Seeing the unseen: AIE luminogens for super-resolution imaging

Conceptually innovative fluorophores for functional bioimaging

Fluorophore chemistry is at the forefront of bioimaging, revolutionizing the visualization of biological processes with unparalleled precision. From the serendipitous discovery of mauveine in 1856 to cutting-edge fluorophore engineering, this field has undergone transformative evolution. Today, the synergy of chemistry, biology, and imaging technologies has produced diverse, specialized fluorophores that enhance brightness, photostability, and targeting capabilities. This review delves into the history and innovation of fluorescent probes, showcasing their pivotal role in advancing our understanding of cellular dynamics and disease mechanisms. We highlight groundbreaking molecules and their applications, envisioning future breakthroughs that promise to redefine biomedical research and diagnostics.

Intermolecular Assembly of Dual Hydrogen Bonding Regio-Isomers Generates High-Performance AIE Probes

Regio-isomers are utilized to design innovative AIE luminogens (AIEgens) by regulating molecular aggregation behavior. However, relevant examples are limited, and the underlying mechanism is not fully understood. Herein, a regio-isomer strategy is used to develop AIEgens by precisely regulating the intermolecular interactions in the solid state. Among the regio-isomers it is investigated, ortho- isomer (DCM-O3-O7) exhibits enhanced AIE-activity than the para- isomer (DCM-P6), and the size of the ortho- substituents is crucial for the AIE performance. The underlying mechanism of the strategy is revealed using DFT calculations and single-crystal analysis. Dual hydrogen bonds (C─H∙∙∙π and C─H∙∙∙N) are generated between the molecules, which contributes to form dimers, tetramers, and 1D supramolecular structures in the crystal. By restricting intramolecular motion and attenuating π-π interactions, solid-state fluorescence is significantly enhanced. This strategy's effectiveness is validated using other donor-acceptor fluorophores, with DCM-O6 and its analogues serving as efficient probes for bioimaging applications. Notably, DCM-OM, which bears a morpholinyl instead of piperidinyl group, displayed strong lysosome-targeting ability and photostability; DCM-OP, incorporated by the hydrophilic quaternary ammonium group, exhibited wash-free imaging and cell membrane-targeting capabilities; and DCM-O6 nanoparticles enabled high-fidelity in vivo tumor imaging. Therefore, this strategy affords a general method for designing bright AIEgens.

Glowing discoveries: Schiff base-cyanostilbene probes illuminating metal ions and biological entities

Schiff bases featuring cyanostilbene units have emerged as versatile and highly effective probes for the selective detection of various metal ions as well as biologically important species. This review comprehensively highlights recent advances in the development and application of the probes, which exhibit remarkable Aggregation-Induced Emission (AIE), Twisted Intramolecular Charge Transfer (TICT), and Excited-State Intramolecular Proton Transfer (ESIPT) properties. These unique structural characteristics facilitate their potential applications in the detection of biologically important metal ions such as Zn2+, Fe3+, Cu2+, Hg2+ and Co2+ ions with high sensitivity and selectivity. Furthermore, these probes have demonstrated significant potential in the recognition of vital biological species, including arginine, hydrazine and hypochlorite (ClO-). The present review discusses the underlying detection mechanisms, emphasizing the role of the Schiff base and cyanostilbene moieties for the selective detection of particular biologically important entities. Moreover, this discussion highlights the practical applications, problems, and future directions in this fast-growing field, emphasizing the vital importance of these probes in both analytical chemistry and bioassays.

Tuning vibration-induced emission through macrocyclization and catenation

In order to investigate the effect of macrocyclization and catenation on the regulation of vibration-induced emission (VIE), the typical VIE luminogen 9,14-diphenyl-9,14-dihydrodibenzo[a, c]phenazine (DPAC) was introduced into the skeleton of a macrocycle and corresponding [2]catenane to evaluate their dynamic relaxation processes. As investigated in detail by femtosecond transient absorption (TA) spectra, the resultant VIE systems revealed precisely tunable emissions upon changing the solvent viscosity, highlighting the key effect of the formation of [2]catenane. Notably, the introduction of an additional pillar[5]arene macrocycle featuring unique planar chirality endows the resultant chiral VIE-active [2]catenane with attractive circularly polarized luminescence in different states. This work not only develops a new strategy for the design of new luminescent systems with tunable vibration induced emission, but also provides a promising platform for the construction of smart chiral luminescent materials for practical applications.

