Rapid Reaction, Slow Dissociation Aggregation, and Synergetic Multicolor Emission for Imaging the Restriction and Regulation of Biosynthesis of Cys and GSH

A ratiometric fluorescent probe with a large Stokes shift for rapid and sensitive detection of Hg2+ in environmental water samples and its applications in living cells and zebrafish

Detection of highly toxic mercury ions (Hg2+) in actual environmental and biological samples is of significant importance for protecting environment and human health. In this paper, a new ratiometric fluorescent probe BTIA was designed and synthesized from 3-pinone based on Internal Charge Transfer (ICT) mechanism. BTIA could selectively recognize Hg2+ over other competitive analytes with short reaction time (5 s), distinct ratiometric response, strong anti-interference ability, large Stokes shift (200 nm), and low detection limit (2.36 × 10-7 M). Furthermore, BTIA was applicable for detecting Hg2+ in actual water samples and it also performed an excellent imaging capability in living RAW264.7 cells, zebrafish and onion tissue.

Differentiation of cellular responses to particulate and soluble constituents in sunscreen products

Despite the growing awareness of potential human and environmental risks associated with sunscreens, identifying the specific constituents responsible for their potential toxicity is challenging. In this study, we applied three different types of sunscreens with contrasting compositions and compared the effects of their particulate and soluble fractions based on 15 cellular biomarkers of HaCaT cells. Multilinear regression analysis revealed that the internalized soluble fractions played a primary role in the overall cytotoxicity of sunscreen mixtures, which was primarily attributed to their biotransformation, generating metabolites with higher toxicity. The presence of plastic microspheres in sunscreens either inhibited the internalization of soluble fractions or led to their redistribution toward lysosomes. Conversely, subcellular toxicity resulting from the sunscreen mixture was predominantly influenced by particulates. Bio-transformable particulates such as ZnO dissolved in the organelles and induced higher subcellular toxicity compared to bioinert particulates such as microplastics. Subcellular biomarkers including lysosomal count, lysosomal size, mitochondrial count and mitochondrial shape emerged as the potential predictors of sunscreen presence. Our study provides important understanding of sunscreen toxicity by elucidating the differential impacts of particulate and soluble fractions in mixture contaminants.

Old drug, new use: The thalidomide-based fluorescent probe for cysteine detection and imaging in living cells

Thalidomide, as a high-profile cereblon (CRBN) ligand, has attracted much attention because of its ability to target protein degradation. In this study, we are committed to developing a new fluorescent probe THD-1 based on thalidomide, aiming at improving the performance of cysteine fluorescent probe in optical properties and biocompatibility. The experimental results showed that THD-1, as a cysteine fluorescent probe, owned the characteristics of obvious colorimetric change, fast response time, good selectivity and high sensitivity. The mechanism of THD-1 sensing cysteine was further verified to ensure its reliability and effectiveness. It was also worth mentioning that THD-1 was successfully applied to the biological imaging of cysteine in living A549 cells, which highlighted its value in practical application. Overall, thalidomide, as a clinically approved drug, not only enriches the fluorescent skeleton library, but also paves a new way for the further development of fluorescent probes.

Biothiols-activated near-infrared frequency up-conversion luminescence probe for early evaluation of drug-induced hepatotoxicity

A novel biothiols-sensitive near-infrared (NIR) fluorescent probe RhDN based on a rhodamine skeleton was developed for early detection of drug-induced hepatotoxicity in living mice. RhDN can be used not only as a conventional large stokes shift fluorescent (FL) probe, but also as a kind of anti-Stokes frequency upconversion luminescence (FUCL) molecular probe, which represents a long wavelength excitation (808 nm) to short wavelength emission (760 nm), and response to Cys/Hcy/GSH with high sensitivity. Compared with traditional FL methods, the FUCL method exhibited a lower detection limit of Cys, Hcy, and GSH in 75.1 nM, 101.8 nM, and 84.9 nM, respectively. We exemplify RhDN for tracking endogenously biothiols distribution in living cells and further realize real-time in vivo bioimaging of biothiols activity in mice with dual-mode luminescence system. Moreover, RhDN has been successfully applied to visualize the detection of drug-induced hepatotoxicity in living mice. Overall, this report presents a unique approach to the development of large stokes shift NIR FUCL molecular probes for in vitro and in vivo biothiols biosensing.

Developing NIR xanthene-chalcone fluorophores with large Stokes shifts for fluorescence imaging

A series of novel near-infrared (NIR) xanthene-chalcone fluorophores were constructed through a modular synthesis with the electron-donating xanthene moiety and the electron-withdrawing chalcone moiety. These fluorophores are convenient for fluorescence imaging in living cells, benefiting from their NIR emissions (650-710 nm), large Stokes shifts (>100 nm), moderate quantum yields and low cytotoxicity. The substituted hydroxyl group of the xanthene-chalcone fluorophore HCA-E facilitates the development of multifunctional fluorescent probes. As an example, a highly sensitive and selective probe N-HCA-E for glutathione (GSH) detection was developed based on the fluorophore HCA-E. A 4-nitrobenzenesulfonyl (4-Ns) group was introduced to cage the hydroxyl group of HCA-E, which was used as a selective recognition site for the thiol of GSH and an effective fluorescence quencher. Probe N-HCA-E revealed NIR "turn-on" fluorescence (709 nm) for endogenous and exogenous GSH detection in lysosomes with a large Stokes shift (129 nm) and high anti-interference ability.

