Molecular Fluorescent Probes for Imaging and Evaluation of Hypochlorite Fluctuations during Diagnosis and Therapy of Osteoarthritis in Cells and in a Mouse Model

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.

Oxidative Dehydroxycyclization of Catechols with o-Mercaptoanilines to Access 1-Hydroxyphenothiazines

The protocol of aerobic oxidative dehydroxycyclization installed in the synthesis of rarely studied 1-hydroxyphenothiazines from catechols and o-mercaptoanilines is presented. Utilizing a natural renewable low-toxicity gallic acid as an organocatalyst, this established transformation proceeded smoothly in an aqueous ethanol solution under mild conditions with good functional group compatibility and up to a 94% isolated yield. This protocol is also characterized by its operational simple workup involving only recrystallization, revealing its sustainability and synthetic practicability.

A triphenylamine-based carbohydrazide hydrazone fluorescent probe for selective detection of hypochlorite and sensing acidic gases

Hypochlorous acid and its hypochlorite are important reactive oxygen species in the body, and are involved in various physiological processes related to immunity; their rapid detection is of great significance. Here, we synthesized a fluorescent probe (TPAS) by condensation of 4-(diphenylamino)benzaldehyde, carbohydrazide, and salicylaldehyde, which can be used for the detection of ClO- in water and sensing of acidic gas in its solid state. The probe showed strong selective recognition of ClO- in acetonitrile and good tolerance to interference ions. There were good linear responses between the intensity of absorbance and fluorescence and the amount of ClO-. The TPAS solid and its paper strips can emit red fluorescence when exposed to volatile acidic vapours. After being treated with NH3, the red fluorescence can be restored to yellow. The response process of TPAS to ClO- and acid gases was characterized using nuclear magnetic resonance, electrospray ionisation mass spectrometry, transmission electron microscopy, and density functional theory calculations. Furthermore, it can be utilized in analyzing ClO- in commercially available bleaching products; the detection results were basically compatible with the labelled values. In addition, the probe is biocompatible and can be applied for imaging ClO- in zebrafish.

A unique phenothiazine-based fluorescent probe using benzothiazolium as a reactivity regulator for the specific detection of hypochlorite in drinking water and living organisms

As a common disinfectant and an essential reactive oxygen species (ROS), hypochlorite (ClO-) plays vital roles in both water treatment and cell metabolism, but its abnormal level can cause serious harm to human health. Therefore, quantifying ClO- level in drinking water and living organisms is extremely significant. Herein, we decorated different cationic heterocycles on phenothiazine core to construct three fluorescent probes for ClO-. According to the results, only benzothiazolium moiety reasonably adjusted the electron cloud density at sulfur atom of phenothiazine core for the specific oxidation with ClO-, thus endowing the prepared probe PT-BT with a perfect selectivity for ClO-. Meanwhile, PT-BT exhibited a low detection limit (38 nM) and a fast response (within 20 s) toward ClO-. Furthermore, this probe was utilized to fabricate a ready-to-use test strip, which could quantitatively measure ClO- level in real water samples by a portable smartphone sensing platform. Notably, PT-BT targeted mitochondria efficiently, and successfully visualized endogenous ClO- in living cells and zebrafish larvae. Especially, PT-BT was able to monitor the dynamic change of ClO- level in inflammatory mice. These results strongly manifested that probe PT-BT was a promising tool for detecting ClO- in drinking water and living organisms.

Fluorescent Biomass-Based Platform for Detection of ClO- in Cells and Water-Soluble Systems

The generation and presence of excessive hypochlorous acid derivative ionic form (ClO-) could cause various diseases, such as arteriosclerosis, DNA damage, and cardiovascular illness. It is a critical need to develop a highly sensitive sensor for reliable detection of ClO- in cells and water-soluble systems. In this work, a hydroxyl group has been introduced into the compound 2-amino-3-(((E)-4-(2-(2-(2-hydroxyethoxy)ethyl)-1,3-dioxo-2,3-dihydro-1H-benzo[de]isoquinolin-6-yl)benzylidene)amino)maleonitrile (NDC) to increase its solubility in water, at the same time, the hydrazone unit was designed as a specific recognition group for the "off-on" fluorescence probe of ClO-. The probe NDC presents high selectivity, sensitivity, anti-interference, and low detection limit (67 nM) for ClO-. The recognition mechanism that ClO- breaks the C=N bond and forms the fluorescent compound 4-(2-(2-(2-hydroxyethoxy)ethyl)-1,3-dioxo-2,3-dihydro-1H-benzo[de]isoquinolin-6-yl)benzaldehyde (ND-3) has been confirmed by time-of-flight mass spectrometry. The probe NDC presents a good performance in the actual test of water samples and can be designed as the test papers for the quick and convenient detection of ClO- range from 0 to 1 μM. Moreover, the practical application was demonstrated by the successful imaging of endogenous and exogenous ClO- in HeLa cells. Our fluorescent biomass-based platform opens vast possibilities for repeatability, sensitivity, and selectivity detection of ClO- in cells and water-soluble systems.

