Fluorescent Determination of Butyrylcholinesterase Activity and Its Application in Biological Imaging and Pesticide Residue Detection

Near-infrared fluorescent probe for ultrasensitive detection of organophosphorus pesticides and visualization of their interaction with butyrylcholinesterase in living cells

The toxicity of organophosphorus pesticides (OPs) can catastrophically cause liver cell damage and inhibit the catalytic activity of cholinesterase. We designed and synthesized a near-infrared fluorescent probe HP-LZB with large Stokes shift which can specifically identify and detect butyrylcholinesterase (BChE) and visually explore the interaction between OPs and endogenous BChE in living cells. Fluorescence was turned on when HP-LZB was hydrolyzed into HP-LZ in the presence of BChE, and OPs could inhibit BChE's activity resulting in a decrease of fluorescence. Six OPs including three oxon pesticides (paraoxon, chlorpyrifos oxon and diazoxon) and their corresponding thion pesticides (parathion, chlorpyrifos and diazinon) were investigated. Both in vitro and cell experiments indicated that only oxon pesticides could inhibit BChE's activity. The limits of detection (LODs) of paraoxon, chlorpyrifos oxon and diazoxon were as low as 0.295, 0.007 and 0.011 ng mL-1 respectively and the recovery of OPs residue in vegetable samples was satisfactory. Thion pesticides themselves could hardly inhibit the activity of BChE and are only toxic when they are converted to their corresponding oxon form in the metabolic process. However, in this work, thion pesticides were found not be oxidized into their oxon forms in living HepG2 cells due to the lack of cytochrome P450 in hepatoma HepG2 cell lines. Therefore, this probe has great application potential in effectively monitoring OPs in real plant samples and visually exploring the interaction between OPs and BChE in living cells.

Triple modal aptasensor arrays driven by CHA-mediated DNAzyme for signal-amplified atrazine pesticide accumulation monitoring in agricultural crops

Developing sensors with high selectivity and sensitivity is of great significance for pesticide analysis in environmental assessment. Herein, a versatile three-way sensor array was designed for the detection of the pesticide atrazine, based on the integration of catalytic hairpin assembly (CHA) amplification and three-mode signal transducers. With atrazine, CHA was triggered to generate abundant G-quadruplex. The produced G-quadruplex hybrid could assemble with thioflavin T (TFT) or hemin to mimic enzyme and induce the fluorescence enhancement by TFT, or the colorimetric increase by the oxidized chromogenic substrate and the naked-eye color change by inhibiting the L-cysteine-mediated aggregation of gold nanoparticles. A distinctive three-mode array was successfully constructed with convenience, on-site accessibility and high sensitivity for enzyme-free practical analysis of atrazine. It is also effective and reliable for analyzing real samples including paddy water, paddy soil and polished rice. The detection limits for atrazine were as low as 7.4 pg/mL by colorimetric observation and 0.25 pg/mL by fluorescent detection. Furthermore, the array was exploited to monitor the residue, distribution and bioaccumulation of atrazine in maize and rice for food security and environmental assessment. Hence, this work presented a versatile example for sensitive and on-site all-in-one pesticide analysis arrays with multiple signal report modes.

A Programmable Microfluidic Paper-Based Analytical Device for Simultaneous Colorimetric and Photothermal Visual Sensing of Multiple Enzyme Activities

