AIE-active two-photon fluorescent nanoprobe with NIR-II light excitability for highly efficient deep brain vasculature imaging

Clinical applications of nanoprobes of high-resolution in vivo imaging

Currently, the primary imaging methods used in clinical diagnosis are X-ray, computed tomography (CT), ultrasound, magnetic resonance imaging (MRI), PET-CT, etc. The sensitivity and accuracy of these imaging methods bring many difficulties in clinical diagnosis; at the same time, CT, X-ray, PET-CT, etc. can cause radiation to the human body; some invasive operations of the gold standard bring much pain to the patients. Some of these tests are costly and do not allow real-time in vivo imaging (IVI). For these reasons, a new field of nanoprobes is gradually being developed in the clinical direction. Nanoprobes are known for their noninvasive, highly sensitive, real-time IVI and can even be expanded to intracellular imaging. This paper introduces the mainstream nanomaterial probes and reviews them regarding imaging means, imaging principles, biosafety, and clinical application effects.

Aggregation-induced emission luminescence for angiography and atherosclerotic diagnosis

Optical imaging technology has become increasingly recognized for its utility in diagnosing atherosclerosis thanks to advantages such as high spatial resolution, rapid data acquisition, lack of radiation exposure, cost-effectiveness, minimal invasiveness, and limited side effects. However, traditional luminogens employed in optical diagnostics are often troubled by aggregation-caused quenching (ACQ) effect, causing diagnostic errors in vivo. Since Professor Tang discovered the aggregation-induced emission (AIE) phenomenon, AIE luminogens (AIEgens) have been rapidly developing and are considered as the next-generation fluorescent contrast agents for angiography and atherosclerotic diagnosis. This mini review will outline the use of AIEgens in angiography and the diagnosis of atherosclerosis, exploring different imaging models, including second near-infrared, two/multi-photon, and photoacoustic imaging, and will provide a forward-looking perspective on their potential in atherosclerotic diagnosis.

A Near-Infrared-II Excitable Pyridinium Probe with 1000-Fold ON/OFF Ratio for γ-Glutamyltranspeptidase and Cancer Detection

Activity-based detection of γ-Glutamyltranspeptidase (GGT) using near-infrared (NIR) fluorescent probes is a promising strategy for early cancer diagnosis. Although NIR pyridinium probes show high performance in biochemical analysis, the aggregation of both the probes and parental fluorochromes in biological environments is prone to result in a low signal-to-noise ratio (SBR), thus affecting their clinical applications. Here, we develop a GGT-activatable aggregate probe called OTBP-G for two-photon fluorescence imaging in various biological environments under 1040 nm excitation. By rationally tunning the hydrophilicity and donor-acceptor strength, we enable a synergistic effect between twisted intramolecular charge transfer and intersystem crossing processes and realize a perfect dark state for OTBP-G before activation. After the enzymatic reaction, the parental fluorochrome exhibits bright aggregation-induced emission peaking at 670 nm. The fluorochrome-to-probe transformation can induce 1000-fold fluorescence ON/OFF ratio, realizing in vitro GGT detection with an SBR > 900. Activation of OTBP-G occurs within 1 min in vivo, showing an SBR > 400 in mouse ear blood vessels. OTBP-G can further enable the early detection of pulmonary metastasis in breast cancer by topically spraying, outperforming the clinical standard hematoxylin and eosin staining. We anticipate that the in-depth study of OTBP-G can prompt the development of early cancer diagnosis and tumor-related physiological research. Moreover, this work highlights the crucial role of hydrophilicity and donor-acceptor strength in maximizing the ON/OFF ratio of the TICT probes and showcases the potential of OTBP as a versatile platform for activity-based sensing.

Aggregation-induced emission-active iridium (III)-based mitochondria-targeting nanoparticle for two-photon imaging-guided photodynamic therapy

