A simple mitochondria-immobilized fluorescent probe for the detection of hydrogen peroxide.

Hydrogen peroxide (H2O2), as one of reactive oxygen species (ROS) widely present in the human body, is involved in a variety of physiological activities. Many human diseases are associated with abnormal levels of H2O2 in the body. Mitochondria are the main organelles producing H2O2 in the human body, and monitoring the level of H2O2 in mitochondria can help to deepen the understanding of the detailed functions of H2O2 in physiological activities. However, due to the highly dynamic nature of the cells, real-time quantitative monitoring of H2O2 levels in mitochondria remains an ongoing challenge. Herein, a novel highly immobilized mitochondria-targeting fluorescent probe (QHCl) for detection of H2O2 was reasonably constructed based on quinolinium dye containing benzyl chloride moiety. Spectral experimental results demonstrated QHCl possessed outstanding selectivity toward H2O2 (λex/em = 380/513 nm). In addition, QHCl can quantitatively detect H2O2 in the concentration range of 0-20 µM with excellent sensitivity (LOD = 0.58 µM) under the PBS buffer solution (10 mM, pH = 7.4). Finally, bioimaging experiments demonstrated that the probe QHCl was able to be used for accurately detecting both endogenous and exogenous H2O2 in the mitochondria of living cells and zebrafish by its unique mitochondrial immobilization.

Exploration of a new approach for detection of nitrite with hydroxyl radical fluorescence probe in aqueous solutions.

Nitrite (NO2-) has been widely recognized by the international community as an important substance affecting water quality safety and human health, and the detection of NO2- has always been a hot topic for researchers. Fluorescent probe method is an emerging and ideal way for detecting NO2-. Due to the high dependence of the reported reactive NO2- fluorescent probes on strong acidic systems, using the idea of photochemistry, a fluorescence analysis method for detecting NO2- was proposed in this work to change the necessity of strong acidic solutions in probe detection process. A 365 nm UV-LED lamp was used to irradiate NO2- in aqueous solution to convert it into hydroxyl radicals (HO·), and capture the photodegradation product of NO2- using coumarin-3-carboxylic acid as probe 3-CCA that can react with HO· to generate only one type of strong fluorescent substance. This probe has excellent photostability, selectivity, and anti-interference ability, and can realize the quantitative detection of NO2- (0-15 µM) in pure aqueous solution with pH of 7.4. In addition, its application in actual water samples is also satisfactory, with a recovery rate of (85.91 %-107.30 %). Importantly, we hope that this photolysis strategy can open up the novel thinking to develop suitable fluorescent probes for the analysis and detection of some hardly detected analytes.

Recent advances in small-molecule fluorescent probes with the function of targeting cancer receptors.

Cancer is "the sword of Damocles" that threatens human life and health. Therefore, the diagnosis and treatment of cancer have been receiving much attention. Many overexpressed receptors on the surface of cancer cells provide us with an effective way to specifically identify the cancer cells, and receptor targeting strategies are becoming one of the hot ideas to enhance the ability of fluorescent probes to target tumors. Fluorescent probes connected to ligands are targeted at cancer cell surfaces through receptor-mediated endocytosis. Receptor-targeting probes can image and track cancer cells, determine tumor boundaries, monitor deep lesions, and play a role in clinical medicine, such as fluorescent imaging-guided surgery. In this review, based on the perspective of small molecule fluorescent probes, we reviewed the design ideas, photophysical properties, and applications of receptor-targeting probes for detecting biomarkers in imaging and tracing cancer cells and prospected the future developmental direction of such probes. We hope that this review will provide more ideas for the design and development of active targeting probes for receptors and lead to more applications in the medical field.

Multifunctional Theranostic Probe Based on the Pim-1 Kinase Inhibitor with the Function of Tracking pH Fluctuations during Treatment.

