Non-Solvatochromic Cell Membrane-Targeted NIR Fluorescent Probe for Visualization of Polarity Abnormality in Drug-Induced Liver Injury Mice

Ultra-photostable fluorescent dye molecular engineering-for measuring plant cells' membrane-spacing through a "deposition-embedding" strategy

The plant cell membrane serves as a barrier, isolating the cell's interior from its external environment. Unlike animal cells, where the cytoplasmic membrane can be easily fluorescently labeled through genetic engineering, plant cells often rely more heavily on small molecule fluorescent probes to address the problem of probe internalization. Meanwhile, due to cellular internalization, current plasma fluorescent probes struggle to stain cell membranes for long periods of time. In addition, these probes tend to accumulate in the cell wall, making it impossible to achieve specific, high-noise-to-noise staining of cell membranes. In response to these challenges, we propose a novel "deposition-embedding" strategy for developing a plant cell membrane probe. The compound PTBT-O-NPh2, with its low solubility and high hydrophobicity, is designed to limit membrane penetration. Instead, it rapidly deposits on the membrane surface and embeds itself into the lipid environment via strong hydrogen bonding with phospholipid molecules. Additionally, its exceptional resistance to photobleaching and long-term retention capability allow it to measure membrane-spacing over a period of 120 hours. These findings suggest that the "deposition-embedding" strategy could be instrumental in developing a new generation of fluorescent dyes for studying plant mechanobiology.

In situ observation of mitochondrial viscosity in liver of mice with drug-induced liver injury by near-infrared fluorescence imaging

Drug-induced liver injury (DILI) has emerged as among of the undesirable drug effects, posing significant threats to human health. However, in clinical practice, there remains a shortage of dependable and pre-diagnosis tools for DILI. Numerous studies indicated that the elevated intrahepatic viscosity levels were closely linked to the onset and progression of DILI. Therefore, establishing reliable tools to monitor mitochondrial viscosity are crucial for prompt diagnosis of DILI in situ. Herein, we proposed a new near-infrared (NIR) fluorescence probe (Wyry-M-V) for detecting mitochondrial viscosity, in which consisted of xanthene, multiple viscosity-responsive rotors (diphenyl, vinyl cyanide, and benzyl chloride) and mitochondrial targeting site (pyridinium cation). Furthermore, the Wyry-M-V was triumphantly utilized in mitochondrial viscosity imaging upon treatment with lipopolysaccharide, nystatin and acetaminophen (APAP). Notably, based on the advantages of NIR emission wavelength, the Wyry-M-V was resoundingly used for the detection of mitochondrial viscosity in APAP-induced DILI mice model.

Polarity-sensitive pyrene fluorescent probes for multi-organelle imaging in living cells

Polarity-sensitive probes (PAS) were synthesized through the attachment of azetidine and sulfonyl substituents to the pyrene fluorescent core. The emission peaks and fluorescence lifetimes of these PAS probes exhibit high sensitivity to polarity, enabling the visualization of microenvironmental characteristics and dynamics across multiple organelles.

Design strategies for organelle-selective fluorescent probes: where to start?

Monitoring physiological changes within cells is crucial for understanding their biological aspects and pathological activities. Fluorescent probes serve as powerful tools for this purpose, offering advantageous characteristics over genetically encoded probes. While numerous organelle-selective probes have been developed in the past decades, several challenges persist. This review explores the strategies and key factors contributing to the successful rationale design of these probes. We systematically discuss the typical mode of cellular uptake generally adopted by fluorescent probes and provide a detailed examination of the key factors to consider in design rationale from two perspectives: the properties of the target organelle and the physicochemical properties of the probe itself. Additionally, recent examples of organelle-targeted probes are presented, along with a discussion of the current challenges faced by fluorescent probes in the field.

