Monitoring the Fluctuation of Hydrogen Peroxide in Diabetes and Its Complications with a Novel Near-Infrared Fluorescent Probe

An activatable "AIE + ESIPT" fluorescent probe for dual-imaging of lipid droplets and hydrogen peroxide in drug-induced liver injury model

BACKGROUND

Drug-induced liver injury (DILI) is one of the most common liver diseases. The crucial role of lipid droplets (LDs) and hydrogen peroxide (H2O2), two important biomarkers in the pathophysiology of DILI, has spurred considerable efforts to accurately visualize H2O2 and LDs for elucidating their functions in the progression of DILI. However, construction of a single fluorescent probe that is able to simultaneously image H2O2 and LDs dynamics remains to be a challenging task. Therefore, it is of great demand to develop a novel fluorescent probe for tracking the LDs status and H2O2 fluctuation in drug-induced liver injury.

RESULTS

We developed an "AIE + ESIPT" fluorescent probe TPEHBT for dual-imaging of LDs and H2O2 during DILI process. TPEHBT displayed greatly enhanced fluorescent response to H2O2 by generating an excited state intramolecular proton transfer (ESIPT) fluorophore TPEHBT-OH with aggregation induced emission (AIE) properties. TPEHBT exhibits high selectivity, sensitivity (LOD = 4.73 nM) and large Stokes shift (320 nm) to H2O2. Interestingly, TPEHBT can light up LDs with high specificity. The probe was favorably applied in the detection of endogenous and exogenous H2O2 in living cells, and notably in the simultaneous real-time visualization of H2O2 generation and LDs accumulation during DILI process. Moreover, TPEHBT was able to image H2O2 generation in zebrafish animal model with APAP-induced liver injury.

SIGNIFICANCE

For the first time, probe TPEHBT was applied in the dual-imaging of H2O2 fluctuation and LDs status in APAP-induced liver injury model in vitro and in vivo. The present findings strongly suggest that TPEHBT is a promising tool for monitoring H2O2 and LDs dynamics in DILI progression.

A near-infrared ratiometric fluorescent probe for the sensing and imaging of sulfur dioxide derivatives in living systems

As a reactive sulfur species, sulfur dioxide (SO2) and its derivatives play crucial role in various physiological processes, which can maintain redox homeostasis at normal levels and lead to the occurrence of many diseases at abnormal levels. So, the development of a suitable fluorescent probe is a crucial step in advancing our understanding of the role of SO2 derivatives in living organisms. Herein, we developed a near-infrared fluorescent probe (SP) based on the ICT mechanism to monitor SO2 derivatives in living organisms in a ratiometric manner. The probe SP exhibited excellent selectivity, good sensitivity, fast response rate (within 50 s), and low detection limit (1.79 µM). In addition, the cell experiment results suggested that the SP has been successfully employed for the real-time monitoring of endogenous and exogenous SO2 derivatives with negligible cytotoxicity. Moreover, SP was effective in detecting SO2 derivatives in mice.

A ratiometric two-photon fluorescent probe for the quantification of nitroreductase in hypoxic neurons

We developed a novel ratiometric two-photon fluorescent probe for the selective and precise detection of nitroreductase (NTR) in neurons. Using this probe, we found that hypoxic stimulation could up-regulate endogenous NTR levels.

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.

Frontiers in fluorescence imaging: tools for the in situ sensing of disease biomarkers

Fluorescence imaging has been recognized as a powerful tool for the real-time detection and specific imaging of biomarkers within living systems, which is crucial for early diagnosis and treatment evaluation of major diseases. Over the years, significant advancements in this field have been achieved, particularly with the development of novel fluorescent probes and advanced imaging technologies such as NIR-II imaging, super-resolution imaging, and 3D imaging. These technologies have enabled deeper tissue penetration, higher image contrast, and more accurate detection of disease-related biomarkers. Despite these advancements, challenges such as improving probe specificity, enhancing imaging depth and resolution, and optimizing signal-to-noise ratios still remain. The emergence of artificial intelligence (AI) has injected new vitality into the designs and performances of fluorescent probes, offering new tools for more precise disease diagnosis. This review will not only discuss chemical modifications of classic fluorophores and in situ visualization of various biomarkers including metal ions, reactive species, and enzymes, but also share some breakthroughs in AI-driven fluorescence imaging, aiming to provide a comprehensive understanding of these advancements. Future prospects of fluorescence imaging for biomarkers including the potential impact of AI in this rapidly evolving field are also highlighted.

A mitochondria-targeted fluorescent probe for discrimination of biothiols by dual-channel imaging in living cells and zebrafish

Biothiols, including cysteine (Cys), homocysteine (Hcy), and glutathione (GSH), play distinct yet crucial roles in various mitochondrial physiological activities. However, due to their similar chemical structures, distinguishing and detecting Cys/Hcy/GSH poses a considerable challenge. In this study, we developed a dual-channel, mitochondrial-targeted fluorescent probe termed QX-NBD, designed specifically for discriminating Cys/Hcy from GSH. The incorporation of a quinolinium group endowed the probe with excellent mitochondrial targeting capabilities. This functionality arose from the positively charged group's ability to selectively bind to negatively charged mitochondrial membranes through electrostatic interactions. Additionally, the ether bond between 4-chloro-7-nitro-1,2,3-benzoxadiazole and the near-infrared fluorophore QX-OH rendered the probe susceptible to nucleophilic attack by biothiols. Upon the introduction of Cys/Hcy, the probe exhibited dual fluorescence emissions in red and green. Conversely, the presence of GSH resulted in only red fluorescence emission. The detection limits of the probe for Cys and Hcy at 542 nm in buffer solution were determined to be 0.044 μM and 0.042 μM, respectively. Similarly, the detection limit for all these biothiols was 0.028 μM at 678 nm. Furthermore, the response times for Cys/Hcy/GSH were recorded as 4.0 min, 5.5 min, and 9.5 min, respectively. Moreover, the probe was employed to monitor fluctuations in biothiol levels during oxidative stress in both HeLa cells and zebrafish, demonstrating its applicability and utility in biological contexts.

In situ images of Cd2+ in rice reveal Cd2+ protective mechanism using DNAzyme fluorescent probe

As a common pollutant, cadmium (Cd) poses a serious threat to the growth and development of plants. Currently, there is no effective method to elucidate the protective mechanism of Cd2+ in plant cells. For the first time, we designed a Cd2+ fluorescent probe to observe the adsorption and sequestration of Cd2+ in rice cell walls and vacuoles. Specifically, Cd2+ is blocked by the Casparian strip and electrostatically attracted to hemicellulose, which is abundantly adsorbed and fixed to the cell walls of the endodermis. For Cd2+ that successfully entered the endodermis, one part entered the cells and was compartmentalised and fixed in the vacuoles, while the other part entered the vascular bundles and precipitated in the cell walls of the sclerenchyma through the ion exchange effect. Furthermore, with prolonged exposure to Cd2+, compartmentalised bodies that were strongly labelled by fluorescence gradually appeared in the vacuoles, which were assumed to be a new heavy metal protective mechanism activated by plants in response to continuous Cd2+ exposure. In conclusion, this study provides an innovative and effective method for the detection of adsorption, transportation, and accumulation of Cd2+ in plant tissues, which can be employed for the rapid identification of crops with low Cd accumulation.