A metal-phenolic coordination framework nanozyme exhibits dual enzyme mimicking activity and its application is effective for colorimetric detection of biomolecules

Biomolecules play vital roles in many biological processes and diseases, making their identification crucial. Herein, we present a colorimetric sensing method for detecting biomolecules like cysteine (Cys), homocysteine (Hcy), and glutathione (GSH). This approach is based on a reaction system whereby colorless 3,3',5,5'-tetramethylbenzidine (TMB) undergoes catalytic oxidation to form blue-colored oxidized TMB (ox-TMB) in the presence of hydrogen peroxide (H2O2), utilizing the peroxidase and catalase-mimicking activities of metal-phenolic coordination frameworks (MPNs) of Cu-TA, Co-TA, and Fe-TA nanospheres. The Fe-TA nanospheres demonstrated superior activity, more active sites and enhanced electron transport. Under optimal conditions, the Fe-TA nanospheres were used for the detection of biomolecules. When present, biomolecules inhibit the reaction between TMB and H2O2, causing various colorimetric responses at low detection limits of 0.382, 0.776 and 0.750 μM for Cys, Hcy and GSH. Furthermore, it was successfully applied to real water samples with good recovery results. The developed sensor not only offers a rapid, portable, and user-friendly technique for multi-target analysis of biomolecules at low concentrations but also expands the potential uses of MPNs for other targets in the environmental field.

Development of a turn-on fluorescent probe for the imaging of intracellular hypochlorous acid (HClO) during ferroptosis

Ferroptosis is a burgeoning iron-dependent cell death form, and has close relation with hypochlorous acid (HClO). Exploring the fluctuation of the HClO level in living cells during ferroptosis could contribute to the profound study of the biological functions of HClO during ferroptosis. Here, we present a turn-on probe (RH-C) for the imaging of intracellular HClO during ferroptosis. The probe RH-C utilized the N,N-dimethylthiocarbamate group as a selective recognition site for HClO, and displayed desirable sensitivity and selectivity to HClO. The probe RH-C could detect the exogenous and endogenous HClO in living cells. Furthermore, RH-C was competent in monitoring the changes of endogenous HClO level during the process of ferroptosis. Biological imaging results suggested that erastin-induced ferroptosis can result in the excessive production of the endogenous HClO, and ferrostatin-1 (Fer-1) and vitamin E (VE) could block the massive accumulation of HClO in living cells.

A novel fluorescent probe for visualizing viscosity changes in lipid droplets during chemotherapy-induced ferroptosis

BACKGROUND

Ferroptosis, as a novel form of cell death, is becoming one of the hot topics in cancer treatment research. It differs from necrosis and autophagy in that it involves the accumulation of lipid peroxides and is triggered by iron dependency. Recent studies have suggested that this mechanism may alter the viscosity or structure of lipid droplets (LDs). The relationship between LDs viscosity and ferroptosis remains an active area of research with limited reports at present. Additionally, there is a lack of effective anticancer drugs targeting the ferroptosis pathway to promote ferroptosis in tumour cells. Therefore, the development of tools to detect viscosity changes during ferroptosis and targeted therapeutic strategies is of great significance.

RESULTS

By coupling 1,3-indandione with naphthalimide, including decamethylamine as a LDs recognition group, we designed and synthesized an environmental fluorescent probe that induces intramolecular charge transfer (TICT) effects. Notably, the diffusion and transport of intracellular substances may be affected in highly viscous environments. Under such conditions, intracellular iron ions may accumulate, leading to peroxide production and cellular damage, which can trigger ferroptosis. Therefore, WD-1 achieved excellent in situ bioimaging of LDs targeting and its viscosity during ferroptosis in HeLa cells and zebrafish. Furthermore, it was observed that WD-1 effectively differentiated between malignant and normal cells during this process, highlighting its potential significance in distinguishing cellular states. In addition, we used the antitumour drug paclitaxel to study ferroptosis in cancer cells. These findings not only provide an excellent tool for the development of the ferroptosis response, but also are crucial for understanding the biological properties of LDs during the ferroptosis response.

SIGNIFICANCE AND NOVELTY

Based on a powerful tool of fluorescent probe with in vivo bioimaging, we developed WD-1 to track the impact of paclitaxel on the process of ferroptosis in living cells. Therefore, we preliminarily believe that paclitaxel may affect the occurrence of ferroptosis and control apoptosis in cancer cells. These findings not only serve as an exceptional tool for advancing our understanding of the ferroptosis response, but furthermore play a vital role in comprehending the biological characteristics of LDs in relation to ferroptosis.

Golgi apparatus-targeting fluorescent probe for the imaging of superoxide anion (O2•-) in living cells during ferroptosis

Ferroptosis is an emerging iron-dependent oxidative cell death type, and recently has been demonstrated to show close relation with Golgi apparatus (GA). Exploring the fluctuation of superoxide anion (O2•-) level in GA during ferroptosis is of great significance to profoundly study the biological functions of GA in ferroptosis. Here, we present a GA-targeting probe (N-GA) to monitor cellular O2•- during ferroptosis. N-GA employed a triflate group and a tetradecanoic amide unit as the recognition site for O2•- and GA-targeting unit, respectively. After the response of N-GA to O2•-, the triflate unit of N-GA converted into hydroxyl group with strong electron-donating ability, generating bright green fluorescence under UV light. N-GA exhibited excellent sensitivity and selectivity towards O2•-. Fluorescence imaging results showed that N-GA could be applied as a GA-targeting probe to monitor cellular O2•-. The stimulation of cells with PMA and rotenone could result in the massive generation of endogenous O2•- in GA. Erastin-induced ferroptosis can markedly induce the increase of O2•- level in GA. Similar to Fer-1 and DFO, dihydrolipoic acid (DHLA) and rutin were demonstrated to inhibit the enormous production of O2•- in GA of the living cells during ferroptosis.

Microenvironment-differential Imaging of Demethylated Metabolites of Methionine for Identifying Ferroptosis Regional Preferences with Path-independent Equifinal Fluorescence Probes

We realized the microenvironment-differential Imaging of demethylated metabolites of methionine and the regional regulation of ferroptosis.

