In Vivo Imaging of Endogenously Produced HClO in Zebrafish and Mice Using a Bright, Photostable Ratiometric Fluorescent Probe

A phenothiazine-based ratiometric fluorescent probe for detecting hypochlorite (ClO-) and its application in foods and water samples

As a significant reactive oxygen species (ROS), ClO- plays versatile roles in daily life and many biological events. However, its abnormal levels are responsible for serious harm to human health. Therefore, it is of crucial interest to develop effective methods for detecting ClO- in foods and living organisms. In this work, a novel fluorescent probe ethyl 2-(3-formyl-2-methoxy-10H-phenothiazin-10-yl)acetate (PEA) for detecting ClO- was presented. It shows the merits of rapid ratiometric response (within 10 s), high selectivity and very large Stokes shift (190 nm). The detection limit of PEA for ClO- was determined to be 0.47 μM. We not only successfully prepared paper test strips for efficient qualitative naked eye ClO- detection, but also demonstrated its potential for the valid detection of ClO- in natural water samples, beverages and foods. Furthermore, the probe PEA was also applied to the fluorescence imaging of ClO- in onion epidermal cells.

High resolution two photon fluorescence probe monitoring ClO- based on anion exchange for the synergistic ROS and ferroptosis activated by thermal energy

Ferroptosis, closely correlated with hypochlorite (ClO-), is an emerging form of iron-dependent cell death. Exploring the ClO- content in living cells will help to further reveal the biological function of ferroptosis. In this work, we have developed a two-photon excited fluorescent probe (CMI-ClO) which can detect the ClO- changes during ferroptosis. CMI-ClO can specifically response to ClO- by exchanging with I-. The multiple reactive oxygen species (ROS) are produced simultaneously in the ClO- identification process. More significantly, CMI-ClO produces ROS through thermal energy, breaking the limitation of light trigged conventional photosensitizers. CMI-ClO can achieve high resolution tracking of ferroptosis under NIR II excitation, where ROS and ferroptosis combine to cause mitochondrial damage and cell death. This work provides a synergistic strategy for enhancing ROS and ferroptosis therapy.

A self-calibrated tri-emission fluorescent probe based on carbon dots assembly for in vitro pepsin detection

A novel self-calibrating triple-emission fluorescent probe (CDs/BSA-SQ-Cy7) was engineered through the strategic integration of blue-emitting carbon dots (CDs) with covalently assembled near-infrared fluorescent dyes (BSA-SQ and BSA-SQ-Cy7) for accurate in vitro pepsin detection. To validate the enhanced performance of the tri-emissive design, a dual-emission control probe (CDs/BSA-SQ) was developed. BSA-SQ-Cy7 undergoes hydrolysis upon interaction with pepsin, resulting in concentration-dependent quenching of the red fluorescence, where the blue CDs serve as a reference emission during the process. The CDs/BSA-SQ-Cy7 probe demonstrated a robust linear correlation with pepsin concentrations ranging from 0.018 to 30 μg/mL (determined by the lowest detection limit). The detection limits were found to be 0.182 μg/mL (I495/I659), 0.033 μg/mL (I495/I808), and 0.018 μg/mL ((I495-I808)/I659), respectively. Additionally, the probe displayed excellent stability and reproducibility over a 72-h period, and its three-channel emission signal ratios can be utilized for self-calibration, thereby improving assay accuracy. This self-calibrated tri-emission probe is distinguished by its stability, reproducibility and high selectivity, offering an effective method for the accurate in vitro detection of pepsin.

A highly sensitive and fast-response fluorescence nanoprobe for in vivo imaging of hypochlorous acid

Fluorescent probes for in vivo hypochlorous acid (HClO) imaging often face challenges of low selectivity and high cytotoxicity, largely due to poor analyte recognition and water-insoluble aromatic skeletons. To address this, we synthesized fluorescein hydrazide by introducing a spiro-lactam unit into fluorescein, which offers high emission intensity and molar absorption. The five-membered heterocycle in fluorescein hydrazide is selectively disrupted by HClO, enhancing the conjugated system and electron delocalization of the fluorophore, resulting in highly sensitive fluorescence detection of HClO. For in vivo imaging, fluorescein hydrazide was covalently grafted onto the surface of silica nanoparticles via nucleophilic substitution reaction, avoiding complex modifications. This fluorescent nanoprobe (Si-FL) leverages the high-density fluorophores and hydroxyl groups on the silica surface to enrich low-concentrations of HClO through weak supramolecular interactions, thereby accelerating the reaction between HClO and the recognition sites. Compared to other molecular probes, Si-FL demonstrates a superior response speed (within 20 s) and a lower detection limit (72 nM), alongside excellent biocompatibility and water solubility. The nanoprobe Si-FL was successfully applied for HClO detection in living cells, zebrafish, and plants, significantly improving the stability of fluorescence imaging.

A novel AIEgen fluorescent probe based on quinoline-malononitrile for monitoring and imaging ClO- and viscosity in biosystem

Hypochlorite (ClO-) and viscosity play a pivotal role in biological immune defense systems, it has been demonstrated that alterations in ClO- may link to the modifications in intracellular viscosity. Consequently, it is crucial to develop a tool that can accurately assess these changes of ClO- and viscosity concurrently. In this work, a dual-responsive fluorescent probe QM-WV based on the ICT effect for simultaneous detection of ClO- and viscosity was constructed. QM-WV exhibited a signally turn-on fluorescence signal at 552 nm for ClO- with favorable selectivity. Meanwhile, QM-WV displayed an exceptional 'off-on' fluorescence response at 650 nm to viscosity changes in glycerol-ethanol system. More importantly, QM-WV is capable of visually detecting ClO- by using smartphone as a portable signal processing device. Based on its low cytotoxicity and stability under physiological conditions, QM-WV further enabled the detection and imaging of ClO- and viscosity in HeLa cells and zebrafish.

"Light-Up" Near-Infrared Fluorescent Probe for Visualization of Hydrogen Sulfide Content and Abiotic Stress Response in Plants

Hydrogen sulfide (H2S) plays a vital role in plant physiology and stress adaptation, but the detection of endogenous H2S remains a challenge. In this work, a near-infrared fluorescent probe (NIR-BOD-HS) was synthesized using boron-dipyrromethene (BODIPY) as the raw material, which showed a good linear relationship in the concentration range of 0.1-70 μM and a detection limit of 56 nM. The long-wavelength emission (712 nm) reduced the interference of plant autofluorescence and improved the imaging quality. The probe combined with fluorescence imaging technology nondestructively realized the spatiotemporal distribution signal of H2S in the deep tissues of plants. In addition, the dynamic changes of H2S content during seed germination and seedling growth under abiotic stress were also demonstrated through the changes in fluorescence signals. This study helps to understand the physiological response mechanism of plants under abiotic stress and provides a scientific basis for further research on plant imaging and agricultural production.

