therefore, LBE could be employed for MG-63 cell imaging, with similar nuclear staining to the DAPI. The effects of different metal ions on the fluorescence emission intensity of LBE were analyzed and exhibited that Fe³⁺ owned obvious fluorescence quenching effect on LBE, while other metal ions possessed little or weak effect. Furthermore, the limit of detection (LOD) of Fe³⁺ was evaluated as 0.17 μM.

Facile Synthesis of Efficient Luminogens with AIE Features for Three-Photon Fluorescence Imaging of the Brain through the Intact Skull

Visualization of the brain in its native environment is important for understanding common brain diseases. Herein, bright luminogens with remarkable aggregation-induced emission (AIE) characteristics and high quantum yields of up to 42.6% in the solid state are synthesized through facile reaction routes. The synthesized molecule, namely BTF, shows ultrabright far-red/near-infrared emission and can be fabricated into AIE dots by a simple nanoprecipitation procedure. Due to their high brightness, large Stokes shift, good biocompatibility, satisfactory photostability, and large three-photon absorption cross section, the AIE dots can be utilized as efficient fluorescent nanoprobes for in vivo brain vascular imaging through the intact skull by a three-photon fluorescence microscopy imaging technique. This is the first example of using AIE dots for the visualization of the cerebral stroke process through the intact skull of a mouse with high penetration depth and good image contrast. Such good results are anticipated to open up a new venue in the development of efficient emitters with strong nonlinear optical effects for noninvasive bioimaging of living brain.

Amplified electrochemiluminescence signals promoted by the AIE-active moiety of D-A type polymer dots for biosensing

Three-component conjugated polymers of a strong donor-acceptor (D-A) type could be synthesized by Pd-catalyzed Suzuki coupling polymerization reaction of 1,2-bis(4-bromophenyl)-1,2-diphenylethene (M-1) with 9-octyl-3,6-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9H-carbazole (M-2) and 4,6-bis((E)-4-bromostyryl)-2,2-difluoro-5-phenyl-2H-1l3,3,2l4-dioxaborinine (M-3). Among them, P-1 and P-2 with high TPE ratios at 0.95 and 0.9 showed obvious aggregation-induced emission (AIE) behavior; in contrast P-3 with a low TPE ratio at 0.8 showed an aggregation-caused quenching (ACQ) phenomenon. In particular, the three resulting polymer dots (P-1 to P-3 Pdots) exhibited a 200 mV lower electrochemiluminescence (ECL) potential due to their strong D-A electronic structure. Most importantly, the ECL signals of Pdots could be enhanced as high as 3 times by increasing their AIE-active TPE moiety ratios from 0.8 (P-3) to 0.95 (P-1) via the band gap emission process. Herein, P-1 Pdots with the strongest ECL signal were successfully used as ECL biosensors for the detection of catechol, epinephrine and dopamine with detection limits of 1, 7 and 3 nM, respectively. This work provides a new strategy for developing highly sensitive ECL biosensors by the smart structure design of the AIE-active Pdots.

Fluorescent Materials With Aggregation-Induced Emission Characteristics for Array-Based Sensing Assay

Array-based sensing is a powerful tool for identifying analytes in complex environments with unknown interferences. In array-based sensing, the sensors, which transduce binding details to signal outputs, are of crucial importance for identifying analytes. Aggregation-induced emission luminogens (AIEgens) enjoy the advantages of easy synthesis and high sensitivity, which enable them to facilely form a sensor pool through structural modifications and sensitively reflect the subtle changes associated with binding events. All these features make AIEgens excellent candidates for array-based sensing, and attempts have been made by several research groups to explore their potentials in array-based sensing. In this review, we introduce the recent progresses of employing AIEgens as sensors in sensing assays and in building up sensor arrays for identification of varied biological analytes, including biomolecules and bacteria. Examples are selected to illustrate the working mechanism, probe design and selection, capability of the sensor array, and implications of these sensing methods.