Currently, kinase inhibitors have been applied in the diagnosis or treatment of cancer with their unique advantages. It is of great significance to develop some comprehensive theranostic reagents based on kinase inhibitors to improve the performance of reagents for biomedical applications. Besides, tracking changes in the intracellular environment (e.g., pH) during cancer development and drug delivery is also critical for cancer research and treatment. Therefore, it is an urgent desire to design some novel multifunctional reagents based on kinase inhibitor strategies that can trace changes in the microenvironment of cancer cells. In this paper, a multifunctional theranostic reagent based on Pim-1 kinase inhibitor 5-bromobenzofuran-2-carboxylic acid is proposed. The theranostic probe binds to tumor-specific Pim-1 kinase, releases strong fluorescence, and produces cytotoxicity, thus achieving cell screening and killing effects. Furthermore, the probe can specifically target lysosomes and sensitively respond to pH. It can be used to track the pH changes in the intracellular environment under conditions of autophagy and external stimulation, as a visual tool to monitor pH fluctuations during cancer treatment. In conclusion, this simple but multifunctional theranostic reagent proposed in this work is expected to provide a promising method for cancer diagnosis and therapy.

A reversible and ratiometric fluorescent probe based on rhodol derivative with an ESIPT unit for monitoring copper ion content and in situ evaluation of related drugs in cells.

The amount of copper ions in the environment has an immediate effect on ecology and food safety, Menkes syndrome and Wilson's disease cause accumulation and deficiency of copper ions in the body, respectively, and neurodegenerative diseases are also closely related to copper ion levels. However, the current copper ion detection technology has a high cost, complex operation, and other disadvantages. In this study, a ratiometric fluorescent probe (RB-DH) was rationally constructed to detect copper ions by coupling benzothiazole to rhodol derivatives. It can be used to determine copper ion concentrations in water samples, agricultural products, cells, and zebrafish. Importantly, due to the reversible response of RB-DH to copper ions, the fluctuation of intracellular copper ion content during the release of copper ion-related drugs (Copper gluconate and D-penicillamine) was successfully monitored with RB-DH for the first time. This study demonstrates RB-DH's potential application in the evaluation of related drug release effects and serves as a guide for the establishment of portable detection techniques for other important substances.

A novel GSH-activable theranostic probe containing kinase inhibitor for synergistic treatment and selective imaging of tumor cells.

Theranostic probe is becoming a powerful tool for diagnosis and treatment of cancer. Although some theranostic probes have been successfully developed, there is still a great room for improvement in sensitive diagnosis and efficient treatment. Herein, we developed a novel GSH-activable theranostic probe NC-G, which uses 1,8-naphthalimide-4-sulfonamide as a fluorescence imaging group and crizotinib as a highly toxic kinase inhibitor to tumor cells. The probe not only has high sensitivity (DL = 74 nM) and specificity, but also can detect GSH sensitively in cells and zebrafish. In addition, probe NC-G can not only show more obvious fluorescence in tumor cells to achieve sensitive diagnosis of tumor cells, but also release the inhibitor crizotinib to achieve high toxicity to tumor cells. It is worth noting that the consumption of GSH can cause oxidative stress response of cells and the release of SO2 can induce cell apoptosis during the recognition process of the probe and GSH. Thus, the synergistic effect of crizotinib, GSH depletion, and SO2 release provides a highly effective therapeutic feature for tumor cells. Therefore, probe NC-G can serve as an excellent theranostic probe for sensitive imaging and highly effective treatment of tumor cells.

H2S-activated fluorescent probe enables dual-channel fluorescence tracking of drug release in tumor cells.

