A Polarity-Sensitive Ratiometric Fluorescence Probe for Monitoring Changes in Lipid Droplets and Nucleus during Ferroptosis

A lipid droplet-targeted probe for imaging of lipid metabolism disorders during mitochondrial myopathy

Lipid metabolism is closely related to various biological processes in cells. The accumulation of Lipid droplets (LDs) is a typical manifestation of certain metabolic diseases, such as mitochondrial myopathy, which shows a significant increase in LDs. The accumulation of LDs can exacerbate the progression of disease, and lysosomes selectively degrade LDs to cope with this phenomenon. Visualizing lipid metabolism disorders and the interaction between LDs and other organelles is of great significance for the diagnosis and understanding of various physiological processes within cells in diseases. In this work, we synthesized two novel LD fluorescent probes and screened the best PDM, which exhibited stable fluorescence performance and strong photobleaching resistance in complex environments. The dynamics of intracellular LDs were tracked using PDM, and abnormal lipid metabolism within mitochondrial myopathy cells was visualized. This provides new tools and perspectives for studying LD dynamics and diagnosing mitochondrial myopathy.

Effects of mono-substituents on the polarity-sensitive fluorescent probe properties of pyrene

This study investigates the effects of mono-substituents (i.e., hydroxyl, methyl, amino and nitro groups) on the polarity-sensitive fluorescent probe properties of pyrene (Pyr) using fluorescence, UV-vis, and circular dichroism absorption spectroscopy. The results indicate that the four mono-substituents altered the fluorescence spectral characteristics of Pyr to varying degrees, with the most to least influential order being: nitro, amino, hydroxyl, and methyl. 1-Aminopyrene (1-APyr) and 1-nitropyrene (1-NPyr) are deemed unsuitable for use as polarity-sensitive fluorescent probes due to their limited or absent spectral characteristics. The I386/I406 and I376/I396 ratios of 1-HPyr and 1-MPyr decrease as solvents polarity increases, contrasting with the I372/I384 ratio of Pyr. Thus, 1-hydroxypyrene (1-HPyr) and 1-methylpyrene (1-MPyr) also exhibit polarity-sensitive characteristics similar to Pyr, and their solubility in PBS buffer surpasses that of Pyr at 298 K. Moreover, 1-HPyr and 1-MPyr are practicable for detecting the polarity of human serum albumin (HSA) under simulated physiological conditions. The results underscore the potential of the polarity-sensitive mono-substituents of Pyr in biological applications, particularly in probing protein polarity and conformational changes, and further providing a potential tool for the related research in biochemistry and pathology.

A non-solvatochromic fluorescent probe for imaging of lipid droplets in live cells and tissues

Lipid droplets (LDs) have recently attracted considerable attention owing to their crucial roles in both biological processes and disease pathogenesis. Visualization of LDs is fundamental for elucidating their roles in biological mechanisms and facilitating the early detection of diseases. Donor-acceptor (D-A) typed fluorescent probes have been extensively designed and utilized for the detection of LDs. However, such probes often exhibit a pronounced solvatochromic effect, leading to several limitations in detecting LDs, such as short excitation/emission wavelength, low specificity. Herein, we reported a non-solvatochromic D-A typed fluorescent probe S7 for LDs imaging in live cells and in vivo. S7 is polarity-dependent, which exhibits a very weak fluorescence in high-polar solvents owing to the photoinduced electron transfer (PET) mechanism but intense fluorescence in low-polarity environments without undergoing a solvatochromic blue shift. Except polarity, the fluorescent signal of S7 remains unaffected by factors such as viscosity, pH, ions, reactive oxygen species, reactive sulfur species, nucleic acids, proteins, and other biological molecules, allowing it to selectively light up LDs in live cells. Furthermore, this probe S7 exhibits an enhanced fluorescence intensity in tumor tissue when compared to normal tissue. This characteristic potentially provides an efficient and straightforward approach for tumor diagnosis.

A novel dual-channel fluorescent probe for the detection of peroxynitrite anions and lipid droplets in epileptic disease

Peroxynitrite (ONOO-) and lipid droplets (LDs) are crucial substances essential for maintaining normal physiological functions in biological systems. They play pivotal roles as biomarkers in the initiation and progression of various diseases, such as epilepsy. Therefore, the simultaneous detection of ONOO- and LDs in epilepsy disorders is of great importance. Here, we discovered that the fluorescence probe composed of trifluoromesulfonate and fluorophore can not only be used as the recognition site of ONOO-, but also has the property of LDs targeting. Therefore, we reasonable designed and synthesized a dual-channel fluorescent probe CBT, capable of simultaneously monitoring ONOO- and LDs. CBT exhibited exceptional dual-response properties: firstly, upon specific reaction with ONOO-, the resulting product BHD emitted a robust red fluorescent signal in the near-infrared region (749 nm); secondly, CBT selectively targeted and labeled LDs, emitting green fluorescence at 482 nm for effective LDs tracking. The signals from these two detection channels did not overlap, which significantly enhanced the accuracy and reliability of detection. Based on these characteristics, CBT has been successfully utilized in real-time imaging of ONOO- and LDs in epilepsy models of cells induced by various drugs. Notably, in a pentylenetetrazole (PTZ)-induced chronic epileptic mice model, CBT exhibited excellent efficacy in ONOO- imaging, further confirming its considerable potential for practical applications. In summary, this study validated CBT as an efficient tool capable of simultaneous detection and differentiation of ONOO- and LDs, presenting a novel and promising strategy for the early diagnosis and treatment of diseases such as epilepsy.

A polarity-sensitive fluorescent probe for visualizing lipid droplets in ferroptosis, cuproptosis, and autophagy

Dynamics of lipid droplets (LDs) in various pathological processes provides important information about lipid metabolism during theses biological processes, while only a few reports focused on this field. In this work, a benzothiazine-fused coumarin chromophore BCLD with strong fluorescence in low-polarity environment is described. It is confirmed that cyclization-induced rigidification might be a promising approach to enhance the LDs specificity of phenothiazine-based strucutres.The probe is found to enter cells through a clathrin-mediated endocytosis, and is able to monitor LDs variations in living cells, especially during various pathological processes. It is found that obvious increase in polarity of LDs during ferroptosis and cuproptosis was visualized while a dramatic decrease in the number of LDs was recorded during autophagy, indicating different lipid metabolism manners and LD dynamics in these pathological processes. This work supports the potentials of LDs as markers for drug design targeting ferroptosis, cuproptosis, and autophagy.

Application of a fluorescent probe exhibiting a large stokes shift after the precise detection of hydrazine in plants, foods and living cells

As a strongly reducing agent and highly reactive alkaline substance, hydrazine is widely used in various industrial productions. Excessive hydrazine may pose a significant risk to the environment and human health. Here, a new fluorescent probe, (E)-6-(2-(3-(dicyanomethylene)-5,5-dimethylcyclohex-1-en-1-yl)vinyl) naphthalen-2-yl-7-(diethylamino)-2-oxo-2H-chromene-3-carboxylate (abbreviated as MNC) for detecting hydrazine in environmental and biological samples was introduced. The probe not only shows a good photostability, a turn-on red fluorescent response with a low detection limit (0.40 μM), but also exhibits a large Stokes shift (215 nm) after reacting with hydrazine. In practical applications, this probe has been effectively used for the detection of hydrazine in environmental, plant, and food samples. It has also been applied to identify the presence of hydrazine in the roots of Arabidopsis thaliana, as well as in zebrafish and living cells. This research introduces a potent and versatile tool for the environmental and biological monitoring of hydrazine.