Two-photon imaging of aptamer-functionalized Copolymer/TPdye fluorescent organic dots targeted to cancer cells

Fluorescent organic dots (O-dots) recently have emerged as a new class of promising contrast reagents for two-photon fluorescence (TPF) imaging. However, most of these developed two-photon absorption (TPA) O-dots have no tumor-targeting group, which hampers their wide application for targeted tumor imaging. Herein, we fabricated Sgc8c aptamer-mediated TPA O-dots as a proof-of-concept of the sensing platform for targeted imaging in live cells or deep tissues. The O-dots composed of trans-4-[p-(N, N-diethylamino)styryl]-4'-(dimethyl amino) stilbene (DEAS) emerged as TPA organic emissive cores and encapsulation by using poly (methyl methacrylate-co-methacrylic acid) (PMMA-co-MAA) as polymeric encapsulating matrix to form DEAS/PMMA-co-MAA O-dots via a co-precipitation strategy. The obtained O-dots enabled an extremely high TPA absorption cross-section, bright two-photon fluorescence (excitation at 720 nm; emission at 412 nm and 434 nm), excellent cell-permeability and high penetration depth. Sgc8c aptamer, as a protein tyrosine kinase-7 (PTK7) receptor-targetable ligand, was further anchored on the surface of O-dots to obtain DEAS/PMMA-co-MAA@Sgc8c nanoprobes by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC)-mediated coupling reaction. Guided by Sgc8c aptamer, DEAS/PMMA-co-MAA@Sgc8c nanoprobes could be rapidly internalized into target acute lymphoblastic leukemia cells (CEM) cells with high specificity and great efficiency. It was also performed that two-photon images of TPA nanoprobes exhibited high two-photon brightness not only in target CEM cells, but also in mouse liver tissue slices even a depth of up to 210 μm. In our perception, it is highly promising that this nanoprobe provides a valuable tool for in vivo targeted imaging.

Highly efficient singlet oxygen generation, two-photon photodynamic therapy and melanoma ablation by rationally designed mitochondria-specific near-infrared AIEgens

Photosensitizers (PSs) with multiple characteristics, including efficient singlet oxygen (¹O₂) generation, cancer cell-selective accumulation and subsequent mitochondrial localization as well as near-infrared (NIR) excitation and bright NIR emission, are promising candidates for imaging-guided photodynamic therapy (PDT) but rarely concerned. Herein, a simple rational strategy, namely modulation of donor-acceptor (D-A) strength, for molecular engineering of mitochondria-targeting aggregation-induced emission (AIE) PSs with desirable characteristics including highly improved ¹O₂ generation efficiency, NIR emission (736 nm), high specificity to mitochondria, good biocompatibility, high brightness and superior photostability is demonstrated. Impressively, upon light irradiation, the optimal NIR AIE PS (DCQu) can generate ¹O₂ with efficiency much higher than those of commercially available PSs. The excellent two-photon absorption properties of DCQu allow two-photon fluorescence imaging of mitochondria and subsequent two-photon excited PDT. DCQu can selectively differentiate cancer cells from normal cells without the aid of extra targeting ligands. Upon ultralow-power light irradiation at 4.2 mW cm^-2, in situ mitochondrial photodynamic activation to specifically damage cancer cells and efficient in vivo melanoma ablation are demonstrated, suggesting superior potency of the AIE PS in imaging-guided PDT with minimal side effects, which is promising for future precision medicine.

Strategies for Tumor Hypoxia Imaging Based on Aggregation-Induced Emission Fluorogens

Hypoxia, as a crucial characteristic of cancer, has become an extremely significant direction for researchers to construct fluorescent probes for early diagnosis of tumors. Aggregation-induced emission fluorogens (AIEgens) possess many superior properties to those of conventional fluorophores due to aggregation-induced emission (AIE) features, such as a linear concentration-dependent increase in brightness, remarkable resistance to photobleaching, and the long-term tracking and imaging of cells. Constructing hypoxic response AIEgen-based probes will be very useful for the early diagnosis of tumors. Herein, several hypoxia-responsive probes based on AIEgens reported in the last three years are reported; these examples may lead to the construction of hypoxia-responsive AIE probes used for tumor hypoxia imaging in the future. In addition, typical, conventional hypoxia-responsive bioprobes are presented to further understand hypoxia-responsive fluorescent probes based on AIEgens.

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.