Nowadays, the selective release of therapeutic drugs into tumor cells has become an important way of tumor treatment due to the high side effects of chemotherapy drugs. As one of the gas mediators, hydrogen sulfide (H2S) is closely related to cancer. Due to the high content of H2S in tumor cells, it can be used as a signaling molecule that triggers the release of drugs to achieve the selective release of therapeutic drugs. In addition, dual-channel fluorescence imaging technology can be better applied to monitor the drug delivery process and distinguish the state before and after drug release, so as to better track the effect of drug therapy. Based on this, we used NBD amines (NBD-NHR) as the recognition group of H2S and connected the tyrosine kinase inhibitor crizotinib to construct an activated dual-channel fluorescent probe CZ-NBD. After the probe enters the tumor cells, it consumes H2S and releases crizotinib, which is highly toxic to the tumor cells. Importantly, the probe displays significant fluorescence changes in different cells, enabling not only the screening of tumor cells, but also tracking and monitoring drug release and tumor cell activity. Therefore, the construction of probe CZ-NBD provides a new strategy for drug release monitoring in tumor cells.

Portable ratiometric fluorescence analytical device for copper ions based on smartphone in environment and living organisms.

The concentration of copper ions (Cu2+) in the environment is closely related to water quality, food, and biological health. As an indispensable metal element for the human body, its content is closely related to many diseases. However, the current detection methods for Cu2+ have some limitations, such as complicated operations and unfavorable on-site analysis. Therefore, this work constructs a novel ratiometric fluorescent probe (QLP), which has the advantages of rapid response, good anti-interference ability and high sensitivity. It has been successfully used for the detection of Cu2+ in water samples, soil, and food. In addition, low cytotoxicity and strong tissue penetration make it suitable for the detection of Cu2+ in living cells and zebrafish, offering a chemical tool for exploring the physiological and pathological processes related to Cu2+. It is important to use probe QLP and portable UV lamp to create an easy-to-operate Cu2+ detection platform, which can quickly detect Cu2+ on-site by combining with a smartphone. This work not only provides a detection tool for on-site analysis of Cu2+, but also provides a reference strategy for the development of on-site detection methods for other environmental pollutants.

Rational design of a water-soluble TICT-AIEE-active fluorescent probe for mercury ion detection.

Considering that mercury ions (Hg2+) have long been a threat to human health and the environment due to their persistence, mobility and bioenrichment, the detection and removal of Hg2+ is of great significance. Therefore, a simple water-soluble naphthalimide derived fluorescent dye with AIEE characteristics was reasonably constructed based on twisted intramolecular charge transfer (TICT) mechanism, a series of probes were synthesized to demonstrate this mechanism. The probe NIDEA (naphthalimide-diethanolamine) bonding Hg2+ through the specific combination of the N-unsubstituted naphthalimide group and Hg2+ to form a classic "imide-Hg-imide" structure. Moreover, the introduction of diethanolamine moiety enhanced the water-solubility of the probe, and also made the dye molecule possess the feature of AIEE. The fluorescence titration experiment showed that there were two good linear relationships between the fluorescence intensity of the probe NIDEA and the concentration of Hg2+ in the range of 0-2.5 µM and 2.5-7.5 µM, and the limit of detection was 46.7 nM. Also, the probe could detect Hg2+ in aqueous solution sensitively, ensuring its application in the actual water sample in the environment and living cells. At the same time, NIDEA can be used to detect Hg2+ by Tyndall effect (TE) without limitation of instrument and technology, the limit of detection was 20.9 nM. Furthermore, this paradigm by introduction of the highly effective TICT structure supports a promising methodology for the construction of simple water-soluble AIE/AIEE-active probes.

In Situ Observation of Lysosomal Hypobromous Acid Fluctuations in the Brain of Mice with Depression Phenotypes by Two-Photon Fluorescence Imaging.