Monitoring the fluctuation of hydrogen peroxide with a near-infrared fluorescent probe for the diagnosis and management of kidney injury

Kidney injury has become an increasing concern for patients because of environmental hazards and physiological factors. However, the early diagnosis of kidney injury remains challenging. Studies have shown that oxidative stress was closely related to the occurrence and development of kidney injury, in which abnormal hydrogen peroxide (H2O2) production was a common characteristic. Consequently, monitoring H2O2 level changes is essential for the diagnosis and management of kidney injury. Herein, based on fluorescence imaging advantages, a near-infrared fluorescent probe DHX-1 was designed to detect H2O2. DHX-1 showed high sensitivity and selectivity toward H2O2, with a fast response time and excellent imaging capacity for H2O2 in living cells and zebrafish. DHX-1 could detect H2O2 in pesticide-induced HK-2 cells, revealing the main cause of kidney injury caused by pesticides. Moreover, we performed fluorescence imaging, which confirmed H2O2 fluctuation in kidney injury caused by uric acid. In addition, DHX-1 achieved rapid screening of active compounds to ameliorate pesticide-induced kidney injury. This study presents a tool and strategy for monitoring H2O2 levels that could be employed for the early diagnosis and effective management of kidney injury.

A novel AIE fluorescent probe for the detection and imaging of hydrogen peroxide in living tumor cells and in vivo

Hydrogen peroxide (H2O2), a key reactive oxygen species (ROS), plays crucial roles in redox signaling pathways and immune responses associated with cell proliferation, differentiation, migration, and disease progression. The selective monitoring of overproduced H2O2 is important for understanding the diagnosis and pathogenesis of diseases such as cardiovascular disease, cancers, diabetes, Parkinson's disease, Alzheimer's disease, and inflammation. In this paper, an AIE fluorescent probe BQM-H2O2 was developed by connecting phenyl borate with the fluorophore BQM-PNH for selective detection of H2O2. In the presence of H2O2 at fw = 99% (pH = 7.4, 1% DMSO), the probe BQM-H2O2 could generate strong fluorescent signals due to the oxidation of the borate ester. The probe exhibited high selectivity and a low detection limit toward H2O2 with the calculated LOD of 112.6 nM. Importantly, it was employed in the detection of exogenous and endogenous hydrogen peroxide in 4T1 cells with low cytotoxicity. This probe has also been successfully applied to imaging of H2O2 in Blab/c mice bearing 4T1 graft tumors.

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.

A Nano-Aggregatable Acedan Derivative for Clathrin-Mediated Cellular Uptake and Two-Photon Imaging of Diabetes-Associated Lipid Droplets

Lipid droplets (LDs), the essential cytosolic fat storage organelles, have emerged as pivotal regulators of cellular metabolism and are implicated in various diseases. The noninvasive monitoring of LDs necessitates fluorescent probes with precise organelle selectivity and biocompatibility. Addressing this need, we have engineered a probe by strategically modifying the structure of a conventional two-photon-absorbing dipolar dye, acedan. This innovative approach induces nanoaggregate formation in aqueous environments, leading to aggregation-induced fluorescence quenching. Upon cellular uptake via clathrin-mediated endocytosis, the probe selectively illuminates within LDs through a disassembly process, effectively distinguishing LDs from the cytosol with exceptional specificity. This breakthrough enables the high-fidelity imaging of LDs in both cellular and tissue environments. In a pioneering investigation, we probed LDs in a diabetes model induced by streptozotocin, unveiling significantly heightened LD accumulation in cardiac tissues compared to other organs, as evidenced by TP imaging. Furthermore, our exploration of a lipopolysaccharide-mediated cardiomyopathy model revealed an LD accumulation during heart injury. Thus, our developed probe holds immense potential for elucidating LD-associated diseases and advancing related research endeavors.

Novel mycophenolic acid precursor-based fluorescent probe for intracellular H2O2 detection in living cells and Daphnia magna and Zebrafish model systems

Innovative for the scientific community and attracting attention in the extensive biomedical field are novel compact organic chemosensing systems built upon unique core molecular frameworks. These systems may demonstrate customized responses and may be adaptable to analytes, showing promise for potential in vivo applications. Our recent investigation focuses on a precursor of Mycophenolic acid, resulting in the development of LBM (LOD = 13 nM) - a specialized probe selective for H2O2. This paper details the synthesis, characterization, and thorough biological assessments of LBM. Notably, we conducted experiments involving living cells, daphnia, and zebrafish models, utilizing microscopy techniques to determine probe nontoxicity and discern distinct patterns of probe localization. Localization involved the distribution of the probe in the Zebrafish model within the gut, esophagus, and muscles of the antennae.

Lysosome-Targeted Polarity-Sensitive NIR Fluorescence Probe for Imaging Injured Lung and Liver in Diabetes

Diabetes is a chronic disease marked by high blood glucose. With the progress of diabetes, complications gradually appear, and various organs may be affected. However, due to the lack of noninvasive in situ detection probes, the diagnosis of organ damage caused by diabetes is significantly delayed, which will cause many complications that cannot be treated in time. Here, we report a BODIPY-based fluorescent probe SNL, which can be used to detect lung and liver damage caused by diabetes. By introducing methylpiperazine and extending the conjugated system, SNL can locate lysosomes and exhibit absorption and emission both in the near-infrared (NIR) region. In addition, SNL is sensitive to polarity and can be used for sensitive detection of lysosomal polarity changes. Unexpectedly, SNL targets and images the lungs and liver of mice. Subsequently, hyperglycemia-stimulated cell models and diabetic mouse models were successfully established, and SNL was utilized to reveal that polarity can be used as a diagnostic signal of diabetic complications. Notably, SNL for the first time confirmed the lung injury and liver injury caused by diabetes using the fluorescent probes method, providing a new approach for the diagnosis of diabetes complications.