Facile Way to Differentiate Normal and Cancerous Tissues via Polarity-Sensitive Fluorescent Probes Based on 1,6-Naphthyridine Derivatives

Cancer is a genetic disorder caused by the long-term interaction of many factors, which has become the most important factor to take away human health; therefore, it is essential to develop a more efficient and sensitive cancer detection technology. This study developed two polarity sensitive probes 1a and 1b based on a 1,6-naphthyridine moiety linked to different targeting groups by vinyl as the π bridge. As the solvent polarity decreased, the emission wavelength of probes 1a and 1b experienced a blue shift, resulting in a significant enhance in fluorescence intensity by 135-fold and 53-fold, respectively, and a good linear relationship between Fmax of probes 1a and 1b and Δf was established with high correlation coefficients. Furthermore, probes 1a and 1b exhibited large Stokes shifts, high photostability, and low cytotoxicity, successfully targeting intracellular lipid droplets and mitochondria. Fluctuation in polarity was detected by real-time changes in fluorescence intensity of probes in lipid droplets and mitochondria. Moreover, probe 1b was capable of real-time monitoring mitochondrial polarity during starvation or rapamycin-induced autophagy. It was worth standing out 1a and 1b could distinguish normal cells from cancer cells, and then the probes also were successfully applied for imaging to differentiate between human normal tissues and cancerous tissues, with the fluorescence intensity of malignant tumor tissues being 15.4-19.9 folds higher than that of normal tissues and 5.3-7.2 times higher than that of benign tumor tissues. Therefore, this research offers potential applications for cancer diagnosis.

Rational development of Nile red derivatives with significantly improved specificity and photostability for advanced fluorescence imaging of lipid droplets

Since the first report of Nile Red as a fluorescent probe for lipid droplets (LDs) imaging was published in 1985, this fluorescent probe has been widely used for nearly 40 years, and so far, it is still one of the most commonly used probes for LDs imaging. Although Nile Red has achieved continuous success, it has gradually emerged two major limitations (poor LDs specificity and low photostability) which directly limit the study of LDs via advanced fluorescence imaging techniques. In this context, we have developed a new synthetic route to conveniently prepare a series of Nile Red derivatives (NR-1 to NR-15). With these 15 derivatives in hand, the relationships between molecular structures and their properties (LDs specificity, photostability) have been comprehensively investigated. Consequently, we have rationally designed a new Nile Red derivative, NR-11, which exhibits significantly improved LDs specificity and photostability. Utilizing this new LDs probe, we have successfully conducted various advanced fluorescence imaging, e.g. time-lapse three-dimensional (3D) confocal imaging of cells, time-lapse 3D dynamic tracking of a single LD, and two-photon 3D imaging of tissues. These advanced imaging results not only demonstrate the utility of this new fluorescent probe but also provide novel insights into the cell biology study of LDs.

Chemical Energy Lights Up Europium-Based Ultra-bright Afterglow for Bioanalysis Application

Photochemical afterglow materials are gaining great attention for the property to continuously emit light after the excitation source is removed. However, their limited luminescence quantum yield (QY) and brightness hinder the use in biological applications. In this study, we introduce a novel photochemical afterglow system that combines a newly designed photoenergy cache unit (PCU) with an emitter through coordination covalent bonds. The PCU boasts a dark state to significantly emit photons only through chemiexcitation in the process of photochemical reactions, facilitating direct energy transfer to the emitter and resulting in bright afterglow. The related mechanisms further guided us to achieve the highest reported afterglow luminescence quantum yield of 27.5 %. The system can be encapsulated and dispersed in aqueous solutions for in vivo bioimaging in living mice under mild and simple conditions (low concentration, low excitation power, short excitation time, short exposure time), and also for in vitro diagnostic through lateral flow immunoassay, enabling the highly sensitive detection of the inflammatory biomarker serum amyloid A (SAA) and demonstrating excellent correlation with clinical test results. This study offers new insights into enhancing luminescence QY and brightness of afterglow, highlighting the potential of such systems for further biomedical applications.

Mapping Dynamic Protein Clustering with AIEgen-Active Chemigenetic Probe

Protein clustering/disassembling is a fundamental process in biomolecular condensates, playing a crucial role in cell fate decision and cellular homeostasis. However, the inherent features of protein clustering, especially for its reversible behavior and subtle microenvironment variation, present significant hurdles in probe chemistry for tracking protein clustering dynamics. Herein, we report a bilateral-tailored chemigenetic probe, in which an "amphiphilic" aggregate-induced emission luminogen (AIEgen) QMSO3Cl is covalently conjugated to a protein tag that is genetically fused to protein-of-interest (POI). Prior to target POI, the "amphiphilic" AIE-active QMSO3Cl achieves a completely dark state in both aqueous biological environment and lipophilic organelles, thereby ensuring an ultra-low intrinsic background interference. Upon reaching POI, the combination of synthetic molecule and genetically encoded protein allows for protein clustering-dependent ultra-sensitive response, with a substantial lighting-up fluorescence (67.5-fold) as protein transitions from disassembling to clustering state. Such ultra-high signal-to-noise ratio enables to monitor the dynamic and fate of inositol requiring enzyme 1 (IRE1) clustering/disassembling under both acute and chronic endoplasmic reticulum (ER) stress in living cells. For the first time, we have demonstrated the use of chemigenetic probe to reveal therapy-induced ER stress and screen drugs in a three-dimensional scenario: microviscosity change, clustering dynamic, and cluster morphology. This chemigenetic probe design strategy would greatly facilitate the advancement of mapping protein dynamics in cell homeostasis and medicine research.

A photostable luminescent iridium(III) complex probe for imaging endogenous mitochondrial sulfur dioxide in living cells

Sulfur dioxide (SO2) is an important signaling gas molecule, but its aberration is highly associated with inflammatory diseases and cancers. Luminescence probes for SO2 have emerged as essential instruments for elucidating its biological roles and facilitating disease diagnosis, owing to their high sensitivity and capabilities for real-time detection. Nevertheless, the majority of current probes lack subcellular selectivity and suffer from limited photostability. In this work, we develop an Ir(III)-based luminescence probe (Ir3) for the rapid, real-time, and accurate detection of SO2 in aqueous solution. This probe exhibits low cytotoxicity and provides exceptional imaging of mitochondrial SO2 in living cells. We anticipate that this probe will serve as a foundational tool for the advancement of effective imaging technologies for SO2, thereby enhancing the clinical and biomedical applications of Ir(III) complex-based detection probes.

A single fluorescent probe for dual-color imaging and polarity precise analysis in lipid droplets and endoplasmic reticulum

BACKGROUND

Elaborating the subcellular polarity is pivotal for pathophysiological research and early disease diagnosis. Despite its significance, achieving simultaneous two-color fluorescence imaging and quantitative analysis of polarity across multiple organelles remains challenging. This limitation primarily stems from the lack of single fluorescent (SF) probes capable of such precise and multifaceted functionality.

RESULTS

We introduce a novel SF probe LE-TPA, designed for concurrent dual-color imaging and precise polarity determination in lipid droplets (LDs) and the endoplasmic reticulum (ER) under a single excitation. LE-TPA adopts a D-π-A-π-D configuration, which demonstrates highly selective and sensitive fluorescence response to polarity variations in Oleic acid-THF or THF-water mixtures, accompanied with an exceptional linearity (R2 > 0.99) between the max λem and polarity parameter Δf, paving the way for quantitative polarity analysis in live samples. Furthermore, LE-TPA enables simultaneous, real-time imaging of these organelles due to their different water contents, and provides compelling evidence for supporting the hypothesis that LDs derive from the ER. Importantly, LE-TPA effectively identifies polarity differences between healthy and cancerous cells at the subcellular level and allows precise polarity mapping of non-alcoholic fatty liver disease (NAFLD) tissues at different pathological stages.

