A carboxylesterase-selective ratiometric fluorescent two-photon probe and its application to hepatocytes and liver tissues

A radical containing micellar probe for assessing esterase enzymatic activity with ultra-low field Overhauser-enhanced magnetic resonance imaging

The ability to track altered enzyme activity using a non-invasive imaging protocol is crucial for the early diagnosis of many diseases but is often challenging. Herein, we show that Overhauser magnetic resonance imaging (OMRI) can be used to monitor enzymatic conversion at an ultra-low field (206 μT) using a highly sensitive "off/on" probe with a nitroxide stable radical containing ester, named T2C12-T80. This TEMPO derivative containing probe forms stable electron paramagnetic resonance (EPR) silent micelles in water that are hydrolysed by esterases, thus yielding narrow EPR signals whose intensities correlate directly with specific enzymatic activity. The responsiveness of the probe to tumours, facilitated by increased esterase activity, was initially determined by comparing EPR signals measured upon incubation with 3T3 (healthy fibroblasts used as control), HepG2 (human hepatoma) and Hs766T (human pancreatic cancer cells) cell lysates and then with Hs766T and 3T3 living cells. Next, Overhauser MR images were detected on a phantom containing the probe and the esterases to show that the approach is well suited for being translated to the in vivo detection at the earth's magnetic field. Regarding detection sensitivity, ultra-low field OMRI (ULF-OMRI) is beneficial over OMRI at higher fields (e.g. 0.2 T) since Overhauser enhancements are significantly higher and the technique is safe in terms of the specific absorption rate.

Design, synthesis, and evaluation of a carboxylesterase detection probe with therapeutic effects

In this study, a lysosomal targeting fluorescent probe recognition on CEs was designed and synthesized. The obtained probe BF2-cur-Mor demonstrated excellent selectivity, sensitivity, pH-independence, and enzyme affinity towards CEs within 5 min. BF2-cur-Mor could enable recognition of intracellular CEs and elucidate that the CEs content of different cancer cells follows the rule of HepG2 > HCT-116 > A549 > HeLa, and the CEs expression level of hepatoma cancer cells far exceeds that of normal hepatic cells, being in good agreement with the previous reports. The ability of BF2-cur-Mor to monitor CEs in vivo was confirmed by zebrafish experiment. BF2-cur-Mor exhibits some pharmacological activity in that it can induce apoptosis in hepatocellular carcinoma cells but is weaker in normal hepatocyte cells, being expected to be a potential "diagnostic and therapeutic integration" tool for the clinical diagnosis of CEs-related diseases.

Construction of a novel aminofluorene-based ratiometric near-infrared fluorescence probe for detecting carboxylesterase activity in living cells

Herein, we constructed a novel aminofluorene-based fluorescence probe (FEN-CE) for the detection of carboxylesterase (CE) in living cells by a ratiometric near-infrared (NIR) fluorescence signal. FEN-CE with NIR emission (650 nm) could be hydrolyzed specifically by CE and transformed to FENH with the release of the self-immolative group, which exhibited a red-shifted emission peak of 680 nm. In addition, FEN-CE showed high selectivity for CE and was successfully used in the detection of CE activity in living cells through its ratiometric NIR fluorescence signals.

Combination of two-photon fluorescent probes for carboxylesterase and ONOO- to visualize the transformation of nonalcoholic fatty liver to nonalcoholic steatohepatitis in liver orthotopic imaging