The efficacy of imaging-guided photodynamic therapy (PDT) is compromised by the attenuation of fluorescence and decline in reactive oxygen species (ROS) generation efficiency in the physiological environment of conventional photosensitizers, limited near-infrared (NIR) absorption, and high systemic cytotoxicity. This paper presents the synthesis of two cyclometalated Ir (III) complexes (Ir-thpy and Ir-ppy) by using a triphenylamine derivative (DPTPA) as the primary ligand and their encapsulation into an amphiphilic phospholipid to form nanoparticles (NPs). These complexes exhibit aggregation-induced emission features and remarkably enhanced ROS generation compared to Chlorin e6 (Ce6). Moreover, Ir-thpy NPs possess the unique ability to selectively target mitochondria, leading to depolarization of the mitochondrial membrane potential and ultimately triggering apoptosis. Notably, Ir-thpy NPs exhibit exceptional photocytotoxicity even towards cisplatin-resistant A549/DDP tumor cells. In vivo two-photon imaging verified the robust tumor-targeting efficacy of Ir-thpy NPs. The in vivo results unequivocally demonstrate that Ir-thpy NPs exhibit excellent tumor ablation along with remarkable biocompatibility. This study presents a promising approach for the development of multifunctional Ir-NPs for two-photon imaging-guided PDT and provides novel insights for potential clinical applications in oncology.

Recent advances of aggregation‐induced emission in body surface organs

The surface organs mainly comprise the superficial layers of various parts of the mammalian body, including the skin, eyes, and ears, which provide solid protection against various threats to the entire body. Damage to surface organs could lead to many serious diseases or even death. Currently, despite significant advancements in this field, there remain numerous enigmas that necessitate expeditious resolution, particularly pertaining to diagnostic and therapeutic objectives. The advancements in nanomedicine have provided a significant impetus for the development of novel approaches in the diagnosis, bioimaging, and therapy of superficial organs. The aggregation‐induced emission (AIE) phenomenon, initially observed by Prof. Ben Zhong Tang, stands out due to its contrasting behavior to the aggregation‐caused quenching effect. This discovery has significantly revolutionized the field of nanomedicine for surface organs owing to its remarkable advantages. In this review of literature, we aim to provide a comprehensive summary of recent advances of AIE lumenogen (AIEgen)‐based nanoplatforms in the fields of detection, diagnosis, imaging, and therapeutics of surface organ‐related diseases and discuss their prospects in the domain. It is hoped that this review will help attract researchers’ attention toward the utilization of this field for the exploration of a wider range of biomedical and clinical applications.

Data-driven coordinated attention deep learning for high-fidelity brain imaging denoising and inpainting

Deep learning offers promise in enhancing low-quality images by addressing weak fluorescence signals, especially in deep in vivo mouse brain imaging. However, current methods struggle with photon scarcity and noise within in vivo deep mouse brains, and often neglecting tissue preservation. In this study, we propose an innovative in vivo cortical fluorescence image restoration approach, combining signal enhancement, denoising, and inpainting. We curated a deep brain cortical image dataset and developed a novel deep brain coordinate attention restoration network (DeepCAR), integrating coordinate attention with optimized residual networks. Our method swiftly and accurately restores deep cortex images exceeding 800 μm, preserving small-scale tissue structures. It boosts the peak signal-to-noise ratio (PSNR) by 6.94 dB for weak signals and 11.22 dB for large noisy images. Crucially, we validate the effectiveness on external datasets with diverse noise distributions, structural features compared to those in our training data, showcasing real-time high-performance image restoration capabilities.

Overcome the "Buckets Effect": Integration of AIEgens into Proteins for Fluorescence-Enhanced Two-Photon Imaging

Luminogens with aggregation-induced emission characteristics (AIEgens) are considered good options for two-photon (2P) probes, owing to their flexibility of design, heavy-metal-free composition, and resistance to photobleaching. However, the design principles for large 2P absorption cross-section (δ) generally require high coplanarity, strong donor-acceptor (D-A) interactions, and long conjugation, which can severely weaken the brightness of AIEgens at the aggregated state and undermine their potential in 2P fluorescence imaging (2PFI). Exploration of a feasible approach to overcome the "Buckets Effect" of AIEgen-based 2P probes is thus a fascinating yet challenging task. Herein, an AIEgen, namely (Z)-2-(4-aminophenyl)-3-(5-(4-(bis(4-methoxyphenyl)amino)phenyl)thiophen-2-yl)acrylonitrile (MTAA) is designed to have a big δ according to the calculation result and a low fluorescence quantum yield (QY) of 2.2% in dimethyl sulfoxide (DMSO). Impressively, upon integrating into bovine serum albumin (BSA), the protein-sized MTAA@BSA dots exhibit a 25-fold higher fluorescence QY compared to MTAA molecules, contributing to an imaging depth of 818 µm in the brain vasculature. The retention and clearance of MTAA@BSA dots in the liver and kidney are also studied using 2PFI. Overall, this work provides a facile approach to overcome the "Buckets Effect" of AIEgen to generate highly efficient, reliable, and biocompatible 2P probes.