SIGNIFICANCE

These findings highlight the versatility of probe LE-TPA as a powerful tool for subcellular polarity studies and related disease diagnosis.

Development of a Near-Infrared Probe for Enhancing Cancer Therapy by Mitigating Pyroptosis-Induced Inflammation

Pyroptosis, a specialized cell death mechanism crucial in cancer therapy, is distinct from apoptosis and primary necrosis. It is linked to inflammation and reactive oxygen species, particularly peroxynitrite (ONOO-), which is implicated in disease. Monitoring pyroptosis is challenging due to its connection with cellular polarity and the tumor environment. In this research, we developed a near-infrared probe, PBQI, which is highly sensitive and responsive to polarity and ONOO- fluctuations. PBQI targets mitochondria and lipid droplets, enabling real-time tracking of pyroptosis-associated subcellular alterations. It was found to differentiate between normal and cancer cells during pyroptosis triggered by cisplatin and metformin. To mitigate pyroptosis-induced inflammation, disulfiram was used as an inhibitor, significantly alleviating excessive inflammation. This study highlights PBQI's utility in studying the interplay between polarity, ONOO-, and pyroptosis, and contributes to the development of more targeted cancer therapies that optimize pyroptosis's antitumor benefits while minimizing inflammatory side effects.

Fluorescent probes with dual-targeting organelles monitor polarity in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) becomes a world health issue due to its rising prevalence and lack of a definitive pathogeny. However, the excessive accumulation of fat droplets has been recognized as a crucial characteristic of NAFLD, accompanied with endoplasmic reticulum stress in its onset and progression as well. Therefore, real-time monitoring the dynamic of lipid droplets (LDs) and endoplasmic reticulum (ER) within cells is paramount. In this regard, four D-A-π-D structural fluorescent probes COB1-COB4 were designed and synthesized wherein coumarin connected with carbazole acted as precursors while the side chains attached to carbazole groups are different. Here, probes COB1-COB4 exhibited high sensitivity towards polarity, while COB2 was chosen for further study attributing to its excellent anti-interference property. Cell imaging demonstrated that COB2 could accurately target both LDs and ER at the same time and monitor the changes of the two organelles under different physiological conditions. Notably, probe COB2 also exhibited the ability to distinguish normal liver from fatty liver at the tissue level. The above results lay an experimental foundation for developing novel dual-targeted probes with potential for early diagnosis of non-alcoholic fatty liver.

A Solvatochromic and Photosensitized Lipid Droplet Probe Detects Local Polarity Heterogeneity and Labels Interacting Proteins in Human Liver Disease Tissue

The intricate morphology, physicochemical properties, and interacting proteins of lipid droplets (LDs) are associated with cell metabolism and related diseases. To uncover these layers of information, a solvatochromic and photosensitized LDs-targeted probe based on the furan-based D-D-π-A scaffold is developed to offer the following integrated functions. First, the turn-on fluorescence of the probe upon selectively binding to LDs allows for direct visualization of their location and morphology. Second, its solvatochromic fluorescence with linear correlation to polarity quantifies micro-environmental heterogeneity among LDs. Third, the unique photosensitized properties enable photocatalytic proximity labeling and enrichment of LDs-interacting proteins, ready for potential downstream proteomic analysis. These functions are exemplified using artificial LDs in buffer, stressed liver cell line, and diseased liver tissues biopsied from patients. While most LD sensors only offer fluorescence imaging functions, the multi-functional LD probe reported herein integrates both singlet fluorescence and triplet photosensitization properties for LDs studies.

Chemical Design of Magnetic Nanomaterials for Imaging and Ferroptosis-Based Cancer Therapy

Ferroptosis, an iron-dependent form of regulatory cell death, has garnered significant interest as a therapeutic target in cancer treatment due to its distinct characteristics, including lipid peroxide generation and redox imbalance. However, its clinical application in oncology is currently limited by issues such as suboptimal efficacy and potential off-target effects. The advent of nanotechnology has provided a new way for overcoming these challenges through the development of activatable magnetic nanoparticles (MNPs). These innovative MNPs are designed to improve the specificity and efficacy of ferroptosis induction. This Review delves into the chemical and biological principles guiding the design of MNPs for ferroptosis-based cancer therapies and imaging-guided therapies. It discusses the regulatory mechanisms and biological attributes of ferroptosis, the chemical composition of MNPs, their mechanism of action as ferroptosis inducers, and their integration with advanced imaging techniques for therapeutic monitoring. Additionally, we examine the convergence of ferroptosis with other therapeutic strategies, including chemodynamic therapy, photothermal therapy, photodynamic therapy, sonodynamic therapy, and immunotherapy, within the context of nanomedicine strategies utilizing MNPs. This Review highlights the potential of these multifunctional MNPs to surpass the limitations of conventional treatments, envisioning a future of drug-resistance-free, precision diagnostics and ferroptosis-based therapies for treating recalcitrant cancers.

Near-Infrared Fluorescent Probe for Simultaneously Imaging Ferrous Ions and Viscosity in a Mouse Model of Hepatocellular Carcinoma

Abnormal ferrous ion (Fe2+) levels lead to an increase in reactive oxygen species (ROS) in cells, disrupting intracellular viscosity and the occurrence of hepatocellular carcinoma (HCC). Simultaneously visualizing Fe2+ and intracellular viscosity is essential for understanding the detailed pathophysiological processes of HCC. Herein, we report the first dual-responsive probe, QM-FV, capable of simultaneously monitoring Fe2+ and viscosity. QM-FV shows highly selective turn-on near-infrared fluorescence (∼30-fold enhancement at 740 nm) for Fe2+ with high sensitivity (LOD = 25 nM) and a significant Stokes shift (290 nm). Moreover, QM-FV shows a distinct orange-red fluorescence enhancement at 587 nm as the viscosity increases. Due to its lower cytotoxicity and high sensitivity, QM-FV can distinguish cancer cells from normal cells by detecting Fe2+ and viscosity in dual channels. More importantly, using QM-FV, we found that the levels of Fe2+ and viscosity elevated in the precancerous stage of HCC and gradually increased as the disease progressed. Overall, this work provides a new potential tool for investigating viscosity and Fe2+-related pathological processes underlying HCC.

Simultaneous Imaging of pH and Peroxynitrite in the Endoplasmic Reticulum and Mitochondria: Revealing Organelle Interactions in Alzheimer's Disease Pathogenesis

pH and peroxynitrite (ONOO-) are two critical biomarkers to unveil the corresponding status of endoplasmic reticulum (ER) stress and mitochondrial dysfunction, which are closely related to Alzheimer's disease (AD). Simultaneously monitoring pH and ONOO- fluctuations in the ER and mitochondria during AD progression is pivotal for clarifying the interplay between the disorders of the two organelles and revealing AD pathogenesis. Herein, we designed and synthesized a dual-channel fluorescent probe (DCFP) to visualize pH and ONOO- in the ER and mitochondria. DCFP possessed excellent sensitivity and selectivity to pH and ONOO- without spectral crosstalk and was utilized in monitoring the two analytes within AD model cells and larval zebrafish. Importantly, DCFP could preferentially target mitochondria in normal cells and be enriched in the ER after mitochondrial depolarization. With the aid of DCFP, the slower acidification rate of the ER than that of mitochondria induced by Aβ oligomers (AβOs) was first identified, which could be ascribed to the relief of the AβOs-triggered ER stress through the Ca2+ migration from the ER to mitochondria. Moreover, continuous exposure to AβOs led to mitochondrial Ca2+ overload, accelerating the acidification and ONOO- overproduction within mitochondria. As a result, intracellular oxidative stress levels were elevated, further exacerbating ER stress and aggravating ER acidification in turn. The advanced understanding of the potential interplay between the ER and mitochondria in this work may offer new insights and methodologies for studying AD pathogenesis. The DCFP developed in this work could also be employed to study other diseases related to ER stress and mitochondrial dysfunction.