A turn-on AIE dual-channel fluorescent probe for sensing Cr3+/ClO- and application in cell imaging

A Cr3+/ClO--enhanced fluorescent probe, DNS (5-(dimethylamino)-N'-(2-hydroxy-4,6-dimethoxybenzylidene)-naphthalene-1-sulfonyl hydrazide), with aggregation-induced emission (AIE) properties was synthesized using dansylhydrazide and 4,6-dimethoxysalicylaldehyde as starting materials. The probe rapidly and selectively detects Cr3+ and ClO- in a solvent system of H2O/DMSO (2:8). Upon binding with Cr3+/ClO-, the probe exhibits a significant fluorescence enhancement, with minimal interference from other ions. The detection limits (LOD) were determined to be 5.36 × 10-7 mol/L for Cr3+ and 3.65 × 10-7 mol/L for ClO-. The binding mechanisms of DNS with Cr3+/ClO- were investigated through Job's plot, 1H NMR titration, and mass spectrometry. Furthermore, the probe's low cytotoxicity and biocompatibility suggest its potential for detecting exogenous Cr3+/ClO- and endogenous ClO- in living cells. DNS shows promise for real-time detection and bioimaging applications.

Super-Resolution Mitochondrial Fluorescent Probe for Accurate Monitoring of Drug-Induced Liver Injury

Drug-induced liver injury (DILI) has emerged as an urgent clinical challenge. It is characterized by mitochondrial dysfunction in liver cells, which leads to abnormal changes in H2O2 levels within the mitochondria. Super-resolution imaging allows for the observation of the fine structure of mitochondria at the nanometer scale, potentially enabling the detection of mitochondrial H2O2 levels during DILI at the subcellular organelle level. Here, we report the design and synthesis of a novel H2O2-activated probe for the detection of mitochondrial H2O2 levels. SML is a near-infrared (NIR) fluorescent probe with a large Stokes shift (260 nm) and a sensing mechanism based on intramolecular charge transfer (ICT) switching. Super-resolution imaging of mitochondrial H2O2 was conducted using structured illumination microscopy (SIM). The improved accuracy in observing periods of mitochondrial dysfunction allows the SML probe to be effectively utilized for the rapid monitoring nanoscale upregulation of H2O2 during DILI and hepatic fibrosis, thus providing SML with the capability to screen for effective therapeutic candidates.

Methionine-Derived Fluorescent Probes Targeting Mitochondria: A Tool for Real-Time Oxidative Stress Monitoring in Live Cells

Reactive oxygen species (ROS) play crucial roles in both cell signaling and defense mechanisms. Hypochlorous acid (HOCl), a strong oxidant, aids the immune response by damaging pathogens. In this study, we developed two pyridinium-based fluorophores PSSM and PSSE for selective hypochlorite detection. Out of these two fluorescent probes, PSSM shows a strong turn-on emission via a photoinduced electron transfer (PeT) mechanism, excellent mitochondrial localization, and rapid response to HOCl with high selectivity among reactive oxygen species by achieving a detection limit of 2.41 μM. It successfully detects both exogenous and endogenous HOCl in live cells, enabling the study of HOCl's role at the organelle level. Structural analysis of PSSM via thioether oxidation confirmed by HPLC, NMR and HRMS further supports its specificity. Confocal imaging and flow cytometry studies further highlights its utility in investigating oxidative stress, positioning this fluorophore as a valuable tool for monitoring HOCl imbalances in biological systems.

Activatable Molecular Probes With Clinical Promise for NIR-II Fluorescent Imaging

The second near-infrared window (NIR-II) fluorescence imaging has been widely adopted in basic scientific research and preclinical applications due to its exceptional spatiotemporal resolution and deep tissue penetration. Among the various fluorescent agents, organic small-molecule fluorophores are considered the most promising candidates for clinical translation, owing to their well-defined chemical structures, tunable optical properties, and excellent biocompatibility. However, many currently available NIR-II fluorophores exhibit an "always-on" fluorescence signal, which leads to background noise and compromises diagnostic accuracy during disease detection. Developing NIR-II activatable organic small-molecule fluorescent probes (AOSFPs) for accurately reporting pathological changes is key to advancing NIR-II fluorescence imaging toward clinical application. This review summarizes the rational design strategies for NIR-II AOSFPs based on four core structures (cyanine, hemicyanine, xanthene, and BODIPY). These NIR-II AOSFPs hold substantial potential for clinical translation. Furthermore, the recent advances in NIR-II AOSFPs for NIR-II bioimaging are comprehensively reviewed, offering clear guidance and direction for their further development. Finally, the prospective efforts to advance NIR-II AOSFPs for clinical applications are outlined.

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

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

Highly sensitive near-infrared fluorescent probe for monitoring peroxynitrite in nonalcoholic fatty liver disease: Toward early diagnosis and therapeutic evaluation

Nonalcoholic fatty liver disease (NAFLD) poses a significant global health concern, necessitating precise diagnostic tools and effective treatment strategies. Peroxynitrite (ONOO-), a reactive oxygen species, plays a pivotal role in NAFLD pathogenesis, highlighting its potential as a biomarker for disease diagnosis and therapeutic evaluation. This study reports on the development of a near-infrared (NIR) fluorescent probe, designated DRP-O, for the selective detection of ONOO- with high sensitivity and photostability. DRP-O exhibits rapid response kinetics (within 2 min) and an impressive detection limit of 2.3 nM, enabling real-time monitoring of ONOO- dynamics in living cells. Notably, DRP-O demonstrates excellent photostability under continuous laser irradiation, ensuring reliable long-term monitoring in complex biological systems. We apply DRP-O to visualize endogenous ONOO- in living cells, demonstrating its potential for diagnosing and monitoring NAFLD-related oxidative stress. Furthermore, DRP-O effectively evaluates the efficacy of therapeutic drugs in NAFLD cell models, underscoring its potential utility in drug screening studies. Moreover, we confirm DRP-O to enable selective identification of fatty liver tissues in a mouse model of NAFLD, indicating its potential for the early diagnosis of NAFLD. Collectively, DRP-O represents a valuable tool for studying ONOO- dynamics, evaluating drug efficacy, and diagnosing NAFLD, offering insights into novel therapeutic strategies for this prevalent liver disorder.

A cyanine based fluorescent probe for detecting hypochlorite in vitro and in vivo

Hypochlorite (ClO-) is recognized as a bioactive substance that plays a crucial role in various physiological and pathological processes. The increase of ClO- content in cells is a key factor in the early atherosclerosis lesions, which are closely linked to cardiovascular and cerebrovascular diseases. Therefore, the development of an efficient and sensitive method for detecting hypochlorite in tap water, serum, and living cells, including animal model in vivo is of paramount importance. In this study, a novel fluorescent probe (Cy-F) based on the cyanine group was designed for the specific detection of ClO-, demonstrating exceptional selectivity, high sensitivity, and rapid response. The probe successfully detected ClO- in tap water and serum with a limit of detection (LOD) of 2.93 × 10-7 M, showcasing excellent anti-interference capabilities. Notably, the probe exhibited good biocompatibility, low biological toxicity, and proved effective for detecting and analyzing ClO- in live cells and zebrafish. This newly developed probe offers a promising approach and valuable tool for detecting ClO- with biosafety considerations, paving the way for the design of functional probes tailored for future biomedical applications.