A stable ratiometric fluorescent probe for hypochlorous acid detection and rheumatoid arthritis evaluation

A ratiometric fluorescent probe (MeO-CNPPV Pdots) based on the principle of fluorescence resonance energy transfer (FRET) was designed for hypochlorous acid (HOCl) and rheumatoid arthritis (RA) detection. The presence of HOCl can block the energy transfer from CNPPV to MeOTPATBT, resulting in a ratio change in the fluorescence of Pdots (I600 nm/I680 nm). This strategy provides a valuable paradigm in early RA evaluation.

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.

Monitoring of Hypochlorite Level in Fruits, Vegetables, and Dairy Products: A BODIPY-Based Fluorescent Probe for the Rapid and Highly Selective Detection of Hypochlorite

Hypochlorite/hypochlorous acid (ClO^-/HOCl), among the diverse reactive oxygen species, plays a vital role in various biological processes. Besides, ClO^- is widely known as a sanitizer for fruits, vegetables, and fresh-cut produce, killing bacteria and pathogens. However, excessive level of ClO^- can lead to the oxidation of biomolecules such as DNA, RNA, and proteins, threatening vital organs. Therefore, reliable and effective methods are of utmost importance to monitor trace amounts of ClO^-. In this work, a novel BODIPY-based fluorescent probe bearing thiophene and a malononitrile moiety (BOD-CN) was designed and constructed to efficiently detect ClO^-, which exhibited distinct features such as excellent selectivity, sensitivity (LOD = 83.3 nM), and rapid response (<30 s). Importantly, the probe successfully detected ClO^- in various spiked water, milk, vegetable, and fruit samples. In all, BOD-CN offers a clearly promising approach to describe the quality of ClO^--added dairy products, water, fresh vegetables, and fruits.

Stimulus-Responsive Drug Delivery Nanoplatforms for Osteoarthritis Therapy

Osteoarthritis (OA) is one of the most prevalent age-related degenerative diseases. With an increasingly aging global population, greater numbers of OA patients are providing clear economic and societal burdens. Surgical and pharmacological treatments are the most common and conventional therapeutic strategies for OA, but often fall considerably short of desired or optimal outcomes. With the development of stimulus-responsive nanoplatforms has come the potential for improved therapeutic strategies for OA. Enhanced control, longer retention time, higher loading rates, and increased sensitivity are among the potential benefits. This review summarizes the advanced application of stimulus-responsive drug delivery nanoplatforms for OA, categorized by either those that depend on endogenous stimulus (reactive oxygen species, pH, enzyme, and temperature), or those that depend on exogenous stimulus (near-infrared ray, ultrasound, magnetic fields). The opportunities, restrictions, and limitations related to these various drug delivery systems, or their combinations, are discussed in areas such as multi-functionality, image guidance, and multi-stimulus response. The remaining constraints and potential solutions that are represented by the clinical application of stimulus-responsive drug delivery nanoplatforms are finally summarized.

Fluorescent phenothiazine-fused boron complexes for ratiometric hypochlorite imaging

Fluorescent hypochlorite probes with ratiometric imaging ability are highly desirable for imaging hypochlorite in biological systems. However, it is still challenging to develop new scaffolds for these probes. In this study, we demonstrate that phenothiazine-fused boron complexes are promising scaffolds for the design of ratiometric fluorescent hypochlorite probes. The synthesized complexes based on the scaffold show ultrafast and ratiometric absorption/fluorescence changes for hypochlorite. We also developed an endoplasmic reticulum-targeting probe and demonstrated that it has excellent real-time imaging ability for both endogenous and exogenous hypochlorite in the endoplasmic reticulum of living cells.