As the most common cause of liver diseases, nonalcoholic fatty liver disease (NAFLD) can be classified into nonalcoholic fatty liver (NAFL) and nonalcoholic steatohepatitis (NASH). While NAFL is generally benign, the transition from NAFL to NASH is a cardinal feature of the non-benign liver disease that leads to cirrhosis and cancer, which indicates that tracking the transformation of NAFL to NASH timely is significant for precision management of liver diseases. Therefore, two fluorescent probes (CNFCl and DRNO) have been developed to visualize this pathological event. α-Fluorochloroacetamide and α-ketoamide was employed as the recognition site for carboxylesterase (CE) in CNFCl and peroxynitrite (ONOO-) in DRNO, respectively. CNFCl (λem = 445 nm) and DRNO (λem = 560 nm) showed high specificity and sensitivity towards CE and ONOO- respectively. By incubating with CE/ONOO- for 0.5 h respectively, both the emission intensity of CNFCl (linear range: 0-0.2 U/mL) and DRNO (linear range: 0-17.5 μM) displayed significant enhancement. As a result, the detection limit of CNFCl and DRNO for CE and ONOO- was calculated as 4.2 mU/L and 0.05 μM respectively. More importantly, the emission spectra of CNFCl and DRNO in the presence of CE and ONOO- respectively were cross-talk free under the two-photon excitation of 720 nm. This greatly facilitated the simultaneous detection of CE and ONOO- at distinctive channel, thus ensuring the high fidelity of the detection. These two probes were combined to image the fluctuation of CE and ONOO- during the conversion of NAFL to NASH in vitro and in vivo. It was found that while CE displayed a tendency to rise and then reduce during the transition from NAFL to NASH, ONOO- increased continuously, confirming that the combined imaging by CNFCl and DRNO might visualize the transformation of NAFL to NASH. The results provide robust visual tool to decipher the relationship between the stage of NAFLD and the level of CE/ONOO-. We anticipate this study may open new avenues to distinguish NASH from NAFL, which may further promote the study of intracellular biological activities of CE and the development of NAFLD diagnostic methods.

New Advances in the Exploration of Esterases with PET and Fluorescent Probes

Esterases are hydrolases that catalyze the hydrolysis of esters into the corresponding acids and alcohols. The development of fluorescent probes for detecting esterases is of great importance due to their wide spectrum of biological and industrial applications. These probes can provide a rapid and sensitive method for detecting the presence and activity of esterases in various samples, including biological fluids, food products, and environmental samples. Fluorescent probes can also be used for monitoring the effects of drugs and environmental toxins on esterase activity, as well as to study the functions and mechanisms of these enzymes in several biological systems. Additionally, fluorescent probes can be designed to selectively target specific types of esterases, such as those found in pathogenic bacteria or cancer cells. In this review, we summarize the recent fluorescent probes described for the visualization of cell viability and some applications for in vivo imaging. On the other hand, positron emission tomography (PET) is a nuclear-based molecular imaging modality of great value for studying the activity of enzymes in vivo. We provide some examples of PET probes for imaging acetylcholinesterases and butyrylcholinesterases in the brain, which are valuable tools for diagnosing dementia and monitoring the effects of anticholinergic drugs on the central nervous system.

An endoplasmic reticulum-specific ratiometric fluorescent probe for imaging esterase in living cells

Esterase is primarily distributed in the endoplasmic reticulum (ER) and often overexpressed in cancer cells. Therefore, the detection of esterase in ER is significant for monitoring the metabolic process of various esters and evaluating the efficacy of chemotherapeutic prodrugs. However, only few fluorescent probes can detect esterase in the ER due to the lack of ER-specificity. More seriously, these probes are often limited by low pearson's colocalization coefficient and one single wavelength emission. To solve those problems, an ER-specific ratiometric fluorescent probe (ER-EST) is designed for detecting esterase in living cells. The ER-EST shows a ratiometric and red-shifted emission (125 nm) from 435 to 560 nm after hydrolysis by esterase. The fluorescence intensity ratio of ER-EST displays quantitative response to the esterase activity (0-0.5 U/mL) with low detection limit of 1.8 × 10^-4 U/mL. Importantly, the ER-EST with good biocompatibility and excellent ER-targeted ability was successfully employed to ratiometric image the endogenous endoplasmic reticulum esterase in living cells.