Application of gold nanoclusters in fluorescence sensing and biological detection

Gold nanoclusters (Au NCs) exhibit broad fluorescent spectra from visible to near-infrared regions and good enzyme-mimicking catalytic activities. Combined with excellent stability and exceptional biocompatibility, the Au NCs have been widely exploited in biomedicine such as biocatalysis and bioimaging. Especially, the long fluorescence lifetime and large Stokes shift attribute Au NCs to good probes for fluorescence sensing and biological detection. In this review, we systematically summarized the molecular structure and fluorescence properties of Au NCs and highlighted the advances in fluorescence sensing and biological detection. The Au NCs display high sensitivity and specificity in detecting iodine ions, metal ions, and reactive oxygen species, as well as certain diseases based on the fluorescence activities of Au NCs. We also proposed several points to improve the practicability and accelerate the clinical translation of the Au NCs.

A self-assembled nanoprobe for rapid detection of hypochlorite in pure water and its application in living cells, food and environmental systems

As an important ROS species participating in various physiological and pathological processes, high level of hypochlorite (ClO-) poses significant health and safety concerns, necessitating efficient detection methods. Herein, this study introduces a water-soluble fluorescent nanoprobe Nano-SJD, effectively detect ClO- in both food samples and living cells. The small molecular probe SJD with N, N-dimethylthiocarbamyl (DMTC) as recognition moiety was constructed based on a naphthalene derivative. To further improve the water solubility, SJD was assembled with an amphiphilic copolymer (mPEG-DSPE) to prepare a water soluble fluorescent nanoprobe Nano-SJD. Fortunately, the nanoprobe preserves the excellent properties of small molecules and performs very well optical response to ClO- in aqueous solution, possessing the advantages including ultra-rapid response (within 1 s), minimal interference, low detection limits (0.39 μM) and good pH stability. What's more important, we have also developed smartphone-compatible test paper strips for convenient on-site detection of ClO- in real-water samples. Additionally, the robust fluorescent imaging behavior of Nano-SJD for visualization of ClO- in living cells highlights its broad potential in biosystem applicability.

Lysosome-Targeted Bifunctional Fluorescent Probe and Type I/II Photosensitizer for Viscosity Imaging and Cancer Photodynamic Therapy

Abnormal lysosomal viscosity is closely associated with cancer progression, underscoring the need for bifunctional fluorescent probes and photosensitizers (PSs) that can both monitor viscosity and facilitate imaging-guided therapy for simultaneous cancer diagnosis and treatment. Despite advances in lysosome-targeted PSs development, few have demonstrated the ability to generate both Type I and Type II reactive oxygen species (ROS). In this study, we present BTTPA, a lysosome-targeted fluorescent probe and photosensitizer, designed to integrate cancer diagnosis via viscosity imaging and cancer treatment through photodynamic therapy (PDT). Our findings reveal that BTTPA selectively targets lysosomes, enabling dynamic monitoring of cellular viscosity and distinguishing cancer cells from normal cells. Upon light activation, BTTPA efficiently generates both Type I and Type II ROS. Apoptosis assays further confirm BTTPA's effectiveness in inducing cancer cell apoptosis, highlighting its potential as a powerful tool for cancer diagnosis and therapy.

Sulfur-based fluorescent probes for biological analysis: A review

The widespread adoption of small-molecule fluorescence detection methodologies in scientific research and industrial contexts can be ascribed to their inherent merits, including elevated sensitivity, exceptional selectivity, real-time detection capabilities, and non-destructive characteristics. In recent years, there has been a growing focus on small-molecule fluorescent probes engineered with sulfur elements, aiming to detect a diverse array of biologically active species. This review presents a comprehensive survey of sulfur-based fluorescent probes published from 2017 to 2023. The diverse repertoire of recognition sites, including but not limited to N, N-dimethylthiocarbamyl, disulfides, thioether, sulfonyls and sulfoxides, thiourea, thioester, thioacetal and thioketal, sulfhydryl, phenothiazine, thioamide, and others, inherent in these sulfur-based probes markedly amplifies their capacity for detecting a broad spectrum of analytes, such as metal ions, reactive oxygen species, reactive sulfur species, reactive nitrogen species, proteins, and beyond. Owing to the individual disparities in the molecular structures of the probes, analogous recognition units may be employed to discern diverse substrates. Subsequent to this classification, the review provides a concise summary and introduction to the design and biological applications of these probe molecules. Lastly, drawing upon a synthesis of published works, the review engages in a discussion regarding the merits and drawbacks of these fluorescent probes, offering guidance for future endeavors.

A new FRET-based fluorescent probe: Colorimetric and ratiometric detection of hypochlorite and anti-counterfeiting applications

Hypochlorite (ClO-), as the main component of widely used disinfectants in daily life, comes into closer contact with the human body, which can lead to a number of diseases. The high-performance method is increasingly needed to detect ClO- in our daily life. In this report, we successfully synthesized a FRET ratiometric fluorescent probe (NDAC) containing benzoxadiazole moieties and coumarin moieties bound via ethylenediamine. As expected, NDAC has excellent selectivity and anti-interference ability toward ClO-, and the ratio of fluorescence intensity (I471 nm/I533 nm) has a very good linear relationship with the concentration of ClO-, with a wide linear range (2.5-1750 μM) and low detection limit (0.887 μM). Furthermore, we have successfully applied it for the quantitative detection of ClO- in water samples in daily life. At the same time, there is a very clear change in the fluorescence color after the reaction of the NDAC with ClO-. The blue/green value (B/G) of this color change also shows a very good linear relationship to ClO- (5.0-1000 μM). Therefore, the NDAC has also been successfully used for test strip detection and quantitative detection of ClO- in actual samples through smartphone-based fluorescence image analysis, and this method can provide faster, more convenient and more accessible detection. In addition, NDAC sensors also have potential applications in the field of information anti-counterfeiting.

Fluorogenic Chemical Probe Strategy for Precise Tracking of Mitochondrial Polarity

Mitochondrial polarity is a critical indicator of numerous pathological and biological processes; thus, the development of fluorescent probes capable of targeting mitochondria and visually monitoring its polarity is of great significance. In this study, fluorescent probes were designed with a N, N-dialkylamino rhodol scaffold as the fluorophore sensitive to polarity environments, in which the alkyl chain length was adjusted rationally to obtain distinct polarity recognition modes. By integrating mitochondria targeting groups, three fluorogenic chemical probes ROML-1, ROML-2, and ROML-3 have been obtained, featuring the capability to target mitochondria and monitor its polarity precisely, dynamically and visually. The probes displayed a distinctive response to the alterations in polarity. ROML-1 and ROML-2 followed a turn-on pattern while ROML-3 was ratiometric. It has been demonstrated that the hypersensitivity to polarity and ratio fluorescence property of ROML-3 was attributed to methyl groups rather than ethyl or butyl groups. The introduction of short methyl chains made the dihedral angle between the dialkylamino substituent and fluorophore of ROML-3 (spirocyclic form) rotatable and enlarged the energy gap between the ground state and excited state, which has been validated by the results of density functional theory (DFT) calculations. Furthermore, ROML-3 was used to monitor mitochondrial polarity via confocal microscopy imaging, which revealed that compared to healthy cells the polarity of mitochondria in cancer cells was enhanced; meanwhile, the polarity of mitochondria in senescent cells was higher in contrast with young cells. The present probe ROML-3 has been proven to be an efficient tool to monitor mitochondrial polarity dynamics, which demonstrated potential significance in biomedical research and disease diagnosis.