A single mitochondria-targetable fluorescent probe for visualizing cysteine and glutathione in ferroptosis of myocardial ischemia/reperfusion injury

Ferroptosis plays an important role in the early stage of myocardial ischemia/reperfusion (MI/R) injury, which is closely associated with the antioxidant damage of mitochondrial cysteine (Cys)/glutathione (GSH)/glutathione peroxidase 4 (GPX4) axis. Visualization of Cys and GSH in mitochondria is meaningful to value ferroptosis and further contributes to understanding and preventing MI/R injury. Herein a mitochondria-targetable thiols fluorescent probe (MTTP) was designed and synthesized based on sulfonyl benzoxadiazole (SBD) chromophore with a triphenylphosphine unit as the mitochondria-targeted functional group. Cys and GSH can be differentiated by MTTP with two distinguishable emission bands (583 nm and 520 nm) through the controllable aromatic substitution-rearrangement reaction. Importantly, MTTP is capable of monitoring ferroptosis and its inhibition by measuring mitochondrial Cys and GSH. MTTP was also employed to non-invasively detect ferroptosis during oxygen and glucose deprivation/reoxygenation (OGD/R)-induced MI/R injury in H9C2 cells. In a word, MTTP provides a visual tool that can simultaneously detect Cys and GSH to monitor ferroptosis processes during MI/R injury, which helps for more deeper understanding of the role of ferroptosis in MI/R injury-related diseases.

Treatment evaluation of Rheumatoid arthritis by in situ fluorescence imaging of the Golgi cysteine

Rheumatoid arthritis (RA) is a long-term systemic inflammatory disease that causes severe joint pain. Golgi stress caused by redox imbalance significantly involves in acute and chronic inflammatory diseases, in which cysteine (Cys), as a representative reducing agent, may be an effective biomarker for RA. Hence, in order to achieve RA early detection and drugs evaluation, based on our previous work about innovative Golgi-targeting group, we established a phenylsulfonamide-modified fluorescence probe, Golgi-Cys, for the selective fluorescence imaging of Cys in Golgi apparatus in vivo. By application of Golgi-Cys, the Cys changes under Golgi stress in cells were elucidated. More importantly, we found that the probe can be effectively utilized for the RA detection and treatment evaluation in situ.

Investigating Oxidative Stress Associated with Myocardial Fibrosis by High-Fidelity Visualization and Accurate Evaluation of Mitochondrial GSH Levels

Myocardial fibrosis is frequently accompanied by elevated levels of oxidative stress. Mitochondrial glutathione (mGSH), an essential biomolecule for maintaining redox homeostasis in mitochondria, could serve as an effective indicator for investigating the oxidative stress associated with myocardial fibrosis. In this study, a ratiometric fluorescent probe named Mito-NS6, capable of being anchored in mitochondria and reversibly responding to GSH with an appropriate dissociation equilibrium constant, was rationally designed and utilized to visualize and evaluate the changes of mGSH levels caused by oxidative stress in myocardial fibrosis. Benefiting from the good performance of Mito-NS6, we successfully achieved the quantification of mGSH in cardiac fibroblasts using a confocal laser-scanning microscope, revealing that salvianolic acid B (SalB) can act as an effective drug to alleviate myocardial fibrosis through depressing oxidative stress. Moreover, we employed ratio fluorescence imaging to track the fluctuation in GSH levels within a mice model of myocardial fibrosis induced by isoproterenol and found that myocardial fibrosis caused a higher oxidative stress level in myocardial tissue as well as heart organs. These results provide a novel point of view for the diagnosis and treatment of myocardial fibrosis.

Development of bishydrazide-based fluorescent probes for the imaging of cellular peroxynitrite (ONOO-) during ferroptosis

Peroxynitrite (ONOO-) is a critical ROS in living systems, and could induce lipid peroxidation which is the driver of ferroptotic cell death. Therefore, precise and rapid detection of cellular ONOO- is critical for the deep study of the biological functions of ONOO- during ferroptosis. Herein, we developed fluorescent probes (Rh-1, Rh-2 and Rh-3) for the rapid detection of intracellular ONOO- during ferroptosis. These probes used bishydrazide groups as the reactive sites for ONOO-. The response of these probes to ONOO- resulted in the production of the emissive xanthene fluorophore, providing a marked enhancement in the fluorescence intensity at 561 nm. The probe Rh-3 exhibited prominent selectivity and sensitivity towards ONOO-. Bioimaging experiments suggested that Rh-3 could be applied to image exogenous and endogenous ONOO- in living cells. By fluorescence imaging, it was demonstrated that erastin-induced ferroptosis caused increased levels of the endogenous ONOO-, and ferrostatin-1 (Fer-1) and vitamin E (VE) could markedly inhibit the excessive production of ONOO- during ferroptosis in living cells.

Cyclo[2]pyridine[8]pyrrole: An Expanded Porphyrinoid with Three Closed-Shell Oxidation States

We report here an expanded porphyrinoid, cyclo[2]pyridine[8]pyrrole, 1, that can exist at three closed-shell oxidation levels. Macrocycle 1 was synthesized via the oxidative coupling of two open chain precursors and fully characterized by means of NMR and UV-vis spectroscopies, MS, and X-ray crystallography. Reduction of the fully oxidized form (1, blue) with NaBH4 produced either the half-oxidized (2, teal) or fully reduced forms (3, pale yellow), depending on the amount of reducing agent used and the presence or absence of air. Reduced products 2 or 3 can be oxidized to 1 by various oxidants (quinones, FeCl3, and AgPF6). Macrocycle 1 also undergoes proton-coupled reductions with I-, Br-, Cl-, SO32-, or S2O32- in the presence of an acid. Certain thiol-containing compounds likewise reduce 1 to 2 or 3. This conversion is accompanied by a readily discernible color change, making cyclo[2]pyridine[8]pyrrole 1 able to differentiate biothiols, such as cysteine (Cys), homocysteine (Hcy), and glutathione (GSH).

Development of Human Serum Albumin Fluorescent Probes in Detection, Imaging, and Disease Therapy

Human serum albumin (HSA) acts as a repository and transporter of substances in the blood. An abnormal concentration may indicate the occurrence of liver- and kidney-related diseases, which has attracted people to investigate the precise quantification of HSA in body fluids. Fluorescent probes can combine with HSA covalently or noncovalently to quantify HSA in urine and plasma. Moreover, probes combined with HSA can improve its photophysical properties; probe-HSA has been applied in real-time monitoring and photothermal and photodynamic therapy in vivo. This Review will introduce fluorescent probes for quantitative HSA according to the three reaction mechanisms of spatial structure, enzymatic reaction, and self-assembly and systematically introduce the application of probes combined with HSA in disease imaging and phototherapy. It will help develop multifunctional applications for HSA probes and provide assistance in the early diagnosis and treatment of diseases.