A glycopolymersome strategy for 'drug-free' treatment of diabetic nephropathy

Diabetic nephropathy is a severe complication of diabetes. Treatment of diabetic nephropathy is an important challenge due to persistent hyperglycemia and elevated levels of reactive oxygen species (ROS) in the kidney. Herein, we designed a glycopolymersome that can treat type 2 diabetic nephropathy by effectively inhibiting hyperglycemia and ROS-associated diabetic nephropathy pathogenesis. The glycopolymersome is self-assembled from phenylboronic acid derivative-containing copolymer, poly(ethylene oxide)45-block-poly[(aspartic acid)13-stat-glucosamine24-stat-(phenylboronic acid)18-stat-(phenylboronic acid pinacol ester)3] [PEO45-b-P(Asp13-stat-GA24-stat-PBA18-stat-PAPE3)]. PBA segment can reversibly bind blood glucose or GA segment for long-term regulation of blood glucose levels; PAPE segment can scavenge excessive ROS for renoprotection. In vitro studies confirmed that the glycopolymersomes exhibit efficient blood glucose responsiveness within 2 h and satisfactory ROS-scavenging ability with 500 μM H2O2. Moreover, the glycopolymersomes display long-acting regulation of blood glucose levels in type 2 diabetic nephropathy mice within 32 h. Dihydroethidium staining revealed that these glycopolymersomes reduced ROS to normal levels in the kidney, which led to 61.7% and 76.6% reduction in creatinine and urea levels, respectively, along with suppressing renal apoptosis, collagen accumulation, and glycogen deposition in type 2 diabetic nephropathy mice. Notably, the polypeptide-based glycopolymersome was synthesized by ring-opening polymerization (ROP) of N-carboxyanhydrides (NCAs), thereby exhibiting favorable biodegradability. Overall, we proposed a new glycopolymersome strategy for 'drug-free' treatment of diabetic nephropathy, which could be extended to encompass the design of various multifunctional nanoparticles targeting diabetes and its associated complications.

A fluorescence probe for imaging lipid droplet and visualization of diabetes-related polarity variations

Diabetes mellitus is a disorder that affects lipid metabolism. Abnormalities in the lipid droplets (LDs) can lead to disturbances in lipid metabolism, which is a significant feature of diabetic patients. Nevertheless, the correlation between diabetes and the polarity of LDs has received little attention in the scientific literature. In order to detect LDs polarity changes in diabetes illness models, we created a new fluorescence probe LD-DCM. This probe has a stable structure, high selectivity, and minimal cytotoxicity. The probe formed a typical D-π-A molecular configuration with triphenylamine (TPA) and dicyanomethylene-4H-pyran (DCM) as electron donor and acceptor parts. The LD-DCM molecule has an immense solvatochromic effect (λem = 544-624 nm), fluorescence enhancement of around 150 times, and a high sensitivity to polarity changes within the linear range of Δf = 0.28 to 0.32, all due to its distinctive intramolecular charge transfer effect (ICT). In addition, LD-DCM was able to monitor the accumulation of LDs and the reduction of LDs polarity in living cells when stimulated by oleic acid, lipopolysaccharide, and high glucose. More importantly, LD-DCM has also been used effectively to detect polarity differences in organs from diabetic, drug-treated, and normal mice. The results showed that the liver polarity of diabetic mice was lower than that of normal mice, while the liver polarity of drug-treated mice was higher than that of diabetic mice. We believe that LD-DCM has the potential to serve as an efficient instrument for the diagnosis of disorders that are associated with the polarity of LDs.

Mitochondria-Targetable Near-Infrared Fluorescent Probe for Visualization of Hydrogen Peroxide in Lung Injury, Liver Injury, and Tumor Models

Hydrogen peroxide (H2O2) overexpressed in mitochondria has been regarded as a key biomarker in the pathological processes of various diseases. However, there is currently a lack of suitable mitochondria-targetable near-infrared (NIR) probes for the visualization of H2O2 in multiple diseases, such as PM2.5 exposure-induced lung injury, hepatic ischemia-reperfusion injury (HIRI), nonalcoholic fatty liver (NAFL), hepatic fibrosis (HF), and malignant tumor tissues containing clinical cancer patient samples. Herein, we conceived a novel NIR fluorescent probe (HCy-H2O2) by introducing pentafluorobenzenesulfonyl as a H2O2 sensing unit into the NIR hemicyanine platform. HCy-H2O2 exhibits good sensitivity and selectivity toward H2O2, accompanied by a remarkable "turn-on" fluorescence signal at 720 nm. Meanwhile, HCy-H2O2 has stable mitochondria-targetable ability and permits monitoring of the up-generated H2O2 level during mitophagy. Furthermore, using HCy-H2O2, we have successfully observed an overproduced mitochondrial H2O2 in ambient PM2.5 exposure-induced lung injury, HIRI, NAFL, and HF models through NIR fluorescence imaging. Significantly, the visualization of H2O2 has been achieved in both tumor-bear mice as well as surgical specimens of cancer patients, making HCy-H2O2 a promising tool for cancer diagnosis and imaging-guided surgery.

A near-infrared fluorescence probe with large Stokes shift for selectively monitoring nitroreductase in living cells and mouse tumor models

Hypoxia is commonly regarded as a typical feature of solid tumors, which originates from the insufficient supply of oxygen. Herein, the development of an efficient method for assessing hypoxia levels in tumors is strongly desirable. Nitroreductase (NTR) is an overexpressed reductase in the solid tumors, has been served as a potential biomarker to evaluate the degrees of hypoxia. In this work, we elaborately synthesized a new near-infrared (NIR) fluorescence probe (MR) to monitor NTR activity for assessment of hypoxia levels in living cells and in tumors. Upon exposure of NTR, the nitro-unit of MR could be selectively reduced to amino-moiety with the help of nicotinamide adenine dinucleotide. Moreover, the obtained fluorophore emitted a prominent NIR fluorescence, because it possessed a classical "push-pull" structure. The MR displayed several distinguished characters toward NTR, including intense NIR fluorescent signals, large Stokes shift, high selectivity and low limit of detection (46 ng/mL). Furthermore, cellular confocal fluorescence imaging results validated that the MR had potential of detecting NTR levels in hypoxic cells. Significantly, using the MR, the elevated of NTR levels were successfully visualized in the tumor-bearing mouse models. Therefore, this detecting platform based on this probe may be tactfully constructed for monitoring the variations of NTR and estimating the degrees of hypoxia in tumors.

A fluorescence probe with targeted mitochondria for detecting hydrogen peroxide in vitro and in diabetic mice

We designed and prepared probe W-1 for the detection of H2O2. W-1 showed excellent selectivity for H2O2 and was accompanied by colorimetric signal changes. The excellent linear relationship between fluorescence intensity and H2O2 concentration (0-100 μM) provided favorable conditions for its quantitative detection. In addition, the combination of portable test strips with a smartphone platform provided great convenience for on-site visual detection of H2O2. Moreover, W-1 possessed targeting mitochondria property and could be applied to image the exogenous and endogenous H2O2 in cells to distinguish normal cells and cancer cells. Lastly, W-1 was used for monitoring the H2O2 fluctuation of the diabetic process in mice, and the results showed an increase in H2O2 levels in diabetes. Therefore, the probe provided a tool for understanding the pathological and physiological mechanisms of diabetes by imaging H2O2.