New strategies for the simultaneous and portable detection of multiple enzyme activities are highly desirable for clinical diagnosis and home care. However, the methods developed thus far generally suffer from high costs, cumbersome procedures, and heavy reliance on large-scale instruments. To satisfy the actual requirements of rapid, accurate, and on-site detection of multiple enzyme activities, we report herein a smartphone-assisted programmable microfluidic paper-based analytical device (μPAD) that utilizes colorimetric and photothermal signals for simultaneous, accurate, and visual quantitative detection of alkaline phosphatase (ALP) and butyrylcholinesterase (BChE). Specifically, the operation of this μPAD sensing platform is based on two sequential steps. Cobalt-doped mesoporous cerium oxide (Co-m-CeO2) with remarkable peroxidase-like activities under neutral conditions first catalytically decomposes H2O2 for effectively converting colorless 3,3',5,5'-tetramethylbenzidine (TMB) into blue oxidized TMB (oxTMB). The subsequent addition of ALP or BChE to their respective substrates produces a reducing substance that can somewhat inhibit the oxTMB transformation for compromised colorimetric and photothermal signals of oxTMB. Notably, these two-step bioenzyme-nanozyme cascade reactions strongly support the straightforward and excellent processability of this platform, which exhibit lower detection limits for ALP and BChE with a detection limit for BChE an order of magnitude lower than those of the other reported paper-based detection methods. The practicability and efficiency of this platform are further demonstrated through the analysis of clinical serum samples. This innovative platform exhibits great potential as a facile yet robust approach for simultaneous, accurate, and on-site visual detection of multiple enzyme activities in authentic samples.

Benzorhodol derived far-red/near-infrared fluorescent probes for selective and sensitive detection of butyrylcholinesterase activity in living cells and the non-alcoholic fatty liver of zebrafish

Liver diseases are a growing public health concern and the development of non-alcoholic fatty liver disease (NAFLD) has a significant impact on human metabolism. Butyrylcholinesterase (BChE) is a vital biomarker for NAFLD, making it crucial to monitor BChE activity with high sensitivity and selectivity. In this study, we designed and synthesized a range of benzorhodol-derived far-red/near-infrared fluorescent probes, FRBN-B, NF-SB, and NF-B, for the quantitative detection and imaging of BChE. These probes differed in the size of their conjugated systems and in the number of incorporated cyclopropanecarboxylates, acting as the recognition site for BChE. Comprehensive characterization showed that FRBN-B and NF-SB fluorescence was triggered by BChE-mediated hydrolysis, while an additional cyclopropanecarboxylate in NF-B impeded the fluorescence release. High selectivity towards BChE was observed for FRBN-B and NF-SB, with a detection limit of 7.2 × 10-3 U mL-1 for FRBN-B and 1.9 × 10-3 U mL-1 for NF-SB. The probes were further employed in the evaluation of BChE inhibitor efficacy and imaging of intracellular BChE activity. Additionally, FRBN-B was utilized for imaging the BChE activity level in liver tissues in zebrafish, demonstrating its potential as a diagnostic tool for NAFLD.

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.

A near-IR ratiometric fluorescent probe for the precise tracking of senescence: a multidimensional sensing assay of biomarkers in cell senescence pathways

Senescence is a complex physiological process that can be induced by a range of factors, and cellular damage caused by reactive oxygen species (ROS) is one of the major triggers. In order to learn and solve age-related diseases, tracking strategies through biomarkers, including senescence-associated β-galactosidase (SA-β-gal), with high sensitivity and accuracy, have been considered as a promising solution. However, endogenous β-gal accumulation is not only associated with senescence but also with other physiological processes. Therefore, additional assays are needed to define cellular senescence further. In this work, a fancy fluorescent probe SA-HCy-1 for accurately monitoring senescence is developed, with SA-β-gal and HClO as targets under high lysosomal pH conditions (pH > 6.0) specifically, on account of the role β-gal commonly played as an ovarian cancer biomarker. Therefore, precise tracking of cellular senescence could be achieved in view of these three dimensions, with response in dual fluorescence channels providing a ratiometric sensing pattern. This elaborate strategy has been verified to be suitable for biological applications by skin photo-aging evaluation and cellular passage tracing, displaying a significantly improved sensitivity compared with the commercial X-gal kit measurement.