Recent advances in super-resolution optical imaging based on aggregation-induced emission

Super-resolution imaging has rapidly emerged as an optical microscopy technique, offering advantages of high optical resolution over the past two decades; achieving improved imaging resolution requires significant efforts in developing super-resolution imaging agents characterized by high brightness, high contrast and high sensitivity to fluorescence switching. Apart from technical requirements in optical systems and algorithms, super-resolution imaging relies on fluorescent dyes with special photophysical or photochemical properties. The concept of aggregation-induced emission (AIE) was proposed in 2001, coinciding with unprecedented advancements and innovations in super-resolution imaging technology. AIE probes offer many advantages, including high brightness in the aggregated state, low background signal, a larger Stokes shift, ultra-high photostability, and excellent biocompatibility, making them highly promising for applications in super-resolution imaging. In this review, we summarize the progress in implementation methods and provide insights into the mechanism of AIE-based super-resolution imaging, including fluorescence switching resulting from photochemically-converted aggregation-induced emission, electrostatically controlled aggregation-induced emission and specific binding-regulated aggregation-induced emission. Particularly, the aggregation-induced emission principle has been proposed to achieve spontaneous fluorescence switching, expanding the selection and application scenarios of super-resolution imaging probes. By combining the aggregation-induced emission principle and specific molecular design, we offer some comprehensive insights to facilitate the applications of AIEgens (AIE-active molecules) in super-resolution imaging.

One Stone, Two Birds: High-Brightness Aggregation-Induced Emission Photosensitizers for Super-Resolution Imaging and Photodynamic Therapy

Most aggregation-induced emission (AIE) luminogens exhibit high brightness, excellent photostability, and good biocompatibility, but these AIE-active agents, which kill two birds with one stone to result in applications in both stimulated emission depletion (STED) super-resolution imaging and photodynamic therapy (PDT), have not been reported yet but are urgently needed. To meet the requirements of STED nanoscopy and PDT, D-A-π-A-D type DTPABT-HP is designed by tuning conjugated π spacers. It exhibits red-shifted emission, high PLQY of 32.04%, and impressive 1O2 generation (9.24 fold compared to RB) in nanoparticles (NPs). Then, DTPABT-HP NPs are applied in cell imaging via STED nanoscopy, especially visualizing the dynamic changes of lysosomes in the PDT process at ultrahigh resolution. After that, in vivo PDT was also conducted by DTPABT-HP NPs, resulting in significantly inhibited tumor growth, with an inhibition rate of 86%. The work here is beneficial to the design of multifunctional agents and the deep understanding of their phototheranostic mechanism in biological research.

A Holistic Perspective on Living Aggregate

Aggregate is one of the most extensive existing modes of matters in the world. Besides the research objectives of inanimate systems in physical science, the entities in life science can be regarded as living aggregates, which are far from being thoroughly understood despite the great advances in molecular biology. Molecular biology follows the research philosophy of reductionism, which generally reduces the whole into parts to study. Although reductionism benefits the understanding of molecular behaviors, it encounters limitations when extending to the aggregate level. Holism is another epistemology comparable to reductionism, which studies objectives at the aggregate level, emphasizing the interactions and synergetic/antagonistic effects of a group of composed single entities in determining the characteristics of a whole. As a representative of holism, aggregation-induced emission (AIE) materials have made great achievements in the past two decades in both physical and life science. In particular, the unique properties of AIE materials endow them with in situ and real-time visual methods to investigate the inconsistency between microscopic molecules and macroscopic substances, offering researchers excellent toolkits to study living aggregates. The applications of AIE materials in life science are still in their infancy and worth expanding. In this Perspective, we summarize the research progress of AIE materials in unveiling some phenomena and processes of living systems, aiming to provide a general research approach from the viewpoint of holism. At last, insights into what we can do in the near future are also raised and discussed.