Peroxynitrite-activated fluorescent probe with two reaction triggers for pathological diagnosis and therapeutic evaluation of inflammation

Excessive peroxynitrite (ONOO-) is closely related to the occurrence and progression of inflammation. Therefore, the development of an efficacious ONOO- activatable probe holds great potential for the early diagnosis of pathological inflammation, and the direct evaluation of the therapeutic efficacy of active protectants. In this work, a new ONOO--activated fluorescent probe (SZP) which greatly improved the specificity and sensitivity (LOD = 8.03 nM) with large Stokes shift (150 nm) through introducing two reaction triggers (diphenyl phosphinate moiety, CC unsaturated bond) was rationally designed for rapid detecting ONOO- (within 2 min). The excellent properties of probe SZP enable it to realize the fluorescence-guided diagnosis of inflammation. More importantly, probe SZP has also been utilized to assess the anti-inflammatory efficacy of traditional Chinese medicines (TCMs) active ingredients for the remediation of inflammation by monitoring ONOO- fluctuation for the first time.

A highly selective probe engineered to detect polarity and distinguish normal cells and tumor cells in tissue sections

Early diagnostics and therapies for diseases such as cancer are limited by the fact that the inducing factors for the development of cytopathies are not clear. The stable polarity of lipid droplets is a potential biomarker for tumor cells; however, the complex intracellular biological environment poses great difficulties for specific detection of the polarity. Therefore, to meet this pressing challenge, we designed a highly selective fluorescent probe, DCI-Cou-polar, which used the ICT mechanism to differentiate normal cells and tumor cells in tissue sections by detecting changes in the polarities of intracellular lipid droplets. The introduction of a cyclic amine at the 7-position of coumarin (benzoquinolizine coumarin) reduced its ability to donate electrons compared with the diethylamino group, which increased the probe selectivity while retaining the sensitivity to polarity. With NIR emission and large Stokes shifts, DCI-Cou-polar has high sensitivity to polarity, excellent photostability, and biocompatibility, and it tracks lipid droplets with high fidelity. Therefore, we believe that this polarity-sensitive probe provides information on the connection between the polarity of lipid droplets and tumors while improving the development of highly selective polarity probes.

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.

Visualized Tracking and Multidimensional Assessing of Mitochondria-Associated Pyroptosis in Cancer Cells by a Small-Molecule Fluorescent Probe

Pyroptosis is closely related to the development and treatment of various cancers; thus, comprehensive studies of the correlations between pyroptosis and its inductive or inhibitive factors can provide new ideas for the intervention and diagnosis of tumors. The dysfunction of mitochondria may induce pyroptosis in cancer cells, which can be reflected by the fluctuations of the microenvironmental parameters in mitochondria as well as the changes of mitochondrial DNA level and morphology, etc. To precisely track and assess the mitochondria-associated pyroptosis process, simultaneous visualization of changes in multiphysiological parameters in mitochondria is highly desirable. In this work, we reported a nonreaction-based, multifunctional small-molecule fluorescent probe Mito-DK with the capability of crosstalk-free response to polarity and mtDNA as well as mitochondrial morphology. Accurate assessment of mitochondria-associated pyroptosis induced by palmitic acid/H2O2 was achieved through monitoring changes in mitochondrial multiple parameters with the help of Mito-DK. In particular, the pyroptosis-inducing ability of an antibiotic doxorubicin and the pyroptosis-inhibiting capacity of an anticancer agent puerarin were evaluated by Mito-DK. These results provide new perspectives for visualizing mitochondria-associated pyroptosis and offer new approaches for screening pyroptosis-related anticancer agents.

Preparation of copper nanoparticles fluorescent probes and detection of hydrogen peroxide and glucose

Fluorescent copper nanoparticles (CuNPs) was synthesized by one-step chemical reduction method using ascorbic acid (AA) and copper sulfate (CuSO4⋅5H2O) as raw materials, which had good water solubility and fluorescence properties. A green, simple and safe CuNPs@Fe2+ fluorescence probe was developed for the detection of hydrogen peroxide and glucose using Fe2+ as a bridge. The prepared CuNPs could obtain the maximum fluorescence emission wavelength at 440 nm when the excitation wavelength was 360 nm. The average particle size of CuNPs was 10 nm, which had good photobleach resistance, stability and salt tolerance. The fluorescence intensity was quenched due to electron transfer (ET) process when hydrogen peroxide was added to CuNPs@Fe2+ system. This result was mainly because Fenton reaction occured between hydrogen peroxide and Fe2+, producing hydroxyl free radicals (OH) and Fe3+. Since glucose could be catalyzed by specific glucose oxidase (GOX) to produce H2O2 and corresponding oxidation products, the quantitative analysis of glucose was realized when glucose oxidase was introduced into the CuNPs@Fe2+ sensor system. Therefore, a novel CuNPs@Fe2+ fluorescent probe sensor study was constructed to further achieve quantitative detection of H2O2 and glucose. Under the optimized experimental conditions, the linear ranges for H2O2 and glucose were 28.219-171.562 μM and 1.237-75.771 μM, respectively. And the detection limits for H2O2 and glucose were 7.169 μM and 0.540 μM, respectively. In addition, the mechanism of fluorescence probe quenching caused by the interaction between H2O2 and CuNPs@Fe2+ was also discussed. The proposed sensing system had been applied successfully to the detection of glucose in human serum samples.

An activatable fluorescent-photoacoustic dual-modal probe for highly sensitive imaging of nitroxyl in vivo

Nitroxyl (HNO) plays a vital role in various biological functions and pharmacological activities, so the development of an excellent near-infrared fluorescent (NIRF) and photoacoustic (PA) dual-modality probe is crucial for understanding HNO-related physiological and pathological progression. Herein, we proposed and synthesized a novel NIRF/PA dual probe (QL-HNO) by substituting an indole with quinolinium in hemicyanine for the sensitive detection of exogenous and endogenous HNO in vivo. The designed probe showed the highest sensitivity in NIRF mode and a desirable PA signal-to-noise ratio for HNO detection in vitro and was further applied for NIRF/PA dual-modal imaging of HNO with high contrast in living cells and tumor-bearing animals. Based on the excellent performance of QL-HNO, we believe that this study provides a promising molecular tool for further understanding of HNO-related physiological and pathological progression.