In-situ evaluation the fluctuation of hypochlorous acid in acute liver injury mice models with a mitochondria-targeted NIR ratiometric fluorescent probe

Acute liver injury (ALI) is a frequent and devastating liver disease that has been made more prevalent by the excessive use of chemicals, drugs, and alcohol in modern life. Hypochlorous acid (HClO), an important biomarker of oxidative stress originating mainly from the mitochondria, has been shown to be intimately connected to the development and course of ALI. Herein, a novel BODIPY-based NIR ratiometric fluorescent probe Mito-BS was constructed for the specific recognition of mitochondrial HClO. The probe Mito-BS can rapidly respond to HClO within 20 s with a ratiometric fluorescence response (from 680 nm to 645 nm), 24-fold fluorescence intensity ratio enhancement (I645/I680), a wide pH adaptation range (5-9) and the low detection limit (31 nM). The probe Mito-BS has been effectively applied to visualize endogenous and exogenous HClO fluctuations in living zebrafish and cells based on its low cytotoxicity and prominent mitochondria-targeting ability. Furthermore, the fluorescent probe Mito-BS makes it possible to achieve the non-invasive in-situ diagnosis of ALI through in mice, and provides a feasible strategy for early diagnosis and drug therapy of ALI and its complications.

Ex Tenebris Lux: Illuminating Reactive Oxygen and Nitrogen Species with Small Molecule Probes

Reactive oxygen and nitrogen species are small reactive molecules derived from elements in the air─oxygen and nitrogen. They are produced in biological systems to mediate fundamental aspects of cellular signaling but must be very tightly balanced to prevent indiscriminate damage to biological molecules. Small molecule probes can transmute the specific nature of each reactive oxygen and nitrogen species into an observable luminescent signal (or even an acoustic wave) to offer sensitive and selective imaging in living cells and whole animals. This review focuses specifically on small molecule probes for superoxide, hydrogen peroxide, hypochlorite, nitric oxide, and peroxynitrite that provide a luminescent or photoacoustic signal. Important background information on general photophysical phenomena, common probe designs, mechanisms, and imaging modalities will be provided, and then, probes for each analyte will be thoroughly evaluated. A discussion of the successes of the field will be presented, followed by recommendations for improvement and a future outlook of emerging trends. Our objectives are to provide an informative, useful, and thorough field guide to small molecule probes for reactive oxygen and nitrogen species as well as important context to compare the ecosystem of chemistries and molecular scaffolds that has manifested within the field.

Design of a high-performance NIR-II nanoprobe by steric regulation for in vivo vasculature and tumor imaging

A novel NIR-II nanoprobe was developed through regulating the steric effect of an A-DA'D-A dye. The probe features the properties of strong fluorescence, high stability, and a large Stokes shift, thereby serving as a remarkable contrast agent for the fluorescence imaging of hindlimb vasculature and tumors in live mice.

Ratiometric Fluorescent Probe for Super-Resolution Imaging of Lysosome HClO in Ferroptosis Cells

Ferroptosis is an iron-dependent programmed cell death that is characterized by the dysregulation of lipid reactive oxygen species (ROS) production, causing abnormal changes in hypochlorous acid (HClO) levels in lysosomes. Super-resolution imaging can observe the fine structure of the lysosome at the nanometer level; therefore, it can be used to detect lysosome HClO levels during ferroptosis at the suborganelle level. Herein, we utilize a ratiometric fluorescent probe, SRF-HClO, for super-resolution imaging of lysosome HClO. Structured-illumination microscopy (SIM) improves the accuracy of lysosome targeting and enables the probe SRF-HClO to be successfully applied to rapidly monitor the up-regulated lysosome HClO at the nanoscale during inflammation and ferroptosis. Importantly, the probe SRF-HClO can also detect HClO changes in inflammatory and ferroptosis mice and evaluate the inhibitory effect of ferroptosis on mice tumors.

A polarity-responsive lysosomes-nucleus translocation probe for the dual-emissive visualization of cell apoptosis

Visualization of cell apoptosis is a critical task playing central roles in the fundamental studies in biology, pathology, and biomedicine. Dual-emissive fluorescent probes are desired molecular tools for study on apoptosis, which however were rarely reported. Herein, utilizing the polarity differences between lysosomes and nucleus, a translocation type of fluorescent probe (NA-S) was developed for the dual-color visualization of cell apoptosis. NA-S was designed to be polarity sensitive, bearing alkalescence group, and with DNA affinity. In living cells, NA-S targeted the lysosomes to give blue fluorescence, which translocated into the nucleus during cell apoptosis to give green emission. Thereby, the cell apoptosis could be visualized with NA-S in dual-emissive manner. With the unique probe, the cell apoptosis induced by oxidative stress, UV irradiation, rotenone, colchicine, and paclitaxel have been successfully visualized.

In Situ Visualizing Carboxylesterase Activity in Type 2 Diabetes Mellitus Using an Activatable Endoplasmic Reticulum Targetable Proximity Labeling Far-Red Fluorescent Probe

Carboxylesterase (CE), an enzyme widely present in organisms, is involved in various physiological and pathological processes. Changes in the levels of CEs in the liver may predict the presence of type 2 diabetes mellitus (T2DM). Here, a novel dicyanoisophorone (DCI)-based proximity-labeled far-red fluorescent probe DCI2F-Ac with endoplasmic reticulum targeting was proposed for real-time monitoring and imaging of the CEs activity. DCI2F-Ac featured very low cytotoxicity and biotoxicity and was highly selective and sensitive for CEs. Compared with traditional CEs probes, DCI2F-Ac was covalently anchored directly to CEs, thus effectively reducing the loss of in situ fluorescent signals due to diffusion. Through the "on-off" fluorescence signal readout, DCI2F-Ac was able to distinguish cell lines and screen for CEs inhibitors. In terms of endoplasmic reticulum (ER) stress, it was found that thapsigargin (Tg) induced upregulation of CEs levels but not tunicamycin (Tm), which was related to the calcium homeostasis of the ER. DCI2F-Ac could efficiently detect downregulated CEs in the livers of T2DM, and the therapeutic efficacy of metformin, acarbose, and a combination of these two drugs was assessed by tracking the fluctuation of CEs levels. The results showed that combining metformin and acarbose could restore CEs levels to near-normal levels with the best antidiabetic effect. Thus, the DCI2F-Ac probe provides a great opportunity to explore the untapped potential of CEs in liver metabolic disorders and drug efficacy assessment.