Determination of Intracellular Esterase Activity Using Ratiometric Raman Sensing and Spectral Phasor Analysis

Carboxylesterases (CEs) are a class of enzymes that catalyze the hydrolysis of esters in a variety of endogenous and exogenous molecules. CEs play an important role in drug metabolism, in the onset and progression of disease, and can be harnessed for prodrug activation strategies. As such, the regulation of CEs is an important clinical and pharmaceutical consideration. Here, we report the first ratiometric sensor for CE activity using Raman spectroscopy based on a bisarylbutadiyne scaffold. The sensor was shown to be highly sensitive and specific for CE detection and had low cellular cytotoxicity. In hepatocyte cells, the ratiometric detection of esterase activity was possible, and the result was validated by multimodal imaging with standard viability stains used for fluorescence microscopy within the same cell population. In addition, we show that the detection of localized ultraviolet damage in a mixed cell population was possible using stimulated Raman scattering microscopy coupled with spectral phasor analysis. This sensor demonstrates the practical advantages of low molecular weight sensors that are detected using ratiometric Raman imaging and will have applications in drug discovery and biomedical research.

A fast fluorescent probe for tracing endoplasmic reticulum-located carboxylesterase in living cells

Carboxylesterase (CEs), mainly localized in endoplasmic reticulum (ER), are responsible for hydrolyzing compounds containing various ester bonds. They have been closely associated with drug metabolism and cellular homeostasis. Although some CE fluorescent probes have been developed, there are still a lack of probes that could target to the ER. Here, we developed a novel fluorescent probe CR with a specific ER anchor for monitoring CEs. In CR, p-toluenesulfonamide was chosen for precise ER targeting. A simple acetyl moiety was used as the CE response site and fluorescence modulation unit. During the spectral tests, CR displayed a fast response speed (within 10 s) towards CEs. In addition, it showed high sensitivity [limit of detection (LOD) = 5.1 × 10^-3 U/ml] and high selectivity with CEs. In biological imaging, probe CR could especially locate in the ER in HepG2 cells. After cells were treated with orilistat, CR succeeded in monitoring the changes in the CEs. Importantly, CR also had the ability to trace the changes in CEs in a tunicamycin-induced ER stress model. Therefore, probe CR could be a powerful molecular tool for further investigating the functions of CEs in the ER.

A hemicyanine-based fluorescent probe for simultaneous imaging of Carboxylesterases and Histone deacetylases in hepatocellular carcinoma

Carboxylesterases (CESs) and Histone deacetylases (HDACs) are regarded as important signaling enzymes highly associated with the development and progression of multiple cancers, including hepatocellular carcinoma (HCC). In this work, a near-infrared (NIR) fluorescent probe named Lys-HXPI was designed and synthesized, which linked a hemicyanine dye and 6-acetamidohexanoic acid via an ester bond. Lys-HXPI displayed a remarkable increase with a NIR emission at 720 nm, a low detection limit (<10 nM) for HDAC1, HDAC 6, CES1 and CES2, as well as a high selectivity for the target enzymes over other relevant analytes. Furthermore, Lys-HXPI was used to image endogenous target enzymes in living cells, tumor-bearing nude mice and tissue slices. The ability of Lys-HXPI to simultaneous image CESs and HDACs was demonstrated with RT-qPCR and the confocal imaging in Hep G2 and MDA-MB-231. Taking advantage of NIR emission, the probe was also successfully applied to imaging Hep G2 tumor mice and tissue slices. Lys-HXPI is expected to be useful for the effective detecting of CESs and HDACs in complex biosystems.

Ultrasensitive fluorescent probe for visual biosensing of esterase activity in living cells and its imaging application

Esterase activity is often used as an index to evaluate the health status of cells and plays an important role in cell metabolism and apoptosis. Herein, we develop two fluorescent probes for visual biosensing of esterase activity and imaging in living cells. In vitro, after the introduction of esterase, enzymolysis destroys the ester bond of the probe, causing the fluorescent color of probe changes from yellow to red, thus realizing the visual strategy for determination of esterase activity, with high sensitivity and selectivity. Especially, probe VA, 2-(4-acetoxystyryl)-3-ethyl-1,1-dimethyl- 1H-benzo[e]indol-3-ium, exhibits higher sensitivity with a lower detection limit (up to 7.15 × 10^-6 U/mL). In the cell experiment, the fluorescent probe VA also shows good biocompatibility and high spatial resolution, and is successfully applied to the intracellular fluorescent imaging and biosensing of esterase in living cells. More importantly, the probe VA can judge the unhealthy state of H₂O₂-induced HeLa cells using dual-fluorescence signals. The results confirm that the fluorescence method is a reliable tool for detecting endogenous esterase in living biological system.

