Ferroptosis Accompanied by •OH Generation and Cytoplasmic Viscosity Increase Revealed via Dual-Functional Fluorescence Probe

A bifunctional mitochondrial targeting AIE-active fluorescent probe with high sensitivity to hydrogen peroxide and viscosity for fatty liver diagnosis

A mitochondrial targeting AIE-active fluorescent probe with highly sensitive dual-detection of hydrogen peroxide and viscosity for fatty liver diagnosis.

A dual-labeling probe to track functional mitochondria-lysosome interactions in live cells

Mitochondria–lysosome interactions are essential for maintaining intracellular homeostasis. Although various fluorescent probes have been developed to visualize such interactions, they remain unable to label mitochondria and lysosomes simultaneously and dynamically track their interaction. Here, we introduce a cell-permeable, biocompatible, viscosity-responsive, small organic molecular probe, Coupa, to monitor the interaction of mitochondria and lysosomes in living cells. Through a functional fluorescence conversion, Coupa can simultaneously label mitochondria with blue fluorescence and lysosomes with red fluorescence, and the correlation between the red–blue fluorescence intensity indicates the progress of mitochondria–lysosome interplay during mitophagy. Moreover, because its fluorescence is sensitive to viscosity, Coupa allowed us to precisely localize sites of mitochondria–lysosome contact and reveal increases in local viscosity on mitochondria associated with mitochondria–lysosome contact. Thus, our probe represents an attractive tool for the localization and dynamic tracking of functional mitochondria–lysosome interactions in living cells.

Dynamic labeling and tracking of organelle–organelle contacts is essential to understand the formation and function of these interactions. Here the authors present a small molecule probe, Coupa, that labels mitochondria and lysosomes with blue and red fluorescence, respectively.

Construction of a novel GQD based ratiometric fluorescent composite probe for viscosity detection

Herein, a novel ratiometric fluorescent composite nanoprobe RV-1@GQDs-OH was developed based on OH-functionalized GQDs (GQDs-OH) and molecular probe (RV-1) viaπ-π stacking. Compared with the conventional "on-off" viscosity probes, RV-1@GQDs-OH can be successfully applied in living systems for the ratiometric detection of viscosity changes in the viscosity range of 0-600 cP.

Synthesis of Dihydroquinolines as Scaffolds for Fluorescence Sensing of Hydroxyl Radical

A mild synthetic method to prepare dihydroquinolines has been presented. These dihydroquinolines, for the first time, showed great potential for fluorescence detection of the important biorelevant hydroxyl radicals (^•OH). Sensitive and selective ^•OH detection and intracellular organelle-targeted fluorescence imaging of ^•OH have been demonstrated by using one of the synthetic dihydroquinolines. Moreover, dihydroquinoline has also exhibited promising potential to construct advanced fluorescence probes for ^•OH with tunable photophysical properties.

A novel fluorescent probe with dual-sites for simultaneously monitoring metabolisms of cysteine in living cells and zebrafishes

Understanding cellular metabolism holds immense potential for developing new drugs that regulate metabolic pathways. Two gas signal molecules, SO₂ and H₂S, are the main metabolites from cysteine (Cys) via oxidation and desulfurization pathways, respectively. However, a few fluorescent probes for real-time monitor of the metabolic pathways of cysteine have been reported. To understand metabolic alterations of cysteine, we have rationally designed and prepared a dual-signal fluorescent probe HN, which could differentiate SO₂ and H₂S through two different fluorescence channels simultaneously, along with similar reaction kinetics and both "off-on" fluorescence responses. Probe HN exhibits the potential to monitor the metabolism pathways of cysteine, and the distinguishment of cancer cells from normal cells could be realized. This methodology will promote further understanding of the physiological and pathological roles of cysteine.

Recent Advances of Organic Near-Infrared II Fluorophores in Optical Properties and Imaging Functions

Near-infrared (NIR) fluorescence imaging (FI) has become a research hotspot because of its distinctive imaging properties: high temporal resolution and sensitivity. Especially in recent years, with the research focus of NIR FI shifting to the NIR-II region, which has better imaging performance, it is expected that NIR FI will find significant applications in the field of in vivo imaging. One of the most crucial directions for research into NIR-II FI is the promotion of novel NIR-II fluorophores with superior imaging properties. The remarkable advantages of organic NIR-II fluorophores in biosafety make them more promising than other fluorescent materials in certain applications. But serious defects in their fluorescence performance preclude particular imaging effects and limit imaging functions. In this review, we summarize and discuss the recent leading literature on overcoming the defects of organic NIR-II fluorophores, demonstrating the potential for further improving their imaging properties. In addition, we cover the functions of NIR-II FI that are promoted by the development of fluorophores, notably including its outlook on molecular imaging in vivo.