Sensing features, on-site detection and bio-imaging application of a tripodal tris(hydroxycoumarin) based probe towards Cu2+/His

A new tripodal tris(hydroxycoumarin) based Schiff base, HCTN was synthesized and characterized by FT-IR, 1H NMR, 13C NMR and ESI-HRMS. The probe, HCTN exhibits cyan emission in DMSO/HEPES buffer (9:1, v/v) which selectively detects Cu2+ ion via turn-off fluorescence. The quenching of the fluorescence was due to the binding of the probe, HCTN towards paramagnetic Cu2+ ion resulting in chelation enhanced quenching effect (CHEQ). From the spectroscopic results, the limit of detection of Cu2+ ion was obtained as very low as 0.40 × 10-9 M. The complexation of the metal ion, Cu2+ towards the probe HCTN was confirmed by the ESI-HRMS and Job's plot analysis which supports 1:1 binding stochiometric ratio. In order to validate the affinity of Cu2+ ion towards histidine, the HCTN+Cu2+ system was utilized for the detection of histidine via turn-on mode by the metal displacement approach. The detection limit of His was found to be 7.31 × 10-10 M. In addition to the above, the probe was utilized for various detection applications such as paper strips, cotton swabs, logic gates and thin film applications. The probe, HCTN extends its application to the confocal bioimaging to sense the Cu2+ and Histidine intracellularly.

General (hetero)polyaryl amine synthesis via multicomponent cycloaromatization of amines

(Hetero)polyaryl amines are extensively prevalent in pharmaceuticals, fine chemicals, and materials but the intricate and varied nature of their structures severely restricts their synthesis. Here, we present a selective multicomponent cycloaromatization of structurally and functionally diverse amine substrates for the general and modular synthesis of (hetero)polyaryl amines through copper(I)-catalysis. This strategy directly constructs a remarkable range of amino group-functionalized (hetero)polyaryl frameworks (194 examples), including naphthalene, binaphthalene, phenanthren, benzothiophene, dibenzothiophene, benzofuran, dibenzofuran, quinoline, isoquinoline, quinazoline, and others, which are challenging or impossible to obtain using alternative methods. Copper(III)-acetylide species are involved in driving the exclusive 7-endo-dig cyclization, suppressing many side-reactions that are susceptible to occur. Due to the easy introduction of various functional units into heteropolyarylamines, multiple functionalized fluorescent dyes can be arbitrarily synthesized, which can serve as effective fluorescent probes for monitoring the pathological processes (e.g. chemotherapy-induced cell apoptosis) and studying the related disease mechanisms.

Advancements in phasor-based FLIM: multi-component analysis and lifetime probes in biological imaging

Fluorescence lifetime imaging microscopy (FLIM) is a reliable method that achieves imaging by detecting fluorescence lifetimes within samples. Owing to its unique temporal characteristic, it can complement fluorescence intensity measurement. Technological and methodological advancements in FLIM have broadened its applications across various domains. The processing of fluorescence lifetime data is crucial for enhancing the speed and accuracy of imaging. Thus, various lifetime fitting algorithms have been developed to improve the imaging speed. The phasor analysis (PA) method is an approach for processing fluorescence lifetime data, capable of directly converting lifetime signals into visual graphics without fitting, which outperforms traditional approaches in speed. Furthermore, lifetime probes with distinct lifetimes are readily implemented for visualization and cluster analysis combined with PA, facilitating the prediction of specific biological states or functions. This review examines various lifetime probes employed in phasor-based FLIM and discusses their roles in the PA method. The methods for multi-component PA within complex biological environments were also described. Additionally, we focused on the advantages of the phasor vector rule and the unmixing of multi-component analysis based on PA. The integration of lifetime probes with phasor-based FLIM facilitates rapid and intuitive detection methods for analyzing complex biological environments.

Rational Design of NIR-II Ratiometric Fluorescence Probes for Accurate Bioimaging and Biosensing In Vivo

Intravital fluorescence imaging in the second near-infrared window (NIR-II, 900-1700 nm) has emerged as a promising method for non-invasive diagnostics in complex biological systems due to its advantages of less background interference, high tissue penetration depth, high imaging contrast, and sensitivity. However, traditional NIR-II fluorescence imaging, which is characterized by the "always on" or "turn on" mode, lacks the ability of quantitative detection, leading to low reproducibility and reliability during bio-detection. In contrast, NIR-II ratiometric fluorescence imaging can realize quantitative and reliable analysis and detection in vivo by providing reference signals for fluorescence correction, generating new opportunities and prospects during in vivo bioimaging and biosensing. In this review, the current design strategies and sensing mechanisms of NIR-II ratiometric fluorescence probes for bioimaging and biosensing applications are systematically summarized. Further, current challenges, future perspectives and opportunities for designing NIR-II ratiometric fluorescence probes are also discussed. It is hoped that this review can provide effective guidance for the design of NIR-II ratiometric fluorescence probes and promote its adoption in reliable biological imaging and sensing in vivo.

A ferrous fluorescence lifetime response probe for monitoring changes in lipid droplets during ferroptosis and imaging in liver disease model

Ferrous ions (Fe2⁺) accumulation and abnormal alterations in lipid droplets (LDs) are closely associated with ferroptosis. In the liver, excessive iron accumulation promotes oxidative stress and exacerbates lipid droplet accumulation, while the disruption of iron homeostasis may also affect the formation and size of lipid droplets, their increased number and size can exacerbate the severity of disease under fatty liver conditions. The leads to hepatocyte damage, further triggering liver inflammation, fibrosis, and ultimately resulting in cirrhosis and hepatocellular carcinoma. Therefore, real-time monitoring of iron ion and lipid droplet changes is crucial for assessing the severity of liver disease, disease progression, and understanding the mechanisms of ferroptosis. We have developed a fluorescent probe, NRFep, for real-time monitoring of iron ion fluctuations and visualization of lipid droplet changes in ferroptosis and liver disease models. NRFep is specific and sensitive to iron ions and exhibits excellent stability in both cells and animal models. In addition, NRFep can be used to monitor changes in iron ions and lipid droplets in mouse liver injury and fatty liver models. Through fluorescence lifetime imaging technology, NRFep can also study the dynamic changes of intracellular iron ion content. NRFep provides a powerful tool for studying ferroptosis and related diseases, and its unique dual-monitoring function opens up new possibilities for developing new diagnostic and therapeutic strategies.

An intelligent NIR fluorescent dye with dual response to pH and viscosity for investigating the interactions between LDs and mitochondria

The interaction between lipid droplets and mitochondria plays a pivotal role in biological processes including cellular stress, metabolic homeostasis, cellular autophagy and apoptosis. Deciphering the complex interplay between lipid droplets and mitochondria is essential for gaining insights into the fundamental workings of the cell and can have broad implications for the development of therapeutic strategies for various diseases, including metabolic disorders, neurodegenerative diseases, and cancer. In this study, we develop a pH and viscosity-responsive near-infrared (NIR) fluorescent probe PTOH to investigate the interaction between lipid droplets and mitochondria. This probe demonstrates a significant enhancement in fluorescence intensity at 470 nm when the pH increases, while under acidic conditions, its fluorescence intensity at 730 nm intensifies by a factor of 35 with rising system viscosity. Cell imaging experiments revealed that PTOH can effectively discriminate between normal and cancerous cells, as well as detect intracellular pH and viscosity alterations induced by drugs. Additionally, PTOH is utilized to visualize the interaction between lipid droplets and mitochondria and to differentiate between cellular autophagy and apoptosis phenomena, providing a valuable tool for elucidating the mechanisms underlying lipid droplet-mitochondria interactions and their associated diseases.