Rapid Two-Photon Fluorescence Imaging of Monoamine Oxidase B for Diagnosis of Early-Stage Liver Fibrosis in Mice

Liver fibrosis could induce cirrhosis and liver cancer, causing serious damages to liver function and even death. Early diagnosis of fibrosis is extremely requisite for optimizing treatment schedule to improve cure rate. In early-stage fibrosis, overexpressed monoamine oxidase B (MAO-B) can serve as a biomarker, which greatly contributes to the diagnosis of early liver fibrosis. However, there is still a lack of desired strategy to precisely monitor MAO-B in situ. In this work, we established a two-photon fluorescence imaging method for in vivo detection of MAO-B activity counting on a simply prepared probe, BiPhAA. The BiPhAA could be activated by MAO-B within 10 min and fluoresced brightly. To our knowledge, this BiPhAA-based imaging platform for MAO-B is more rapid than other current detection methods. Furthermore, BiPhAA allowed the dynamic observation of endogenous MAO-B level changes in hepatic stellate cells (LX-2). Through two-photon fluorescence imaging, we observed six times higher fluorescence brightness in the liver tissue of fibrosis mice than that of normal mice, thus successfully distinguishing mice with liver fibrosis from normal mice. Our work offers a simple, fast, and highly sensitive approach for imaging MAO-B in situ and paves a way to the diagnosis of early liver fibrosis with accuracy.

Two-Photon Fluorescent Probes for Detecting Enzyme Activities in Live Tissues

Enzyme regulation is crucial in living organisms to catalyze various biosyntheses to maintain several physiological functions. On the contrary, abnormal enzyme activities can affect bioactivities leading to various serious disorders including cancer, Alzheimer's disease, Parkinson's disease, heart disease, and so on. This biological significance led to the development of various techniques to map specific enzyme activities in living systems to understand their role and distribution. Two-photon microscopy (TPM) in particular has emerged as a promising system for in situ real-time bioimaging owing to its robustness, high sensitivity, and noninvasiveness. It was achieved through the use of a two-photon (TP) light source of an optical window (700-1450 nm) beneficial in deeper light penetration and extraordinary spatial selectivity. Therefore, developing enzyme sensors utilized in TPM has significance in obtaining in vivo enzyme activities with minimal perturbation. The development of an efficient detection tool for enzymes has been continuously reported in the previous literature; here, we meticulously review the TP design strategies that have been attempted by researchers to develop enzyme TP fluorescent sensors that are proving very useful in providing insights for enzyme investigation in the biological system. In this review, the representative TP enzymatic probes that have been made in the past 5 years and their applications in tissue imaging are discussed in brief. In addition, the prospects and challenges of TP enzymatic probe development are also discussed.

A highly selective near infrared fluorescent probe for carboxylesterase 2 and its biological applications

Carboxylesterase 2 (CES 2) is a key enzyme in the activation of the prodrug irinotecan (CPT-11) in the treatment against colorectal cancer and also has some relationship with the side effect of CPT-11 in clinical applications. Herein, a near infrared (NIR) fluorescent probe (DSAB) has been designed for CES 2 which possesses the advantages of prominent selectivity and high sensitivity, and DSAB has been successfully applied for the imaging of endogenous CES 2 in living cells. Moreover, a high-throughput screening method for CES 2 inhibitors has been established using DSAB and discovered four novel CES 2 inhibitors from various herbal medicines. These results fully demonstrated that DSAB is a promising molecular tool for the investigation of the biological functions of CES 2 in living systems and the discovery of novel CES 2 inhibitors for the treatment of CES 2 related physiological diseases.