Excessive oxidative stress is the main cause of neurotransmitter metabolism disorder in the brain with depression. Lysosomal hypobromic acid (HOBr) is an important reactive oxygen species produced in oxidative stress. Its abnormal content can lead to macromolecular damage and neurodegenerative diseases. However, due to the high reactivity and low concentration of HOBr and the lack of in situ imaging methods, the role of HOBr in depression is not clear. Herein, based on the HOBr-initiated aromatic substitution of a tertiary amine, we developed a novel two-photon (TP) fluorescence probe (NH-HOBr) for real-time visual monitoring of trace HOBr in living systems. NH-HOBr introduces N-(2-aminoethyl)-morpholine as a new recognition receptor for HOBr and a targeting group for lysosomes. It not only has excellent selectivity compared with other biomolecules (including hypochlorous acid), fast response (≤5 s) and high sensitivity (LOD = 15 nM) but also realizes sensitive detection of HOBr in cells, zebrafish, and mice tissues. It is worth noting that the in situ TP fluorescence imaging of mouse brain reveals the positive correlation between HOBr content and depression phenotype for the first time, providing strong direct evidence for the relationship between oxidative stress and depression. This work can provide reference to further study depression and the pathological mechanism of HOBr. In addition, HOBr-initiated aromatic substitution of a tertiary amine provides a new idea for the construction of specific and sensitive HOBr probes.

A novel ratiometric fluorescent probe for the detection of nickel ions in the environment and living organisms.

Nickel resources are abundant in the world, and the application of nickel in production and life is more and more extensive. However, excessive nickel entering the environment will not only cause environmental pollution but also seriously endanger plants, animals and human health. Nickel compounds are carcinogenic and have been classified as a class 1 carcinogen. Nickel mainly exists in the form of divalent ions in the environment. However, there are few simple and effective methods for the detection of nickel ions, and these methods still have certain limitations. At present, the mechanisms of nickel influence in organisms are also unclear. Therefore, we constructed a ratiometric fluorescent probe Ra-Ni, which can achieve its own self-calibration and avoid the interference of other factors, thereby realizing the specific identification of nickel ions. The probe can detect nickel ions sensitively with a detection limit as low as 26.2 nM and can respond in a short time (< 2 min), which proves the great potential of the probe in the detection of nickel ions. At the same time, Ra-Ni has also been successfully used for imaging nickel ions in living cells and zebrafish, providing an effective tool for the study of physiological and pathological processes. The detection effect of nickel ions in actual water sample is also satisfactory, which further demonstrates the practicability of Ra-Ni in environmental applications.

Concise Biothiol-Activatable HPQ-NBD Conjugate as a Targeted Theranostic Probe for Tumor Cells.

Cancer, as a malignant tumor, seriously endangers human health. The study of cancer diagnosis and therapy has great practical significance. The development of theranostic agents has become a very important research topic. Nevertheless, some existing agents still have imperfections, such as complex structures and difficult syntheses. Therefore, it is urgent for researchers to develop simple novel theranostic agents. In this study, the precipitated fluorophore HAPQ was used as a simple drug molecule for the first time and combined with NBD-Cl to construct a simple and efficient theranostic probe (HAPQ-NBD). The theranostic probe can distinguish between tumor cells and normal cells based on the higher levels of biothiol in tumor cells. In addition, the probe can use biothiol as a control switch to release higher levels of precipitated fluorophore HAPQ in tumor cells, leading to selective high toxicity to tumor cells, thus achieving the goal of selectively killing tumor cells. The construction of probe HAPQ-NBD provides a practical tool for the diagnosis and therapy of cancer. It is expected that the development and utilization of precipitated fluorophore will provide a new method and strategy for cancer diagnosis and therapy.

A new-type HOCl-activatable fluorescent probe and its applications in water environment and biosystems.