Targeted Conversion from Mitochondria to the Nucleus of Hydroxystyrylpyridinium by Introducing Only an Additional o-Hydroxyl Group

Aromatic cationic groups serve as crucial building blocks for the design of fluorescent probes targeting both the nucleus and mitochondria. Therefore, it is a significant challenge to develop aromatic cation-based probes that accurately image the nucleus without interference from mitochondria. However, this also presents an opportunity for rational design by modifying probes originally targeting mitochondria to redirect their targeting toward the nucleus. This study showcases the rapid development of a novel nucleus-targeting probe (DHSP) through a targeted conversion strategy based on structure modification of hydroxystyrylpyridinium (HSP), a well-established two-photon fluorescent probe that targets mitochondria. Importantly, DHSP, which is derived exclusively from introducing only an additional o-hydroxyl group into HSP, exhibits robust DNA-binding capability comparable to a commercially available nuclear dye 4',6-diamidino-2-phenylindole (DAPI). As a result, it rapidly enters the nucleus within 5 min and finds successful application in two-photon cellular and intravital imaging of the nucleus.

A Novel ⋅OH-Monitor ER-Targeted Probe to Expose the Function of Sorafenib

The hydroxyl radical (⋅OH), widely recognized as the most potent free radical, plays a crucial role in numerous physiological and pathological pathways due to its strong oxidizability.Ferroptosis, as a novel mode of cell death, is initiated by the accumulation of iron-dependent lipid peroxidation. Among them, ⋅OH as the original reactive oxygen species (ROSs)is mass-produced due to Fenton reaction in vivo and closely related to cancer treatment.Besides, endoplasmic reticulum (ER) as a membrane-rich structure organelle, is a crucial organelle in all eukaryotes where excessive expression of ROSs, including ⋅OH can triggerER stress which was reported thatwasclosely related toferroptosis. So developing a new probe for their interrelationship research is important. In this paper, we constructed a1,8-naphthalimide-based ER-targeted fluorescence probe named M-1 to monitor ⋅OH variation in vitro and vivo. What's more, we achieved the monitor of ⋅OH during ER stress andferroptosis processesin cancer cells, andfurther explored the important role of ER stress and ferroptosis processes in SF (sorafenib) involved cancer cells.

Coumarin-aurone based fluorescence probes for cysteine sensitive in-situ identification in living cells

The quantification of cysteine (Cys) levels in the organisms holds paramount significance in biological research and disease diagnosis, which can give the correlation between abnormal Cys levels and diseases. In this study, two fluorescent probes, designated as DEA-OH and DEA-AC, featuring a coumarin-aurone backbone specifically engineered for Cys detection, were meticulously designed and synthesized. The diethylamino coumarin-aurone probe DEA-OH and the acrylate-substituted probe DEA-AC demonstrated remarkable sensitivity in detecting cysteine by means of copper displacement (DEA-OH) and acrylate hydrolysis mechanisms (DEA-AC) with fluorescence detection limits of 7.25 μM and 1.65 μM, respectively. Moreover, the fluorescence peak wavelength of the two probes displayed a linear relationship with solvent polarity in the ET (30) range of 30-65 kcal•mol-1, indicating the potential for monitoring changes in environmental polarity within this ET (30) range. The outstanding attributes exhibited by DEA-AC including superior photostability, remarkable selectivity, and swift response (kinetic rate constant: 0.00747 s-1), coupled with the exceptional anti-interference ability, have significantly broadened its scope of applications, for example detecting alterations in Cys within biological systems.

Observation of polarity changes in Sjogren's syndrome mice using a targeting lysosomes and ratiometric fluorescent probe

Utilizing non-invasive, real-time dynamic imaging and high-resolution detection tools to track polarity changes in Sjögren's syndrome (SS) contributes to a better understanding of the disease progression. Herein, a ratiometric polarity-sensitive fluorescent probe (DIM) was designed and synthesized, DIM consisted of dicyanoisophorone as the fluorophore and morpholine moiety as lysosome targeting. DIM showed a ratiometric response to polarity and high selectivity (unaffected by viscosity, pH, ROS, RNS, etc.), offering a more accurate analysis of intracellular polarity through a built-in internal reference calibration. The polarity abnormality of submandibular glands in non-obese diabetic (NOD) mice was revealed and verified by in vivo ratiometric fluorescence imaging of DIM, suggesting that fluorescent probe have great potential in the diagnosis of salivary gland abnormalities.

Clog P-Guided Development of Multi-Colored Buffering Fluorescent Probes for Super-Resolution Imaging of Lipid Droplet Dynamics

Super-resolution fluorescence imaging of live cells increasingly demands fluorescent probes capable of multi-color and long-term dynamic imaging. Understanding the mechanisms of probe-target recognition is essential for the engineered development of such probes. In this study, it is discovered that the molecular lipid solubility parameter, Clog P, determines the staining performance of fluorescent dyes on lipid droplets (LDs). Fluorescent dyes with Clog P values between 2.5 and 4 can form buffering pools outside LDs, replacing photobleached dyes within LDs to maintain constant fluorescence intensity in LDs, thereby enabling dynamic super-resolution imaging of LDs. Guided by Clog P, four different colored buffering LD probes spanning the visible light spectrum have been developed. Using Structured Illumination Microscopy (SIM), the role of LD dynamics have been tracked during cellular ferroptosis with the secretion, storage, and degradation of overexpressed ACSL3 proteins. It is found that LDs serve as storage sites for these proteins through membrane fusion, and further degrade overexpressed proteins via interactions with organelles like lysosomes or through lipophagy, thereby maintaining cellular homeostasis.

Light switchable Ir(III)-based photosensitizers: a dual-state system for non-invasive, reversible ROS control in tumor therapy

Photodynamic therapy (PDT), a powerful anticancer approach converting oxygen to ROS for tumor ablation, encounters hurdles like limited spatio-temporal selectivity and the consequent unnecessary damage to normal tissues. Addressing these challenges, developing controllable Ir(III)-based photosensitizers (PSs) emerges as a promising solution, offering enhanced efficacy and precision in cancer therapy, while propelling the clinical progression of metal-based PSs. Herein, we proposed a series of light-controlled PSs, integrating an Ir(III)-based moiety with a light-responsive module, enabling non-invasive "off-on" control of ROS production via efficient energy transfer. The open form (OF) in this dual-state system has better lipid solubility and cellular uptake compared to the closed form (CF), which facilitates targeted delivery of metal drugs. Comprehensive intracellular experiments demonstrated the OF complex's superior cytotoxicity under light irradiation, with the CF complex achieving comparable toxicity post-conversion. Notably, the PSs inhibited 3D tumor growth and modulated intracellular ROS production. These findings underscore the potential of Ir(III)-based dual-state photoswitchable complexes as a platform for non-invasive, reversible ROS control, offering broad prospects in tumor therapy and beyond.

Rational design of an AIEgen for imaging lipid droplets polarity change during ferroptosis

Ferroptosis can regulate cell death by accumulating lipid peroxides, affecting the structure and polarity of lipid droplets (LDs), but clear evidence is still lacking. Fluorescence imaging is the most powerful technique for studying LDs' function. However, developing AIE fluorescent probes with high selectivity and sensitivity for targeting LDs remains challenging. In this study, we rationally designed an AIEgen, as a novel fluorescent probe TPE-BD, by constructing a push-pull electron structure. The probe has benzo[b]thiophene-3(2H)-one 1,1-dioxide as the electron acceptor, tetraphenylethylene (AIE skeleton) as the electron donor, and thiophene as the bridging group. The optical performance of probe TPE-BD indicated that the UV-visible absorption spectrum of the probe was minimally affected by solvent polarity (except for glycerol and PBS solvents), but the fluorescence of probe is very sensitive to changes in polarity, achieving the goal of polarity detection in LDs. CCK-8 assay and cell imaging experiments demonstrated that probe TPE-BD exhibited good cell compatibility and effectively targeted LDs, enabling the monitoring of LDs' polarity and quantity during ferroptosis.