Improved antiallodynic, antihyperalgesic and anti-inflammatory response achieved through potential prodrug of curcumin, curcumin diethyl diglutarate in a mouse model of neuropathic pain

Neuropathic pain is a debilitating chronic pain condition, and its treatment remains a clinical challenge. Curcumin, a naturally occurring phenolic compound, possesses diverse biological and pharmacological effects but has not yet been approved as a drug due to its low bioavailability. In order to overcome this limitation, we synthesized a potential ester prodrug of curcumin, curcumin diethyl diglutarate (CurDDG). In this study, we evaluated the pharmacological advantages of CurDDG over curcumin in a mouse model of chronic constriction injury (CCI), and the anti-inflammatory effect of CurDDG in LPS-induced RAW 264.7 macrophage cells was accessed to clarify the underline mechanism. Mice were treated with various oral doses of curcumin (25, 50, 100 and 200 mg/kg/day, daily for 14 days) or equimolar doses of CurDDG. CurDDG at all doses tested significantly attenuated CCI-induced thermal hyperalgesia and mechanical allodynia compared with the CCI-control group. CurDDG at 25, 50 and 100 mg/kg demonstrated significantly greater efficacy on both mechanical and thermal hypersensitivities compared to that of curcumin. The effect of CurDDG correlated well with the inhibition of TNF-α and IL-6 levels in both the sciatic nerve and the spinal cord, as compared to its respective control groups. Similarly, in the in vitro study, CurDDG significantly reduced the LPS-induced expression of TNF-α and IL-6. Moreover, CurDDG significantly decreased COX-2 and iNOS levels and attenuated p38, JNK, and ERK1/2 phosphorylation as compared to the curcumin-treated cells. Altogether, this study demonstrated the improved pharmacological effects of curcumin by its diglutarate conjugate, CurDDG.

Macrophage imaging and subset analysis using single-cell RNA sequencing

Macrophages have been associated with drug response and resistance in diverse settings, thus raising the possibility of using macrophage imaging as a companion diagnostic to inform personalized patient treatment strategies. Nanoparticle-based contrast agents are especially promising because they efficiently deliver fluorescent, magnetic, and/or radionuclide labels by leveraging the intrinsic capacity of macrophages to accumulate nanomaterials in their role as professional phagocytes. Unfortunately, current clinical imaging modalities are limited in their ability to quantify broad molecular programs that may explain (a) which particular cell subsets a given imaging agent is actually labeling, and (b) what mechanistic role those cells play in promoting drug response or resistance. Highly multiplexed single-cell approaches including single-cell RNA sequencing (scRNAseq) have emerged as resources to help answer these questions. In this review, we query recently published scRNAseq datasets to support companion macrophage imaging, with particular focus on using dextran-based nanoparticles to predict the action of anti-cancer nanotherapies and monoclonal antibodies.

A sensitive and rapid "off-on" fluorescent probe for the detection of esterase and its application in evaluating cell status and discrimination of living cells and dead cells

The discrimination of living and dead cells shows great importance in the development of biology, pathology, medicine, and pharmacology research. Herein, we synthesized a simple benzothiazole-based probe, EP, which was characterized via1H NMR (hydrogen nuclear magnetic resonance) spectroscopy, 13C NMR (carbon nuclear magnetic resonance) spectroscopy and HRMS (high-resolution mass spectroscopy). The fluorescence changes in response to esterase were characterized via fluorescence spectroscopy. EP exhibited a 70-fold fluorescence enhancement in the presence of esterase and possessed a very low limit of detection (4.73 × 10-5 U mL-1). EP also showed high selectivity to esterase compared to other biological species. Bright fluorescence appeared in living cells, which was activated by esterase when incubated with EP. In paraformaldehyde or H2O2 pretreated cells, the fluorescence became very weak since esterase became inactive in these cells. In summary, the EP probe can monitor esterase activity both in vitro and in living cells and can be used to evaluate the health status of cells and discriminate living and dead cells effectively.