Fluorination of Aza-BODIPY for Cancer Cell Plasma Membrane-Targeted Imaging and Therapy

Photodynamic therapy (PDT) holds great potential in cancer treatment, leveraging photosensitizers (PSs) to deliver targeted therapy. Fluorination can optimize the physicochemical and biological properties of PSs for better PDT performance. Here, we report some high-performance multifunctional PSs specifically designed for cancer PDT by fluorinating aza-BODIPY with perfluoro-tert-butoxymethyl (PFBM) groups. Fluorination plays several roles, including enhancing selective cancer cell uptake, plasma membrane (PM) targeting, and inducing pyroptosis. It also enables fluorescence imaging (FLI) and fluorine-19 magnetic resonance imaging (19F MRI) as well as facilitates oxygen delivery and oxygen partial pressure (pO2) measurements. Comparative physicochemical and biological studies, along with molecular dynamics simulations, reveal that fluorinated PSs selectively eradicate cancer cells by oxidizing PM phospholipids with singlet oxygen (1O2) and inducing pyroptosis, which enables effectively suppressed tumor growth by self-oxygenated 19F MRI-FLI-guided PDT in mice. This study demonstrates a fluorination strategy for tailoring high-performance multifunctional cancer PM-targeting materials for cancer therapy and beyond.

Simultaneous visualization of lipid droplets and tracking of the endogenous hypochlorous acid in psoriatic mice models with a novel fluorescent probe in a wash-free fashion

Psoriasis is an autoimmune inflammation-related disease accompanied by a variety of complications. Reactive oxygen species (ROS) are modulators of inflammation, and their excessive production caused by oxidative/anti-oxidative imbalance has been observed in psoriatic patients. Hypochlorous acid (HOCl) is a ROS produced by myeloperoxidase (MPO) from chloride ions (Cl-) and hydrogen peroxide (H2O2). Endogenous HOCl has recently been studied as a potential biomarker of psoriasis underlying the necessity for the development of efficient analytical tools for its detection and real time monitoring. Herein, we designed a novel highly sensitive and selective coumarin-based fluorescent probe for HOCl detection, named CN2-CF3-S. The probe itself featured negligible fluorescence because of the heavy atom effect of the thiocarbonyl group. However, upon responding to HOCl a conversion to sulfur-free derivative CN2-CF3-O occurs, resulting in a dramatical fluorescent enhancement setting the detection limit for HOCl of 3.2 nM. The HOCl-recognition mechanism could be ascribed to the HOCl-triggered oxidative desulfurization process that agrees with liquid chromatography-mass spectrometry (LC-MS) analysis and density functional theory (DFT) computations. The probe's design incorporated a synergistic combination of two structural features for efficient lipid droplets (LDs)-targeting imaging. An efficient push-pull system reinforced by the presence of two strongly electron-donating dimethylamino groups equipped CN2-CF3-O with pronounced solvatochromism realized through the enhanced blue-shifted emission in non-polar media. Meanwhile, the presence of trifluormethylphenyl moiety at the acceptor side led to an increased lipophilicity. The CN2-CF3-S probe has been successfully utilized to track the endogenous HOCl in cells and on skin of the psoriatic mice in a wash-free manner. As a result, we have demonstrated that the concentration of HOCl in skin might correlate positively with the degree of inflammation in psoriasis. Thus, CN2-CF3-S constitutes the first example of LDs-imaging fluorescent probe for detecting the psoriasis-linked HOCl, offering a convenient tool for further in-depth investigation of psoriasis pathophysiology.

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.

A dual-response fluorescence sensor for SO2 derivatives and polarity and its application in real water and food samples

As an important gaseous pollutant, SO2 derivatives generally exist and significantly threaten the environment and organism health. Meanwhile, polarity is a disease-related indicator in the organism's microenvironment, where an unregulated variation may disturb the physiological metabolisms. Hence, a superior FRET-based fluorescent sensor (TLA) is presented to track polarity and sulfur dioxide derivatives by dual emission channel, i.e. an elevated red emission at 633 nm with decreasing polarity as well as a reduced red emission at 633 nm and improved blue emission at 449 nm with increasing concentration of SO2 derivatives. The probe TLA could sensitively detect SO2 derivatives with ultra-large Stokes shift (273 nm), excellent stability, high selectivity, and low detection limit. Importantly, TLA can accurately detect sulfur dioxide derivatives in real food as well as water samples. Besides, TLA was also fabricated as testing strips and applied to detect SO2 derivatives in the solution.