A dual-functional photosensitizer for mitochondria-targeting photodynamic therapy and synchronous polarity monitoring

Mitochondria-targeting photodynamic therapy (PDT) has been validated as an effective strategy for inducing cell death through the disruption of mitochondrial function. The mitochondrial microenvironment, such as viscosity, polarity, pH and proteins, undergoes dynamic changes during PDT treatment, and investigating these parameters is crucial for comprehending the intrinsic mechanisms at the cellular level. In this context, disclosure of mitochondrial microenvironment alterations holds significant importance. Nevertheless, a probe capable of visualizing mitochondrial polarity fluctuations during PDT treatment has not been reported. Importantly, a dual-functional photosensitizer (PS) with polarity detection capability is highly advantageous as it can mitigate potential metabolic and localization disparities between the PS and the polarity probe, thus improving the accuracy of detection. In this contribution, a series of potential PSs were prepared by integrating the 2,1,3-benzoxadiazole (BD) scaffold with various heteroatom-incorporated electron-withdrawing groups. Among them, BDI exhibited potent phototoxicity against cancer cells and remarkable sensitivity to polarity changes, establishing it as a dual-functional PS for both photodynamic therapy and polarity detection. Leveraging its polarity detection capability, BDI successfully discriminated mitochondrial polarity discrepancy between cancer cells and normal cells, and indicated mitochondrial polarity fluctuations during drug-induced mitophagy. Crucially, BDI was employed to unveil mitochondrial polarity variations during PDT treatment, underscoring its dual function. Altogether, the meticulous design of the dual-functional PS BDI offers valuable insights into intracellular microenvironment variations during the PDT process, thereby enhancing our understanding and guiding the optimization of PDT treatment.

Synergistically Activated Aggregation-Induced Emission Probe for Precise In Situ Staining of Lipids in Atherosclerotic Plaques

Visualizing the localization and distribution of lipids within arteries is crucial for studying atherosclerosis. However, existing lipid-specific probes face challenges such as strong hydrophobicity and nonspecific staining of lipophilic organelles or tissues, making them impractical for the precise identification of atherosclerotic plaques. To address this issue, we design a synergistically activated probe, Cbz-Lys-Lys-TPEB, which responds to cathepsin B (CTB) and H2O2 for the in situ generation of aggregation-induced emission luminogens (AIEgens). This enables specific staining of lipids within arteries and precise imaging of atherosclerotic plaques. The probe combines a tetraphenylethene building block with a hydrophilic peptide sequence (Cbz-Lys-Lys) and phenylboric acid module, providing excellent water solubility and fluorescence quenching in a molecular dispersion state. Upon interaction with H2O2 and CTB within plaques, the hydrophilic Cbz-Lys-Lys-TPEB probe is specifically cleaved and converted into hydrophobic AIEgens, leading to rapid aggregation and significant fluorescence enhancement. Interestingly, the in situ-liberated AIEgens display distinct lipid binding ability, effectively tracking the location and distribution of lipids in plaques. This synergistic target-activated AIEgen liberation strategy demonstrates significant feasibility for the reliable and accurate identification of atherosclerotic plaques, holding tremendous potential for clinical diagnosis and risk stratification of atherosclerosis.

A Novel Near-Infrared Tricyanofuran-Based Fluorophore Probe for Polarity Detection and LD Imaging

In this paper, LD-TCF, a targeting probe for lipid droplets (LDs) with a near-infrared emission wavelength and large Stokes shift, was fabricated for polarity detection by assembling a donor-π-acceptor (D-π-A) molecule with typical twisted intramolecular charge transfer (TICT) characteristics. Surprisingly, the fluorescence emission wavelength of the newly constructed probe LD-TCF was stretched to 703 nm, and the Stokes shift was amplified to 126 nm. Furthermore, LD-TCF could specifically answer the change in polarity efficiently and did not experience interference from other biologically active materials. Importantly, LD-TCF exhibited the ability to target lipid droplets, providing valuable insights for the early diagnosis and tracking of pathophysiological processes underlying LD polarity.

Facile construction of dual-response super-resolution probes for tracking organelles dynamics

Super-resolution imaging techniques, such as structured illumination microscopy (SIM), have enabled researchers to obtain nanoscale organelle-level outputs in living systems, but they impose additional stringent requirements on fluorescence probes. However, high-performance, custom-designed SIM probes that can explain underlying biological processes remain unavailable. Herein, a customizable engineering toolkit is developed for the facile assembly of SIM probes suitable for subcellular component detection. This toolkit is used to customize a fluorescent molecule, CPC (coumarin-phenylhydrazine-carboxyl), capable of simultaneously monitoring peroxynitrite (ONOO-) and polarity distribution in mitochondria and lipid droplets (LDs), respectively, through functional ON-OFF mechanisms. The customized CPC molecule demonstrated excellent imaging capabilities under SIM, enabled the successful localization of multiple organelles, and reliably tracked the distribution of different components, thus facilitating the study of the interplay between organelles. Using CPC, the physical transition of intracellular LDs is demonstrated from heterogeneity to homogeneity. This was specifically observed during ferroptosis where the polarity of the LDs increased and their morphology became more contracted. Furthermore, the loss of LDs functionality could not counteract the accumulation of ONOO- within the mitochondria, leading to the decoupling of mitochondrial LDs during ferroptosis. These results confirmed the potential mechanism of LDs dysfunction and decoupling triggered via cumulative mitochondrial oxidative stress during ferroptosis. To summarize, this toolkit will be a powerful tool for examining subtle variations among components during the interplay between different organelles, thus offering novel avenues for understanding and treating related diseases.

Revealing the polarity decrease of cardiomyocyte in the septic cardiomyopathy by a lipid droplets-targeting fluorescent probe with NIR emission

Septic cardiomyopathy (SCM) is the main cause of death in critically ill patients with sepsis. However, its definitive pathogenic mechanisms remain to be elucidated. Lipid droplets (LDs) are important sub-organelles that store lipids and participate in intracellular lipid metabolism. Abnormal aggregation and altered polarity of LDs are associated with the development of several cardiac diseases. To date, visualization of abnormal polarity in models of SCM has not been achieved. Herein, we designed and synthesized the probe BDP-551, a polarity-sensitive probe possessing a donor-π-acceptor (D-π-A) structure. BDP-551 exhibits excellent photostability, high LDs targeting, near-infrared (NIR) emission (up to 678 nm) and strong polarity sensitivity. With the help of confocal imaging microscopy, the BDP-551 was able to detect the polarity changes induced in the SCM model cells and visualize the yolk sac region in hypoxic as well as inflamed living zebrafish. In addition, the BDP-551 has been successfully applied to visualize the polarity changes of mice hearts with SCM, proving a decrease of microenvironmental polarity in the development of SCM. Therefore, BDP-551 in this study can be used as a reliable tool to investigate polarity fluctuations and provide new insights into the associated pathogenic and therapeutic mechanisms on SCM.