Probing the dynamic crosstalk of lysosomes and mitochondria with structured illumination microscopy

Structured illumination microscopy (SIM) is a super-resolution technology for imaging living cells and has been used for studying the dynamics of lysosomes and mitochondria. Recently, new probes and analyzing methods have been developed for SIM imaging, enabling the quantitative analysis of these subcellular structures and their interactions. This review provides an overview of the working principle and advances of SIM, as well as the organelle-targeting principles and types of fluorescence probes, including small molecules, metal complexes, nanoparticles, and fluorescent proteins. Additionally, quantitative methods based on organelle morphology and distribution are outlined. Finally, the review provides an outlook on the current challenges and future directions for improving the combination of SIM imaging and image analysis to further advance the study of organelles. We hope that this review will be useful for researchers working in the field of organelle research and help to facilitate the development of SIM imaging and analysis techniques.

Construction of aggregation-induced emission photosensitizers through host-guest interactions for photooxidation reaction and light-harvesting

In the present work, we have designed and synthesized a triphenylamine modified cyanophenylenevinylene derivative (TPCI), which can self-assembly with cucurbit[6]uril (CB[6]) and cucurbit[8]uril (CB[8]) through host-guest interactions to form supramolecular complexes (TPCI-CB[6]) and supramolecular polymers (TPCI-CB[8]) in the aqueous solution. The supramolecular assemblies of TPCI-CB[6] and TPCI-CB[8] not only exhibited high singlet oxygen (1O2) production efficiency as photosensitizers, but also realized the application in the construction of artificial light-harvesting systems due to the excellent fluorescence properties in the aqueous solution. The production efficiency of 1O2 has been effectively improved after the addition of CB[6] and CB[8] for TPCI, which were applied as efficient photosensitizers in the photooxidation reactions of thioanisole and its derivatives with the highest yield of 98% in the aqueous solution. The excellent fluorescence properties of TPCI-CB[6] and TPCI-CB[8] can be used as energy donors in artificial light-harvesting systems with energy acceptors sulforhodamine 101 (SR101) and cyanine dye 5 (Cy5), in which one-step energy transfer processes of TPCI-CB[6]+SR101 and TPCI-CB[8]+Cy5, and a two-step sequential energy transfer process of TPCI-CB[6]+SR101+Cy5 were constructed to simulate the natural photosynthesis system.

Xanthene, cyanine, oxazine and BODIPY: the four pillars of the fluorophore empire for super-resolution bioimaging

In the realm of biological research, the invention of super-resolution microscopy (SRM) has enabled the visualization of ultrafine sub-cellular structures and their functions in live cells at the nano-scale level, beyond the diffraction limit, which has opened up a new window for advanced biomedical studies to unravel the complex unknown details of physiological disorders at the sub-cellular level with unprecedented resolution and clarity. However, most of the SRM techniques are highly reliant on the personalized special photophysical features of the fluorophores. In recent times, there has been an unprecedented surge in the development of robust new fluorophore systems with personalized features for various super-resolution imaging techniques. To date, xanthene, cyanine, oxazine and BODIPY cores have been authoritatively utilized as the basic fluorophore units in most of the small-molecule-based organic fluorescent probe designing strategies for SRM owing to their excellent photophysical characteristics and easy synthetic acquiescence. Since the future of next-generation SRM studies will be decided by the availability of advanced fluorescent probes and these four fluorescent building blocks will play an important role in progressive new fluorophore design, there is an urgent need to review the recent advancements in designing fluorophores for different SRM methods based on these fluorescent dye cores. This review article not only includes a comprehensive discussion about the recent developments in designing fluorescent probes for various SRM techniques based on these four important fluorophore building blocks with special emphasis on their effective integration into live cell super-resolution bio-imaging applications but also critically evaluates the background of each of the fluorescent dye cores to highlight their merits and demerits towards developing newer fluorescent probes for SRM.