An AIE probe for imaging mitochondrial SO2-induced stress and SO2 levels during heat stroke

A probe, MITO-TPE, was developed for imaging mitochondrial SO₂ with good selectivity, high sensitivity, and a fast response time. Cell imaging indicated that SO₂-induced oxidative stress may cause damage to cells through O₂˙^- bursting. MITO-TPE has here been used to image the misregulation of SO₂ levels in mitochondria during heat stroke for the first time.

Preparation and Photoluminescent Properties of Three 5-Amino Benzothiadiazoles (5-amBTDs)

Three D-A compounds were designed and synthesized based on a benzothiadiazole acceptor. Azepane (AP), iminodubenzyl (IDB) and iminostilbene (ISB) were used, respectively, as donors and installed on the 5-position of BTD to afford 1, 2 and 3, respectively. Their photophysical properties in different states (solution, film, crystal, and powder) are systematically investigated. Among them, AIE-active compounds 2 and 3 were found to have good sensitivity toward viscosity and display quite good linear relationship with an increase in viscosity. Compound 2 displayed dual emission in solutions which largely depended on the polarity of the solvent. Meanwhile, compound 2 exhibits a mechanochromic character with disappearance and reappearance of a dual-emissive peak induced by mechanical grinding and solvent fuming. Furthermore, these three compounds can be used in the fabrication of blue OLED devices.

Designing enhanced and ratiometric probes for detecting OCl- based on substituents influencing the fluorescence of HBT and their application in strips and bioimaging

Nitro groups with a strong electron-withdrawing effect can powerfully influence the fluorescence of fluorophores. In this work, through adjusting the nitro group at the HBT fluorophore to construct a phenylhydrazone structure, two probes (HBTN and HBTH) were synthesized to detect OCl-. Consequently, HBTN with the nitro group quenched the fluorescence of HBT and HBTH without the nitro group causing a redshift of the fluorescence, which resulted in enhanced and ratiometric fluorescence signal changes during the detection process. Among them, HBTN shows good ability to selectively detect OCl- in the concentration range of 0-14 μM with the detection limit of 2.06 nM. Based on HBTN, a portable test strip for detecting OCl- was made for the convenient quantification of the OCl- concentration with a spectrophotometer, and exogenous and endogenous OCl- was successfully imaged in cells.

Visible and Reversible Restrict of Molecular Configuration by Copper Ion and Pyrophosphate

Molecular configuration strongly impacts on its functions; however, due to complicated and diverse configuration as well as easy and rapid conversion among various configurations, research of molecular configuration is extremely difficult. If the free rotation of a molecule could be "slowed down" or even "frozen" by an external stimulus, such as ultralow temperature, then one configuration of the molecule could be captured and characterized relatively easily. Here, we show that the rotation of a hemicyanine-labeled 2-(2'-hydroxyphenyl)-4-methyloxazole (H-HPMO) molecule could be specifically and reversibly restricted by sequential additions of copper ion (Cu²⁺) and pyrophosphate (P₂O₇^4-), reflecting as remarkable fluorescence quenching and recovery, which could be directly observed by naked eyes. Binding affinity tests and cryogenic ¹H NMR indicate that Cu²⁺ forms intensive coordinate bonds with phenolic hydroxyl, oxazole, and methoxyl groups of HPMO, which strongly restricts the free rotations of these groups and blocks charge transfer. This study provides a precise, rapid, visible, reversible, and low-cost method to monitor the molecular configuration, indicating the broad application prospects of near-infrared fluorescent sensors in configuration analysis, biosensing, and drug-substrate complexation.

