Charge-driven tripod somersault on DNA for ratiometric fluorescence imaging of small molecules in the nucleus

Real-Time Monitoring of mtDNA Aggregation and Mitophagy Induced by a Fluorescent Platinum Complex in Living Cells

Mitochondrial DNA (mtDNA) is pivotal for mitochondrial morphology and function. Upon mtDNA damage, mitochondria undergo quality control mechanisms, including fusion, fission, and mitophagy. Real-time monitoring of mtDNA enables a deeper understanding of its effect on mitochondrial function and morphology. Controllable induction and real-time tracking of mtDNA dynamics and behavior are of paramount significance for studying mitochondrial function and morphology, facilitating a deeper understanding of mitochondria-related diseases. In this work, a fluorescent platinum complex was designed and developed that not only induces mitochondrial DNA (mtDNA) aggregation but also triggers mitochondrial autophagy (mitophagy) through the MDV pathway for damaged mtDNA clearance in living cells. Additionally, this complex allows for the real-time monitoring of these processes. This complex may serve as a valuable tool for studying mitochondrial microautophagy and holds promise for broader applications in cellular imaging and disease research.

A ratiometric fluorescent probe with dual-targeting capability for heat shock imaging

HSO3- is an important reactive sulfur species that maintains the normal physiological activities of living organisms and participates in a variety of redox homeostatic processes. It has been found that changes in HSO3- levels is closely related to the heat stroke phenomenon of the organism. Heat stroke causes damage to normal cells, which in turn causes damage to the body and even death. It is crucial to accurately monitor and track the physiological behavior of HSO3- during heat stroke. Herein, a ratiometric multifunctional fluorescent probe DRM-SO2 with dual-targeting ability to rapidly and precisely recognize HSO3- being constructed based on the FRET mechanism. DRM-SO2 has extra Large Stokes shift (216 nm), very high sensitivity (DL = 12.2 nM), fast response time and good specificity. When DRM-SO2 undergoes Michael addition with HSO3-, the fluorescence emission peak was blue-shifted from 616 nm to 472 nm, and a clear ratiometric signal appeared. The interaction between lysosomes and mitochondria in maintaining cellular homeostasis was investigated by the dual-targeting ability of the probe using HSO3- as a mediator. DRM-SO2 achieved successful targeting and real-time monitoring of exogenous and endogenous HSO3- in the cells. More importantly, imaging experiments in heat stroke mice revealed high HSO3- expression in intestinal tissues. This provides new ideas and research tools for early prevention of heat stroke-induced diseases such as intestinal injuries. In addition, the semi-quantitative monitoring experiments for paper-based visualization of HSO3- make the probe promising for the design of portable detectors.

Molecular probes for super-resolution imaging of drug dynamics

Super-resolution molecular probes (SRMPs) are essential tools for visualizing drug dynamics within cells, transcending the resolution limits of conventional microscopy. In this review, we provide an overview of the principles and design strategies of SRMPs, emphasizing their role in accurately tracking drug molecules. By illuminating the intricate processes of drug distribution, diffusion, uptake, and metabolism at a subcellular and molecular level, SRMPs offer crucial insights into therapeutic interventions. Additionally, we explore the practical applications of super-resolution imaging in disease treatment, highlighting the significance of SRMPs in advancing our understanding of drug action. Finally, we discuss future perspectives, envisioning potential advancements and innovations in this field. Overall, this review serves to inform and practitioners about the utility of SRMPs in driving innovation and progress in pharmacology, providing valuable insights for drug development and optimization.

A translocation fluorescent probe for analyzing cellular physiological parameters in neurological disease models

Neurological disorders are closely linked to the alterations in cell membrane permeability (CMP) and mitochondrial membrane potential (MMP). Changes in CMP and MMP may lead to damage and death of nerve cells, thus triggering the onset and progression of neurological diseases. Therefore, monitoring the changes of these two physiological parameters not only benefits the accurate assessment of nerve cell health status, but also enables providing key information for the diagnosis and treatment of neurological diseases. However, the simultaneous monitoring of these two cellular physiological parameters is still challenging. Herein, we design and synthesize two quinolinium-carbazole-derivated fluorescent probes (OQ and PQ). As isomers, the only difference in their chemical structures is the linking position of the carbazole unit in quinoline rings. Strikingly, such a subtle difference endows OQ and PQ with significantly different organelle-staining behaviors. PQ mainly targets at the nucleus, OQ can simultaneously stain cell membranes and mitochondria in normal cells, and performs CMP and MMP-dependent translocation from the cell membrane to mitochondria then to the nucleus, thus holding great promise as an intracellular translocation probe to image the changes of CMP and MMP. After unraveling the intrinsic mechanism of their different translocation abilities by combining experiments with molecular dynamics simulations and density functional theory calculations, we successfully used OQ to monitor the continuous changes of CMP and MMP in three neurological disease-related cell models, including oxidative stress-damaged, Parkinson's disease, and virus-infected ones. Besides providing a validated imaging tool for monitoring cellular physiological parameters, this work paves a promising route for designing intracellular translocation probes to analyze cellular physiological parameters associated with various diseases.