Equivalent Response Strategy for Sensing Total Biothiols in Human Serums and Living Cells Using a Hemicyanine-Based Self-Immolative Probe

Biothiols including cysteine (Cys), homocysteine (Hcy), and glutathione (GSH) are crucial in maintaining the redox balance in the body, and the metabolism and transportation of biothiols rely on the coreaction of diverse proteins and enzymes. The abnormal concentrations and metabolism of biothiols are closely associated with many diseases. However, due to the same active reaction site of the sulfydryl group in biothiols, it is inevitable to bear a confused signal of mutual influence on both nonselective detection and discriminate detection, which presents a serious challenge of accurately sensing or imaging the three biothiols. By assigning an α,β-unsaturated ketone moiety as a Michael acceptor to trigger thiols to complete the irreversible equivalent domino response processes of nucleophilic addition, olefinic bond migration, and self-immolation, a targeted strategy was rationally pointed out, and herein, a hemicyanine-based probe CyOCy was prepared as a proof of strategy demonstration. The new probe could be equivalently lit up by Cys, Hcy, GSH, and even biothiol combinations (Cys/Hcy, Cys/GSH, Hcy/GSH, or Cys/Hcy/GSH) with unified linear ranges, detection limits, and response times. The probe CyOCy has been successfully used for the accurate quantification of total biothiols in the serum samples of healthy persons and coronary heart disease patients. In addition, the probe has been applied for cell screening, exogenous biothiol imaging, and monitoring drug-induced biothiol fluctuations. The purposive thinking of this work may provide an effective avenue for the accurate sensing of multicomponent samples.

A fluorescent probe for bioimaging of GSH in cancer cells

A fluorescent probe CTP2-IMC was designed for bioimaging of glutathione (GSH) in cancer cells with indomethacin (IMC), coumarin and bromide as the targeting group, fluorophore and receptor, respectively. Due to the π-π interaction between coumarin and IMC, CTP2-IMC mainly exists in the form of folded state in aqueous solution. The non-radiative transitions caused by the photo-induced electron transfer (PET) process from IMC to the fluorophore as well as the heavy-atom effect led to non-fluorescent of CTP2-IMC. The substitution of Br by GSH and unfolded conformation induced by IMC acceptor on cancer cells resulted in significant fluorescence enhancement, which enabled CTP2-IMC to bioimage GSH in cancer cells rather than in normal one.

Prediction of Early Atherosclerotic Plaques Using a Sequence-Activated Fluorescence Probe for the Simultaneous Detection of γ-Glutamyl Transpeptidase and Hypobromous Acid

Atherosclerosis is a lipoprotein-driven disease, and there is no effective therapy to reverse atherosclerosis or existing plaques. Therefore, it is urgently necessary to create a noninvasive and reliable approach for early atherosclerosis detection to prevent initial plaque formation. Atherosclerosis is intimately associated with inflammation, which is accompanied by an excess of reactive oxygen species (ROS), leading to cells requiring more glutathione (GSH) to resist severe oxidative stress. Therefore, the GSH-hydrolyzed protein γ-glutamyl transpeptidase (GGT) and the ROS-hypobromous acid (HBrO) are potential biomarkers for predicting atherogenesis. Hence, to avoid false-positive diagnoses caused by a single biomarker, we constructed an ingenious sequence-activated double-locked TP fluorescent probe, C-HBrO-GGT, in which two sequential triggers of GGT and HBrO are meticulously designed to ensure that the probe fluoresces in response to HBrO only after GGT hydrolyzes the probe. By utilization of C-HBrO-GGT, the voltage-gated chloride channel (CLC-1)-HBrO-catalase (CAT)-GGT signaling pathway was confirmed in cellular level. Notably, the forthcoming atherosclerotic plaques were successfully predicted before the plaques could be observed via the naked eye or classical immunofluorescent staining. Collectively, this research proposed a powerful tool to indicate the precise position of mature plaques and provide early warning of atherosclerotic plaques.

An ortho-activation strategy to develop NIR fluorescent probe for rapid imaging of biothiols in vivo

Biothiols are the main antioxidants in regulating the redox balance and resisting oxidative stress in various biological processes, but the long detection time of current fluorescent probes hinders their rapid imaging in vitro and in vivo. To reveal the influx of biothiols, we rationally develop an ortho-activation approach to accelerate the reaction between the probe and biothiols, by introducing electron-withdrawing fluorine atom into the ortho-site of the phenolic hydroxyl group in the NIR probe to generate an ortho-inductive effect. The ortho-fluorine helps to increase the chemical reactivity of the molecular structure, resulting in a significantly shorter detection time (within 5 min) as compared to previous reports (> 20 min for acrylates-based probes in aqueous solution). Based on this approach, our near-infrared probe 2F-RBX can sensitively and efficiently detect endogenous biothiols in living HepG2 cells and in vivo. These data suggest that ortho-activation is a simple and flexible approach to construct sensitive fluorescent probes for rapid imaging of biothiols, and perhaps other molecules in future, under biological circumstances.

A novel AIE material for sensing of Erythromycin in pure water by hydrogen bond in portable test strips and cellular imaging applications

Erythromycin could be used to treat various bacterial infection, but it was harmful to the colonic microflora. Therefore, it is highly desirable to develop a fluorescence probe that could selectively and sensitively detect Erythromycin in pure water. In this work, a fluorescent probe named EHMC, which exhibited aggregation-induced emission (AIE) characteristic in solid state and water/EtOH binary solvent was developed for "turn on" sensing Erythromycin in pure water with high selectivity and sensitivity (detection limit: 1.78 × 10-8 M). Also, there are fewer interference from other antibiotics in the detection process of probe EHMC for Erythromycin. Moreover, probe EHMC could as a portable test strips for highly selective detection of Erythromycin and identification of different concentrations of Erythromycin. In addition, living cells imaging experiments displayed that probe EHMC could detect Erythromycin in A549 cells and BEAS-2B cells successfully. Combined with the theoretical calculation results The sensing mechanisms that the CO in Erythromycin and OH in EHMC formed intermolecular hydrogen bond and further formed new aggregates were confirmed by job' plot, 1H NMR, FT-IR, ESI-MS, DLS and TEM and DFT calculation.