Lighting Up Nucleolus To Report Mitochondria Damage Using a Mitochondria-to-Nucleolus Migration Probe

Visualization of the mitochondrial state is crucial for tracking cell life processes and diagnosing disease, while fluorescent probes that can accurately assess mitochondrial status are currently scarce. Herein, a fluorescent probe named "SYN" was designed and prepared, which can target mitochondria via the mitochondrial membrane potential. Upon pathology or external stimulation, SYN can be released from the mitochondria and accumulate in the nucleolus to monitor the status of mitochondria. During this process, the brightness of the nucleolus can then serve as an indicator of mitochondrial damage. SYN has demonstrated excellent photostability in live cells as well as an extremely inert fluorescence response to bioactive molecules and the physiological pH environment of live cells. Spectroscopic titration and molecular docking studies have revealed that SYN can be lit up in nucleoli due to the high viscosity of the nucleus and the strong electrostatic interaction with the phosphate backbone of RNA. This probe is expected to be an exceptional tool based on its excellent imaging properties for tracking mitochondrial state in live cells.

A specific dual-locked fluorescence probe to visualize the dynamic changes of lipid droplets and hypochlorous acid in inflammation

Inflammation is a key factor leading to the occurrence and development of many diseases, both lipid droplets (LDs) and hypochlorous acid (HClO/ClO-) are regarded as the important biomarkers of inflammation. Therefore, it is of great significance to develop an efficient single chemical sensor that can simultaneously detect these two biomarkers. To achieve the goal, we developed a dual-locked fluorescence probe (TPA-DNP) by fusing two targets activated reporting system, its implementation was achieved by turning-on the fluorescence of TPA-DNP through LDs and HClO/ClO- simultaneously. In simulated LDs environment, TPA-DNP displayed excellent selectivity to HClO/ClO-, high sensitivity (LOD = 0.527 μM) and strong anti-interference ability. In addition, cell and zebrafish imaging experiments showed that TPA-DNP could be utilized to visualize exogenous/endogenous HClO/ClO- in LDs environment, and could also be used to observe the impact of LDs changes on the HClO/ClO- detection. On the basis, TPA-DNP served as a favorable tool to achieve visualization of inflammatory dynamic changes.

A novel dual near-infrared fluorescent probe for bioimaging and visualization of viscosity in acute alcoholic liver injury

A dual NIR fluorescent probe Cy-ND is developed for viscosity sensing with λex/em = 766/806 nm, making it apt for biological analysis, whose response is validated through DFT and TDDFT computations. Cy-ND successfully detected viscosity changes amidst acute alcohol-induced liver injury and liver ischemia-reperfusion injury.

Semiconducting polymer dots based l-lactate sensor by enzymatic cascade reaction system

BACKGROUND

l-lactate detection is important for not only assessing exercise intensity, optimizing training regimens, and identifying the lactate threshold in athletes, but also for diagnosing conditions like L-lactateosis, monitoring tissue hypoxia, and guiding critical care decisions. Moreover, l-lactate has been utilized as a biomarker to represent the state of human health. However, the sensitivity of the present l-lactate detection technique is inadequate.

RESULTS

Here, we reported a sensitive ratiometric fluorescent probe for l-lactate detection based on platinum octaethylporphyrin (PtOEP) doped semiconducting polymer dots (Pdots-Pt) with enzymatic cascade reaction. With the help of an enzyme cascade reaction, the l-lactate was continuously oxidized to pyruvic and then reduced back to l-lactate for the next cycle. During this process, oxygen and NADH were continuously consumed, which increased the red fluorescence of Pdots-Pt that responded to the changes of oxygen concentration and decreased the blue fluorescence of NADH at the same time. By comparing the fluorescence intensities at these two different wavelengths, the concentration of l-lactate was accurately measured. With the optimal conditions, the probes showed two linear detection ranges from 0.5 nM to 5.0 μM and 5.0 μM-50.0 μM for l-lactate detection. The limit of detection was calculated to be 0.18 nM by 3σ/slope method. Finally, the method shows good detection performance of l-lactate in both bovine serum and artificial serum samples, indicating its potential usage for the selective analysis of l-lactate for health monitoring and disease diagnosis.

SIGNIFICANCE

The successful application of the sensing system in the complex biological sample (bovine serum and artificial serum samples) demonstrated that this method could be used for sensitive l-lactate detection in practical clinical applications. This detection system provided an extremely low detection limit, which was several orders of magnitude lower than methods proposed in other literatures.

Taming Janus-Faced Quinoline-Derived Fluorescent Probes for Dual-Channel Distinguishable Visualization of HSO3- and HClO in Dried Foods and Living Cells

With the booming development of food manufacturing, developing ideal analytical tools to precisely quantify food additives is highly sought after in the food science field. Herein, a new series of quinoline-derived multifunctional fluorescent probes has been synthesized. Bearing double reactive sites, these compounds display fluorescence response toward both bisulfite (HSO3-) and hypochlorous acid (HClO). Among these compact structures, compound ethyl-2-cyano-3-(6-(methylthio)quinolin-2-yl)acrylate (QTE) was screened out. Probe QTE not only shows ratiometric variation toward HSO3- with little cross talk but also performs turn-off signal toward HClO. In addition, probe QTE has been utilized for bioimaging of HClO in living cells. Furthermore, the HSO3- content in dried food samples has been appraised by QTE with satisfactory results. Meanwhile, relying on the apparent chromaticity change, a flexible dark-box device has been elaborated for chromatic analysis, promoting visualization of HSO3- in the field.

Dual-Functional AIE Fluorescent Probe for Visualization of Lipid Droplets and Photodynamic Therapy of Cancer

Abnormal lipid droplets (LDs) are known to be intimately bound with the occurrence and development of cancer, allowing LDs to be critical biomarkers for cancers. Aggregation-induced emission luminogens (AIEgens), with efficient reactive oxygen species (ROS) production performance, are prime photosensitizers (PSs) for photodynamic therapy (PDT) with imaging. Therefore, the development of dual-functional fluorescent probes with aggregation-induced emission (AIE) characteristics that enable both simultaneous LD monitoring and imaging-guided PDT is essential for concurrent cancer diagnosis and treatment. Herein, we reported the development of a novel LD-targeting fluorescent probe (TDTI) with AIE performance, which was expected to realize the integration of cancer diagnosis through LD visualization and cancer treatment via PDT. We demonstrated that TDTI, with typical AIE characteristics and excellent photostability, could target LDs with high specificity, which enables the dynamic tracking of LDs in living cells, specific imaging of LDs in zebrafish, and the differentiation of cancer cells from normal cells for cancer diagnosis. Meanwhile, TDTI exhibited fast ROS generation ability (achieving equilibrium within 60 s) under white light irradiation (10 mW/cm2). The cell apoptosis assay revealed that TDTI effectively induced growth inhibition and apoptosis of HeLa cells. Further, the results of PDT in vivo indicated that TDTI had a good antitumor effect on the tumor-bearing mice model. Collectively, these results highlight the potential utility of the dual-functional fluorescent probe TDTI in the integrated diagnosis and treatment of cancer.