Next-generation red ultra-bright fluorescent dyes for nuclear imaging and peripheral blood leukocytes sorting

The nucleus is a membrane-bound organelle in eukaryotic cells and plays a crucial role in cellular processes. Visualizing nuclear morphology is essential for investigating nuclear functions and understanding the relationship between nuclear morphological alterations and multiple diseases. Fluorescent dyes have been developed to visualize nuclear morphology, but the selection of red nuclear-labeling fluorescent dyes remains limited (high price, unknown structure, or high toxicity). Herein, we have developed a red ultra-bright nuclear-targeted dye, BPC1, through the engineering of unsymmetrical cyanine dyes derived from D-π-A systems. BPC1 exhibits ultrahigh fluorescence brightness and exceptional cell permeability, and selectively stains nuclear DNA rather than mitochondrial DNA, enabling the visualization of the nucleus in diverse cells at extremely low doses (100 nM) and laser power (0.8 μW). Furthermore, BPC1 is utilized for nuclear staining in blood cells, aiding in the distinct visualization of the white blood cell nucleus and facilitating the identification and enumeration of various leukocyte types. Our study implies considerable commercial potential for BPC1 and underscores its capacity to serve as a powerful tool in life sciences and cell biology research.

Dual-stimuli responsive theranostic agents based on small molecules

Stimuli-responsive theranostic agents represent a class of molecules that integrate therapeutic and diagnostic functions, offering the capability to respond to disease-associated biomarkers. Dual-stimuli responsive agents, particularly those based on small molecules, have shown considerable promise for precise imaging-guided therapeutic applications. In this Highlight, we summarize the progress of dual-stimuli responsive theranostic agents based on small molecules, for diagnostic and therapeutic studies in biological systems. The Highlight focuses on comparing different responsive groups and chemical structures of these dual-stimuli responsive theranostic agents towards different biomarkers. The potential future directions of the agents for further applications in biological systems are also discussed.

Development of a high quantum yield probe for detection of mitochondrial G-quadruplexes in live cells based on fluorescence lifetime imaging microscopy

Mitochondrial G-quadruplexes are components that are potentially involved in regulating mitochondrial function and play crucial roles in the replication and transcription of mitochondrial genes. Consequently, it is imperative to develop probes that can detect mitochondrial G-quadruplexes to understand their functions and mechanisms. In this study, a triphenylamine fluorescent probe, TPPE, which has excellent cytocompatibility and does not affect the natural state of G-quadruplexes, was designed and demonstrated to localize primarily to the mitochondria. Owing to the unique binding mode between TPPE and G-quadruplexes, TPPE was able to distinguish G-quadruplexes from other substances due to the higher fluorescence lifetime and quantum yield. On the basis of the photon counts determined via fluorescence lifetime imaging microscopy, we analyzed the differences in the numbers of mitochondrial G-quadruplexes in various cell lines. We observed reductions in the number of mitochondrial G-quadruplexes during apoptosis, ferroptosis and glycolysis inhibition. This study shows the great potential of using TPPE to track and analyze mitochondrial G-quadruplexes and presents a novel perspective in the development of probes to detect mitochondrial G-quadruplexes in live cells.

Simultaneous two-color visualization of lipid droplets and lysosomes for cell homeostasis monitoring using a single fluorescent probe

Lipid droplets (LDs) and lysosomes are vital organelles that play crucial roles in various physiological and pathological processes. However, simultaneous two-color visualization of these two organelles using a single probe for cell homeostasis monitoring remains a challenge due to the lack of rational design strategies. To address this issue, we have developed an aggregation-induced emission (AIE) fluorescent probe named TPE-NDI-Mor with an electron donor (D)-acceptor (A) structure, which can stain both LDs and lysosomes with high selectivity through green and red fluorescence imaging, respectively. A detailed mechanism study revealed that TPE-NDI-Mor, with a twisted intramolecular charge transfer (TICT) effect, shows a high affinity for a polar microenvironment. Additionally, the probe also demonstrates good stability, high anti-interference performance and a large Stokes shift, making it suitable for visualizing cell homeostasis and further disease diagnosis by tracking the dynamic changes of LDs and lysosomes.

Dual-targeted fluorescent probe for tracking polarity and phase transition processes during lipophagy

Eukaryotic cells regulate various cellular processes through membrane-bound and membrane-less organelles, enabling active signal communication and material exchange. Lysosomes and lipid droplets are representative organelles, contributing to cell lipophagy when their interaction and metabolism are disrupted. Our limited understanding of the interacting behaviours and physicochemical properties of different organelles during lipophagy hinders accurate diagnosis and treatment of related diseases. In this contribution, we report a fluorescent probe, PTZ, engineered for dual-targeting of lipid droplets and lysosomes. PTZ can track liquid-liquid phase separation and respond to polarity shifts through ratiometric fluorescence emission, elucidating the lipophagy process from the perspective of organelle behavior and physicochemical properties. Leveraging on the multifunctionality of PTZ, we have successfully tracked the polarity and dynamic changes of lysosomes and lipid droplets during lipophagy. Furthermore, an unknown homogeneous transition of lipid droplets and lysosomes was discovered, which provided a new perspective for understanding lipophagy processes. And this work is expected to serve as a reference for diagnosis and treatment of lipophagy-related diseases.

Targeted mitochondrial fluorescence probe with large stokes shift for detecting viscosity changes in vivo and in ferroptosis process

We created four fluorescent sensors in our work to determine the viscosity of mitochondria. Following screening, the probe Mito-3 was chosen because in contrast to the other three probes, it had a greater fluorescence enhancement, large Stokes shift (113 nm) and had a particular response to viscosity that was unaffected by polarity or biological species. As the viscosity increased from PBS to 90 % glycerol, the fluorescence intensity of probe at 586 nm increased 17-fold. Mito-3 has strong biocompatibility and is able to track changes in cell viscosity in response to nystatin and monensin stimulation. Furthermore, the probe has been successfully applied to detect changes in viscosity caused by nystatin and monensin in zebrafish. Above all, the probe can be applied to the increase in mitochondrial viscosity that accompanies the ferroptosis process. Mito-3 has the potential to help further study the relationship between viscosity and ferroptosis.

A TICT-AIE activated dual-channel fluorescence-on probe to reveal the dynamics mechanosensing of lipid droplets during ferroptosis

Mechanical forces play a crucial role in cellular processes, including ferroptosis, a form of regulated cell death associated with various diseases. However, the mechanical aspects of organelle lipid droplets (LDs) during ferroptosis are poorly understood. In this study, we designed and synthesized a fluorescent probe, TPE-V1, to enable real-time monitoring of LDs' viscosity using a dual-channel fluorescence-on model (red channel at 617 nm and NIR channel at 710 nm). The fluorescent imaging of using TPE-V1 was achieved due to the integrated mechanisms of the twisted intramolecular charge transfer (TICT) and aggregation-induced emission (AIE). Through dual-emission channel fluorescence imaging, we observed the enhanced mechanical energy of LDs triggering cellular mechanosensing, including ferroptosis and cell deformation. Theoretical calculations confirmed the probe's behavior, showing that high-viscosity media prevented the rotation processes and restored fluorescence quenching in low viscosity. These findings suggest that our TICT-TPE design strategy provides a practical approach to study LDs' mechanical properties during ferroptosis. This development enhances our understanding of the interplay between mechanical forces and LDs, contributing to the knowledge of ferroptotic cell death and potential therapeutic interventions targeting dysregulated cell death processes.