TPE-based fluorescent probe for dual channel imaging of pH/viscosity and selective visualization of cancer cells and tissues

The development of efficient fluorescence-based detection tools with high contrast and accuracy in cancer diagnosis has recently attracted extensive attention. Changes in the microenvironments between cancer and normal cells provide new biomarkers for precise and comprehensive cancer diagnosis. Herein, a dual-organelle-targeted probe with multiple-parameter response is developed to realize cancer detection. We designed a tetraphenylethylene (TPE)-based fluorescent probe TPE-PH-KD connected with quinolinium group for simultaneous detection of viscosity and pH. Due to the restriction on the double bond's rotation, the probe respond to viscosity changes in the green channel with extreme sensitivity. Interestingly, the probe exhibited strong emission of red channel in acidic environment, and the rearrangement of ortho-OH group occurred in the basic form with weak fluorescence when pH increased. Additionally, cell colocalization studies revealed that the probe was located in the mitochondria and lysosome of cancer cells. Following treatment with carbonyl cyanide m-chloro phenylhydrazone (CCCP), chloroquine, and nystatin, the pH or viscosity changes in the dual channels are also monitored in real-time. Furthermore, the probe TPE-PH-KD could effectively discriminate cancer from normal cells and organs with high-contrast fluorescence imaging, which sparked more research on an efficient tool for highly selectively visualizing tumors at the organ level.

A Novel Fluorescence Probe Based on Azamonardine for Detecting and Imaging Cysteine in Cells and Zebrafish with High Selectivity and Sensitivity

A novel fluorescent probe based on azamonardine (Aza) fluorophore was designed and synthesized for the highly selective detection of cysteine (Cys) in vivo and in vitro. After reacting with acryloyl chloride, the fluorescence of Aza is effectively quenched, resulting in the formation of the Aza-acryl probe. Upon the addition of Cys, the ester bond of Aza-acryl is cleaved, releasing a new compound (Compound 1) with strong fluorescence, thereby achieving fluorescence turn-on detection of Cys. The structure of Aza-acryl was characterized using X-ray crystallography and NMR spectroscopy. Additionally, density functional theory was employed to elucidate the quenching mechanism of the acyl group on the Aza. Aza-acryl exhibits high selectivity towards Cys and distinguishes it from other biothiols such as homocysteine (Hcy) and glutathione (GSH). The mechanism of Aza-acryl for detecting Cys was investigated through HPLC, NMR spectroscopy, high-resolution mass spectrometry, and reaction kinetics experiments. Aza-acryl demonstrates excellent imaging capabilities for Cys in cells and zebrafish, providing a reliable and selectable tool for the detection and imaging of Cys in biological systems.

Tumor-Targeting Probe for Dual-Modal Imaging of Cysteine In Vivo

Cysteine (Cys) is a crucial biological thiol that has a vital function in preserving redox homeostasis in organisms. Studies have shown that Cys is closely related to the development of cancer. Thus, it is necessary to design an efficient method to detect Cys for an effective cancer diagnosis. In this work, a novel tumor-targeting probe (Bio-Cy-S) for dual-modal (NIR fluorescence and photoacoustic) Cys detection is designed. The probe exhibits high selectivity and sensitivity toward Cys. After reaction with Cys, both NIR fluorescence and photoacoustic signals are activated. Bio-Cy-S has been applied for the dual-modal detection of Cys levels in living cells, and it can be used to distinguish normal cells from cancer cells by different Cys levels. In addition, the probe is capable of facilitating dual-modal imaging for monitoring changes in Cys levels in tumor-bearing mice. More importantly, the excellent tumor-targeting ability of the probe greatly improves the signal-to-noise ratio of imaging. To the best of our knowledge, this is the first Cys probe to combine targeting and dual-modal imaging performance for cancer diagnosis.

GSH-specific fluorescent probe for sensing, bioimaging, rapid screening of natural inhibitor Celastrol and ccRCC theranostics

High level of intracellular glutathione (GSH) has been identified as a major barrier for cancer therapy. Therefore, effective regulation of GSH can be regarded as a novel approach for cancer therapy. In this study, an off-on fluorescent probe (NBD-P) is developed for selective and sensitive sensing GSH. NBD-P has a good cell membrane permeability that can be applied in bioimaging endogenous GSH in living cells. Moreover, the NBD-P probe is used to visualize GSH in animal models. In addition, a rapid drug screening method is successfully established using the fluorescent probe NBD-P. A potent natural inhibitor of GSH is identified as Celastrol from Tripterygium wilfordii Hook F, which effectively triggers mitochondrial apoptosis in clear cell renal cell carcinoma (ccRCC). More importantly, NBD-P can selectively respond to GSH fluctuations to distinguish cancer tissues from normal tissues. Thus, the present study provides insights into fluorescence probes for the screening GSH inhibitors and cancer diagnosis, as well as in-depth exploration of the anti-cancer effects of Traditional Chinese Medicine (TCM).

A Substituted-Rhodamine-Based Reversible Fluorescent Probe for In Vivo Quantification of Glutathione

Quantifying glutathione (GSH) in cells and organisms is of great significance for understanding the mechanism of oxidative stress in various physiological and pathological processes. However, the quantification by fluorescence bioimaging in living tissues has much stricter requirements than the "Petri dish"-cultured cells in flat plates. Based on the evaluation of the electronic structure and steric hindrance-tuned reactivity of phospha-substituted rhodamine with GSH, a reversible Förster resonance energy transfer (FRET) probe ZpSiP with a distinct performance (K_d =4.9 mM, t_1/2 =0.57 s, k=81 M^-1  s^-1 ) is developed for real time quantifying GSH in living cells. Furthermore, the near-infrared (NIR) probe succeeded in sensitively tracking the dynamics of GSH in the real organisms bearing tumors, chronic renal failure, and liver fibrosis for unveiling the related pathological processes. We believe that the advance in chemistry with quantitative analysis methods will initiate more promising progress and broad applications.