De Novo Design of a Highly Stable Ratiometric Probe for Long-Term Continuous Imaging of Endogenous HClO Burst

Long-term continuous imaging of endogenous HClO burst is of great importance for the elucidation of various physiological or pathological processes. However, most of the currently reported HClO probes have failed to achieve this goal due to their insufficient photobleaching resistance under a laser source. Herein, a highly stable ratiometric probe, HFTC-HClO 1, which is capable of continuously monitoring endogenous HClO burst over a long period of time, has been judiciously developed. Briefly, the de novo development of HFTC-HClO 1 mainly involved three main steps: (1) novel coumarins (HFTC 1-5) were designed and synthesized; (2) the most stable scaffold, HFTC 3, was selected through dye screening and cell imaging validation; and (3) based on HFTC 3, three candidate HClO probes were constructed, and HFTC-HClO 1 was finally selected due to its superior sensing properties toward HClO. Furthermore, HFTC-HClO 1 can quantitatively measure HClO levels in various real samples with excellent recovery (>90.4%), and the use of HFTC-HClO 1-coated test strips for qualitative analysis of HClO in real samples was also achieved. In addition, the application of HFTC-HClO 1 for long-term continuous monitoring of intracellular HClO burst was successfully demonstrated. Significantly, HFTC-HClO 1 was able to visualize HClO generated in the rheumatoid arthritis mouse model.

Dual-Responsive Near-Infrared BODIPY-Based Fluorescent Probe for the Detection of F- and HClO in Organisms

Fluoride anions (F-) play a crucial role in human physiological processes. However, excessive intake of F- would affect oxygen metabolism and promote the generation of oxygen-free radicals. Hence, it is essential to develop a precise and efficient fluorescent probe for visualizing F--induced oxidative stress. In this work, we developed the first bifunctional BODIPY-based fluorescent probe dfBDP with p-tert-butyldimethylsilanolate benzyl thioether as the sensing site for the detection of F- and HClO via two distinct reactions, the self-immolative removal and the thioether oxidation, which generate the sensing products with two nonoverlap fluorescence bands: 800-1200 and 500-750 nm, respectively. The probe dfBDP displays rapid response, high specificity, and sensitivity for the detection of F- (LOD, 316.2 nM) and HClO (LOD, 33.9 nM) in vitro. Cellular imaging reveals a correlation between F--induced oxidative stress and the upregulation of HClO. Finally, probe dfBDP was employed to detect F- and HClO in mice under the stimulation of F-. The experimental results display that the level of HClO elevates in the liver of mice.

Fe-doped carbon dots: a novel fluorescent nanoprobe for cellular hypochlorous acid imaging

Real-time monitoring of hypochlorous acid (HClO) in biological systems is of great significance for exploring and regulating its pathological functions because abnormal production of HClO is closely related with many diseases, such as atherosclerosis, rheumatoid arthritis, and cancer. Herein, we developed a reliable fluorescent Fe-doped carbon dots (Fe-CDs) for the sensitive and selective detection of biological HClO using ferrocenecarboxylic acid and m-phenylenediamine as precursors through a one-step solvothermal procedure. The Fe-CDs exhibited excellent a wide HClO detection range from 20 nmol/L to 1000 nmol/L with corresponding limits of detection at 7.8 nmol/L. The sensing mechanism is based on the chemical oxidation of the hydroxyl groups on the surface of Fe-CDs by HClO. In addition, Fe-CDs also displayed high photoluminescence yield, excitation-independence emission, as well as good biocompatibility, enabling the successful imaging of endogenous and exogenous HClO in HeLa cells. These results revealed that Fe-CDs holds great promise as a robust fluorescent probe for investigating HClO-mediated biological events.

A facile strategy for the large-scale preparation of starch-based AIE luminescent nanoaggregates via host-guest interactions and their versatile applications

Luminescent nanomaterials with outstanding optical properties have attracted growing interest due to their widespread applications. However, large-scale fabrication of luminescent nanomaterials with desired properties through a simple and economical process remains challenging. As a renewable natural resource, starch is non-toxic, easily accessible, and inexpensive, making it a popular choice for uses in various biomedical fields. In this work, we present a facile assembly strategy for the fabrication of starch-based luminescent nanoaggregates using starch as the host material and aggregation-induced emission luminogens (AIEgens) as guest molecules. By employing simple procedures under mild conditions, highly luminescent nanoparticles with small sizes, high water dispersibility, and low cytotoxicity are prepared on a large scale. The resulting nano-assemblies demonstrate significantly enhanced fluorescence intensities, reduced susceptibility to photobleaching and low cytotoxicity. These fluorescent supramolecular aggregates can be employed in various application fields, including the fabrication of fluorescent hydrogels, fingerprint detection, cell imaging and in vivo lymphatic system imaging. The methodology developed in this work has immense potential to greatly promote the production of high-quality nanoparticles on the industrial scale, offering a cost-effective solution that can meet the needs of various applications and pave the way for wider implementation of nanotechnology.

Dual-emissive Eu(III)-functionalized metal-organic frameworks for visual, rapid, and intelligent sensing of albendazole and albendazole sulfoxide in animal-origin food

Albendazole (ABZ), a benzimidazole-based anthelmintic, is widely used to treat helminth infections. The extensive and improper use of ABZ may cause drug residues in animal-origin food and anthelmintics resistance, which potentially threaten human health. Meanwhile, albendazole sulfoxide (ABZSO), a metabolite of ABZ, also exhibits toxic effects. Therefore, the detection of ABZ and ABZSO in animal-derived food is significantly necessary. Herein, a dual-emission europium fluorescent sensor (EuUHC-30) was rationally designed and constructed. EuUHC-30 exhibits high selectivity and sensitivity towards ABZ and ABZSO with a detection limit of 0.10 and 0.13 μM, respectively. Furthermore, EuUHC-30 was successfully applied for quantification of ABZ and ABZSO in milk and pig kidney, which were verified by HPLC analysis. Moreover, a smartphone-assisted EuUHC-30 fluorescent paper sensor was fabricated for the practical determination of ABZ and ABZSO in real food. Overall, this work provides a visual, rapid, and intelligent method for the detection of ABZ and ABZSO in animal-origin food.

One-step synthesis of a dual-functional AIE-active probe for ClO- detection and photodynamic therapy

An amphiphilic fluorescent probe (BHSMP) with aggregation-induced emission (AIE) features was synthesized via a one-step route. The probe showed high water dispersibility, low toxicity and the ability of selective and sensitive (limit of detection of 0.11 µM) detection of ClO- with fast-response (≤30 s) in aqueous solution and living organisms. Owing to the donor-acceptor (D-A) structure and existence of cationic groups, BHSMP could also generate reactive oxygen species under light-irradiation and potentially be utilized for photodynamic therapy. The strategy described in this work is of great significance for the design and synthesis of multifunctional AIE-active functional materials to facilitate their biomedical applications.