A novel near-infrared fluorescent probe for high-sensitivity detection of butyrylcholinesterase in various pathological states

Butyrylcholinesterase (BChE) is a crucial hydrolytic enzyme predominantly synthesized in the liver, playing a significant role in conditions like liver disorders, diabetes, Alzheimer's disease, and fat metabolism regulation. This study aims to address the current limitations in visualizing BChE activity in diseases at various states by introducing an ultra-sensitive near-infrared fluorescent probe, FDCM-BChE. The probe was engineered to have several properties, such as a large Stokes shift, rapid response time, high stability, excellent selectivity, and low detection limits. We validated the efficacy of FDCM-BChE in quantifying BChE activity in human serum and leveraged its low cytotoxicity for cellular imaging. The study revealed the downregulation of BChE activity in liver cancer and hepatic injury and the upregulation in diabetes. Thus, FDCM-BChE shows promise as a tool for specific applications, providing insights into diseases associated with BChE activity.

Detection of acetylcholinesterase and butyrylcholinesterase in vitro and in vivo using a new fluorescent probe

A new fluorescence probe OHPD that could specifically identify acetylcholinesterase/butyrylcholinesterase has been developed and successfully applied to imaging in vivo. Probe OHPD shows significant color change, high selectivity, high sensitivity, and low detection limit for the detection of cholinesterase. Moreover, the real-time imaging in situ indicated that endogenous cholinesterase was mainly present in the yolk sac of zebrafish.

Ratiometric Fluorescent Probe for Real-Time Detection of β-Galactosidase Activity in Lysosomes and Its Application in Drug-Induced Senescence Imaging

Senescence is an important biological process, which leads to the gradual degradation of its physiological function and increases morbidity and mortality. Herein, a novel ratiometric fluorescent probe (P1) was constructed by using benzothiazolyl acetonitrile dye as fluorophore, exhibiting significantly enhanced blue-shifted emission to indicate the activity of β-galactosidase (β-gal), a commonly used biomarker for the detection of senescent cells. After incubation with β-gal, the excimer emission of P1 at 620 nm was weakened, while the emission at 533 nm was significantly enhanced, forming an obvious ratiometric probe with high sensitivity and low detection limit (2.7 mU·mL-1). More importantly, probe P1 can locate lysosomes accurately, allowing us to monitor the emergence of living cell senescence in real time. P1 was successfully used to detect β-gal activity in PC-12 cells, Hep G2 cells, and RAW 264.7 cells. It showed strong green fluorescence signal in senescent cells and red fluorescence signal in normal cells, indicating that it can detect endogenous senescence-related β-gal content in living cells. For in vivo drug-induced senescence imaging, after 5 weeks of injection of D-galactose or hydroxyurea, the mice showed significant fluorescence enhancement in specific channels to indicate the activity of β-gal in vivo. At the same time, the senescence of cell-specific organs and skin tissues at the organ level were also detected, which proved that the drug-induced senescence of brain, skin, and muscle tissues was the most serious. These results supported the important application value of P1 in senescence biomedical research.

Optical imaging probes for selective detection of butyrylcholinesterase

Butyrylcholinesterase (BChE), a member of the human serine hydrolase family, is an essential enzyme for cholinergic neurotransmission as it catalyzes the hydrolysis of acetylcholine. It also plays central roles in apoptosis, lipid metabolism, and xenobiotic detoxification. On the other side, abnormal levels of BChE are directly associated with the formation of pathogenic states such as neurodegenerative diseases, psychiatric and cardiovascular disorders, liver damage, diabetes, and cancer. Thus, selective and sensitive detection of BChE level in living organisms is highly crucial and is of great importance to further understand the roles of BChE in both physiological and pathological processes. However, it is a very complicated task due to the potential interference of acetylcholinesterase (AChE), the other human cholinesterase, as these two enzymes share a very similar substrate scope. To this end, optical imaging probes have attracted immense attention in recent years as they have modular structures, which can be tuned precisely to satisfy high selectivity toward BChE, and at the same time they offer real time and nondestructive imaging opportunities with a high spatial and temporal resolution. Here, we summarize BChE selective imaging probes by discussing the critical milestones achieved during the development process of these molecular sensors over the years. We put a special emphasis on design principles and biological applications of highly promising new generation activity-based probes. We also give a comprehensive outlook for the future of BChE-responsive probes and highlight the ongoing challenges. This collection marks the first review article on BChE-responsive imaging agents.