Real-Time Imaging Redox Status in Biothiols and Ferric Metabolism of Cancer Cells in Ferroptosis Based on Switched Fluorescence Response of Gold Carbon Dots

Ferroptosis is an iron-dependent form of regulated cell death. In this study, a ratiometric fluorescent probe, gold carbon dots (GCDs) consisting of carbon skeleton and gold nanoclusters, was used for in situ imaging to monitor redox status in biothiols (glutathione and cysteine) and ferric metabolism of cancer cells in ferroptosis. The as-prepared GCDs can selectively respond to biothiols, interestingly, the fluorescence may be switched to sense ferric ions without interference by biothiols under proper conditions. The robust GCDs-probe exhibits excellent photobleaching resistance and can reversibly respond to intracellular biothiols/ferric ion with high temporal resolution. The 8 h real-time imaging of living cells was employed to track the fluctuation of biothiols, showing the change of redox status in ferroptosis. In addition, release of ferric ions in cells was monitored. The real-time imaging of depletion of biothiols and release of ferric ion in cells indicates the GCDs-probe can monitor how the ferroptosis regulates redox status in biothiols and ferric metabolism.

In vivo real-time tracking of tumor-specific biocatalysis in cascade nanotheranostics enables synergistic cancer treatment

Glucose oxidase (GOD)-based synergistic cancer therapy has aroused great research interest in the context of cancer treatment due to the inherent biocompatibility and biodegradability. However, this emerging therapeutic system still lacks a strategy to predict and regulate the in vivo biocatalytic behavior of GOD in real time to minimize the side effects on normal tissues. Herein, we developed a tumor-specific cascade nanotheranostic system (BNG) that combines GOD-catalyzed oxidative stress and dual-channel fluorescent sensing, significantly improving the synergistic therapeutic efficacy with real-time feedback information. The nanotheranostic system remains completely silent in the blood circulatory system and selectively releases GOD enzymes in the tumor site, with enhanced near-infrared (NIR) fluorescence at 825 nm. Subsequently, GOD catalyzes H2O2 production, triggering cascade reactions with NIR fluorescence at 650 nm as an optical output, along with GSH depletion, enabling synergistic cancer treatment. The designed nanotheranostic system, integrated with tumor-activated cascade reactions and triggering a dual-channel output at each step, represents an insightful paradigm for precise cooperative cancer therapy.

Heat Stroke in Cell Tissues Related to Sulfur Dioxide Level Is Precisely Monitored by Light-Controlled Fluorescent Probes

Heat stroke (HS) can cause serious organism damage or even death. Early understanding of the mechanism of heat cytotoxicity can prevent or treat heat stroke related diseases. In this work, probe Ly-NT-SP was synthesized, characterized, and used for sulfur dioxide (SO₂) detection in lysosomes. PBS solutions of probe Ly-NT-SP at pH 5.0 present a marked broad emission band in the green zone (535 nm). After UV irradiation, the spiropyran group in Ly-NT-SP isomerizes to the merocyanine form (Ly-NT-MR), which presented a weak red-shifted emission at 630 nm. In addition, photocontrolled isomerization of Ly-NT-SP to Ly-NT-MR generated a C═C-C═N⁺ fragment able to react, through a Michael addition, with SO₂ to yield a highly emissive adduct with a marked fluorescence in the green channel (535 nm). In vitro studies showed a remarkable selectivity of photoactivated Ly-NT-MR to SO₂ with a limit of detection as low as 4.7 μM. MTT viability assays demonstrated that the Ly-NT-SP is nontoxic to HeLa cells and can be used to detect SO₂ in lysosomes. Taking advantage of this, the sensor is successfully applied to image increasing SO₂ values in lysosomes during heat shock for the first time. Moreover, we also confirmed that the increased SO₂ can protect the small intestine against damage induced by heat shock through regulating oxidative stress in cells and mice.

A novel carbazolyl GFP chromophore analogue: synthesis strategy and acidic pH-activatable lysosomal probe for tracing endogenous viscosity changes

A novel, acidic pH-activatable carbazolyl GFP chromophore analogue was designed for tracing lysosomal viscosity changes.

A FRET-based supramolecular nanoprobe with switch on red fluorescence to detect SO2 derivatives in living cells

A fluorescent nanoprobe for detection of SO₂, an important gasotransmitter, is reported.

A new FRET probe for ratiometric fluorescence detecting mitochondria-localized drug activation and imaging endogenous hydroxyl radicals in zebrafish

A new FRET probe has been prepared and successfully used for imaging hydroxyl radicals generated by drug activation and endogenous hydroxyl radicals in zebrafish.

An endoplasmic reticulum-targeting fluorescent probe for imaging ˙OH in living cells

A new ER-targeting fluorescent probe for ˙OH is developed and applied to imaging ˙OH generation as well as lipid droplet formation in ER stress.