A recyclable Eu3+-functionalized dual-emissive metal-organic framework for portable, rapid detection and efficient removal of malachite green

A europium-functionalized, dual-emissive, metal-organic framework-based fluorescence sensor (EuUCNDA) was constructed via post-synthetic modification of an UiO-66-type precursor through coordination interactions. EuUCNDA exhibited extremely high selectivity and sensitivity for malachite green (MG) with a low detection limit of 13.01 nM, a wide linear concentration range (0.05-50 μM), excellent anti-interference properties, a rapid response (<1 min), and the possibility of recycling. The good sensing performance of EuUCNDA enables the practical detection of MG in fish pond water and grass carp with good recoveries. Moreover, EuUCNDA can be reused for sensing MG and over 90% of fluorescence intensity can be restored after 7 cycles. Furthermore, EuUCNDA-embedded paper-based sensors combined with smartphone imaging afford portable and visual monitoring of MG in real samples. Notably, besides good sensing performance, EuUCNDA could efficiently remove MG from water. Hence, this work provides a recyclable and sensitive fluorescence sensor for portable, visual, rapid detection and efficient removal of MG.

A ratiometric fluorescent probe for rapid and specific detection of hypochlorite

Hypochlorite (ClO- ), as a kind of essential reactive oxygen species, plays a crucial role in vitro and in vivo. Here, a ratiometric fluorescent probe (TPAM) was designed and constructed for sensing ClO- based on substituted triphenylamine and malononitrile, which exhibited obvious colour transfer from orange to colourless under daylight accompanied by noticeable fluorescence change from red to green in response to ClO- . TPAM could effectively monitor ClO- with the merits of fast response, excellent selectivity, high sensitivity and a low detection limit of 0.1014 μM. 1 H NMR, mass spectra and theoretical calculations proved that ClO- caused the oxidation of the carbon-carbon double bond in TPAM, resulting in compound 1 and marked changes in colour and fluorescence. In addition, TPAM was utilized for imaging ClO- in living cells successfully with good photostability and biocompatibility.

Endogenous CO imaging in bacterial pneumonia with a NIR fluorescent probe

Bacterial pneumonia is a serious respiratory illness that poses a great threat to human life. Rapid and precise diagnosis of bacterial pneumonia is crucial for symptomatic clinical treatment. Endogenous carbon monoxide (CO) is regarded as a significant indicator of bacterial pneumonia; herein, we developed a near-infrared (NIR) probe for fluorescence and photoacoustic (PA) dual-mode imaging of endogenous CO in bacterial pneumonia. NO2-BODIPY could rapidly and specifically react with CO to produce strong NIR fluorescence as well as ratiometric PA signals. NO2-BODIPY has outstanding features including fast response, fluorescence/PA dual mode signals, good specificity, and a low limit of detection (LOD = 20.3 nM), which enables it to image endogenous CO in cells and bacterial pneumonia mice with high sensitivity and high contrast ratio. In particular, NO2-BODIPY has two-photon excited (1340 nm, σ1 = 1671 GM) NIR fluorescence and has been utilized to image endogenous CO in bacterial pneumonia mice with deep tissue penetration. NO2-BODIPY has been demonstrated a good capability of fluorescence/PA dual-mode imaging of CO in bacterial pneumonia mice, providing a precise manner to diagnose bacterial pneumonia.

New dual-responsive fluorescent sensor for hypochlorite and cyanide sensing and its imaging application in live cells and zebrafish

Excessive levels of cyanide (CN-) and hypochlorite (ClO-) anions are the significant threats to the human health and the environment. Thus, great efforts have been to design and synthesize molecular sensors for the simple, instantaneous and efficient detecting environmentally and biologically important anions. Currently, developing a single molecular sensor for multi-analyte sensing is still a challenging task. In our present work, we developed a new molecular sensor (3TM) based on oligothiophene and Meldrum's acid units for detecting cyanide and hypochlorite anions in biological, environmental and food samples. The detecting ability of 3TM has been examined to various testing substances containing amino acids, reactive oxygen species, cations and anions, showing its high selectivity, excellent sensitivity, short response time (ClO-: 30 s, CN-: 100 s), and broad pH working range (4-10). The detection limits were calculated as 4.2 nM for ClO- in DMSO/H2O (1/8, v/v) solution and 6.5 nM for CN- in DMSO/H2O (1/99, v/v) solution. Sensor 3TM displayed sharp turn-on fluorescence increasement (555 nm, 435 nm) and sensitive fluorescence color changes caused by CN-/ClO-, which is ascribed to the nucleophilic addition and oxidation of ethylenic linkage by cyanide and hypochlorite, respectively. Moreover, sensor 3TM was applied for hypochlorite and cyanide detecting in real-world water, food samples and bio-imaging in live cells and zebrafish. To our knowledge, the developed 3TM sensor is the seventh single-molecular sensor for simultaneous and discriminative detecting hypochlorite and cyanide in food, biological and aqueous environments using two distinct sensing modes.

Development of a novel hypochlorite ratio probe based on coumarin and its application in living cells

Hypochlorous acid is a reactive oxygen species that is widely present in the body and has been found to exhibit an elevated concentration in tumors. As a result, fluorescent probes for tumor detection have recently gained significant attention. In this study, we designed and synthesized a novel ratiometric fluorescent probe, LW-1, using coumarin as a scaffold, and characterized its spectral properties. LW-1 displayed indigo blue fluorescence at low concentrations of hypochlorous acid. As the concentration of hypochlorous acid increased, the probe underwent a reaction, resulting in a red shift in its fluorescence peak and exhibiting green fluorescence. The fluorescence intensity ratio (green/blue) was a susceptible detection signal for HClO. LW-1 exhibited favorable characteristics, including a low detection limit, high sensitivity, good stability, and low background interference. The detection limit has reached 2.4642 nM. Moreover, we successfully employed LW-1 to image normal human liver and colon cancer cells in vitro, demonstrating its potential as a promising tool for tumor detection. Overall, our findings suggest that LW-1 could serve as a valuable addition to the current arsenal of fluorescent probes for tumor detection, with potential applications in the diagnosis and treatment of cancer.

A new class of teraryl-based AIEgen for highly selective imaging of intracellular lipid droplets and its detection in advanced-stage human cervical cancer tissues

Lipid droplets (LDs) have drawn much attention in recent years. They serve as the energy reservoir of cells and also play an important role in numerous physiological processes. Furthermore, LDs are found to be associated with several pathological conditions, including cancer and diabetes mellitus. Herein, we report a new class of teraryl-based donor-acceptor-appended aggregation-induced emission luminogen (AIEgen), 6a, for selective staining of intracellular LDs in in vitro live 3T3-L1 preadipocytes and the HeLa cancer cell line. In addition, AIEgen 6a was found to be capable of staining and quantifying the LD accumulation in the tissue sections of advanced-stage human cervical cancer patients. Unlike commercial LD staining dyes Nile Red, BODIPY and LipidTOX, AIEgen 6a showed a high Stokes shift (195 nm), a good fluorescence lifetime decay of 12.7 ns, and LD staining persisting for nearly two weeks.