The outbreak and spread of Corona Virus Disease 2019 (COVID-19) has led to a significant increase in the consumption of sodium hypochlorite (NaOCl) disinfectants. NaOCl hydrolyzes to produce hypochlorous acid (HOCl) to kill viruses, which is a relatively efficient chlorine-based disinfectant commonly used in public disinfection. While people enjoy the convenience of NaOCl disinfection, excessive and indiscriminate use of it will affect the water environment and threaten human health. Importantly, HOCl is an indispensable reactive oxygen species (ROS) in human body. Whether its concentration is normal or not is closely related to human health. Excessive production of HOCl in the body contributes to some inflammatory diseases and even cancer. Also, we noticed that the concentration of ROS in cancer cells is about 10 times higher than that in normal cells. Herein, we developed a HOCl-activatable biotinylated dual-function fluorescent probe BTH. For this probe, we introduced biotin on the naphthalimide fluorophore, which increased the water solubility and enabled the probe to aggregate in cancer cells by targeting specific receptor overexpressed on the surface of cancer cell membrane. After reacting to HOCl, the p-aminophenylether moiety of this probe was oxidatively removed and the fluorescence of the probe was recovered. As expected, in the PBS solution with pH of 7.4, BTH could give full play to the performance of detecting HOCl, and it has made achievements in detecting the concentration of HOCl in actual water samples. Besides that, BTH had effectively distinguished between cancer cells and normal cells through a dual-function discrimination strategy, which used biotin to enrich the probe in cancer cells and reacted with overexpressed HOCl in cancer cells. Importantly, this dual-function discrimination strategy could obtain the precision detection of cancer cells, thereby offering assistance for improving the accuracy of early cancer diagnosis.

A new isothiocyanate-based Golgi-targeting fluorescent probe for Cys and its bioimaging applications during the Golgi stress response.

When the cell environment changes or is stimulated, the Golgi apparatus will respond to the corresponding stress, through the opening of related pathways, the expression of corresponding substances can be promoted or inhibited to achieve the purpose of controlling cell redox homeostasis and reducing cytotoxicity. Intuitive analysis of the changes in the content of various substances in the process of stress has important guiding value for the further study of stress response, drug evaluation and clinical diagnosis. Therefore, for the Cys overexpressed during the oxidative stress of the Golgi apparatus, we developed a specific and sensitive fluorescent probe (Gol-NCS) to visually monitor the biologically important Cys in real time. The probe has low cytotoxicity and shows great potential in cell and zebrafish imaging, it can detect the changes of endogenous and exogenous cysteine. It is important to explore the synthetic pathway of Cys during Golgi stress by using the Golgi targeting performance of the probe Gol-NCS. It is confirmed by fluorescence imaging for the first time that the activity of CSE enzyme plays a decisive role in the formation of Cys. Therefore, probe Gol-NCS with excellent photochemical properties is expected to provide help for the research on the involvement of Cys in Golgi stress.

Rational design of a fluorescent probe and its applications of imaging and distinguishing between exogenous and endogenous H2S in living cells.

Hydrogen sulfide (H2S), a recognized environmental pollutant, comes from a wide range of sources. For example, H2S will be produced in the process of plant protein corruption, the decomposition of domestic sewage and garbage, food processing (wine brewing), etc. and once the concentration is too high, it will cause significant damage of environment and human body. Besides H2S is an important gas signal molecule in vivo, which can be transferred through lipid membrane. Its existence level is closely related to many diseases. If we can "visually" trace the transmembrane transmission of hydrogen sulfide, it will be very helpful for the study of oxidative stress processes, cell protection, signal transduction and related diseases closely related to H2S. Although some probes can detect H2S in environment, cytoplasm and organelles, there are few reports on the release and internalization of H2S. In this work, we report a H2S fluorescence probe that can retain on the cell membrane, named PCM. The probe PCM can not only detect endogenous and exogenous H2S, but also distinguish them, this provides a general strategy for the construction of probes to detect other biomarkers. In addition, PCM has been successfully applied to the detection of endogenous and exogenous H2S in zebrafish, which has the potential to become a new chemical tool and provide help for the research of H2S-related diseases.

An Integrated Fluorescent Probe for Ratiometric Detection of Glutathione in the Golgi Apparatus and Activated Organelle-Targeted Therapy.