Dual-Channel/Localization Single-Molecule Fluorescence Probe for Monitoring ATP and HOCl in Early Diagnosis and Therapy of Rheumatoid Arthritis

Rheumatoid arthritis (RA), a common chronic inflammatory illness, is still incurable, reducing the sufferers' quality of life significantly. Adenosine 5'-triphosphate (ATP) and hypochlorous acid (HOCl) are key indicators in RA, but their precise mechanisms in RA pathophysiology are unknown. As a result, in order to detect ATP and HOCl simultaneously, we created two new dual-channel/localization single-molecule fluorescence probes, RhTNMB and RhFNMB. Furthermore, RhFNMB outperformed RhTNMB in terms of detection performance. ATP and HOCl produce independent fluorescence responses in the light red channel (λex = 520 nm, λem = 586 nm) and deep red channel (λex = 620 nm, λem = 688 nm), respectively, without spectral crosstalk. It should be noted that the probe RhFNMB successfully imaged ATP in mitochondria and HOCl in cells. Surprisingly, the probe RhFNMB demonstrated remarkable detection ability in the diagnosis and treatment of Pseudomonas aeruginosa-induced abdominal inflammation in mice. We continued to apply the probe RhFNMB to track ATP and HOCl in RA and discovered that ATP and HOCl concentrations were considerably greater in RA joints than in normal joints. We also confirmed the therapeutic effect of methotrexate on RA. This study is the first to achieve dual-channel imaging of ATP and HOCl, which is of great value for the early diagnosis and therapy of RA.

Tumor Microenvironment Activatable Nanoprodrug System for In Situ Fluorescence Imaging and Therapy of Liver Cancer

The development of new imaging and treatment nanoprodrug systems is highly demanded for diagnosis and therapy of liver cancer, a severe disease characterized by a high recurrence rate. Currently, available small molecule drugs are not possible for cancer diagnosis because of the fast diffusion of imaging agents and low efficacy in treatment due to poor water solubility and significant toxic side effects. In this study, we report the development of a tumor microenvironment activatable nanoprodrug system for the diagnosis and treatment of liver cancer. This nanoprodrug system can accumulate in the tumor site and be selectively activated by an excess of hydrogen peroxide (H2O2) in the tumor microenvironment, releasing near-infrared solid-state organic fluorescent probe (HPQCY-1) and phenylboronic acid-modified camptothecin (CPT) prodrug. Both HPQCY-1 and CPT prodrugs can be further activated in tumor sites for achieving more precise in situ near-infrared (NIR) fluorescence imaging and treatment while reducing the toxic effects of drugs on normal tissues. Additionally, the incorporation of hydrophilic multivalent chitosan as a carrier effectively improved the water solubility of the system. This research thus provides a practical new approach for the diagnosis and treatment of liver cancer.

Recent progress of near-infrared fluorescent probes in the determination of reactive oxygen species for disease diagnosis

Reactive oxygen species (ROS), a chemically defined group of reactive molecules derived from molecular oxygen, are involved in a variety of physiological and pathological processes, including immune defense, cellular metabolism, and other physiological processes. To access their detailed function in these processes, it is critical to establish rapid, accurate and in situ assays for these species in vivo. Among the potential assays, fluorescent probes are considered as the most promising candidate to monitor the biological ROS in vivo with great spatial and temporal resolution and are extensively used as an excellent tool in modern redox biology discovery. Recently, abundant fluorescent probes have been successively developed for in vitro or intracellular detection of ROS, but most of them could not be used for in vivo imaging due to their intrinsic shortcomings such as short emission wavelengths, phototoxicity and poor tissue penetration. Recent development of fluorescent ROS probes with near-infrared emission aim to address these concerns to develop practical assays. Herein, we review recent developments of ROS-sensitive near-infrared fluorescent probes, with an emphasis on the design, synthesis, characteristics of fluorescent probes, as well as their applications. We hope this review will aid the development of a new generation of efficient, sensitive and biocompatible fluorescent probes for in vivo ROS detection.

A biocompatible chitosan-based fluorescent polymer for efficient H2O2 detection in living cells and water samples

As a biomarker of oxidative stress, hydrogen peroxide (H2O2) plays a complex role in organisms, including regulating cell signaling, respiration, the immune system, and other life processes. Therefore, it is important to develop a tool that can simply and effectively monitor H2O2 levels in organisms and the environment. In this work, naphthalene fluorophores with a borate structure were introduced into chitosan (CTS) azide, and a CTS-based fluorescence sensor (CTS-HP) was designed for sensitive H2O2 detection. The biocompatibility and degradability of CTS endowed CTS-HP with reduced biotoxicity compared with organic fluorescent dyes, and the substitution degree of fluorophores on the CTS chains was 0.703. The randomly coiled chain structure of the CTS-HP probe enabled the boronic acid recognition sites on the fluorophores to achieve the enrichment of analyte H2O2 through a synergistic effect. Therefore, the probe CTS-HP (10 μg mL-1) exhibited a 21-fold fluorescence enhancement and good detection limit (LOD = 8.98 nM) in H2O2 solution, reaching the maximum fluorescence response faster (within 16 min). The probe also successfully achieved the fluorescence imaging of endogenous and exogenous H2O2 in zebrafish and living cells and labeled the recovery experiment of H2O2 in real water samples (recoveries rates of 90.93-102.9 % and RSD < 3.09 %).

Visualization of the Ferroptosis in Atherosclerotic Plaques with Nanoprobe Engineered by Macrophage Cell Membranes

Atherosclerosis (AS) is the root cause of cardiovascular diseases. Ferroptosis is characterized by highly iron-dependent lipid peroxidation and has been reported to play an important role in the pathogenesis of AS. Visualization of the ferroptosis process in atherosclerotic plaques is of great importance for diagnosing and treating AS. In this work, the rationally designed fluorescent probe FAS1 exhibited excellent advantages including large Stokes shift, sensitivity to environmental viscosity, good photostability, and improved water solubility. It also could co-locate with commercial lipid droplets (LDs) probes (BODIPY 493/503) well in RAW264.7 cells treated by the ferroptosis inducer. After self-assembly into nanoparticles and then encapsulation with macrophage membranes, the engineered FAS1@MM NPs could successfully target the atherosclerotic plaques in Western diet-induced apolipoprotein E knockout (ApoE-/-) mice and reveal the association of ferroptosis with AS through fluorescence imaging in vivo. This study may provide additional insights into the roles of ferroptosis in the diagnosis and treatment of AS.

De Novo Design of Near-Infrared Fluorescent Agents Activated by Peroxynitrite and Glutathione-Responsive Imaging for Diabetic Liver Disease

Diabetes and its complications, such as diabetes liver disease, is a major problem puzzling people's health. The detection of redox states in its pathological process can effectively help us gain a deeper understanding of the disease. The pair of oxidation-reduction substances peroxynitrite (ONOO- ) and glutathione (GSH) is considered to be closely related to their occurrence and development. Thus, direct visualization of ONOO- and GSH in diabetes liver disease is critical to evaluate the disease at the molecular level. Herein, two activatable agents NTCF-ONOO- and NTCF-GSH are prepared for selectively detecting ONOO- and GSH through protection and deprotection strategies based on hydroxyl and amino groups of near-infrared fluorophore. Fluorescence imaging of exogenous and endogenous ONOO- and GSH changes in living cells and in vivo is observed. The ONOO- and GSH level in the diabetes liver disease cellular model are visualized and the possible redox imbalance mechanism related to the oxidized (NAD+ ) and reduced (NADH) nicotinamide adenine dinucleotides is explored in this process. Moreover, these probes can sensitively recognize ONOO- and GSH in the process of oxidative stress resulting from streptozotocin and streptozotocin/acetaminophen-induced complex diabetic liver disease in vivo. In addition, they can be applied for monitoring the clinical serum sample related with diabetic patients.