Transport and interaction mechanism of four pesticide residues from Chaenomeles speciosa across Caco-2 cells

The presence of multiple pesticide residues in agricultural production highlights the need for studying mixture interaction during transepithelial transport. This study applied the Caco-2 cell model to investigate the interaction of four pesticide residues (carbendazim, epoxiconazole, phoxim, and chlorpyrifos) in Chaenomeles speciosa during transepithelial transport. Results demonstrated that co-treatment with pesticide mixtures generally increased the cumulative transport amount of carbendazim and epoxiconazole by 0.32-1.60 times and 0.32-0.98 times, respectively, compared to individual treatments. Notably, the combination of carbendazim and epoxiconazole displayed a significant synergistic effect. The use of transporter inhibitors and molecular docking analysis provided insights into the interaction mechanism, suggesting that the competitive inhibition of MRP2 and/or BCRP binding via π-bonds contributed to the inhibition of BL-to-AP efflux and a significant increase in AP-to-BL influx of carbendazim and epoxiconazole. The results are of great theoretical significance and practical value for risk assessment of multiple pesticide residues in agricultural products.

Customized fluorescent probe for peering into the expression of butyrylcholinesterase in thyroid cancer

BACKGROUND

Thyroid cancer has been increasingly prevalent in recent years. The main diagnostic methods for thyroid are B-ultrasound scan, serum detection and puncture detection. However, these methods are invasive and complex. It is a pressing need to develop non-invasive or minimally invasive methods for thyroid cancer diagnosis. Fluorescence method as a non-invasive detection method has attracted much attention. Butyrylcholinesterase (BChE) is a common enzyme in the human body, and many diseases affect its reduction. We found that BChE is also a marker for thyroid cancer. Therefore, it is of certain clinical value to explore the expression of BChE in thyroid cancer cells through a customized fluorescent probe to provide valuable experimental data and clues for studying the expression of thyroid cancer marker to reflect thyroid status.

RESULTS

In this study, we customized a fluorescent probe named Kang-BChE, which is easy to synthesize with a high yield. The experimental results show that the probe Kang-BChE can detect BChE in the linear range of 0-900 U L-1 (R2 = 0.9963), and the detection limit is as low as 3.93 U L-1 (λex/em = 550/689 nm). In addition, Kang-BChE probes have low cytotoxicity, good specificity, and can completely eliminate interference from acetylcholinesterase (AChE). Kang-BChE showed excellent stability in the detection of complex biological samples in serum recovery experiments (95.64-103.12 %). This study was the first time using Kang-BChE to study the low expression of BChE in thyroid cancer cells (Tpc-1 cells). In addition, we observed that H2O2 concentration in Tpc-1 cells was positively correlated with BChE activity.

SIGNIFICANCE

Kang-BChE is expected to be an important tool for monitoring the change of BChE content in complex biological environments due to its excellent performance. Kang-BChE can also be used to explore the influence of molecules in more organisms on the change of BChE content due to its excellent anti-interference ability. We expect that Kang-BChE can play a significant role in the clinical diagnosis and treatment of thyroid cancer.

A lipid droplet-targeting fluorescent probe for specific H2S imaging in biosamples and development of smartphone platform