Cancer is a serious threat to human health, and there is an urgent need to develop new treatment methods to overcome it. Organelle targeting therapy, as a highly effective and less toxic side effect treatment strategy, has great research significance and development prospects. Being an essential organelle, the Golgi apparatus plays a particularly major role in the growth of cancer cells. Acting as an indispensable and highly expressed antioxidant in cancer cells, glutathione (GSH) also contributes greatly during the Golgi oxidative stress. Therefore, it counts for much to track the changes of GSH concentration in Golgi for monitoring the occurrence and development of tumor cells, and exploring Golgi-targeted therapy is also extremely important for effective treatment of cancer. In this work, we designed and synthesized a simple Golgi-targeting fluorescent probe GT-GSH for accurately detecting GSH. The probe GT-GSH reacting with GSH decomposes toxic substances to Golgi, thereby killing cancer cells. At the same time, the ratiometric fluorescent probe can detect the concentration changes of GSH in Golgi stress with high sensitivity and selectivity in living cells. Therefore, such a GSH-responsive fluorescent probe with a Golgi-targeted therapy effect gives a new method for accurate treatment of cancer.

A novel fluorescent probe for detecting hydrogen sulfide in osteoblasts during lipopolysaccharide-mediated inflammation under periodontitis.

Periodontitis, one of the most common chronic inflammatory diseases, affects the quality of life. Osteogenesis plays an important role in the disease. There is a connection between hydrogen sulfide (H2S) and periodontitis, but according to the study has been published, the precise role of H2S in inflammation remains in doubt. The main reason for the lack of research is that H2S is an endogenous gasotransmitter, difficult to discern through testing. So, we synthesized a novel fluorescence probe which can detect H2S in vitro. By using the novel H2S fluorescence probe, we found that H2S changes in osteoblasts mainly by cystathionine-γ-lyase, and H2S increases under LPS stimulation. H2S could be a potential marker for diagnosis of inflammatory diseases of bone, and might help deepen studies of the changes of H2S level and promote the progression on the researches about pathogenesis of periodontitis.

A simple sensitive ratiometric fluorescent probe for the detection of mercury ions in living cells and zebrafish.

Mercury, as a highly toxic heavy metal, can cause very serious harm to human health and even death in severe cases. Therefore, we synthesized a novel ratiometric fluorescent probe for detecting mercury ions, with mercaptoethanol as the recognition receptor. Probe CMER could determine mercury ions in 0-1.6 µM and the detection limit is 7.6 nM. Moreover, CMER manifested a fast response for Hg2+ (within 5 s) and simultaneously observed that the color changed from light yellow to orange by naked eye. In addition to these preeminent spectral properties, the probe also had satisfactory bioimaging results in RAW 264.7 macrophage cells and zebrafish.

A coumarin-based fluorescent probe for Hg2+ and its application in living cells and zebrafish.

Mercury (Hg) is a heavy metal with high toxicity and easy migration; it can be enriched through the food chain, and cause serious threats to the natural environment and human health. So, the development of a method that can be used to detect mercury ions (Hg2+ ) in the environment, in cells, and in organisms is very important. Here, a new 7-hydroxycoumarin-derived carbonothioate-based probe (CC-Hg) was designed and synthesized for detection of Hg2+ . After addition of Hg2+ , a large fluorescence enhancement was observed due to the formation of 7-hydroxyl, which reinforced the intramolecular charge transfer process. The CC-Hg probe had good water solubility and selectivity. Moreover, the probe was able to detect Hg2+ quantitatively over the concentration range 0-2 µM and with a detection limit of 7.9 nM. Importantly, we successfully applied the probe to detect Hg2+ in water samples, in living cells, and in zebrafish. The experimental results demonstrated its potential value in practical applications.

A new phenylsulfonamide-based Golgi-targeting fluorescent probe for H2S and its bioimaging applications in living cells and zebrafish.

We have synthesized a simple Golgi-targeting H2S fluorescent probe which can detect endogenous and exogenous H2S in cells and zebrafish. In addition, this probe provides a new chemical tool for the detailed study of generation pathways of H2S under Golgi stress response.