Synthesis, photophysical and electropolymerization properties of thiophene-substituted 2,3-diphenylbuta-1,3-dienes

Electropolymerizable diphenylbuta-1,3-diene derivatives with AIE or AEE properties were synthesized allowing low bandgap polymers to be obtained through electropolymerization processes.

Recent advances of AIE dots in NIR imaging and phototherapy

Nanomaterials are indispensable tools for imaging and therapy. Organic dots with aggregation-induced emission characteristics (AIE dots) have emerged as a new nanolight for their ultra-brightness, excellent photostability and biocompatibility. Due to the rotor structures, most of the reported AIE luminogens show short wavelength absorption and emission, an intrinsic disadvantage for their biomedical applications. Recently, more exciting examples reveal that properly designed AIE dots can easily reach NIR emission, excitable by near-infrared (NIR) light via multiphoton processes, which also have great potentials in photoacoustic imaging (PAI) and phototherapy. In this review, we summarize the recent advances of AIE nanomaterials for NIR fluorescence imaging, PAI, image-guided photodynamic and photothermal therapy (PDT and PTT). We highlight various strategies to improve the energy conversion efficiency of AIE dots through controlling different energy decay pathways. With this review, we hope to encourage more precise design of organic nanomaterials for biomedical applications.

Aggregation-Induced Nonlinear Optical Effects of AIEgen Nanocrystals for Ultradeep In Vivo Bioimaging

Nonlinear optical microscopy has become a powerful tool in bioimaging research due to its unique capabilities of deep optical sectioning, high-spatial-resolution imaging, and 3D reconstruction of biological specimens. Developing organic fluorescent probes with strong nonlinear optical effects, in particular third-harmonic generation (THG), is promising for exploiting nonlinear microscopic imaging for biomedical applications. Herein, a simple method for preparing organic nanocrystals based on an aggregation-induced emission (AIE) luminogen (DCCN) with bright near-infrared emission is successfully demonstrated. Aggregation-induced nonlinear optical effects, including two-photon fluorescence (2PF), three-photon fluorescence (3PF), and THG, of DCCN are observed in nanoparticles, especially for crystalline nanoparticles. The nanocrystals of DCCN are successfully applied for 2PF microscopy at 1040 nm NIR-II excitation and THG microscopy at 1560 nm NIR-II excitation, respectively, to reconstruct the 3D vasculature of the mouse cerebral vasculature. Impressively, the THG microscopy provides much higher spatial resolution and brightness than the 2PF microscopy and can visualize small vessels with diameters of ≈2.7 µm at the deepest depth of 800 µm in a mouse brain. Thus, this is expected to inspire new insights into the development of advanced AIE materials with multiple nonlinearity, in particular THG, for multimodal nonlinear optical microscopy.

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.

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.

Recent Advances in Aggregation-Induced Electrochemiluminescence

The emergence of the rising alliance between aggregation-induced emission (AIE) and electrochemiluminescence (ECL) is defined as aggregation-induced electrochemiluminescence (AIECL). The booming science of AIE has proved to be not only distinguished in luminescent materials but could also inject new possibility into ECL analysis. Especially in the aqueous phase and solid state for hydrophobic materials, AIE helps ECL circumvent the dilemma between substantial emission intensity and biocompatible media. The wide range of analytes makes ECL an overwhelmingly interesting analytical technique. Therefore, AIECL has gained potential in clinical diagnostics, environmental assays, and biomarker detections. This review will focus on introduction of the novel concept of AIECL, current applied luminophores, and related applications developed in recent years.

In vitro anticancer activity of AIEgens

Fluorogens with aggregation-induced emission (AIE) characteristics (AIEgens) possess unique optical properties, design flexibility, and multi-functional capabilities and have established their niche as smart materials since their discovery in 2001. In recent years, AIEgens have found varied applications in sensing, imaging, and therapy in biomedical research. In this work, we systematically and comprehensively investigate the in vitro anticancer activity of AIEgens. We report the high cytotoxicity of AIEgens against cancer cells, especially against cancer stem cells (CSCs) which show high resistance to existing therapeutic drug regimens. Furthermore, we explore the role of AIEgens as novel image-guided chemotherapy agents that offer a new avenue for efficient cancer treatment.