Strategy for Fluorescence/Photoacoustic Signal Maximization Using Dual-Wavelength-Independent Excitation

Dual-mode imaging of fluorescence-photoacoustics has emerged as a promising technique for biomedical applications. However, conventional dual-mode imaging is based on single-wavelength excitation, which often results in opposing fluorescence and photoacoustic signals due to competing photophysical processes in one agent, rendering the maximization of both signals infeasible. To meet this challenge, we herein propose a new strategy by using the dual-excitation approach, where one excitation wavelength generates a fluorescence signal and the other produces a photoacoustic signal, thus achieving simultaneous maximization of both signals in one fluorescence-photoacoustic molecule. Based on this strategy, three dye molecules were employed for comparison, and it was surprising to find that QHD dye with two types of excitation wavelengths could generate fluorescence and photoacoustic signals, respectively. Furthermore, this strategy was successfully implemented in dual-mode imaging of rheumatoid arthritis mice. Importantly, this study emphasizes a new design guideline for the maximization of fluorescence-photoacoustic signals by using dual-wavelength-independent excitation.

A "Turn-on" Fluorescent Probe Based on Phenothiazine for Selectively Recognizing ClO- and its Practical Applications

Hypochlorous acid (HClO), a highly reactive oxygen species, has important effects on human health. High selectivity and sensitivity remain challenges of fluorescent probes for detection of ClO- with a large Stokes shift. This work designed and synthesized a novel phenothiazine-based fluorescent probe TF which can detect ClO- by colorimetric and fluorescent dual signals. TF displayed turn-on fluorescence effect toward ClO- with high selectivity (≥ 28-folds) and sensitivity (LOD = 0.472 μM), fast response time (< 1 min) and large Stokes shift (150 nm) in PBS (pH = 7.4, 40% DMSO). Meanwhile, TF can visualize ClO- on the mung bean sprouts model and apply as testing strips for portable and rapid detecting ClO- by the naked eyes. A phenothiazine-based fluorescent probe with large Stokes shift was synthesized and its responding rapidly ability to detect ClO- was studied.

Engineering of cyanine-based nanoplatform with tunable response toward reactive species for ratiometric NIR-II fluorescent imaging in mice

High-quality second near-infrared (NIR-II) nanoprobes are of great significance for real-time bioimaging and medical diagnosis. Cyanine is an important class of fluorophores to construct activatable probes; however, there are still significant challenges hindering their biological applications, including weak fluorescence in aqueous solution, instability, and insufficient specificity. Herein, an integrated engineering strategy is conducted to develop the cyanine-based activatable NIR-II nanoplatforms with bright, stable emission and high specificity. Specifically, poly(styrene-co-maleic anhydride) (PSMA) is employed to encapsulate NIR-II fluorescent molecules (IR1048) to render the stable and bright NIR-II nanoparticles (PSMA@IR1048 NPs). By charge-modulated strategy, a series of cyanine-fluorophores are loaded on the surface of PSMA@IR1048 NPs and exhibit tunable response toward reactive species. Combing those two strategies, NIR-II ratiometric fluorescent nanoprobes (RNPs, including RNP1, RNP2, and RNP3) are constructed; among them, RNP2 displays hypochlorous acid (HClO) responsive performance and generates a higher NIR-II fluorescent ratio (FL2/FL1) signal. Such nanoprobe can reliably report the pathological HClO level in models of diabetic liver injury and lower limb ischemia-reperfusion (I/R) injury mice. Our study paves an engineering strategy to construct cyanine-based stable, bright, and specific NIR-II probes for bioimaging.

Engineering a near-infrared LAP fluorescent probe with high sensitivity and selectivity for surgical resection of liver cancer

Hepatocellular carcinoma (HCC) is a type of cancer associated with a high rate of mortality and morbidity. In order to achieve precise HCC theranostics, it is important to develop excellent fluorescent probes. However, the existing probes are not sensitive or specific enough to accurately identify HCC margins and contours. For diagnosing HCC and identifying tumors during surgery, it is urgent to engineer highly sensitive and selective fluorescent probes. Liver tumor progression is closely associated with leucine aminopeptidase (LAP) overexpression, a biomarker of liver cancer. Herein, we have rationally designed a NIR fluorescent probe, NLAP, which is specially activated by LAP. The probe exhibited high sensitivity (detection limit = 6.8 mU L-1) and superior affinity (Km = 2.98 μM) for LAP. With this probe, we distinguished cancer cells overexpressing LAP from normal cells and applied it intraoperatively to guide liver tumor excisions. Furthermore, NLAP was employed to successfully detect the LAP of intestinal and splenic metastatic tumors in orthotopic liver tumor mice by "in situ spraying" and good performances were demonstrated.

Dual Key-Activated Nir-I/II Fluorescence Probe for Monitoring Photodynamic and Photothermal Synergistic Therapy Efficacy

As cancer markers, hydrogen peroxide (H2 O2 ) and viscosity play an essential role in the development of tumors. Meanwhile, based on the performance of near-infrared (NIR) fluorescence imaging and the high efficiency of photodynamic therapy (PDT) and photothermal therapy (PTT) synergistic therapy, it is urgent to develop a dual-key (H2 O2 and viscosity) activated fluorescence probe for cancer phototherapy. Herein, a NIR-I/II fluorescence probe named BX-B is reported. In the presence of both H2 O2 and viscosity, the fluorescence signal of NIR-I (810 nm) and NIR-II (945 nm) can be released. In the presence of H2 O2 , the PDT and PTT effects are observed. BX-B is used to monitor its therapeutic effects in cancer cells and tumor-bearing mice due to the increased viscosity caused by PDT and PTT. In addition, the tumors of mice treated with BX-B are almost completely ablated after the laser irradiation based on its PDT and PTT synergistic therapy. This work provides a reliable platform for effective cancer treatment and immediate evaluation of therapeutic effects.

Multiple fluorescence and hydrogen peroxide-responsive properties of novel triphenylamine-benzothiazole derivatives

A novel fluorescent dye molecule - triphenylamine (TPA)-benzothiazole (BZT) - based on excited state intramolecular proton transfer (ESIPT) was prepared by the Suzuki coupling reaction. The photophysical property assay indicates that BZT-TPA appeared in distinguishable colors in mixed solvents with different water contents. Moreover, BZT-TPA exhibited observable AIE behavior. On this basis, a fluorescent probe BZT-TPA-BO was synthesized for detecting H2O2. This probe molecule was found to have excellent selectivity, rapid response, and good linear relationship (R2 = 0.989) for detecting H2O2 in aqueous medium. Through DFT calculation, fluorescence spectrum, nuclear magnetic titration and HR-MS, the mechanism of recognition of H2O2 by the probe BZT-TPA-BO is proposed. In addition, the probe BZT-TPA-BO to some extent exhibited better performance for detecting exogenous H2O2 in HeLa cells.