Fluorescence and Lifetime Imaging of Endoplasmic Reticulum Polarity Change During Ferroptosis

As a new form of regulated cell death, ferroptosis is closely related to various diseases. Tracing ferroptosis related biological behavior is helpful to better understand this process and its related biology. Considering that ferroptosis is featured with remarkable lipid peroxidation which can easily change the membranes' compositions and structures, it is potential to detect intracellular environmental changes for direct assessment of ferroptosis. In view of the close relationship between endoplasmic reticulum (ER) and ferroptosis, we designed an ER-targeted and polarity-sensitive fluorescent probe SBD-CH, which has superior photostability and can respond to polarity with high selectivity without the affection of viscosity. SBD-CH can monitor the trend of ER polarity during ferroptosis by confocal laser scanning microscopy (CLSM), and analyze the distribution of polarity in ferroptosis by fluorescence lifetime imaging microscopy (FLIM). During Erastin induced ferroptosis, the polarity of ER in HT-1080 cells increased and the polarity distribution in ER was more dispersed. Our work provides an effective strategy for evaluating the process of ferroptosis by monitoring the changes of ER polarity.

Visualization of Acrolein Upregulation during Ferroptosis by a Ratiometric Fluorescent Probe

Ferroptosis is a pattern of cell death caused by iron-dependent accumulation of lipid peroxides and is closely associated with the occurrence and development of multiple diseases. Acrolein (ACR), one of the final metabolites of lipid peroxidation, is a reactive carbonyl species with strong biotoxicity. Effective detection of ACR is important for understanding its role in the progression of ferroptosis and studying the specific mechanisms of ferroptosis-mediated diseases. However, visualization detection of ACR during ferroptosis has not yet been reported. In this work, the first ratiometric fluorescent probe (HBT-SH) based on 2-(2'-hydroxyphenyl) benzothiazole (HBT) was designed for tracing endogenous ACR with an unprecedented regiospecific ACR-induced intramolecular cyclization strategy, which employs 2-aminoethanethiol as an ACR-selective recognition receptor. The experimental results showed that HBT-SH has excellent selectivity, high sensitivity (LOD = 0.26 μM) and good biocompatibility. More importantly, the upregulation of ACR levels was observed during ferroptosis in HeLa cells and zebrafish, indicating that ACR may be a specific active molecule that plays an essential biological role during ferroptosis or may serve as a potential marker of ferroptosis, which has great significance for studying the pathological process and treatment options of ferroptosis-related diseases.

Chemical Control of Fluorescence Lifetime towards Multiplexing Imaging

Fluorescence lifetime imaging has been a powerful tool for biomedical research. Recently, fluorescence lifetime-based multiplexing imaging has expanded imaging channels by using probes that harbor the same spectral channels and distinct excited state lifetime. While it is desirable to control the excited state lifetime of any given fluorescent probes, the rational control of fluorescence lifetimes remains a challenge. Herein, we chose boron dipyrromethene (BODIPY) as a model system and provided chemical strategies to regulate the fluorescence lifetime of its derivatives with varying spectral features. We find electronegativity of structural substituents at the 8' and 5' positions is important to control the lifetime for the green-emitting and red-emitting BODIPY scaffolds. Mechanistically, such influences are exerted via the photo-induced electron transfer and the intramolecular charge transfer processes for the 8' and 5' positions of BODIPY, respectively. Based on these principles, we have generated a group of BODIPY probes that enable imaging experiments to separate multiple targets using fluorescence lifetime as a signal. In addition to BODIPY, we envision modulation of electronegativity of chemical substituents could serve as a feasible strategy to achieve rational control of fluorescence lifetime for a variety of small molecule fluorophores.

Harnessing a simple ratiometric fluorescent probe for albumin recognition and beyond

A commercially available naphthalene fluorophore serves as a ratiometric indicator for albumin, showcasing its applications in albumin-based supramolecular recognition.

A ratiometric fluorescent probe revealing the abnormality of acetylated tau by visualizing polarity in Alzheimer's disease

Abnormal neuronal polarity leads to early deficits in Alzheimer's disease (AD) by affecting the function of axons. Precise and rapid evaluation of polarity changes is very important for the early prevention and diagnosis of AD. However, due to the limitations of existing detection methods, the mechanism related to how neuronal polarity changes in AD is unclear. Herein, we reported a ratiometric fluorescent probe characterized by neutral molecule to disclose the polarity changes in nerve cells and the brain of APP/PS1 mice. Cy7-K showed a sensitive and selective ratiometric fluorescence response to polarity. Remarkably, unlike conventional intramolecular charge transfer fluorescent probes, the fluorescence quantum yield of Cy7-K in highly polar solvents is higher than that in low polar solvents due to the transition of neutral quinones to aromatic zwitterions. Using the ratiometric fluorescence imaging, we found that beta-amyloid protein (Aβ) inhibits the expression of histone deacetylase 6, thereby increasing the amount of acetylated Tau protein (AC-Tau) and ultimately enhancing cell polarity. There was a high correlation between polarity and AC-Tau. Furthermore, Cy7-K penetrated the blood-brain barrier to image the polarity of different brain regions and confirmed that APP/PS1 mice had higher polarity than Wild-type mice. The probe Cy7-K will be a promising tool for assessing the progression of AD development by monitoring polarity.

A benzothiophene-based fluorescent probe with dual-functional to polarity and cyanide for practical applications in living cells and real water samples

Polarity is a significant intracellular environmental parameter associated with cancer, while cyanide (CN-) is known to be highly toxic to humans. In this work, we designed a dual-functional fluorescent probe (TPABT) for simultaneous detection of polarity and CN-. As a polarity sensor, the probe exhibits NIR emission at 766 nm in 1,4-dioxane (non-polar solvent), whose emission intensity is 71-fold stronger than that in water (polar solvent). Meanwhile, the fluorescence intensity and quantum yield are linearly related to solvent polarity, confirming the polarity response ability of TPABT. For cell polarity detection, low cytotoxicity and polarity sensitivity of probe enable the applications for differentiating cancer cells (HeLa, 4TI) from normal cells (HUV, 3 T3) and monitoring the polarity changes of 4TI cells. As a CN- sensor, TPABT displays a turn-on fluorescence at 640 nm upon the addition of CN-, with advantages of anti-interference, response in aqueous media and low detection limit (22 nM). Additionally, we further explored the practical applications of TPABT for CN- determination in three types of real water samples (drinking water, tap water and lake water) and living cells. Notably, TPABT responses to polarity and CN- in two independent fluorescence channels of 766 and 640 nm, respectively, ensuring the dual functions for polarity and CN- sensing. Consequently, this multi-responsive fluorescent probe TPABT is promising to diagnose polarity-related diseases and detect CN- in real environments.

Two-Photon-Responsive "TICT + AIE" Active Naphthyridine-BF2 Photoremovable Protecting Group: Application for Specific Staining and Killing of Cancer Cells

The combined effects of twisted intramolecular charge transfer (TICT) and aggregation-induced emission (AIE) phenomena have demonstrated a significant influence on excited-state chemistry. These combined TICT and AIE features have been extensively utilized to enhance photodynamic and photothermal therapy. Herein, we demonstrated the synergistic capabilities of TICT and AIE phenomena in the design of the photoremovable protecting group (PRPG), namely, NMe2-Napy-BF2. This innovative PRPG incorporates TICT and AIE characteristics, resulting in four remarkable properties: (i) red-shifted absorption wavelength, (ii) strong near-infrared (NIR) emission, (iii) viscosity-sensitive emission property, and (iv) accelerated photorelease rate. Inspired by these intriguing attributes, we developed a nanodrug delivery system (nano-DDS) using our PRPG for cancer treatment. In vitro studies showed that our nano-DDS manifested effective cellular internalization, specific staining of cancer cells, high-resolution confocal imaging of cancerous cells in the NIR region, and controlled release of the anticancer drug chlorambucil upon exposure to light, leading to cancer cell eradication. Most notably, our nano-DDS exhibited a substantially increased two-photon (TP) absorption cross section (435 GM), exhibiting its potential for in vivo applications. This development holds promise for significant advancements in cancer treatment strategies.