A Highly Water-Soluble Aggregation-Induced Emission Luminogen with Anion-π+ Interactions for Targeted NIR Imaging of Cancer Cells and Type I Photodynamic Therapy

The low oxygen dependence of type I photosensitizers (PSs) has made them a popular choice for treating solid tumors. However, the drawbacks of poor water solubility, short emission wavelength, poor stability, and inability to distinguish cancer cells from normal cells limit the application of most type I PSs in clinical therapy. Thereby, developing novel type I PSs for overcoming these problems is an urgent but challenging task. Herein, by utilizing the distinctive structural characteristics of anion-π+ interactions, a highly water-soluble type I PS (DPBC-Br) with aggregation-induced emission (AIE) characteristic and near-infrared (NIR) emission is fabricated for the first time. DPBC-Br displays remarkable water solubility (7.3 mM) and outstanding photobleaching resistance, enabling efficient and precise differentiation between tumor cells and normal cells in a wash-free and long-term tracking manner via NIR-I imaging. Additionally, the superior type I reactive oxygen species (ROS) produced by DPBC-Br provide both specific killing of cancer cells in vitro and inhibition of tumor growth in vivo, with negligible systemic toxicity. This study rationally constructs a highly water-soluble type I PS, which has higher reliability and controllability compared with conventional nanoparticle formulating procedures, offering great potential for clinical cancer treatment.

Aggregation-Induced Emission (AIE), Life and Health

Light has profoundly impacted modern medicine and healthcare, with numerous luminescent agents and imaging techniques currently being used to assess health and treat diseases. As an emerging concept in luminescence, aggregation-induced emission (AIE) has shown great potential in biological applications due to its advantages in terms of brightness, biocompatibility, photostability, and positive correlation with concentration. This review provides a comprehensive summary of AIE luminogens applied in imaging of biological structure and dynamic physiological processes, disease diagnosis and treatment, and detection and monitoring of specific analytes, followed by representative works. Discussions on critical issues and perspectives on future directions are also included. This review aims to stimulate the interest of researchers from different fields, including chemistry, biology, materials science, medicine, etc., thus promoting the development of AIE in the fields of life and health.

Understanding H-aggregates crystallization induced emissive behavior: insights from theory

We conducted a theoretical investigation into how the molecular stacking effect impacts the photophysical properties in solid phases. Our findings indicated that in the aggregated state, the out-of-plane distorted vibration and imidazole ring stretching vibration of triimidazo-[1,3,5] triazinethe are significantly suppressed, which decreased the Huang-Rhys factor and the corresponding reorganization energy of the photophysical process, as a result, this restricted intramolecular motions and dissipation pathways of excess energy in the excited state, therefore, aggregation induced enhancement emission (AIEE) was found for the title compound from dichloromethane solution to solid state. Analysis of the emission spectrum through discrete spectral lines revealed that the main peak was affected by the vibrational modes with lower frequencies, while the middle-frequency modes influenced the shoulder peak. Furthermore, the predicted intersystem crossing rate (k_iosk) and reverse intersystem crossing rate (k_risc) using Marcus theory confirmed that an electron can successfully shift from its S₁ state to the T₁ state, however, the reverse T₁ → S₁ process can not come into being due to very small k_risc (10^-6-10^-9 s^-1), therefore the phosphorescence can be observed. At last, we explored the influence of charge transfer process of the title compound, our theoretical data declared this process can be ignored due to its low transfer rate.

Synthesis and Characterization of Tetraphenylethene AIEgen-Based Push-Pull Chromophores for Photothermal Applications: Could the Cycloaddition-Retroelectrocyclization Click Reaction Make Any Molecule Photothermally Active?

Three new tetraphenylethene (TPE) push-pull chromophores exhibiting strong intramolecular charge transfer (ICT) are described. They were obtained via [2 + 2] cycloaddition-retroelectrocyclization (CA-RE) click reactions on an electron-rich alkyne-tetrafunctionalized TPE (TPE-alkyne) using both 1,1,2,2-tetracyanoethene (TCNE), 7,7,8,8-tetracyanoquinodimethane (TCNQ) and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F₄-TCNQ) as electron-deficient alkenes. Only the starting TPE-alkyne displayed significant AIE behavior, whereas for TPE-TCNE, a faint effect was observed, and for TPE-TCNQ and TPE-F₄-TCNQ, no fluorescence was observed in any conditions. The main ICT bands that dominate the UV-Visible absorption spectra underwent a pronounced red-shift beyond the near-infrared (NIR) region for TPE-F₄-TCNQ. Based on TD-DFT calculations, it was shown that the ICT character shown by the compounds exclusively originated from the clicked moieties independently of the nature of the central molecular platform. Photothermal (PT) studies conducted on both TPE-TCNQ and TPE-F4-TCNQ in the solid state revealed excellent properties, especially for TPE-F4-TCNQ. These results indicated that CA-RE reaction of TCNQ or F₄-TCNQ with donor-substituted are promising candidates for PT applications.