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.

DNA-AgNC Loaded Liposomes for Measuring Cerebral Blood Flow Using Two-Photon Fluorescence Correlation Spectroscopy

Unraveling the transport of drugs and nanocarriers in cerebrovascular networks is important for pharmacokinetic and hemodynamic studies but is challenging due to the complexity of sensing individual particles within the circulatory system of a live animal. Here, we demonstrate that a DNA-stabilized silver nanocluster (DNA-Ag16NC) that emits in the first near-infrared window upon two-photon excitation in the second NIR window can be used for multiphoton in vivo fluorescence correlation spectroscopy for the measurement of cerebral blood flow rates in live mice with high spatial and temporal resolution. To ensure bright and stable emission during in vivo experiments, we loaded DNA-Ag16NCs into liposomes, which served the dual purposes of concentrating the fluorescent label and protecting it from degradation. DNA-Ag16NC-loaded liposomes enabled the quantification of cerebral blood flow velocities within individual vessels of a living mouse.

Tracking tumor heterogeneity and progression with near-infrared II fluorophores

Heterogeneous cells are the main feature of tumors with unique genetic and phenotypic characteristics, which can stimulate differentially the progression, metastasis, and drug resistance. Importantly, heterogeneity is pervasive in human malignant tumors, and identification of the degree of tumor heterogeneity in individual tumors and progression is a critical task for tumor treatment. However, current medical tests cannot meet these needs; in particular, the need for noninvasive visualization of single-cell heterogeneity. Near-infrared II (NIR-II, 1000-1700 nm) imaging exhibits an exciting prospect for non-invasive monitoring due to the high temporal-spatial resolution. More importantly, NIR-II imaging displays more extended tissue penetration depths and reduced tissue backgrounds because of the significantly lower photon scattering and tissue autofluorescence than traditional the near-infrared I (NIR-I) imaging. In this review, we summarize systematically the advances made in NIR-II in tumor imaging, especially in the detection of tumor heterogeneity and progression as well as in tumor treatment. As a non-invasive visual inspection modality, NIR-II imaging shows promising prospects for understanding the differences in tumor heterogeneity and progression and is envisioned to have the potential to be used clinically.

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.

Novel aggregation-induced emission-photosensitizers with built-in capability of mitochondria targeting and glutathione depletion for efficient photodynamic therapy

Owing to its non-invasive feature and excellent therapeutic effect, photodynamic therapy has received considerable interest in cancer therapy. However, the therapeutic efficacy of photodynamic therapy is limited by some intrinsic drawbacks of photosensitizers such as aggregation-caused quenching and non-specificity towards cellular organelles. Moreover, the overexpressed glutathione in tumour cells which exhibits a potent scavenging effect on reactive oxygen species generated during the photodynamic therapy process also reduces the efficacy of photodynamic therapy. Therefore, the synthesis of aggregation-induced emission based photosensitizers with cellular organelle targeting and glutathione-depletion capability is highly desirable in photodynamic therapy. Here, two new aggregation-induced emission based photosensitizers namely tetraphenylethylene-1-phenyvinyl-pyridine-phenylboronic acid (TPEPy-BA) and tetraphenylethylene-1-phenyvinyl-pyridine-phenylboronic acid pinacol ester (TPEPy-BE) were synthesized which easily aggregated under aqueous conditions and showed bright emission in the near infra-red region. Furthermore, these photosensitizers were encapsulated into an amphiphilic block copolymer (DSPE-PEG) to improve the aqueous stability and cellular internalization of photosensitizers. The developed photosensitizer nanoparticles showed high reactive oxygen species generation efficacy, mitochondria-targeting and glutathione-depletion capability. The results showed that tetraphenylethylene-1-phenyvinyl-pyridine-phenylboronic acid pinacol ester nanoparticles exhibited a highly efficient photodynamic ablation of MCF-7 cells compared to tetraphenylethylene-1-phenyvinyl-pyridine-phenylboronic acid nanoparticles, upon white light irradiation, due to its high intracellular reactive oxygen species generation efficiency and mitochondria-dysfunction ability. Moreover, tetraphenylethylene-1-phenyvinyl-pyridine-phenylboronic acid pinacol ester nanoparticles produced a glutathione-depleting adjuvant, quinone methide, which greatly reduced the glutathione level in cancer cells, thus enhancing the efficacy of photodynamic therapy. This study provides a new strategy for the synthesis of aggregation-induced emission based photosensitizers with combined mitochondria-targeting and glutathione-depletion capability for efficacious photodynamic therapy.