A new lysosome-targeted fluorescent probe for hydrogen peroxide based on a benzothiazole derivative

As an important member of reactive oxygen species, hydrogen peroxide (H2O2) plays a key role in oxidative stress and cell signaling. Abnormal levels of H2O2 in lysosomes can induce damage or even loss of lysosomal function, leading to certain diseases. Therefore, real-time monitoring of H2O2 in lysosomes is very important. In this work, we designed and synthesized a novel lysosome-targeted fluorescent probe for H2O2-specific detection based on a benzothiazole derivative. A morpholine group was used as a lysosome-targeted unit and a boric acid ester was chosen as the reaction site. In the absence of H2O2, the probe exhibited very weak fluorescence. In the presence of H2O2, the probe showed an increased fluorescence emission. The fluorescence intensity of the probe for H2O2 displayed a good linear relationship in the concentration range of H2O2 from 8.0 × 10-7 to 2.0 × 10-4 mol·L-1. The detection limit was estimated to be 4.6 × 10-7 mol·L-1 for H2O2. The probe possessed high selectivity, good sensitivity and short response time for the detection of H2O2. Moreover, the probe had almost no cytotoxicity and had been successfully applied to confocal imaging of H2O2 in lysosomes of A549 cells. These results illustrated that the developed fluorescent probe in this study could provide a good tool for the determination of H2O2 in lysosomes.

Construction of a novel ESIPT and AIE-based fluorescent sensor for sequentially detecting Cu2+ and H2S in both living cells and zebrafish

The development of effective methods for tracking Cu²⁺ and H₂S in living organisms is urgently required due to their vital function in a variety of pathophysiological processes. In this work, a new fluorescent sensor BDF with excited-state intramolecular proton transfer (ESIPT) and aggregation-induced emission (AIE) features for the successive detection of Cu²⁺ and H₂S was constructed by introducing 3,5-bis(trifluoromethyl)phenylacetonitrile into the benzothiazole skeleton. BDF showed a fast, selective and sensitive fluorescence "turn off" response to Cu²⁺ in physiological media, and the situ-formed complex can serve as a fluorescence "turn on" sensor for highly selective detection of H₂S through the Cu²⁺ displacement approach. In addition, the detection limits of BDF for Cu²⁺ and H₂S were determined to be 0.05 and 1.95 μM, respectively. Encouraged by its favourable features, including strong red fluorescence from the AIE effect, large Stokes shift (285 nm), high anti-interference ability and good function at physiological pH as well as a low toxicity, BDF was successfully applied for the consequent imaging of Cu²⁺ and H₂S in both living cells and zebrafish, making it an ideal candidate for detecting and imaging of Cu²⁺ and H₂S in live systems.

High-fidelity fluorescent probes for visualizing the inhibitory behavior of selenium on cadmium uptake in rice

Cadmium (Cd), a widespread and highly toxic environmental contaminant, has seriously impacted the growth of rice and the quality of its products. Hence, it is crucial to monitor and employ robust means to reduce Cd levels in rice, and selenium (Se) has been proven to chelate cadmium ion (Cd²⁺) in rice with rational use. Herein, for the first time, the reported selenocysteine (Sec) probe NN-Sec and the newly designed Cd²⁺ probe SCP were chosen as visualization tools to monitor Sec-inhibited Cd²⁺ uptake in rice. Specifically, reduced fluorescence of rice precultured with Cd²⁺ was observed by SCP after Se application, while similarly decreased fluorescence of rice pretreated with Se was observed by NN-Sec after Cd²⁺ addition. The diminished fluorescence indicated the formation of Cd-Se complexes reduced the Cd²⁺ content in rice. Additionally, it was Cd²⁺ and Se that entered the rice causing the fluorescence generation, as demonstrated by inductively coupled plasma mass spectrometry (ICP-MS). To conclude, the two probes successfully visualized Se inhibited Cd²⁺ uptake in rice, which could provide a robust tool for supporting the development of novel organic fertilizers and reagents to reduce Cd²⁺ content in rice and the environment.

Recent progress in the development of fluorescent probes for imaging pathological oxidative stress

Oxidative stress is closely related to the physiopathology of numerous diseases. Reactive oxygen species (ROS), reactive nitrogen species (RNS), and reactive sulfur species (RSS) are direct participants and important biomarkers of oxidative stress. A comprehensive understanding of their changes can help us evaluate disease pathogenesis and progression and facilitate early diagnosis and drug development. In recent years, fluorescent probes have been developed for real-time monitoring of ROS, RNS and RSS levels in vitro and in vivo. In this review, conventional design strategies of fluorescent probes for ROS, RNS, and RSS detection are discussed from three aspects: fluorophores, linkers, and recognition groups. We introduce representative fluorescent probes for ROS, RNS, and RSS detection in cells, physiological/pathological processes (e.g., Inflammation, Drug Induced Organ Injury and Ischemia/Reperfusion Injury etc.), and specific diseases (e.g., neurodegenerative diseases, epilepsy, depression, diabetes and cancer, etc.). We then highlight the achievements, current challenges, and prospects for fluorescent probes in the pathophysiology of oxidative stress-related diseases.

Regulating the photophysical properties of ESIPT-based fluorescent probes by functional group substitution: a DFT/TDDFT study

CONTEXT

In recent years, fluorescent probe technology has received more and more attention. However, the photophysical and photochemical properties of probe molecules still need to be further explored. This paper presents the excited state intramolecular proton transfer (ESIPT) processes and photophysical properties of the probe molecule 4-bromo-2-((E)-((Z)-((5-bromo-1H-indol-2-yl) methylene) hydrazono) methyl) phenol (BHPL) and its four derivatives (BHPL2, BHPL3, BHPL4, and BHPL5). Infrared spectra and geometric structure analyses revealed that introducing the -NH₂ group on the benzene ring with the hydroxyl group will enhance the intramolecular hydrogen bond, which benefits the ESIPT process. Combining their absorption and fluorescence spectra, it can be concluded that BHPL2 and BHPL4 are both excellent probe candidates due to their large Stokes shift. The hole and electron and root mean square displacement analyses manifest that the fluorescence quenching of BHPL4 may be due to the intramolecular charge transfer process. Potential energy curves of BHPL and its four derivatives noted that ESIPT process of the BHPL2 is the most favorable to occur. The frontier molecular orbital and NBO analyses indicated that besides introducing electron-donating groups to reduce the energy gap and enhance fluorescence emission, introducing double electron-withdrawing groups can also achieve this effect, explaining why the energy barrier of ESIPT process for BHPL2 is lower than BHPL5. This work would provide the theoretical basis for designing novel fluorescence probes with more prominent properties.