Precisely modulating the chromatin tracker via substituent engineering: reporting pathological oxidative stress during mitosis

An in-depth understanding of cancer-cell mitosis presents unprecedented advantages for solving metastasis and proliferation of tumors, which has aroused great interest in visualizing the behavior via a luminescence tool. We developed a fluorescent molecule CBTZ-yne based on substituent engineering to acquire befitting lipophilicity and electrophilicity for anchoring lipid droplets and the nucleus, in which the low polarity environment and nucleic acids triggered a "weak-strong" fluorescence and "short-long" fluorescence-lifetime response. Meaningfully, CBTZ-yne visualized chromatin condensation, alignment, pull-push, and separation as well as lipid droplet dynamics, for the first time, precisely unveiling the asynchronous cellular mitosis processes affected by photo-generation reactive oxygen species according to the subtle change of fluorescence-lifetime. Our work suggested a new guideline for tracking the issue of the proliferation of malignant tumors in photodynamic therapy.

"Two-Stage Rocket-Propelled" Strategy Boosting Theranostic Efficacy with Mitochondria-Specific Type I-II Photosensitizers

Imaging-guided photodynamic therapy (PDT) holds great potential for tumor therapy. However, achieving the synergistic enhancement of the reactive oxygen species (ROS) generation efficiency and fluorescence emission of photosensitizers (PSs) remains a challenge, resulting in suboptimal image guidance and theranostic efficacy. The hypoxic tumor microenvironment also hinders the efficacy of PDT. Herein, we propose a "two-stage rocket-propelled" photosensitive system for tumor cell ablation. This system utilizes MitoS, a mitochondria-targeted PS, to ablate tumor cells. Importantly, MitoS can react with HClO to generate a more efficient PS, MitoSO, with a significantly improved fluorescence quantum yield. Both MitoS and MitoSO exhibit less O2-dependent type I ROS generation capability, inducing apoptosis and ferroptosis. In vivo PDT results confirm that this mitochondrial-specific type I-II cascade phototherapeutic strategy is a potent intervention for tumor downstaging. This study not only sheds light on the correlation between the PS structure and the ROS generation pathway but also proposes a novel and effective strategy for tumor downstaging intervention.

Simultaneous detection of SO2 and viscosity in drug-induced inflammation in live cells and zebrafish

The viscosity within cells is a crucial microenvironmental factor, and sulfur dioxide (SO2 ) has essential functions in regulating cellular apoptosis and inflammation. Some evidence has been confirmed that changes in viscosity and overexposure of SO2 within the cell may cause detrimental effects including, but not limited to, respiratory and cardiovascular illnesses, inflammation, fatty liver, and various types of cancer. Therefore, precise monitoring of SO2 and viscosity in biological entities holds immense practical importance. Therefore, in this research, we developed a versatile fluorescent TCF-Cou that enables the dual detection of SO2 and viscosity in the living system. Probe TCF-Cou possessed a response to viscosity and SO2 through red and green emissions. The alteration of SO2 and viscosity levels in live cells and zebrafish were also monitored using probe TCF-Cou. We hope that this fluorescent probe could be a potential tool for revealing the related pathological and physiological processes through monitoring the changes in SO2 and viscosity.

A nucleophilic addition-elimination based ratiometric fluorescent probe for monitoring N2H4 in biological systems and actual samples

Hydrazine (N₂H₄) is an important reagent in the field of fine chemical engineering. However, its accumulation in the environment and food chain could pose a great threat to food safety and human health. Therefore, designing a fluorescent probe with good cell penetration and high selectivity and sensitivity to detect N₂H₄ in actual samples and in vivo is a meaningful project. Herein, due to the nucleophilicity of hydrazine, we utilized naphthalimide as the fluorescence chromophore and pyrone as the recognition site to achieve the ratiometric detection of hydrazine by ring opening. In addition, we introduced the ester to improve the lipid solubility of the probe, which allowed the probe to better penetrate the cell membrane to realize the fluorescent imaging of probes in cells. Meanwhile, to our delight, the probe showed high selectivity and sensitivity to N₂H₄ in the test system, so we further applied the probe in water samples and food, in vitro and in vivo.