Fluorescence imaging of drug target proteins using chemical probes

Fluorescence imaging can provide valuable information on the expression, distribution, and activity of drug target proteins. Chemical probes are useful small-molecule tools for fluorescence imaging with high structural flexibility and biocompatibility. In this review, we briefly introduce two classes of fluorescent probes for the visualization of drug target proteins. Enzymatically activatable probes make use of the specific enzymatic transformations that generally produce a fluorogenic response upon reacting with target enzymes. Alternatively, specific imaging can be conferred with a ligand that drives the probes to target proteins, where the labeling relies on noncovalent binding, covalent inhibition, or traceless labeling by ligand-directed chemistry.

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Fluorescence imaging of drug target proteins is useful for studying their localization and interaction with drugs.

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Enzymatically activatable probes provide high-contrast imaging and a readout of enzyme activity.

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Targeted probes favor specific imaging of non-enzymatic proteins, and LD chemistry allows for traceless labeling.

A molecular-logic gate for COX-2 and NAT based on conformational and structural changes: visualizing the progression of liver disease

Lighting up the relevant lesion boundaries during operations is vital for guiding the effective resection of hepatopathic tissue.

Lighting up the relevant lesion boundaries during operations is vital for guiding the effective resection of hepatopathic tissue. We envisioned that molecular-logic gates, which are known for their excellent digital correlation between input and output signals, could be used to facilitate differential visualization of lesion boundaries. Herein, a series of flexible molecules, naphthalene imide-indole derivatives (IAN) were prepared and evaluated as molecular-logic gates. The input and output signals of the IAN derivatives were successfully used to highlight different hepatopathic regions in order to facilitate boundary differentiation. The IAN derivatives produce different signals due to collaborative changes in the conformation and structure. The hepatopathy-related enzymes (COX-2 and NAT) were used to induce conformational and structural changes in IAN derivatives. Based on these enzyme induced synergistic effects, IAN can sensitively emit different coloured signals such as green, cyan and blue (output signals) as a function of the different input signals, i.e. the different activity of COX-2 and NAT in solution and living cells. Significantly, the IAN derivatives were successfully used to distinguish the boundaries of hepatopathic lesions in tissues after spraying with IAN derivatives (mild cirrhosis, severe cirrhosis, in addition to early and late hepatocellular carcinoma) under a hand held lamp at 365 nm by naked eye.

Recent advances in two-photon absorbing probes based on a functionalized dipolar naphthalene platform

Two-photon microscopy (TPM) techniques have been highlighted over the past two decades throughout various fields, including physics, chemistry, biology, and medicine. In particular, the two-photon near-infrared excitation of fluorophores or molecular probes emitting fluorescence have ushered in a new biomedical era, specifically in the deep-tissue imaging of biologically relevant species. Non-linear two-photon optics enables the development of 3D fluorescence images via focal point excitation of biological samples with low photo-damage and photo-bleaching. Many studies have disclosed the relationship between the chemical structure of fluorophores and their two-photon absorbing properties. In this review, we have summarized the recent advances in two-photon absorbing probes based on a functionalized electron donor (D)-acceptor (A) type dipolar naphthalene platform (FDNP) that was previously reported between 2015 and 2019. Our systematic outline of the synthesis, photophysical properties, and examples of two-photon imaging applications will provide useful context for the future development of new naphthalene backbone-based two-photon probes.

Recent advances in multiphoton microscopy combined with nanomaterials in the field of disease evolution and clinical applications to liver cancer

Multiphoton microscopy (MPM) is expected to become a powerful clinical tool, with its unique advantages of being label-free, high resolution, deep imaging depth, low light photobleaching and low phototoxicity. Nanomaterials, with excellent physical and chemical properties, are biocompatible and easy to prepare and functionalize. The addition of nanomaterials exactly compensates for some defects of MPM, such as the weak endogenous signal strength, limited imaging materials, insufficient imaging depth and lack of therapeutic effects. Therefore, combining MPM with nanomaterials is a promising biomedical imaging method. Here, we mainly review the principle of MPM and its application in liver cancer, especially in disease evolution and clinical applications, including monitoring tumor progression, diagnosing tumor occurrence, detecting tumor metastasis, and evaluating cancer therapy response. Then, we introduce the latest advances in the combination of MPM with nanomaterials, including the MPM imaging of gold nanoparticles (AuNPs) and carbon dots (CDs). Finally, we also propose the main challenges and future research directions of MPM technology in HCC.