Albumin-Consolidated AIEgens for Boosting Glioma and Cerebrovascular NIR-II Fluorescence Imaging

The application of an exogenous polymer matrix to construct aggregation-induced emission (AIE) nanoprobes promotes the utility of AIE luminogens (AIEgens) in diagnosing brain diseases. However, the limited fluorescence (FL) and low active-targeting abilities of AIE-based nanoprobes impede their imaging application. Here, we employed endogenous albumin as an effective matrix to encapsulate AIEgens to enhance FL quantum yield (QY) and active-targeting ability. The albumin-consolidated strategy effectively inhibited the intramolecular vibration of AIEgens and enhanced endocytosis mediated by the gp60 receptor. The QYs of three kinds of albumin-based AIE nanoprobes with FL emissions ranging from the visible (400-650 nm) to the second near-infrared (NIR-II, 1000-1700 nm) region was at least 10% higher, and the tumor-targeting efficiency was ∼25% higher, compared with those of nanoprobes constructed by the exogenous polymer. Albumin-based AIE nanoprobes have achieved active-targeting NIR-II imaging of brain tumors and cerebrovascular imaging with a high signal-to-background ratio (SBR, ∼90) and high resolution (∼70 μm) in mouse models. Therefore, the albumin-based AIE nanoprobes will enable FL imaging-guided surgery of brain tumors and cerebral ischemia, which will improve surgical efficacy to prevent recurrence and side effects.

Structural and functional imaging of brains

Analyzing the complex structures and functions of brain is the key issue to understanding the physiological and pathological processes. Although neuronal morphology and local distribution of neurons/blood vessels in the brain have been known, the subcellular structures of cells remain challenging, especially in the live brain. In addition, the complicated brain functions involve numerous functional molecules, but the concentrations, distributions and interactions of these molecules in the brain are still poorly understood. In this review, frontier techniques available for multiscale structure imaging from organelles to the whole brain are first overviewed, including magnetic resonance imaging (MRI), computed tomography (CT), positron emission tomography (PET), serial-section electron microscopy (ssEM), light microscopy (LM) and synchrotron-based X-ray microscopy (XRM). Specially, XRM for three-dimensional (3D) imaging of large-scale brain tissue with high resolution and fast imaging speed is highlighted. Additionally, the development of elegant methods for acquisition of brain functions from electrical/chemical signals in the brain is outlined. In particular, the new electrophysiology technologies for neural recordings at the single-neuron level and in the brain are also summarized. We also focus on the construction of electrochemical probes based on dual-recognition strategy and surface/interface chemistry for determination of chemical species in the brain with high selectivity and long-term stability, as well as electrochemophysiological microarray for simultaneously recording of electrochemical and electrophysiological signals in the brain. Moreover, the recent development of brain MRI probes with high contrast-to-noise ratio (CNR) and sensitivity based on hyperpolarized techniques and multi-nuclear chemistry is introduced. Furthermore, multiple optical probes and instruments, especially the optophysiological Raman probes and fiber Raman photometry, for imaging and biosensing in live brain are emphasized. Finally, a brief perspective on existing challenges and further research development is provided.

Recent Advances in Biomedical Applications of Polymeric Nanoplatform Assisted with Two-Photon Absorption Process

Polymers are well-recognized carriers useful for delivering therapeutic drug and imaging probes to the target specified in the defined pathophysiological site. The functional drug molecules and imaging agents were chemically attached or physically loaded in the carrier polymer matrix via cleavable spacers. Using appropriate targeting moieties, these polymeric carriers (PCs) loaded with functional molecules were designed to realize target-specific delivery at the cellular level. The biodistribution of these carriers can be tracked using imaging agents with suitable imaging techniques. The drug molecules can be released by cleaving the spacers either by endogenous stimuli (e.g., pH, redox species, glucose level and enzymes) at the targeted physiological site or exogenous stimuli (e.g., light, electrical pulses, ultrasound and magnetism). Recently, two-photon absorption (2PA)-mediated drug delivery and imaging has gained significant attention because TPA from near-infrared light (700-950 nm, NIR) renders light energy similar to the one-photon absorption from ultraviolet (UV) light. NIR has been considered biologically safe unlike UV, which is harmful to soft tissues, cells and blood vessels. In addition to the heat and reactive oxygen species generating capability of 2PA molecules, 2PA-functionalized PCs were also found to be useful for treating diseases such as cancer by photothermal and photodynamic therapies. Herein, insights attained towards the design, synthesis and biomedical applications of 2PA-activated PCs are reviewed. In particular, specific focus is provided to the imaging and drug delivery applications with a special emphasis on multi-responsive platforms.