A two-photon iridium(III) complex probe for sensitive detection of SO2 derivatives in living cell mitochondria

The derivatives of sulfur dioxide (HSO₃^-) formed in the biological environment play a vital role in the circulation system. Excessive SO₂ derivatives will cause serious damage to the living system. Herein, a two-photon phosphorescent probe based on Ir(III) complex (named as Ir-CN) was designed and synthesized. Ir-CN is extremely selective and sensitive to SO₂ derivatives with significant phosphorescent enhancement and increased phosphorescent lifetime. The detection limit of Ir-CN for SO₂ derivatives reaches 0.17 μM. More importantly, Ir-CN preferentially accumulates in mitochondria, so bisulfite derivatives can be detected at subcellular level, which enriching the application of metal complex probe in biological detection. In addition, both single-photon and two-photon images can clearly show that Ir-CN is targeted to mitochondria. Benefits from its good biocompatibility, Ir-CN may be used as a reliable tool to detect SO₂ derivatives in mitochondrion of living cells.

Migration from Lysosome to Nucleus: Monitoring Lysosomal Alkalization-Related Biological Processes with an Aminofluorene-Based Probe

Aberrant lysosomal alkalization is associated with various biological processes, such as oxidative stress, cell apoptosis, ferroptosis, etc. Herein, we developed a novel aminofluorene-based fluorescence probe named FAN to monitor the lysosomal alkalization-related biological processes by its migration from lysosome to nucleus. FAN possessed NIR emission, large Stokes shift, high pH stability, and high photostability, making it suitable for real-time and long-term bioimaging. As a lysosomotropic molecule, FAN can accumulate in lysosomes first and then migrate to the nucleus by right of its binding capability to DNA after lysosomal alkalization. In this manner, FAN was successfully used to monitor these physiological processes which triggered lysosomal alkalization in living cells, including oxidative stress, cell apoptosis, and ferroptosis. More importantly, at higher concentrations, FAN could also serve as a stable nucleus dye for the fluorescence imaging of the nucleus in living cells and tissues. This novel multifunctional fluorescence probe shows great promise for application in lysosomal alkalization-related visual research and nucleus imaging.

A julolidine-chalcone-based fluorescent probe for detection of Al3+ in real water sample and cell imaging

A fluorescent probe 1 based on julolidine-chalcone derivative, which can specifically recognize aluminum ion with high selectivity and anti-interference, was developed. Probe 1 has good fluorescence stability and can detect Al³⁺ with turn-on fluorescence in a wide pH range of 4.0-9.0. The probe has good repeatability for the detection of Al³⁺ and fluorescence turn-on and off can be repeated with the alternate Al³⁺ and EDTA. The sensing mechanism is speculated that Al³⁺ will coordinate with hydroxyl oxygen and carbonyl oxygen on the probe through in situ ¹H NMR and HRMS combing with Job's plot. The probe can also detect Al³⁺ in actual water samples and applied to monitor Al³⁺ in biological system.

A Nuclear-Targeted AIE Photosensitizer for Enzyme Inhibition and Photosensitization in Cancer Cell Ablation

The nucleus is considered the ideal target for anti-tumor therapy because DNA and some enzymes in the nucleus are the main causes of cell canceration and malignant proliferation. However, nuclear target drugs with good biosafety and high efficiency in cancer treatment are rare. Herein, a nuclear-targeted material MeTPAE with aggregation-induced emission (AIE) characteristics was developed based on a triphenylamine structure skeleton. MeTPAE can not only interact with histone deacetylases (HDACs) to inhibit cell proliferation but also damage telomere and nucleic acids precisely through photodynamic treatment (PDT). The cocktail strategy of MeTPAE caused obvious cell cycle arrest and showed excellent PDT anti-tumor activity, which offered new opportunities for the effective treatment of malignant tumors.

MnO2 nanosheet-mediated target-binding-induced FRET strategy for multiplexed microRNAs detection and imaging in living cells