An ultrasensitive GSH-specific fluorescent probe unveils celastrol-induced ccRCC ferroptosis

Glutathione (GSH) is closely related to the occurrence and development of tumors. The intracellular GSH levels are abnormally altered when tumor cells undergo programmed cell death. Therefore, real-time monitoring of the dynamic changes of intracellular GSH levels can better enable the early diagnosis of diseases and evaluate the effects of cell death-inducing drugs. In this study, a stable and highly selective fluorescent probe AR has been designed and synthesized for the fluorescence imaging and rapid detection of GSH in vitro and in vivo, as well as patient-derived tumor tissue. More importantly, the AR probe can be used to track changes in GSH levels and fluorescence imaging during the treatment of clear cell renal cell carcinoma (ccRCC) with celastrol (CeT) via inducing ferroptosis. These findings demonstrate that the developed fluorescent probe AR exhibits high selectivity and sensitivity, as well as good biocompatibility and long-term stability, which can be used to image endogenous GSH in living tumors and cells. Also, a significant decrease in GSH levels was observed by the fluorescent probe AR during the treatment of ccRCC with CeT-induced ferroptosis in vitro and in vivo. Overall, these findings will provide a novel strategy for celastrol targeting ferroptosis in the treatment of ccRCC and the application of fluorescent probes to help reveal the underlying mechanism of CeT in the treatment of ccRCC.

Design of a Coumarin-Based Fluorescent Probe for Efficient In Vivo Imaging of Amyloid-β Plaques

Amyloid-β (Aβ) is the core constituent protein of senile plaques, which is one of the key pathological hallmarks of Alzheimer's disease (AD). Here we describe the design, synthesis, and evaluation of coumarin-derived small molecule fluorophores for Aβ imaging. By embedding the aromatic coumarin framework into π bridge of a push-pull chromophore, a novel fluorescence probe XCYC-3 applicable to efficient Aβ recognition was discovered. XCYC-3 displays higher fluorescent enhancement for aggregated Aβ than monomeric Aβ, and possesses good blood-brain barrier permeability. In vitro staining and in vivo imaging studies demonstrated that XCYC-3 could efficiently recognize Aβ plaques in the brain of AD transgenic mice. These results suggest that XCYC-3 is a promising fluorescence imaging agent for Aβ, which might provide important clues for the future development of potent NIR fluorescent probes for Aβ diagnosis.

Rapid GSH detection and versatile peptide/protein labelling to track cell penetration using coumarin-based probes

Biothiols play essential roles in balancing the redox state and modulating cellular functions. Fluorescent probes for monitoring/labelling biothiols often suffer from slow reaction rates, strong background fluorescence and cytotoxic byproduct release. Thus, developing facile and versatile probes to overcome the challenges is still in high demand. Here, we report four coumarin-maleimides as fast responding and fluorogenic probes to detect GSH or label peptides/proteins. The probes quantitatively and selectively react with GSH via Michael addition within 1-2 min, achieving an 11-196-fold increase in fluorescence quantum yield via blockage of the photoinduced electron transfer (PET) process. Optimized probe 4 is applied for the detection of GSH in vitro (A549 cells) and in vivo (zebrafish embryos). Taking advantage of the fast Michael addition between the maleimide moiety and the sulfhydryl group, we expand the application of our method for fluorescent labelling of peptides/proteins and for tracking their cellular uptake process. The labelling strategy works for both Cys-bearing and Cys-free proteins after the introduction of a sulfhydryl group using Traut's reagent. Fluorescence assay reveals that the TAT-peptide can efficiently enter cells, but H3 protein, part of nucleosomes, prefers to bind on the cell membrane by electrostatic interactions, shedding light on the cellular uptake activity of nucleosomes and affording a potential membrane staining strategy. Overall, our study illustrates the broad potential of coumarin-maleimide based dual-functional probes for GSH detection and versatile protein labelling in biochemical research.

Simple and efficient PET and AIEE mechanism-based fluorescent probes for sensing Tabun mimic DCNP

The highly sensitive, selective, easy-to-prepare, aqueous media based on two novel probes 2-(pyren-1-yl)imidazo[1,2-a]pyridine (IMP-Py) and (2-(pyren-1-yl)imidazo[1,2-a]pyridin-3-yl)methanol (IMP-Py-OH) are synthesized for the detection of toxic chemical warfare nerve agent mimic diethylcyanochlorophosphonate (DCNP). Both probes are found effective in the detection of DCNP but comparatively, IMP-Py shows better properties in terms of instantaneous response, specificity, selectivity and a low detection limit of 16.9 nM. A significant enhancement of fluorescence intensity of IMP-Py due to aggregation-induced emission enhancement (AIEE) and photoinduced electron transfer (PET) phenomenon was inhibited due to phosphorylation of the hydroxy group of IMP-Py-OH in presence of DCNP has been observed. Taking the advantages of good sensitivity and fast response, probe IMP-Py has been fabricated into a viable paper strips portable product, tested for its potential for the detection of DCNP in tap water as well as with its vapor and response is visible under a UV lamp of 365 nm wavelength.

Dual-Site Chemosensor for Monitoring ·OH-Cysteine Redox in Cells and In Vivo

The reaction between hydroxyl radical (^·OH) and cysteine (Cys) plays an important role in the redox balance of living cells. A deeper insight into this intracellular reaction modulation and process is necessary and draws great interest. A highly effective technique consists of the real-time visualization of the two bioactive species and the perception of their respective changes by using a fluorescent probe. In this study, a dual-site chemosensor SPI based on phenothiazine-cyanine was developed, which realized quantitative detection and real-time imaging of ^·OH and Cys at their own fluorescence channels (^·OH: λ_ex = 485 nm, λ_em = 608 nm; Cys: λ_ex = 426 nm, λ_em = 538 nm) without spectral crosstalk. The fluorescent sensor showed excellent anti-interference and selectivity for common biological substances, apart from the successful imaging of exogenous and endogenous ^·OH and Cys. We further visualized the redox dynamic reaction and explored the correlation of ^·OH and Cys generated by different inhibitors (sulfasalazine and (1S, 3R)-RSL3). Notably, the chemosensor also possesses the capacity to clearly monitor ^·OH and Cys in living mice and zebrafish. This study reports on the first chemosensor to investigate the process of intracellular redox modulation and control between ^·OH and Cys, which show potential to further explore some metabolic and physiological mechanisms.