Hydrogen sulfide (H2S), a significant gas signal molecule, is closely related to various physiological/pathological processes. The monitoring of H2S is crucial in understanding the occurrence and development of diseases such as cancers. Emerging evidence suggests that abnormal regulation of Lipid droplets (LDs) is associated with many human diseases. For example, cancer cells are characterized by the abnormal accumulation of LDs. Therefore, understanding the relationship between LDs and cancer is of great significance for developing therapies against cancer. To address this challenge, we designed and developed a LD-targeting and H2S-activated probe (BTDA-DNB) by engineering a 2,4-dinitrophenyl ether (DNBE) as the H2S reactive site. In the presence of H2S, a strongly fluorescent emitter, 3-(benzo[d]thiazol-2-yl)-N,N-diethyl-2-imino-2H-chromen-7-amine (BTDA) was obtained with the leaving of DNBE group. BTDA-DNB displayed favorable sensitivity, selectivity and functioning well at physiological pH. The probe features excellent LD-targeting specificity and low cellular toxicity. The practical applications of LD-targeting probe BTDA-DNB as H2S probe in living cells, cancer tissues and Arabidopsis seedling have been evaluated. The excellent imaging performance demonstrates a potential ability for cancer diagnosis. Benefitted from the excellent performance on visual recognition H2S, a robust smartphone-integrated platform for H2S analysis was also successfully established.

Near-infrared ratiometric fluorescent strategy for butyrylcholinesterase activity and its application in the detection of pesticide residue in food samples and biological imaging

Butyrylcholinesterase (BChE) is an essential esterase synthesized by the liver, and its level is considered as a vital index for health evaluation. Therefore, it is of great need to develop a highly sensitive and selective tool to monitor BChE activity, which remains a considerable challenge on account of its usage in complex biological systems. A near-infrared (NIR) fluorescent probe was elaborated in this work, employing cyanine backbone to provide the intrinsic NIR fluorescence and avoid interference from bioluminescence. There presented an intriguing structural transformation upon the sensing event to shrink the conjugation in this protocol, leading to an eye-catching fluorescence change from NIR (816 nm) to red (637 nm) region, which gave rise to the proposed ratiometric assay. After an overall investigation, this receptor was verified to be applicable in a wide bio-area with ratiometric pattern, including the cellular level and slice platform. It was worth mentioning that this receptor was also discovered to be capable of monitoring pesticide dichlorvos (DDVP) residue in food samples with high sensitivity and accuracy, with significant potential to be developed as an alternative candidate for monitoring environmental pollution.

Construction of a Label-Free Ratiometric Biosensor Based on Target Recycling Amplification and Hg-ZnSe QDs for Assay of BChE and OPs

Herein, we constructed a label-free ratiometric fluorescence biosensing strategy for the determination of butyrylcholinesterase (BChE) activity and organophosphorus (OPs) concentration. BChE promoted the hydrolysis of iodized s-butyrylthiocholine (BTCh) into a reducing substance thiocholine, which can decompose CoOOH nanosheets (CoOOH NSs) to Co2+. Subsequently, the single-stranded DNA (ssDNA) on the surface of CoOOH NSs was released. Then, ssDNA hybridized with hairpin DNA (h-DNA) and triggered the target recycling amplification process, producing large amounts of G-quadruplex. After adding thioflavin T (ThT), the target BChE was converted into activatable G-quadruplex/ThT with an amplified yellow fluorescence signal. The addition of OPs could significantly inhibit the hydrolysis of BTCh by BChE and thus unable to produce the yellow fluorescence G-quadruplex/ThT complex. Throughout the entire process, the fluorescence intensity of Hg-ZnSe QDs as a reference signal remained unchanged at 630 nm. Furthermore, this work provided an effective approach for detecting the BChE activity in serum samples and OPs in fruits and vegetables.

Dual-Mode Ratiometric Electrochemical and Turn-On Fluorescent Detection of Butyrylcholinesterase Utilizing a Single Probe for the Diagnosis of Alzheimer's Disease