H2S-based fluorescent imaging for pathophysiological processes

Hydrogen sulfide (H₂S), as an important endogenous signaling molecule, plays a vital role in many physiological processes. The abnormal behaviors of hydrogen sulfide in organisms may lead to various pathophysiological processes. Monitoring the changes in hydrogen sulfide is helpful for pre-warning and treating these pathophysiological processes. Fluorescence imaging techniques can be used to observe changes in the concentration of analytes in organisms in real-time. Therefore, employing fluorescent probes imaging to investigate the behaviors of hydrogen sulfide in pathophysiological processes is vital. This paper reviews the design strategy and sensing mechanisms of hydrogen sulfide-based fluorescent probes, focusing on imaging applications in various pathophysiological processes, including neurodegenerative diseases, inflammation, apoptosis, oxidative stress, organ injury, and diabetes. This review not only demonstrates the specific value of hydrogen sulfide fluorescent probes in preclinical studies but also illuminates the potential application in clinical diagnostics.

A mitochondrial-targeted near-infrared fluorescent probe for visualizing the fluctuation of hypochlorite acid in idiopathic pulmonary fibrosis mice

Idiopathic pulmonary fibrosis (IPF) is a chronic inflammatory disease destroying lungs irreversibly with high mortality rates. There are challenges in diagnosing IPF and treating it at an early stage. Mounting evidence suggests that hypochlorous acid (HClO) can help in diagnosing inflammation and relevant conditions. Pulmonary fibrosis is linked to the mitochondrial oxidative stress where excessive HClO production is a key molecular mechanism. Measuring mitochondrial HClO levels assists in the investigations of how the mitochondrial oxidative stress affects IPF. Herein, NIR-PTZ-HClO was developed and optimized as a probe for detecting fluctuations in HClO concentrations of cells and mice models through near-infrared (NIR) fluorescence. The probe featured large Stokes shift of 150 nm, NIR turn-on signal at 650 nm, high sensitivity (45-fold) and quick HClO detection (2 s). The probe is selective for HClO in the presence of range of other analytes. NIR-PTZ-HClO visualized both endogenous and exogenous HClO in living cells (RAW264.7, H460 and A549). The probe monitored HClO in mice models with IPF and moreover the HClO profile could be tracked during the IPF process. The probe also detected precipitous decrease in HClO levels in IPF mice treated with OFEV. NIR-PTZ-HClO probe has thus the potential for earlier diagnosis of lung fibrosis, thereby improving the treatment efficacy.

Advances in the Development of Water-Soluble Fluorogenic Probes for Bioimaging of Hypochlorite/Hypochlorous Acid in Cells and Organisms

This mini-review summarizes the development of intracellular fluorogenic probes for biological investigations of hypochlorous acid/hypochlorite (HOCl/OCl^-) in living cells and tissues. Monitoring the formation or effects of reactive oxygen species (ROS) inside living systems is critical in determining their roles in human physiology. HOCl/OCl^- is considered as an important member of the nonradical ROS family for its decisive microbicidal action in the innate immune system. Even though HOCl/OCl^- plays a defensive role in human health, abnormal or overexpression may have detrimental effects on the host physiology leading to many diseases, including neurodegeneration and cancer. In recent years, progress in the development of fluorescent imaging probes for observing HOCl/OCl^- levels in live cells and tissues has been made. Despite considerable advancement, challenges still exist in areas like working solvent/media, pH, response time, buffer selection, emission region, and others. In addition, this account aims to discuss the design strategies and sensing mechanisms of the representative fluorogenic probes for bioimaging of HOCl/OCl^-, endogenously and exogenously. Herein, we also have tried to provide the future direction to develop HOCl/OCl^- specific probes for disease diagnosis with particular attention to the requirement of the recognition group, solvent, and buffer media, which will be beneficial for those working in the domain of biomedical research.