Visualization of the elevated levels of hypochlorous acid in Alzheimer's disease with a ruthenium(II) complex-based luminescence probe

Alzheimer's disease (AD) is an age-related neurodegenerative disorder that devastatingly affects people's lives. Accumulating evidence indicates that the pathological progression of AD is inseparably connected with hypochlorous acid (HClO). However, further exploring the biological function remains an open challenging due to a lack of effective tools to image HClO in AD brains. To this end, a ruthenium(II) luminescence probe, Ru-HClO, is developed for quantitative detection and visualization of HClO in nerve cells and AD brains. Ru-HClO shows quenched luminescence due to the PET process (excited electron transfer from Ru(II) center to diaminomaleonitrile) and the CN bond isomerization in the excited state. The HClO-triggered specific cleavage reaction with Ru-HClO cleaves the CN bond to form highly luminescent Ru-COOH. Ru-HClO shows rapid response speed, high sensitivity and selectivity, excellent biocompatibility, which makes the probe to be applied to semi-quantitative analysis of HClO in nerve cells and high-throughput screening of anti-AD drugs in the AD cell model. Moreover, using Ru-HClO as a probe, present work further validated that the elevated levels of HClO secretion were accompanied by the AD progressed. These findings may provide valuable results for figuring out the biological roles that HClO played in AD but also for accelerating anti-AD therapeutic discovery.

Highly sensitive and rapid detection of hypochlorous acid in aqueous media and its bioimaging in live cells and zebrafish using an ESIPT-driven mycophenolic acid-based fluorescent probe

Excessive production of potent biological oxidants such as HOCl has been implicated in numerous diseases. Thus, it is crucial to develop highly specific and precise methods to detect HOCl in living systems, preferably with molecules that can show a distinct therapeutic effect. Our study introduces the synthesis and application of a highly sensitive fluorescence "turn-on" probe, Myco-OCl, based on the mycophenolic acid scaffold with exceptional water solubility. The ESIPT-driven mechanism enables Myco-OCl to specifically and rapidly detect (<5 s) HOCl with an impressive Stokes shift of 105 nm (λex = 417 nm, λem = 522 nm) and a sub-nanomolar (97.3 nM) detection limit with the detection range of 0 to 50 μM. The potential of Myco-OCl as an excellent biosensor is evident from its successful application for live cell imaging of exogenous and endogenous HOCl. In addition, Myco-OCl enabled us to detect HOCl in a zebrafish inflammatory animal model. These underscore the great potential of Myco-OCl for detecting HOCl in diverse physiological systems. Our findings thus offer a highly promising tool for detecting HOCl in living organisms.

Construction of a novel chitosan-based macromolecular nanoprobe for specific fluorescent detection of H2S in live animals

H2S is one of the signal molecules in live organisms and a poisonous gas, which is closely related to our life. The traditional synthetic small molecular organic probes often have the disadvantages of low biocompatibility. In this paper, a fluorescent nanoprobe for detecting H2S in live organisms was constructed based on chitosan. The structure of CH-CN was characterized by infrared spectroscopy, nuclear magnetic resonance, x-ray photoelectron spectroscopy (XPS), XRD and scanning electron microscope (SEM). In the presence of Na2S, the fluorescence intensity at 560 nm was significantly enhanced, and showed high selectivity and sensitivity toward H2S. Based on the good fluorescence response of CH-CN, the probe was also successfully applied to H2S imaging in HepG2 cells and zebrafish. These experimental results indicate that the probe has lower cytotoxicity and excellent stability. The present research shows a typical example of construction of chitosan-based macromolecular fluorescent materials and their bio-imaging application.

A Reversible Fluorescent Probe for In Situ Monitoring Redox Imbalance during Mitophagy

Mitophagy is the lysosome-dependent degradation of damaged and dysfunctional mitochondria, which is closely associated with H2O2-related redox imbalance and pathological processes. However, development of fast-responding and highly sensitive reversible fluorescent probes for monitoring of mitochondrial H2O2 dynamics is still lacking. Herein, we report a reversible fluorescent probe (M-HP) that enables real-time imaging of H2O2-related redox imbalance. In vitro studies demonstrated that M-HP had a rapid response and high sensitivity to the H2O2/GSH redox cycle, with a detection limit of 17 nM for H2O2. M-HP was applied to imaging of H2O2 fluctuation in living cells with excellent reversibility and mitochondrial targeting. M-HP reveals an increase in mitochondrial H2O2 under lipopolysaccharide stimulation and a decrease in H2O2 following the combined treatment with rapamycin. This suggests that the level of oxidative stress is significantly suppressed after the enhancement of mitophagy. The rationally designed M-HP offers a powerful tool for understanding redox imbalance during mitophagy.

An ESIPT solvatochromic fluorescent and colorimetric probe for sensitive and selective detection of copper ions in environmental samples and cell lines

Copper is one of the most important transition metals in our body for various physiological functions. An imbalance in the homeostasis of copper in our body can lead to various neurological disorders such as Alzheimer's disease, Parkinson's, and Menkes disease. As a result, there is a need for the detection of excess copper present in the environment and the human system. In this work, we have designed a quinoline-based fluorescent/colorimetric probe (QHS) for rapid and selective detection of copper ions via quenching of fluorescence/color change from yellow to peach which is visible to the naked eye. The probe displayed high selectivity towards copper(II), i.e., Cu(II) in the presence of different metal analytes in water samples. The sensing mechanism of the probe was confirmed by NMR, HRMS, IR spectroscopy, and SEM. The detection limit of Cu(II) ions was found to be 0.493 μM which is lower than the tolerable limit of copper (20 μM) in drinking water as per the EPA. The probe was also utilized for the visualization of Cu(II) in cell lines. The probe was also demonstrated for its application in real-time detection of aqueous samples using portable paper strips.

Visualize intracellular β-galactosidase using an asymmetric near-infrared fluorescent probe with a large Stokes shift

β-galactosidase (β-Gal) is an important biomarker of cell senescence and primary ovarian cancer. Therefore, it is of great significance to construct a near-infrared fluorescent probe with deep tissue penetration and a high signal-to-noise ratio for visualization of β-galactosidase in biological systems. However, most near-infrared probes tend to have small Stokes shifts and low signal-to-noise ratios due to crosstalk between excitation and emission spectra. Using d-galactose residues as specific recognition units and near-infrared dye TJ730 as fluorophores, a near-infrared fluorescence probe SN-CR with asymmetric structure was developed for the detection of β-Gal. The probe has a fast reaction equilibrium time (<12 min) with β-Gal, excellent biocompatibility, near-infrared emission (738 nm), low detection limit (0.0029 U/mL), and no crosstalk between the excitation spectrum and emission spectrum (Stokes shifts 142 nm) of the probe. Cell imaging studies have shown that SN-CR can visually trace β-Gal in different cells and distinguish ovarian cancer cells from other cells.