Aggregation-Induced Emission Luminogen-Encapsulated Fluorescent Hydrogels Enable Rapid and Sensitive Quantitative Detection of Mercury Ions

Hg²⁺ contamination in sewage can accumulate in the human body through the food chains and cause health problems. Herein, a novel aggregation-induced emission luminogen (AIEgen)-encapsulated hydrogel probe for ultrasensitive detection of Hg²⁺ was developed by integrating hydrophobic AIEgens into hydrophilic hydrogels. The working mechanism of the multi-fluorophore AIEgens (TPE-RB) is based on the dark through-bond energy transfer strategy, by which the energy of the dark tetraphenylethene (TPE) derivative is completely transferred to the rhodamine-B derivative (RB), thus resulting in intense photoluminescent intensity. The spatial networks of the supporting hydrogels further provide fixing sites for the hydrophobic AIEgens to enlarge accessible reaction surface for hydrosoluble Hg²⁺, as well create a confined reaction space to facilitate the interaction between the AIEgens and the Hg²⁺. In addition, the abundant hydrogen bonds of hydrogels further promote the Hg²⁺ adsorption, which significantly improves the sensitivity. The integrated TPE-RB-encapsulated hydrogels (TR hydrogels) present excellent specificity, accuracy and precision in Hg²⁺ detection in real-world water samples, with a 4-fold higher sensitivity compared to that of pure AIEgen probes. The as-developed TR hydrogel-based chemosensor holds promising potential as a robust, fast and effective bifunctional platform for the sensitive detection of Hg²⁺.

The power of super-resolution microscopy in modern biomedical science

Super-resolution microscopy (SRM) technology that breaks the diffraction limit has revolutionized the field of cell biology since its appearance, which enables researchers to visualize cellular structures with nanometric resolution, multiple colors and single-molecule sensitivity. With the flourishing development of hardware and the availability of novel fluorescent probes, the impact of SRM has already gone beyond cell biology and extended to nanomedicine, material science and nanotechnology, and remarkably boosted important breakthroughs in these fields. In this review, we will mainly highlight the power of SRM in modern biomedical science, discussing how these SRM techniques revolutionize the way we understand cell structures, biomaterials assembly and how assembled biomaterials interact with cellular organelles, and finally their promotion to the clinical pre-diagnosis. Moreover, we also provide an outlook on the current technical challenges and future improvement direction of SRM. We hope this review can provide useful information, inspire new ideas and propel the development both from the perspective of SRM techniques and from the perspective of SRM's applications.

Photochemical Mechanisms of Fluorophores Employed in Single-Molecule Localization Microscopy

Decoding cellular processes requires visualization of the spatial distribution and dynamic interactions of biomolecules. It is therefore not surprising that innovations in imaging technologies have facilitated advances in biomedical research. The advent of super-resolution imaging technologies has empowered biomedical researchers with the ability to answer long-standing questions about cellular processes at an entirely new level. Fluorescent probes greatly enhance the specificity and resolution of super-resolution imaging experiments. Here, we introduce key super-resolution imaging technologies, with a brief discussion on single-molecule localization microscopy (SMLM). We evaluate the chemistry and photochemical mechanisms of fluorescent probes employed in SMLM. This Review provides guidance on the identification and adoption of fluorescent probes in single molecule localization microscopy to inspire the design of next-generation fluorescent probes amenable to single-molecule imaging.

Instantaneous High-Resolution Visual Imaging of Latent Fingerprints in Water Using Color-Tunable AIE Pincer Complexes

Instant visualization of latent fingerprints is developed by using a series of water-soluble terpyridine zinc complexes as aggregation-induced emission probes in pure water, under UV light or ambient sunlight. By simply soaking, or spraying with an aqueous solution of the probe, bright yellow fluorescence images with high contrast and resolution are readily developed on various surfaces including tinfoil, glass, paper, steel, leather, and ceramic tile. Remarkably, latent fingerprints can be visualized within seconds including details of whorl and sweat pores. The color of emission can be tuned from blue to orange by modifying the pincer ligands, allowing direct imaging under sunlight. These inexpensive, water-resistant, and color-tunable probes provide a practical approach for latent fingerprints recording and analysis, security protection, as well as criminal investigation in different scenarios.