In the regulatory network, miRNAs play a regulatory role in a cooperative or antagonistic manner. Simultaneous accurate detection and imaging of multiplexed miRNAs in living cells are of great significance for miRNA-associated biological research and disease diagnosis and treatment. Herein, a MnO₂ nanosheet-mediated target-binding-induced fluorescence resonance energy transfer (FRET) strategy was developed for detection and imaging of multiplexed miRNAs in living cells. Two pairs of DNA probes (P1-AF 488/P1'-Cy3 and P2-AF 488/P2'-AF 594) contained the complementary sequence to target miRNAs (miRNA-373 and miRNA-96) and labelled with different fluorescence dyes were designed. They were adsorbed onto MnO₂ nanosheets by physisorption to form DNA/MnO₂ nanocomposite probes. When the DNA/MnO₂ nanocomposite probes were taken up by cells, the MnO₂ nanosheets were reduced by intracellular glutathione, accompanying the release of DNA probe pairs. Then the DNA probe pairs specifically recognized and combined with miRNA-373 and miRNA-96 to form stable duplexes, respectively, bringing labelled fluorophores into close proximity to occur FRET. Based on this, the simultaneous imaging of miRNA-373 and miRNA-96 in MDA-MB-231 and L02 cells was successfully implemented. The results displayed a higher expression level of target miRNAs in MDA-MB-231 cells compared to L02 cells. The changes in expression levels of miRNA-96 induced by anti-miRNA-96 or mimics in MDA-MB-231 cells could also be monitored. In addition, the ratiometric detections of multiplexed miRNAs were achieved by utilizing the DNA probe pairs. The proposed strategy provides an alternative method for simultaneous accurate detection and imaging of multiplexed miRNAs and has potential application in biomedical applications.

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

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

Light-Driven Cascade Mitochondria-to-Nucleus Photosensitization in Cancer Cell Ablation

Nuclei and mitochondria are the only cellular organelles containing genes, which are specific targets for efficient cancer therapy. So far, several photosensitizers have been reported for mitochondria targeting, and another few have been reported for nuclei targeting. However, none have been reported for photosensitization in both mitochondria and nucleus, especially in cascade mode, which can significantly reduce the photosensitizers needed for maximal treatment effect. Herein, a light-driven, mitochondria-to-nucleus cascade dual organelle cancer cell ablation strategy is reported. A functionalized iridium complex, named BT-Ir, is designed as a photosensitizer, which targets mitochondria first for photosensitization and subsequently is translocated to a cell nucleus for continuous photodynamic cancer cell ablation. This strategy opens new opportunities for efficient photodynamic therapy.

Ratiometric Fluorescence Imaging for the Distribution of Nucleic Acid Content in Living Cells and Human Tissue Sections

The misregulation of nucleic acids behavior leads to cell dysfunction and induces serious diseases. A ratiometric fluorescence probe is a powerful tool to study the dynamic behavior and function relationships of nucleic acids. However, currently, no such effective probe has been reported for in situ, real-time tracking of nucleic acids in living cells and tissue sections. Herein, the unique probe named QPP-AS was rationally designed for ratiometric fluorescence response to nucleic acids through skillful regulation of the intramolecular charge-transfer capabilities of the electron acceptor and donor. Encouraged by the advantages of the selective nucleic acid response, ideal biocompatibility, and high signal-to-noise ratio, QPP-AS has been applied for in situ, real-time ratiometric fluorescence imaging of nucleic acids in living cells for the first time. Furthermore, we have demonstrated that QPP-AS is capable of visualizing the dynamic behavior of nucleic acids during different cellular processes (e.g., cell division and apoptosis) by ratiometric fluorescence imaging. More significantly, QPP-AS has been successfully used for ratiometric fluorescence imaging of nucleic acids in human tissue sections, which provides not only the cell contour, nuclear morphology, and nuclear-plasma ratio but also the nucleic acid content information and may greatly improve accuracy in clinicopathological diagnosis.

In Situ Monitoring of Mitochondria Regulating Cell Viability by the RNA-Specific Fluorescent Photosensitizer

Cell viability is greatly affected by external stimulus eliciting correlated dynamical physiological processes for cells to choose survival or death. A few fluorescent probes have been designed to detect whether the cell is in survival state or apoptotic state, but monitoring the regulation process of the cell undergoing survival to death remains a long-standing challenge. Herein, we highlight the in situ monitor of mitochondria regulating the cell viability by the RNA-specific fluorescent photosensitizer L. At normal conditions, L anchored mitochondria and interacted with mito-RNA to light up the mitochondria with red fluorescence. With external light stimulus, L generated reactive oxide species (ROS) and cause damage to mitochondria, which activated mitochondrial autophagy to prevent death, during which the red fluorescence of L witnessed dynamical distribution in accordance with the evolution of vacuole structures containing damaged mitochondria into autophagosomes. However, with ROS continuously increasing, the mitochondrial apoptosis was eventually commenced and L with red fluorescent was gradually accumulated in the nucleoli, indicating the programmed cell death. This work demonstrated how the delicate balance between survival and death are regulated by mitochondria.

A molecular rotor sensor for detecting mitochondrial viscosity in apoptotic cells by two-photon fluorescence lifetime imaging

A two-photon fluorescent probe was developed for detecting mitochondrial viscosity during apoptosis of living cells by two-photon microscopy (TPM) and fluorescence lifetime imaging microscopy (FLIM) with good selectivity and highly biocompatible.