Fast-Responsive HClO-Activated Near-Infrared Fluorescent Probe for In Vivo Diagnosis of Inflammatory Bowel Disease and Ex Vivo Optical Fecal Analysis

Inflammatory bowel disease (IBD) is an idiopathic intestinal inflammatory disease, whose etiology is intimately related to the overproduction of hypochlorous acid (HClO). Optical monitoring of HClO in the living body favors real-time diagnosis of inflammatory diseases. However, HClO-activated near-infrared (NIR) fluorescent probes with rapid response and high inflammatory cell uptake are still lacking. Herein, we report an activatable acceptor-π-acceptor (A-π-A)-type NIR fluorescent probe (Cy-DM) bearing two d-mannosamine groups for the sensitive detection of HClO in early IBD and stool testing. Once reacted with HClO, nonfluorescent Cy-DM could be turned on within 2 s by generating a donor-π-acceptor (D-π-A) structure due to the enhanced intramolecular charge transfer mechanism, showing intense NIR fluorescence emission at 700 nm and a large Stokes shift of 115 nm. Moreover, it was able to sensitively and selectively image exogenous and endogenous HClO in the lysosomes of living cells with a detection limit of 0.84 μM. More importantly, because of the d-mannosamine modification, Cy-DM was efficiently taken up by inflammatory cells in the intestine after intravenous administration, allowing noninvasive visualization of endogenous HClO in a lipopolysaccharide-induced IBD mouse model with a high fluorescence contrast of 6.8/1. In addition, water-soluble Cy-DM has also been successfully applied in ex vivo optical fecal analysis, exhibiting a 3.4-fold higher fluorescence intensity in the feces excreted by IBD mice. We believe that Cy-DM is promising as an invaluable tool for rapid diagnosis of HClO-related diseases as well as stool testing.

Tracking Plasma Membrane Damage Using a Ruthenium(II) Complex Phosphorescent Indicator Paired with Cholesterol

Long-term in situ plasma membrane-targeted imaging is highly significant for investigating specific biological processes and functions, especially for the imaging and tracking of apoptosis processes of cells. However, currently developed membrane probes are rarely utilized to monitor the in situ damage of the plasma membrane. Herein, a transition-metal complex phosphorescent indicator, Ru-Chol, effectively paired with cholesterol, exhibits excellent properties on staining the plasma membrane, with excellent antipermeability, good photostability, large Stokes shift, and long luminescence lifetime. In addition, Ru-Chol not only has the potential to differentiate cancerous cells from normal cells but also tracks in real time the entire progression of cisplatin-induced plasma membrane damage and cell apoptosis. Therefore, Ru-Chol can serve as an efficient tool for the monitoring of morphological and physiological changes in the plasma membrane, providing assistance for drug screening and early diagnosis and treatment of diseases, such as immunodeficiency, diabetes, cirrhosis, and tumors.

A ratiometric fluorescent probe for imaging the fluctuation of HOBr during endoplasmic reticulum stress

Endoplasmic reticulum (ER) stress is closely associated with cell apoptosis, autophagy, DNA damage, metabolism, and migration. When ER stress occurs, a large number of reactive oxygen species, including hypobromous acid (HOBr), are generated. The degree of ER stress can be understood by accurately detecting the HOBr concentration in the ER. Unfortunately, no ER-targetable probes for detecting HOBr have been reported to date. To solve this problem, we developed a naphthalimide-based fluorescent probe (ER-NABr) for imaging HOBr in the ER. Upon reaction with HOBr, a red shift in the fluorescence spectrum occurs due to the difference in the molecular conjugation between the original ER-NABr and the reaction product. ER-NABr showed a fast response (within 30 s) and high selectivity towards HOBr, with a ratiometric quantitative response (5-40 μM) and high sensitivity (138 nM). With its excellent biocompatibility and remarkable ER-targetable ability, ER-NABr was successfully utilized to ratiometrically image intracellular HOBr, particularly during ER stress, which is beneficial for revealing the role of HOBr in ER-associated diseases.