Observation of HOCl generation associated with diabetic cataract using a highly sensitive fluorescent probe

Diagnosis of diabetic cataract (DC) in the early stage is of great significance for drug intervention and surgery circumvention for DC patients. However, the lack of reliable imaging tools greatly limits the diagnosis of early DC. In this context, a fluorescent probe BBPy for hypochlorous acid (HOCl) is presented based on the oxidation of phenothiazine. The probe displays apparent emission enhancement at 562 nm toward HOCl with high selectivity, superb sensitivity (detection limit: 12.6 nM), and rapid response (within seconds). Using the probe, the HOCl generation in diabetic human lens epithelial cells was monitored, as well as the HOCl down-regulation during antioxidant treatment. Therefore, it is proposed that HOCl can be a promising biomarker for DC and fluorescence imaging technique can be regarded as a candidate tool for DC diagnosis.

Fluorescent Quinoline-Based Supramolecular Gel for Selective and Ratiometric Sensing Zinc Ion with Multi-Modes

A gelator 1 containing functional quinoline and Schiff base groups that could form organogels in DMF, DMSO, acetone, ethanol and 1,4-dioxane was designed and synthesized. The self-assembly process of geator 1 was characterized by field emission scanning electron microscopy (FESEM), UV-vis absorption spectroscopy, fluorescence emission spectroscopy, Fourier transform infrared spectroscopy(FTIR), X-ray powder diffraction (XRD) and water contact angle. Under non-covalent interactions, gelator 1 self-assembled into microbelts and nanofiber structures with different surface wettability. Weak fluorescence was emitted from the solution and gel state of 1. Interestingly, gelator 1 exhibited good selectivity and sensitivity towards Zn2+ in solution and gel states along with its emission enhancement and change. The emission intensity at 423 nm of solution 1 in 1,4-dioxane was slightly enhanced, and a new emission peak appeared at 545 nm along with its intensity sequentially strengthened in the titration process. The obvious ratiometric detection process was presented with a limit of detection (LOD) of 5.51 μM. The detection mechanism was revealed by a theoretical calculation and NMR titration experiment, which was that Zn2+ induced the transition from trans- to cis- of molecule 1 and further coordinated with 1. This study will introduce a new method for the construction of functional self-assembly gel sensors for the detection of Zn2+.

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.

Recent development of small-molecule fluorescent probes based on phenothiazine and its derivates

Fluorescence probes, as analytical tools with the ability to perform rapid and sensitive detection of target analytes, have made outstanding contributions to environmental analysis and bioassays. Considering the expanding developments in these areas, fluorophores play a key role in the de-sign of fluorescence probes. Compared to classical fluorophores, phenothiazines with elec-tron-rich characteristics have been widely applied to construct electron donor-acceptor dyes, which exhibit outstanding performance in both fluorimetric and colorimetric analysis. In addition, these probes also exhibit the pronounced ability in both solution and solid-state, achieving portable detection for environmental analysis. In this review, we summarize recent advances in the performance of phenothiazine-based fluorescent probes for detecting various analytes, especially in cations, anions, ROS/RSS, enzyme and other small molecules. The general design rules, response mechanisms and practical applications of the probes are analyzed, followed by a discussion of exiting challenges and future research perspectives. It is hoped that this review will provide a few strategies for the development of phenothiazine-based fluorescent 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.

Recent Progress in Fluorescent Probes for Diabetes Visualization and Drug Therapy

Diabetes has become one of the most prevalent endocrine and metabolic diseases that threaten human health, and it is accompanied by serious complications. Therefore, it is vital and pressing to develop novel strategies or tools for prewarning and therapy of diabetes and its complications. Fluorescent probes have been widely applied in the detection of diabetes due to the fact of their attractive advantages. In this report, we comprehensively summarize the recent progress and development of fluorescent probes in detecting the changes in the various biomolecules in diabetes and its complications. We also discuss the design of fluorescent probes for monitoring diabetes in detail. We expect this review will provide new ideas for the development of fluorescent probes suitable for the prewarning and therapy of diabetes in future clinical transformation and application.

A NIR fluorescent probe for the specific detection of hypochlorite and its application in vitro and in vivo

It is of great necessity to exploit a real-time, highly selective and sensitive method for hypochlorite (ClO^-) detection in both the environment and living systems because of the complex influence of ClO^- on health. In this paper, based on the intramolecular charge transfer (ICT) effect, a NIR fluorescent probe (probe DAB) was designed for the accurate detection of ClO^-, which produced a fluorescence response to ClO^- with high selectivity and rapid response (within 1 min). The probe DAB could determine ClO^- over the linear range of 0-80 μM with a low detection limit of 1.46 μM. And the sensing mechanism between the probe and ClO^- was verified using HPLC and MS. To further prove its practicability, the probe was applied for detecting ClO^- in actual water samples. In addition, owing to its good sensing properties and low cytotoxicity, probe DAB could be expediently applied to visualize ClO^- in living cells and zebrafish, and it is expected to be a useful tool for investigating the detailed functions and mechanisms of ClO^- in living systems.