Reactive Species-Activatable AIEgens for Biomedical Applications

Precision medicine requires highly sensitive and specific diagnostic strategies with high spatiotemporal resolution. Accurate detection and monitoring of endogenously generated biomarkers at the very early disease stage is of extensive importance for precise diagnosis and treatment. Aggregation-induced emission luminogens (AIEgens) have emerged as a new type of excellent optical agents, which show great promise for numerous biomedical applications. In this review, we highlight the recent advances of AIE-based probes for detecting reactive species (including reactive oxygen species (ROS), reactive nitrogen species (RNS), reactive sulfur species (RSS), and reactive carbonyl species (RCS)) and related biomedical applications. The molecular design strategies for increasing the sensitivity, tuning the response wavelength, and realizing afterglow imaging are summarized, and theranostic applications in reactive species-related major diseases such as cancer, inflammation, and vascular diseases are reviewed. The challenges and outlooks for the reactive species-activatable AIE systems for disease diagnostics and therapeutics are also discussed. This review aims to offer guidance for designing AIE-based specifically activatable optical agents for biomedical applications, as well as providing a comprehensive understanding about the structure-property application relationships. We hope it will inspire more interesting researches about reactive species-activatable probes and advance clinical translations.

Rock CT Image Super-Resolution Using Residual Dual-Channel Attention Generative Adversarial Network

Because of its benefits in terms of high speed, non-destructiveness, and three-dimensionality, as well as ease of integration with computer simulation, computed tomography (CT) technology is widely applied in reservoir geology research. However, rock imaging is restricted by the device used as there is not a win–win for both the image receptive field and corresponding resolution. Convolutional neural network-based super-resolution reconstruction has become a hot topic in improving the performance of CT images. With the help of a convolution kernel, it can effectively extract characteristics and ignore disturbance information. The dismal truth is that convolutional neural networks still have numerous issues, particularly unclear texture details. To address these challenges, a generative adversarial network (RDCA-SRGAN) was designed to improve rock CT image resolution using the combination of residual learning and a dual-channel attention mechanism. Specifically, our generator employs residual attention to extract additional features; similarly, the discriminator builds on dual-channel attention and residual learning to distinguish generated contextual information and decrease computational consumption. Quantitative and qualitative analyses demonstrate that the proposed model is superior to earlier advanced frameworks and is capable to constructure visually indistinguishable high-frequency details. The quantitative analysis shows our model contributes the highest value of structural similarity, enriching the more detailed texture information. From the qualitative analysis, in enlarged details of the reconstructed images, the edges of the images generated by the RDCA-SRGAN can be shown to be clearer and sharper. Our model not only performs well in subtle coal cracks but also enriches more dissolved carbonate and carbon minerals. The RDCA-SRGAN has substantially enhanced the reconstructed image resolution and our model has great potential to be used in geomorphological study and exploration.

Recent advances in aggregation-induced emission luminogens in photoacoustic imaging

Photoacoustic imaging (PAI) is a rapidly emerging modality in biomedical research with the advantages of noncontact operation, high optical resolution, and deep penetration. Great efforts and progress in the development of PAI agents with improved imaging resolution and sensitivity have been made over the past 2 decades. Among them, organic agents are the most promising candidates for preclinical/clinical applications due to their outstanding in vivo properties and facile biofunctionalities. Motivated by the unique properties of aggregation-induced emission (AIE) luminogens (AIEgens), various optical probes have been developed for bioanalyte detection, multimodal bioimaging, photodynamic/photothermal therapy, and imaging-guided therapeutics. In particular, AIE-active contrast agents have been demonstrated in PAI applications with excellent performance in imaging resolution and tissue permeability in vivo. This paper presents a brief overview of recent progress in AIE-based agents in the field of photoacoustic imaging. In particular, we focus on the basic concepts, data sorting and comparison, developing trends, and perspectives of photoacoustic imaging. Through numerous typical examples, the way each system realizes the desired photoacoustic performance in various biomedical applications is clearly illustrated. We believe that AIE-based PAI agents would be promising multifunctional theranostic platforms in clinical fields and will facilitate significant advancements in this research topic.