Near-Infrared Probes for Biothiols (Cysteine, Homocysteine, and Glutathione): A Comprehensive Review

Biothiols (cysteine, homocysteine, and glutathione) are an important class of compounds with a free thiol group. These biothiols plays an important role in several metabolic processes in living bodies when present in optimum concentration. Researchers have developed several probes for the detection and quantification of biothiols that can absorb in UV, visible, and near-infrared (NIR) regions of the electromagnetic spectrum. Among them, NIR organic probes have attracted significant attention due to their application in in vivo and in vitro imaging. In this review, we have summarized probes for these biothiols, which could work in the NIR region, and discussed their sensing mechanism and potential applications. Along with focusing on the pros and cons of the reported probes we have classified them according to the fluorophore used and summarized their photophysical and sensing properties (emission, response time, limit of detection).

Fluorescence Imaging of Intracellular Glutathione Levels in the Endoplasmic Reticulum to Reveal the Inhibition Effect of Rutin on Ferroptosis

Ferroptosis is an emerging form of nonapoptotic cell death, and the search for novel ferroptosis inhibitors is of great importance to explore unique cytoprotective strategies against ferroptosis-relevant diseases. In this work, we present an endoplasmic reticulum-targeting fluorescent probe (ER-G) for the imaging of intracellular glutathione (GSH) levels and revealed the inhibition effect of rutin on ferroptosis. Structurally, ER-G utilized a cyclohexyl sulfonylurea as the endoplasmic reticulum-targeting unit, and single-crystal X-ray diffraction analysis confirmed that ER-G possessed a N-oxide pyridine sulfinyl group instead of sulfone. After the response of ER-G to GSH, the fluorescence intensity at 523 nm displayed a significant increase by 3900-fold. ER-G showed extreme sensitivity and selectivity to GSH. The fluorescence imaging results demonstrated that ER-G exhibited excellent endoplasmic reticulum-targeting properties and could be applied to monitor GSH levels in the endoplasmic reticulum during the erastin-induced ferroptosis process. By the fluorescence imaging of GSH levels in the endoplasmic reticulum, it was demonstrated that rutin could efficiently block the depletion of GSH during erastin-induced ferroptosis and potentially act as a novel ferroptosis inhibitor. Moreover, unlike traditional ferroptosis inhibitors, it was speculated that the inhibition mechanism of rutin to ferroptosis was the integration of the chelate effect on Fe(II) ions and antioxidant effect. We expect that fluorescence imaging of GSH levels in the endoplasmic reticulum could provide a convenient and feasible method to evaluate the inhibition effect of small molecules on ferroptosis.

Multicolor emission based on a N, N'-Disubstituted dihydrodibenzo [a, c] phenazine crown ether macrocycle

Dynamic fluorophore 9,14-diphenyl-9,14-dihydrodibenzo[a,c]phenazine (DPAC) affords a new platform to produce diverse emission outputs. In this paper, a novel DPAC-containing crown ether macrocycle D-6 is synthesized and characterized. Host-guest interactions of D-6 with different ammonium guests produced a variety of fluorescence with hypsochromic shifts up to 130 nm, which are found to be affected by choice of solvent or guest and host/guest stoichiometry. Formation of supramolecular complexes were confirmed by UV-vis titration, ¹H NMR and HRMS spectroscopy.

An indanone-based fluorescent probe for detection and imaging of Cys/Hcy in living cells

Effective detection of Cys and Hcy plays an important role in the diagnosis of diseases. In this work, a novel indanone-based fluorescent probe INIAc-CN for sensitively and effectively detecting Cys and Hcy was developed. The probe exhibited weak fluorescence, but obvious fluorescent enhancement after reacted with Cys/Hcy. Moreover, the good anti-interference and low cytotoxicity of the probe made it successfully applied for monitoring Cys and Hcy of in living cells.

Two Ratiometric Fluorescent Probes Based on the Hydroxyl Coumarin Chalcone Unit with Large Fluorescent Peak Shift for the Detection of Hydrazine in Living Cells

Hydrazine is widely used in industrial and agricultural production, but excessive hydrazine possesses a serious threat to human health and environment. Here two new ratiometric fluorescence probes, DDP and DDC, with the hydroxyl coumarin chalcone unit as the sensing site are developed, which can achieve colorimetric and ratiometric recognition for hydrazine with good sensitivity, excellent selectivity, and anti-interference. The calculated fluorescence limits of detections are 0.26 μM (DDC) and 0.14 μM (DDP). The ratiometric fluorescence response to hydrazine is realized through the adjustment of donor and receptor units in coumarin conjugate structure terminals, accompanied by fluorescence peak shift about 200 nm (DDC, 188 nm; DDP, 229 nm). Stronger electropositivity in the carbon-carbon double bond is helpful to the first phase addition reaction between the probe and hydrazine. Higher phenol activity in the hydroxyl coumarin moiety will facilitate the following dihydro-pyrazole cyclization reaction. In addition, both of these probes realized the convenient detection of hydrazine vapor. The probes were also successfully applied to detect hydrazine in actual water samples, different soils, and living cells.