Aggregation-induced emission (AIE)-Based nanocomposites for intracellular biological process monitoring and photodynamic therapy

As a non-invasive visualization technique, photoluminescence imaging (PLI) has found its huge value in many biological applications associated with intracellular process monitoring and early and accurate diagnosis of diseases. PLI can also be combined with therapeutics to build imaging-guided theragnostic platforms for achieving early and precise treatment of diseases. Photodynamic therapy (PDT) as a quintessential phototheranostics technology has gained great benefits from the combination with PLI. Recently, aggregation-induced emission (AIE)-active materials have emerged as one of the most promising bioimaging and phototheranostic agents. Most of AIEgens, however, need to be chemically engineered to form versatile nanocomposites with improved their photophysical property, photochemical activity, biocompatibility, etc. In this review, we focus on three categories of AIE-active nanocomposites and highlight their application progresses in the intracellular biological process monitoring and PLI-guided PDT. We hope this review can guide further development of AIE-active nanocomposites and promote their practical applications for monitoring intracellular biological processes and imaging-guided PDT.

Optical molecular imaging and theranostics in neurological diseases based on aggregation-induced emission luminogens

Optical molecular imaging and image-guided theranostics benefit from special and specific imaging agents, for which aggregation-induced emission luminogens (AIEgens) have been regarded as good candidates in many biomedical applications. They display a large Stokes shift, high quantum yield, good biocompatibility, and resistance to photobleaching. Neurological diseases are becoming a substantial burden on individuals and society that affect over 50 million people worldwide. It is urgently needed to explore in more detail the brain structure and function, learn more about pathological processes of neurological diseases, and develop more efficient approaches for theranostics. Many AIEgens have been successfully designed, synthesized, and further applied for molecular imaging and image-guided theranostics in neurological diseases such as cerebrovascular disease, neurodegenerative disease, and brain tumor, which help us understand more about the pathophysiological state of brain through noninvasive optical imaging approaches. Herein, we focus on representative AIEgens investigated on brain vasculature imaging and theranostics in neurological diseases including cerebrovascular disease, neurodegenerative disease, and brain tumor. Considering different imaging modalities and various therapeutic functions, AIEgens have great potential to broaden neurological research and meet urgent needs in clinical practice. It will be inspiring to develop more practical and versatile AIEgens as molecular imaging agents for preclinical and clinical use on neurological diseases.

Two-Photon Absorption: An Open Door to the NIR-II Biological Window?

The way in which photons travel through biological tissues and subsequently become scattered or absorbed is a key limitation for traditional optical medical imaging techniques using visible light. In contrast, near-infrared wavelengths, in particular those above 1000 nm, penetrate deeper in tissues and undergo less scattering and cause less photo-damage, which describes the so-called "second biological transparency window". Unfortunately, current dyes and imaging probes have severely limited absorption profiles at such long wavelengths, and molecular engineering of novel NIR-II dyes can be a tedious and unpredictable process, which limits access to this optical window and impedes further developments. Two-photon (2P) absorption not only provides convenient access to this window by doubling the absorption wavelength of dyes, but also increases the possible resolution. This review aims to provide an update on the available 2P instrumentation and 2P luminescent materials available for optical imaging in the NIR-II window.

Rigid metal/liquid metal nanoparticles: Synthesis and application for locally ablative therapy

Locally ablative therapy, as the main therapy for advanced tumors, has fallen into a bottleneck in recent years. The breakthrough of metal nanoparticles provides a novel approach for ablative therapy. Previous studies have mostly focused on the combined field of rigid metal nanoparticles and ablation. However, with the maturity of the preparation process of liquid metal nanoparticles, liquid metal nanoparticles not only have metallic properties but also have fluid properties, showing the potential to be combined with ablation. At present, there is no review on the combination of liquid metal nanoparticles and ablation. In this article, we first review the preparation, characterization and application characteristics of rigid metal and liquid metal nanoparticles in ablation applications, and then summarize the advantages, disadvantages and possible future development trends of rigid and liquid metal nanoparticles.