METHODS

The ground (S₀) and excited (S₁) state structures of all compounds were optimized by density functional theory (DFT) and time-dependent (TDDFT) method, with B3LYP/6-311+G(d,p) level, respectively. The infrared spectra and potential energy curves were simulated at the same theoretical level. The reduced density gradient scatter plots and interaction region indicator isosurfaces were drawn using Multiwfn and VMD programs. The absorption and fluorescence spectra were simulated by the TDDFT/B3PW91/6-311+G(d,p) method. All the calculations in this work are carried out in Gaussian 16 program package.

Monitoring Hg2+ and MeHg+ poisoning in living body with an activatable near-infrared II fluorescence probe

Noninvasively imaging mercury poisoning in living organisms is critical to understanding its toxicity and treatments. Especially, simultaneous fluorescence imaging of Hg²⁺ and MeHg⁺in vivo is helpful to disclose the mysteries of mercury poisoning. The key limitation for mercury imaging in vivo is the low imaging signal-to-background ratio (SBR) and limited imaging depth, which may result in unreliable detection results. Here, we designed and prepared a near-infrared II (NIR II) emissive probe, NIR-Rh-MS, leveraging the "spirolactam ring-open" tactic of xanthene dyes for in situ visualization of mercury toxicity in mice. The probe produces a marked fluorescence signal at 1015 nm and displays good linear responses to Hg²⁺ and MeHg⁺ with excellent sensitivity, respectively. The penetration experiments elucidate that the activated NIR-II fluorescence signal of the probe penetrates to a depth of up to 7 mm in simulated tissues. Impressively, the probe can monitor the toxicity of Hg²⁺ in mouse livers and the accumulation of MeHg⁺ in mouse brains via intravital NIR-II imaging for the first time. Thus, we believe that detecting Hg²⁺ and MeHg⁺ in different organs with a single NIR-II fluorescence probe in mice would assuredly advance the toxicologic study of mercury poisoning in vivo.

A turn-on NIR fluorescent probe for risk-assessing oxidative stress in cabbage roots under abiotic stress

Oxidative stress is closely related to the crop health status under stress conditions. H₂O₂ is an important signaling molecule in plants under stress. Therefore, monitoring H₂O₂ fluctuations is of great significance when risk-assessing oxidative stress. However, few fluorescent probes have been reported for the in situ tracking of H₂O₂ fluctuations in crops. Herein, we designed a "turn-on" NIR fluorescent probe (DRP-B) to detect and in situ-image H₂O₂ in living cells and crops. DRP-B exhibited good detection performance for H₂O₂ and could image endogenous H₂O₂ in living cells. More importantly, it could semi-quantitatively visualize H₂O₂ in cabbage roots under abiotic stress. Visualization of H₂O₂ in cabbage roots revealed H₂O₂ upregulation in response to adverse environments (metals, flood, and drought). This study provides a new method for risk-assessing oxidative stress in plants under abiotic stress and is expected to provide guidance for the development of new antioxidant defense strategies to enhance plant resistance and crop productivity.

Dihydroxanthene-Based Near-infrared Fluorescent Probes for Monitoring Mitochondrial Viscosity in Living Cells and Mice

Aberrant mitochondrial viscosity is closely associated with many diseases and cellular malfunctions. Thus, the development of reliable methods for monitoring mitochondrial viscosity variations has attracted considerable attention. Herein, through stepwise structural modulation of the dihydroxanthene fluorophore (DHX), we developed three NIR fluorescent probes, named DHX-V-1-3, for detecting mitochondrial viscosity. Among them, DHX-V-3 displayed the highest signal-to-noise ratio (67-fold) for viscosity with outstanding selectivity and showed excellent mitochondria targeting and immobilization ability. At the cellular level, the DHX-V-3 probe was successfully applied to image the mitochondrial viscosity in live cells upon treatment with lipopolysaccharide (LPS) or nystatin. Moreover, benefiting from its NIR emission and the increased depth of tissue imaging, DHX-V-3 demonstrated the ability to visualize the increased viscosity in LPS-treated mice.

A dual-site multifunctional fluorescent probe for selective detection of endogenous H2O2 and SO2 derivatives based on ICT process and its bioimaging application

In this paper, we reported a coumarin-based fluorescent probe for selective detection of H₂O₂/SO₂ derivatives via ICT process. To the best of our knowledge, it was few reported with the same probe to enable visual detection of H₂O₂/SO₂ derivatives in vivo and in vitro. H₂O₂ and SO₃^2- were selectively sensed over other analytes, and the probe displayed 20-fold and 220-fold relative fluorescence intensity respectively, as well as the good linear relationship and the excellent detection limits of 2.7 * 10³ nM and 19.3 nM. Furthermore, the probe was successfully used for fluorescence imaging of the HeLa cells and the mice to monitor exogenous and endogenous H₂O₂ and SO₃^2-, suggesting its potential biomedical application for investigation and detection the intermediate indicator of oxidative stress in vitro and in vivo.

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.

Recent Advancements in the Design and Development of Near Infrared (NIR) Emitting Fluorescent Probes for Sensing and their Bio-Imaging Applications

Fluorescent bio-imaging will be the future in the medical diagnostic for visualising inner cellular and tissues. Near-infrared (NIR) emitting fluorescent probes serve dynamically for targeted fluorescent imaging of live cells and tissues. NIR imaging is advantageous because of its merits like deep tissue penetration, minimum damage to the tissue, reduced auto fluorescence from the background, and improved resolution in imaging. The Development of the NIR emitting probe was well explored recently and growing drastically. In this review, we summarise recent achievements in NIR probes in between 2018-2021. The merits and future applications have also been discussed in this review.

Engineered Nanoprobes for Immune Activation Monitoring

The activation of the immune system is critical for cancer immunotherapy and treatments of inflammatory diseases. Non-invasive visualization of immunoactivation is designed to monitor the dynamic nature of the immune response and facilitate the assessment of therapeutic outcomes, which, however, remains challenging. Conventional imaging modalities, such as positron emission tomography, computed tomography, etc., were utilized for imaging immune-related biomarkers. To explore the dynamic immune monitoring, probes with signals correlated to biomarkers of immune activation or prognosis are urgently needed. These emerging molecular probes, which turn on the signal only in the presence of the intended biomarker, can improve the detection specificity. These probes with "turn on" signals enable non-invasive, dynamic, and real-time imaging with high sensitivity and efficiency, showing significance for multifunctionality/multimodality imaging. As a result, more and more innovative engineered nanoprobes combined with diverse imaging modalities were developed to assess the activation of the immune system. In this work, we comprehensively review the recent and emerging advances in engineered nanoprobes for monitoring immune activation in cancer or other immune-mediated inflammatory diseases and discuss the potential in predicting the efficacy following treatments. Research on real-time in vivo immunoimaging is still under exploration, and this review can provide guidance and facilitate the development and application of next-generation imaging technologies.