Activatable Near-Infrared Fluorescent Organic Nanoprobe for Hypochlorous Acid Detection in the Early Diagnosis of Rheumatoid Arthritis

Early diagnosis of rheumatoid arthritis (RA) is crucial to prevent deterioration and improve the prognosis of disease outcome. However, current clinical diagnostic methods are unable to achieve accurate and early detection of RA. In this work, we designed an activatable organic nanoprobe (ONP-CySe) capable of specific and real-time imaging of ClO^- in early RA. ONP-CySe comprises a near-infrared fluorescent selenomorpholine-caged cyanine dye as the sensing component and an amphiphilic triblock copolymer triphenyl phosphine derivative for mitochondria targeting. Our results showed that ONP-CySe successfully detected elevated levels of ClO^- in the mitochondria of macrophages with high selectivity, low limit of detection (31.5 nM), excellent photostability, and good biocompatibility. Furthermore, ONP-CySe can also be used to monitor anti-inflammatory responses and efficacies of RA therapeutics, such as selenocysteine and methotrexate, in BALB/c mouse models. Therefore, our research proposes a universal molecular design strategy for the detection of ClO^-, which holds potential for early diagnosis and drug screening for RA.

Chlorination-induced pKa decrease: an improved strategy to design ratiometric hypochlorite fluorescent probes with ideally high selectivity

Based on the ClO−-triggered chlorination reaction and the subsequent pKa decrease, a two-photon ratiometric ClO− fluorescent probe was designed.

M, Patra M, Butcher RJ, Manjare ST. Selective detection of hypochlorous acid in living cervical cancer cells with an organoselenium-based BOPPY probe

The synthesis and crystal structure of the first selenium-containing BOPPY probe. The probe is selective for exogenous and endogenous HOCl detection in HeLa cells with a “turn-on” fluorescence response.

Two-photon ratiometric fluorescent probe for imaging of hypochlorous acid in acute lung injury and its remediation effect

Acute lung injury (ALI) is a pulmonary inflammatory disease with high morbidity and mortality rates. However, owing to the unknown etiology and rapid progression of the disease, the diagnosis of ALI is full of challenges with no effective treatment. Since the inflammatory response and oxidative stress played vital roles in the development of ALI, we herein developed the largest emission cross-shift (△λ = 145 nm) two-photon ratiometric fluorescent probe of TPRS-HOCl with high selectivity and short response time toward hypochlorous acid (HOCl) for exploring the relevance between the degree of ALI and HOCl concentration in the development process of the disease. In addition, the inhibition effect of HOCl during different treatment periods was also evaluated. Moreover, the tendency of imaging results was basically in accordance with that of hematoxylin and eosin (H&E) staining and the treatment effect became better in the early stage when using N-acetylcysteine (NAC), demonstrating the sensitivity of TPRS-HOCl toward ALI response. Thus, TPRS-HOCl has great potential to diagnose ALI in the early stage and guide for effective treatment.

Graphene Biodevices for Early Disease Diagnosis Based on Biomarker Detection

The early diagnosis of diseases plays a vital role in healthcare and the extension of human life. Graphene-based biosensors have boosted the early diagnosis of diseases by detecting and monitoring related biomarkers, providing a better understanding of various physiological and pathological processes. They have generated tremendous interest, made significant advances, and offered promising application prospects. In this paper, we discuss the background of graphene and biosensors, including the properties and functionalization of graphene and biosensors. Second, the significant technologies adopted by biosensors are discussed, such as field-effect transistors and electrochemical and optical methods. Subsequently, we highlight biosensors for detecting various biomarkers, including ions, small molecules, macromolecules, viruses, bacteria, and living human cells. Finally, the opportunities and challenges of graphene-based biosensors and related broad research interests are discussed.