Enantioselective determination of chiral acids and amino acids by chiral receptors with aggregation-induced emissions

The chiral AIEgens showed satisfying enantiomer discrimination not only for amino acids but also for chiral acids.

Mitochondrion-Anchored Photosensitizer with Near Infrared-I Aggregation-Induced Emission for Near Infrared-II Two-Photon Photodynamic Therapy

Two-photon photodynamic therapy (2P-PDT) that employs photosensitizers (PSs) with 2P absorption is particularly intriguing in cancer treatment, in that 2P excitation enables precise spatial localization and deep tissue penetration. Here, a donor-π-acceptor PS (named TPBPy) with near infrared (NIR) aggregation-induced emission (AIE) is designed and synthesized for imaging-guided 2P-PDT. The maximal photoluminescence (PL) peak of TPBPy is as high as 720 nm when it is encapsulated in liposomes. Upon 2P irradiation by a laser in NIR-II window (λ = 1000 nm), TPBPy exhibits strong NIR-I PL in a multicellular tumor spheroids (MCTSs) model, showing an imaging depth of 210 µm that is significantly higher than upon one-photon irradiation. Moreover, TPBPy localizes specifically on mitochondrion, an important organelle in cell oxidative metabolism and apoptosis. When exposed to the NIR-II irradiation, TPBPy can efficiently generate singlet oxygen (¹ O₂ ) and trigger cell death. The efficacy of TPBPy-mediated 2P-PDT has also been validated using 4T1 tumor mouse model, the growth of which is significantly suppressed upon NIR-II laser irradiation. TPBPy herein serves as an excellent candidate to suppress deep tumor tissues through NIR-II 2P-PDT, and also renders a new paradigm to construct mitochondrion-anchored AIE luminogens for future cancer theranostic applications.

Activatable Second Near-Infrared Fluorescent Probes: A New Accurate Diagnosis Strategy for Diseases

Recently, second near-infrared (NIR-II) fluorescent imaging has been widely applied in biomedical diagnosis, due to its high spatiotemporal resolution and deep tissue penetration. In contrast to the "always on" NIR-II fluorescent probes, the activatable NIR-II fluorescent probes have specific targeting to biological tissues, showing a higher imaging signal-to-background ratio and a lower detection limit. Therefore, it is of great significance to utilize disease-associated endogenous stimuli (such as pH values, enzyme existence, hypoxia condition and so on) to activate the NIR-II probes and achieve switchable fluorescent signals for specific deep bioimaging. This review introduces recent strategies and mechanisms for activatable NIR-II fluorescent probes and their applications in biosensing and bioimaging. Moreover, the potential challenges and perspectives of activatable NIR-II fluorescent probes are also discussed.

Mn(II)-directed dual-photosensitizers co-assemblies for multimodal imaging-guided self-enhanced phototherapy

Phototherapy has attracted increasing attention in cancer therapy owing to its non-invasive nature, high spatiotemporal selectivity, and negligible side effects. However, a single photosensitizer often exhibits poor photothermal conversion efficiency or insufficient reactive oxygen species (ROS) productivity. Even worse, the ROS can be consumed by tumor overexpressed reductive glutathione, resulting in severely compromised phototherapy. In this paper, we prepared a Mn^II-coordination driven dual-photosensitizers co-assemblies (IMCP) for imaging-guided self-enhanced PDT/PTT. Specifically, a photothermal agent indocyanine green (ICG), a photodynamic agent chlorin e6 (Ce6), and a transition metal ion (Mn^II/III) were chosen to synthesize the nanodrug via coordination-driven co-assembly. The as-prepared IMCP exhibited extremely high photosensitizer payload (96 wt%), excellent physiological stability, and outstanding tumor accumulation. Moreover, the existence of Mn^II not only assists the nanostructure formation but also could competitively coordinate with GSH to minimize the unnecessary ROS consumption, thus improving PDT efficiency. Meanwhile, benefiting from the intrinsic fluorescence, photoacoustic imaging ability of photosensitizers, and the MRI contrast potential of Mn^II/III, IMCP exhibited superior imaging potential for guiding tumor phototherapy. By changing the excitation wavelength suitably, IMCP could realize the switch between PTT and PDT. In short, the dual-PSs co-assembled nanotheranostic has great potential for multi-modal imaging guided phototherapy.