Biomarkers detection in blood with high accuracy is crucial for the diagnosis and treatment of many diseases. In this study, the proof-of-concept fabrication of a dual-mode sensor based on a single probe (Re-BChE) using a dual-signaling electrochemical ratiometric strategy and a "turn-on" fluorescent method is presented. The probe Re-BChE was synthesized in a single step and demonstrated dual mode response toward butyrylcholinesterase (BChE), a promising biomarker of Alzheimer's disease (AD). Due to the specific hydrolysis reaction, the probe Re-BChE demonstrated a turn-on current response for BChE at -0.28 V, followed by a turn-off current response at -0.18 V, while the fluorescence spectrum demonstrated a turn-on response with an emission wavelength of 600 nm. The developed ratiometric electrochemical sensor and fluorescence detection demonstrated high sensitivity with BChE concentrations with a low detection limit of 0.08 μg mL^-1 and 0.05 μg mL^-1, respectively. Importantly, the dual-mode sensor presents the following advantages: (1) dual-mode readout can correct the impact of systematic or background error, thereby achieving more accurate results; (2) the responses of dual-mode readout originate from two distinct mechanisms and relatively independent signal transduction, in which there is no interference between two signaling routes. Additionally, compared with the reported single-signal electrochemical assays for BChE, both redox potential signals were detected in the absence of biological interference within a negative potential window. Furthermore, it was discovered that the outcomes of direct dual-mode electrochemical and fluorescence quantifications of the level of BChE in serum were in agreement with those obtained from the use of commercially available assay kits for BChE sensing. This method has the potential to serve as a useful point-of-care tool for the early detection of AD.

Near-infrared-excitable acetylcholinesterase-activated fluorescent probe for sensitive and anti-interference detection of pesticides in colored food

The development of a common and anti-interference acetylcholinesterase (AChE) inhibition assay for plant-originated food samples has been of great challenge because of the prevalent and strong signal interferences from natural pigments. Plant pigments normally exhibit non-negligible absorbance in the UV-visible region. As a result, the signals of a typical near-infrared (NIR) fluorescent probe could be disturbed through primary inner filter effect if it is excited by UV-visible light during plant sample analysis. In this work, an NIR-excitable AChE-activated fluorescent probe was biomimetically designed and synthesized. And the NIR-excitation strategy was utilized for the anti-interference detection of organophosphate and carbamate pesticides in colored samples with this probe. Sensitive and rapid response to AChE and pesticides was achieved due to the high affinity of the biomimetic recognition unit in the probe. The limits of detection for four representative pesticides including dichlorvos, carbofuran, chlorpyrifos and methamidophos reached 0.0186 μg/L, 2.20 μg/L, 12.3 μg/L and 13.6 μg/L, respectively. Most importantly, fluorescent response to pesticide contents could be accurately measured in the coexistence of different plant pigments by this probe, and the measured results showed completely irrelevance to the plant pigments and their colors. Taking advantage of such probe, the new developed AChE inhibition assay showed good sensitivity and anti-interference ability in the detection of organophosphate and carbamate pesticides in real samples.

A turn-on fluorescent probe based on ESIPT and AIEE mechanisms for the detection of butyrylcholinesterase activity in living cells and in non-alcoholic fatty liver of zebrafish

Butyrylcholinesterase (BChE) and acetylcholinesterase (AChE) are two important cholinesterase enzymes in human metabolism which are closely related to various diseases of the liver. BChE and AChE are difficult to be distinguished due to their similarity in biochemical properties. Therefore, developing BChE-specific probes with high sensitivity and low background reading is desirable for the relevant biological applications. Herein, we reported the design and synthesis of a fluorescent probe HBT-BChE for biological detection and imaging of BChE. The probe is triggered by BChE-mediated hydrolysis, releasing a fluorophore that holds AIEE and ESIPT properties with large Stokes shift (>100 nm), rendering the probe features of low background interference and high sensitivity. The probe can also distinguish BChE from AChE with a low detection limit of 7.540 × 10^-4 U/mL. Further in vitro studies have shown the ability of HBT-BChE to detect intracellular BChE activity, as well as to evaluate the efficiency of the BChE inhibitor. More importantly, the in vivo studies of imaging the BChE activity level in liver tissues using zebrafish as the model animal demonstrated the potential of HBT-BChE as a powerful tool for non-alcoholic fatty liver disease.