Measuring human carboxylesterase 2 activity in pancreatic cancer patient-derived xenografts using a ratiometric fluorescent chemosensor

Irinotecan-based therapy is a common treatment for pancreatic cancer. To elicit its anticancer activity, the drug requires first the hydrolysis action of the enzyme human carboxylesterase 2 (hCES2). It has been established that pancreatic cancer patients have various levels of hCES2, whereby patients having low levels respond poorer to Irinotecan than patients with higher levels, suggesting that hCES2 can be used to predict response. However, current methods that measure hCES2 activity are inaccurate, complex or lengthy, thus being incompatible for use in a clinical setting. Here, we developed a small molecule ratiometric fluorescent chemosensor that accurately measures hCES2 activity in a single-step within complex mixtures. Our chemosensor is highly selective for hCES2 over hCES1, cell permeable and can measure hCES2 activity in pancreatic cancer patient-derived xenografts. Given the simplicity, accuracy and tissue compatibility of our assay, we anticipate our chemosensor can be used to predict patient response to Irinotecan-based therapy.

Ratiometric fluorescent probe for sensing Streptococcus mutans glucosyltransferase, a key factor in the formation of dental caries

We report on a naphthalimide ratiometric fluorescent probe for the real-time sensing and imaging of pathogenic bacterial glucosyltransferases, which are associated with the development of dental caries. Using a high-throughput screening method, we identified that several natural polyphenols from green tea were GTFs inhibitors that could eventually lead to suitable oral treatments to prevent the development of dental caries.

Ratiometric two-photon fluorescent probe for in situ imaging of carboxylesterase (CE)-mediated mitochondrial acidification during medication

A probe for imaging of mitochondrial carboxylesterase and pH has been developed for the visualization of carboxylesterase-mediated acidification in hepatoma cells and hepatic tissues during the administration of antipyretic and anti-inflammatory drugs.

A novel fluorescent off–on probe for the sensitive and selective detection of fluoride ions

A highly sensitive and selective fluorescent probe for fluoride ions has been developed by incorporating the dimethylphosphinothionyl group as a recognition moiety into the fluorophore of coumarin. The detection mechanism is based on the fluoride ion-triggered cleavage of the dimethylphosphinothionyl group, followed by the release of coumarin, which leads to a large fluorescence enhancement at 455 nm (λ_ex = 385 nm). Under the optimized conditions, the fluorescence enhancement of the probe is directly proportional to the concentration of fluoride ions in the range of 0–30 μM with a detection limit of 0.29 μM, which is much lower than the maximum content of fluoride ions guided by WHO. Notably, satisfying results have been obtained by utilizing the probe to determine fluoride ions in real-water samples and commercially available toothpaste samples. The proposed probe is rather simple and may be useful in the detection of fluoride ions in more real samples.

A sensitive and selective fluorescent off–on probe is developed for fluoride ion detection, and its applicability has been demonstrated by determining fluoride ions in real-water samples and toothpaste samples.

Unusual fluorescence of o-phenylazonaphthol derivatives with aggregation-induced emission and their use in two-photon cell imaging

Unusual fluorescence of o-phenylazonaphthol derivatives with aggregated-induced emission (AIE) is reported for the first time, which can be used in two-photon cell imaging applications.

Detection of carboxylesterase by a novel hydrosoluble near-infrared fluorescence probe

A novel hydrosoluble near-infrared fluorescence off–on probe has been developed for detecting carboxylesterase activity.

A red lysosome-targeted fluorescent probe for carboxylesterase detection and bioimaging

A red lysosome-targeting probe for carboxylesterase activity has been successfully applied in complex biological samples.

An iridium complex-based probe for photoluminescence lifetime imaging of human carboxylesterase 2 in living cells

A novel photoluminescence lifetime probe (Ir-TB) has been developed for the detection and imaging of hCE2 in living cells. A large lifetime increase by around 300 ns after the enzymatic reaction makes it an ideal tool to distinguish hCE2-hydrolyzed probes from those non-hydrolyzed ones via PLIM for the first time.