Versatile Electrochemical Biosensor Based on the Target-Controlled Capture and Release of DNA Nanotubes for the Ultrasensitive Detection of Multiplexed Biomarkers

Herein, an ultrasensitive and versatile electrochemical biosensor was developed through the target-controlled capture and release of signal probe-loaded DNA nanotube for the ultrasensitive detection of two different types of cancer-related biomarkers, microRNA-21 (miRNA-21) and glutathione (GSH). In this system, target 1 (miRNA-21) first triggered duplex-specific nuclease (DSN)-assisted recycle amplification to generate numerous disulfide-linked DNA strands (DL), which could effectively capture DNA nanotube to immobilize methylene blue (MB) to produce remarkable electrochemical signals and achieve the ultrasensitive detection of miRNA-21 with a detection limit down to 32.6 aM. Furthermore, in the presence of target 2 (GSH), the electrochemical signal was significantly reduced by a thiol-disulfide bond exchange reaction on DL to release MB-immobilized DNA nanotubes away from the sensing interface, which enabled the sensitive analysis of GSH with a detection limit of 0.379 nM. Impressively, this strategy could achieve ultrasensitive detection of different types of biomarkers to prominently lessen false-positive responses from the current sensing methods toward a single biomarker or the same type of biomarker and remarkably heighten the accuracy and precision of early cancer diagnosis. Meanwhile, the proposed electrochemical biosensor made it possible to realize the regenerative analysis of targets over four times without extra fuel, which could conspicuously improve the analytical efficiency compared with that of traditional biosensing assays. As a result, this study might open up novel insights to design a versatile and multifunctional sensing platform and encourage deeper exploration for detecting different types of biomarkers in the fields of early disease diagnosis and biochemical research.

Dual-channel detection of viscosity and pH with a near-infrared fluorescent probe for cancer visualization

Compared to ordinary cells, tumor cells have a unique microenvironment, characterized by high viscosity, low pH, high reactive oxygen species level and the overexpression of certain proteases. Therefore, viscosity and pH can be used as important parameters for visualizing cancer. We designed a spiro-oxazolidine compound (In-1) for the dual-channel detection of viscosity and pH, with the red channel for detecting viscosity and the blue channel for pH. Interestingly, In-1 can locate different organelles under different conditions. Under physiological conditions, In-1 efficiently targeted lysosomes and showed that the viscosity of lysosomes increases in cancer cells while the pH decreases, which can be used to distinguish and detect cancer cells and normal cells. When we treated HL-7702 cells with CCCP, the probe could effectively target the mitochondria, and the fluorescence intensity in the pH channel decreased. This indicates that In-1 can be used as a powerful tool to simultaneously monitor viscosity and pH in different organelles, and may have a guiding role in diseases caused by mitochondrial and lysosomal microenvironments.

Selective, Rapid, and Ratiometric Fluorescence Sensing of Homocysteine in Live Neurons via a Reaction-Kinetics/Sequence-Differentiation Strategy Based on a Small Molecular Probe

Small molecular biothiols, including cysteine (Cys), homocysteine (Hcy), and glutathione (GSH), play essential roles in maintaining the redox homeostasis of biological systems, the disorders of which are closely associated with neuropathology. To date, many probes have been developed to identify Cys and GSH; however, due to the relatively low content and the high structural homology with Cys, there is still a lack of effective strategies to design probes enabling Hcy detection in physiological environments with high selectivity, high sensitivity, and rapid response. Herein, we developed a reaction-kinetics/sequence-differentiation strategy based on a dual-binding-site boron-dipyrrin (BODIPY) fluorophore, which was able to selectively distinguish Hcy from Cys and GSH within 50 s though a ratiometric fluorescence response mode. Benefiting from these features, the probe is capable of real-time imaging and quantitative analysis of intracellular Hcy in living neurons. Moreover, results of the disease-model experiments at the cellular level indicated a gradual increase of the Hcy level in neurons during the processes of aggregated amyloid-β (Aβ) peptide or ischemia treatment, which would further promote the neuron apoptosis. These findings provide the first direct experimental evidence for the impact of Alzheimer's disease and ischemic stroke on the Hcy metabolism of brain neurons and the associated neuron injury.

A lipid droplet-targetable and biothiol-sensitive fluorescent probe for the diagnosis of cancer cells/tissues

Lipid droplets (LDs) have recently been reported as an attractive target for cancer diagnosis and treatment, owing to their special structure or microenvironment changes in cancer development and resistance. However, the relationship between the biothiol level of LDs and cancer is still poorly understood, partially owing to the absence of effective molecular tools. Herein, we developed a LD-targetable and biothiol-sensitive fluorescent probe, BTDA-RSS, by introducing 2,4-dinitrobenzenesulfonyl (DNBS) as the biothiol reaction group into a benzothiazolyl derivative. BTDA-RSS displayed a marked and rapid fluorescence turn-on response toward biothiols, due to the biothiol-triggered cleavage of DNBS to yield the highly fluorescent benzothiazolyl iminocoumarin BTDA. In addition, the probe shows significant LD-targetable ability, and has been applied for imaging endogenous/exogenous biothiol changes in LDs. Importantly, BTDA-RSS has successfully been utilized to distinguish cancerous cells/tissues from normal cells/tissues with excellent contrast. Surprisingly, we demonstrated for the first time the visualization of LD biothiols in surgical specimens from cancer patients, thereby holding great potential for the application of BTDA-RSS in the clinical diagnosis of human cancers.

A fluorescent probe derived from Berberrubine for detecting hydrogen polysulfide in food samples

In this work, we chose the fluorophore Berberrubine to develop a selective probe for hydrogen polysulfide (H₂S_n), and applied it into the detection in both food samples and living cells. The developed probe, HER9SS, suggested practical steadiness and serviceability, especially for multi-scene detection. The detecting system was stable in relatively wide pH (7.0-11.0) and temperature (25-45 °C) ranges. Both the storage of BER9SS in solid or in solution could maintain the steadiness over 7 d. BER9SS also indicated advantages including rapid response (within 15 min), high sensitivity (LOD = 0.02 μM; LOQ = 0.01 μM), long linear range (0-15.0 equivalent) and high selectivity among competing analytes. The recovery ranging in 95.23% - 104.8% in the applications in food sources samples (including water and plants) and food samples inferred the practical potential of BER9SS. In biological imaging, BER9SS could achieve both the dose-dependent monitoring and the β-lapachone-induced generation of H₂S_n. Therefore, the information in this work might be useful for the development of fluorescent probes from natural products for multi-scene applications in future, especially with the corresponding attentions on the practicability and serviceability.