A Fast-Responsive OFF-ON Near-Infrared-II Fluorescent Probe for In Vivo Detection of Hypochlorous Acid in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a common chronic autoimmune inflammatory disease, and its etiology is closely related to the overproduction of hypochlorous acid (HClO). However, early detection of RA using an activatable near-infrared-II (NIR-II, 1000-1700 nm) fluorescent probe remains challenging. Herein, we first report an "OFF-ON" NIR-II fluorescent probe named PTA (phenothiazine triphenylamine) for imaging HClO in deep-seated early RA. Electron-rich phenothiazine in the core of PTA was utilized as both an HClO-recognition moiety and a precursor of electron acceptors, displaying a typical donor-acceptor-donor structure with excellent NIR-II emission at 936/1237 nm once reacted with HClO. The probe PTA exhibited good water solubility, high photostability, and rapid response capability toward HClO within 30 s. Moreover, it was able to sensitively and specifically detect exogenous and endogenous HClO in living cells in both visible and NIR-II windows. Notably, PTA enabled the sensitive and rapid visualization of HClO generation in an inflammatory RA mouse model, showing a 4.3-fold higher NIR-II fluorescence intensity than that in normal hindlimb joints. These results demonstrate that PTA holds great promise as a robust platform for diagnosis of HOCl-mediated inflammatory disorders.

Ratiometric Detection of Hypochlorous Acid in Brain Tissues of Neuroinflammation and Maternal Immune Activation Models with a Deep-Red/Near-Infrared Emitting Probe

Reactive oxygen species (ROS) produced by an inflammatory response in the brain are associated with various neurological disorders. To investigate ROS-associated neuroinflammatory diseases, fluorescent probes with practicality are in demand. We have investigated hypochlorous acid, an important ROS, in the brain tissues of neuroinflammation and maternal immune activation (MIA) model mice, using a new fluorescent probe. The probe has outstanding features over many known probes, such as providing two bright ratio signals in cells and tissues in deep-red/near-infrared wavelength regions with a large spectral separation, in addition to being strongly fluorescent, photo- and chemo-stable, highly selective and sensitive, fast responding, and biocompatible. We have found that the level of hypochlorous acid in the brain tissue of a neuroinflammatory mouse model was higher (2.7-4.0-fold) compared with that in normal brain tissue. Furthermore, the level of hypochlorous acid in the brain tissue of a MIA mouse model was higher (1.2-1.3-fold) compared with that in the normal brain tissue. The "robust" probe provides a practical tool for studying ROS-associated neurological disorders.

Quinoline-based fluorescent probe for the detection and monitoring of hypochlorous acid in a rheumatoid arthritis model

The development of effective bioanalytical methods for the visualization of hypochlorous acid (HOCl) in situ in rheumatoid arthritis (RA) directly contributes to better understanding the roles of HOCl in this disease. In this work, a new quinoline-based fluorescence probe (HQ) has been developed for the detection and visualization of a HOCl-mediated inflammatory response in a RA model. HQ possesses a donor–π–acceptor (D–π–A) structure that was designed by conjugating p-hydroxybenzaldehyde (electron donor) and 1-ethyl-4-methylquinolinium iodide (electron acceptor) through a C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C double bond. In the presence of HOCl, oxidation of phenol to benzoquinone led to the red-shift (93 nm) of the adsorption and intense quenching of the fluorescence emission. The proposed response reaction mechanism was verified by high performance liquid chromatography (HPLC) and high-resolution mass spectroscopy (HRMS) titration analysis. The remarkable color changes of the HQ solution from pale yellow to pink enabled the application of HQ-stained chromatography plates for the “naked-eye” detection of HOCl in real-world water samples. HQ featured high selectivity and sensitivity (6.5 nM), fast response time (<25 s) to HOCl, reliability at different pH (3.0 to 11.5) and low cytotoxicity. HQ's application in biological systems was then demonstrated by the monitoring of HOCl-mediated treatment response to RA. This work thus provided a new tool for the detection and imaging of HOCl in inflammatory disorders.

A quinoline-based fluorescent probe (HQ) has been designed and synthesized for the monitoring of HOCl-mediated treatment response of a rheumatoid arthritis (RA) model and “naked-eye” detection of HOCl in real water samples.