Aggregation-Induced Emission (AIE) in Super-resolution Imaging: Cationic AIE Luminogens (AIEgens) for Tunable Organelle-Specific Imaging and Dynamic Tracking in Nanometer Scale

Organelle-specific imaging and dynamic tracking in ultrahigh resolution is essential for understanding their functions in biological research, but this remains a challenge. Therefore, a facile strategy by utilizing anion-π⁺ interactions is proposed here to construct an aggregation-induced emission luminogen (AIEgen) of DTPAP-P, not only restricting the intramolecular motions but also blocking their strong π-π interactions. DTPAP-P exhibits a high photoluminescence quantum yield (PLQY) of 35.04% in solids, favorable photostability and biocompatibility, indicating its potential application in super-resolution imaging (SRI) via stimulated emission depletion (STED) nanoscopy. It is also observed that this cationic DTPAP-P can specifically target to mitochondria or nucleus dependent on the cell status, resulting in tunable organelle-specific imaging in nanometer scale. In live cells, mitochondria-specific imaging and their dynamic monitoring (fission and fusion) can be obtained in ultrahigh resolution with a full-width-at-half-maximum (fwhm) value of only 165 nm by STED nanoscopy. This is about one-sixth of the fwhm value in confocal microscopy (1028 nm). However, a migration process occurs for fixed cells from mitochondria to nucleus under light activation (405 nm), leading to nucleus-targeted super-resolution imaging (fwhm= 184 nm). These findings indicate that tunable organelle-specific imaging and dynamic tracking by a single AIEgen at a superior resolution can be achieved in our case here via STED nanoscopy, thus providing an efficient method to further understand organelle's functions and roles in biological research.

Exploiting the Twisted Intramolecular Charge Transfer Effect to Construct a Wash-Free Solvatochromic Fluorescent Lipid Droplet Probe for Fatty Liver Disease Diagnosis

The prominent pathological feature of fatty liver disease lesions is excessive fat accumulation in lipid droplets in hepatocytes. Thus, developing fluorescent lipid droplet-specific probes with high permeability and a high imaging contrast provides a robust tool for diagnosing fatty liver diseases. Herein, we rationally developed a novel donor-acceptor lipophilic fluorescent probe ANI with high photostability for wash-free visualization of lipid droplets and fatty liver disease characteristics. ANI showed a typical twisted intramolecular charge transfer effect with very faint fluorescence in high-polar solvents, but dramatically boosted emissions in low-polar environments. The solvatochromic probe can selectively light up lipid droplets with a high contrast in a wash-free manner. Further use of ANI to reveal the excessive accumulation of lipid droplets with a significantly large size in the liver tissues from the fatty liver disease model mice was successfully demonstrated. The remarkable imaging performances rendered ANI an alternative tool for accurately evaluating fatty liver disease in intraoperative diagnosis.

Facilely prepared aggregation-induced emission (AIE) nanocrystals with deep-red emission for super-resolution imaging

Organic nanocrystals (NCs) with high brightness are highly desirable for biological imaging. However, the preparation of NCs by a facile and fast method is still challenging. Herein, an aggregation-induced emission (AIE) luminogen of 4,4'-(5,6-difluorobenzo[c][1,2,5]thiadiazole-4,7-diyl)bis(N,N-bis(4-methoxyphenyl)aniline) (DTPA-BT-F) in the deep-red region is designed with intensive crystalline features to obtain NCs by kinetically controlled nanoprecipitation. The prepared AIE NCs with high brightness and good photo-stability are then applied in super-resolution imaging via stimulated emission depletion (STED) nanoscopy. As observed, the nanostructures in lysosomes of both fixed and live cells are well visualized with superior lateral resolutions under STED nanoscopy (full width at half maximum values, 107 and 108 nm) in contrast to that in confocal imaging (548 and 740 nm). More importantly, dynamic monitoring and long-term tracking of lysosomal movements in live HeLa cells, such as lysosomal contact, can also be carried out by using DTPA-BT-F NCs at a superior resolution. To the best of our knowledge, this is the first case of AIE NCs prepared by nanoprecipitation for STED nanoscopy, thus providing a new strategy to develop high performance imaging agents for super-resolution imaging.