Evaluation Selenocysteine Protective Effect in Carbon Disulfide Induced Hepatitis with a Mitochondrial Targeting Ratiometric Near-Infrared Fluorescent Probe

As important active sites of oxidoreductase in mitochondria, selenocysteine (Sec) takes the responsibility for cytoprotective effect and intracellular redox homeostasis. Carbon disulfide (CS₂) is a common solvent in industry, which can inhibit the activities of oxidoreductase and induce oxidative stress. It is necessary to investigate the cytoprotective effect of Sec against CS₂ exposure. After integrated, the response moiety 2,4-dinitrobenzenesulfonamide and mitochondrial targeting moiety into the near-infrared heptamethine cyanine fluorophore, we develop a mitochondrial targeting near-infrared ratiometric fluorescent probe Mito- diNO₂ for the selective and sensitive analysis of Sec concentration fluctuations in living cells and in mice models under the stimulation of CS₂. The probe can effectively accumulate in mitochondria and selectively detect the endogenous Sec concentrations in BRL 3A, RH-35, HL-7702, HepG2, and SMMC-7721 cell lines. The results indicate that CS₂ exposure can lead to a decrease of Sec level and result in mitochondrial related acute inflammation. The exogenous supplement of Sec can protect cells from oxidative damage and reduce the symptoms of inflammation. We also establish CS₂ induced acute and chronic hepatitis mice models to examine the tissue toxicity of CS₂ and cytoprotection of Sec in liver. The organism can increase the concentration of Sec to deal with the damage caused by CS₂ in acute hepatitis mice model. Also the exogenous supplement of Sec for the two mice models can effectively defend the CS₂ induced liver damage. The real-time imaging of Sec concentrations in liver can be used to assess the degrees of liver injury during CS₂ poisoning. The above applications make our probe a potential candidate for the clinical accurate diagnosis and treatment of CS₂ poisoning.

A fast responsive, highly selective and light-up fluorescent probe for the two-photon imaging of carboxylesterase in living cells

A fast responsive and two photon fluorescent probe (HCyNAc) for carboxylesterase (CaE) has been designed and used for the two-photon imaging of the endogenous CaE level in living HeLa cells under 800 nm NIR excitation.

A Two-Photon Ratiometric Fluorescent Probe for Imaging of Hydrogen Peroxide Levels in Rat Organ Tissues

Hydrogen peroxide (H2O2) is important in the regulation of a variety of biological processes and is involved in various diseases. Quantitative measurement of H2O2 levels at the subcellular level is important for understanding its positive and negative effects on biological processes. Herein, a two-photon ratiometric fluorescent probe (SHP-Cyto) with a boronate-based carbamate leaving group as the H2O2 reactive trigger and 6-(benzo[d]thiazol-2'-yl)-2-(N,N-dimethylamino) naphthalene (BTDAN) as the fluorophore was synthesized and examined for its ability to detect cytosolic H2O2 in situ. This probe, based on the specific reaction between boronate and H2O2, displayed a fluorescent color change (455 to 528 nm) in response to H2O2 in the presence of diverse reactive oxygen species in a physiological medium. In addition, ratiometric two-photon microscopy (TPM) images with SHP-Cyto revealed that H2O2 levels gradually increased from brain to kidney, skin, heart, lung, and then liver tissues. SHP-Cyto was successfully applied to the imaging of endogenously produced cytosolic H2O2 levels in live cells and various rat organs by using TPM.

Recent progresses in small-molecule enzymatic fluorescent probes for cancer imaging

An overview of recent advances in small-molecule enzymatic fluorescent probes for cancer imaging, including design strategies and cancer imaging applications.

Lighting-up breast cancer cells by a near-infrared fluorescent probe based on KIAA1363 enzyme-targeting

NB-AX, the first NIR KIAA1363-targeting fluorescent probe, could be used for the ultrafast lighting up of breast cancer cells and detection of tissues and tumors in vivo.