Synthesis of charged chitosan nanoparticles as functional biolubricant

Osteoarthritis has been a major disease in recent years, which is mainly related to the breakdown of the lubrication function of the cartilage sliding interface, along with the inflammation of the joint capsule. In this paper, one kind of novel biomimetic nanoparticles (NPs) lubricant, named CS-PS, is synthesized through chemically grafting hydrophilic sulfonic acid (SO₃^-) groups onto the surface of biocompatible and biodegradable chitosan (CS) NPs. Compared with control CS NPs, the as-synthesized CS-PS NPs exhibits excellent hydration and stability because of negatively charged surface zeta potential, along with extraordinary lubrication performance in water for realizing a super-low friction coefficient (COF) as ∼0.01 at the sliding interface of PDMS elastomer-Ti₆Al₄V disk. Correspondingly, the CS-PS NPs can also be used as a drug carrier for aspirin, which presents very good drug loading and release behavior in PBS (pH = 7.4). MCS cells culture experiment proves that this kind of novel lubricant is nontoxic and biocompatible, for which may be expected to use as potential articular injective material for the treatment of osteoarthritis.

Tackling the Selectivity Dilemma of Benzopyrylium-Coumarin Dyes in Fluorescence Sensing of HClO and SO2

Benzopyrylium-coumarin fluorescent probes for sensing hypochlorous acid (HClO) or sulfur dioxide (SO₂) are unable to distinguish between HClO and SO₂ because the two compounds can react with the 4-position of benzopyrylium-coumarin dyes through the nucleophilic attack. In the current work, we introduced a phenoxazine moiety to the benzopyrylium-coumarin dye to synthesize a new fluorescent probe PBC1, which can dually sense HClO and SO₂ and generate distinct fluorescence signals with rapid response time and high sensitivity and selectivity. Moreover, probe PBC1 was also successfully utilized to detect intracellular HClO and SO₂ in HeLa cells and zebrafish.

Microfluidics-Based Sensing of Biospecies

Over the past decades, microfluidic devices based on many advanced techniques have aroused widespread attention in the fields of chemical, biological, and analytical applications. Integration of microdevices with a variety of chip designs will facilitate promising functionality. Notably, the combination of microfluidics with functional nanomaterials may provide creative ideas to achieve rapid and sensitive detection of various biospecies. In this review, focused on the microfluids and microdevices in terms of their fabrication, integration, and functions, we summarize the up-to-date developments in microfluidics-based analysis of biospecies, where biomarkers, small molecules, cells, and pathogens as representative biospecies have been explored in-depth. The promising applications of microfluidic biosensors including clinical diagnosis, food safety control, and environmental monitoring are also discussed. This review aims to highlight the importance of microfluidics-based biosensors in achieving high throughput, highly sensitive, and low-cost analysis and to promote microfluidics toward a wider range of applications.

A lysosome-targetable two-photon excited near-infrared fluorescent probe for visualizing hypochlorous acid-involved arthritis and its treatment

Lysosome of phagocyte is the main site of hypochlorous acid (HClO) production, and HClO can be employed as the biomarker for the diagnosis and treatment evaluation of arthritis. In recent years, developing fluorescent probes for lysosomal HClO has attracted considerable attention, but most of them still have some defects, such as autofluorescence, phototoxicity and photobleaching because of their excitation and emission located in short-wavelength region. Due to the advantages of two-photon fluorescent probes with near-infrared emissions, a lysosome-targetable two-photon fluorescent probe (Lyso-TP-HClO) with a near-infrared emission was reported in this paper. Lyso-TP-HClO has a high selectivity and a high sensitivity to HClO in the linear range (10.0 × 10^-8 to 5.0 × 10^-6 M), with a detection limit of 3.0 × 10^-8 M. Due to the two-photon excited near-infrared emission, Lyso-TP-HClO has excellent imaging performances, such as small autofluorescence, excellent photostability, and large imaging depth. Furthermore, Lyso-TP-HClO was successfully employed for visualizing lysosomal HClO in bacteria-infected cells. At last, we have successfully used Lyso-TP-HClO to image the arthritis and evaluate the treatment of arthritis in mice. All the results confirm that Lyso-TP-HClO is a useful chemical tool for imaging of lysosomal HClO, the diagnosis of arthritis, and treatment evaluation of arthritis.

A simple pyridine-based highly specific fluorescent probe for tracing hypochlorous acid in lysosomes of living cells

A simple pyridine-based highly specific fluorescent probe was constructed to trace hypochlorous acid in lysosomes of living cells.