Pseudo-irreversible butyrylcholinesterase inhibitors: Structure-activity relationships, computational and crystallographic study of the N-dialkyl O-arylcarbamate warhead

Alongside reversible butyrylcholinesterase inhibitors, a plethora of covalent butyrylcholinesterase inhibitors have been reported in the literature, typically pseudo-irreversible carbamates. For these latter, however, most cases lack full confirmation of their covalent mode of action. Additionally, the available reports regarding the structure-activity relationships of the O-arylcarbamate warhead are incomplete. Therefore, a follow-up on a series of pseudo-irreversible covalent carbamate human butyrylcholinesterase inhibitors and the structure-activity relationships of the N-dialkyl O-arylcarbamate warhead are presented in this study. The covalent mechanism of binding was tested by IC₅₀ time-dependency profiles, and sequentially and increasingly confirmed by kinetic analysis, whole protein LC-MS, and crystallographic analysis. Computational studies provided valuable insights into steric constraints and identified problematic, bulky carbamate warheads that cannot reach and carbamoylate the catalytic Ser198. Quantum mechanical calculations provided further evidence that steric effects appear to be a key factor in determining the covalent binding behaviour of these carbamate cholinesterase inhibitors and their duration of action. Additionally, the introduction of a clickable terminal alkyne moiety into one of the carbamate N-substituents and in situ derivatisation with azide-containing fluorophore enabled fluorescent labelling of plasma human butyrylcholinesterase. This proof-of-concept study highlights the potential of this novel approach and for these compounds to be further developed as clickable molecular probes for investigating tissue localisation and activity of cholinesterases.

A water-soluble fluorescent probe for the determination of γ-glutamyltransferase activity and its application in tumor imaging

γ-glutamyltransferase (GGT), an important tumor marker, is highly expressed in tumor tissues, and precise detection of its activity provides a vital indicator for the diagnosis and treatment. In this work, a "lighting-on" probe (TCF-GGT) was elaborated to detect endogenous GGT with high selectivity and sensitivity. Dicyanomethyldifuranyl (TCF-OH) was employed as the fluorescence reporter and short peptide glutathione (GSH) worked as the GGT-active trigger, the introduction of which prevented the initial proton transfer of TCF-OH contributing to a blank sensing background. A bright red fluorescence could be switched on upon GGT catalytic hydrolysis, avoiding the potential interference from background. There displayed an excellent water-solubility, and little organic solvent was required during the exploration, which otherwise avoided the potential damage to enzyme and organism. TCF-GGT has been proved to be workable at cellular and organism level with highly effective imaging and a short metabolic cycle, which is expected to offer an alternative solution or reference to the early diagnosis and treatment of tumor.

A surfactant-assisted approach enables the fluorescence tracking of benfluralin in plants

Developing an effective detection method for benfluralin (BFA) is of great significance, since BFA as most widely used herbicides can be bioaccumulated by aquatic organisms in environment, possessing potential risks to human health. Owing to aggregation-caused quenching effect, most fluorescent detection methods based on donor-acceptor organic fluorophores suffered from very low sensitivity towards BFA in water system, hampering the bioimaging application in plants. In this work, we reported a novel surfactant-assisted fluorescent probe enabling detection of BFA in water with a high sensitivity. The involvement of specific surfactant Triton X100 (TX100) could amplify the response signal of probe more than 100-fold. The detection limit for BFA was determined to be 80 nM, satisfying the environmental protection requirements. Moreover, we demonstrated applications of this strategy for the fluorescent imaging of BFA in plant. The absorbance of BFA into roots of Arabidopsis thaliana and castor seedlings was successfully observed based on this method.

Diagnosis of Alzheimer's Disease and In Situ Biological Imaging via an Activatable Near-Infrared Fluorescence Probe

Alzheimer's disease (AD) is a common neurodegenerative disease that makes the brain nervous system degenerate rapidly and is accompanied by some special cognitive and behavioral dysfunction. Recently, butyrylcholinesterase (BChE) was reported as an important enzyme, whose activity can provide predictive value for timely discovery and diagnosis of AD. Therefore, it is indispensable to design a detection tool for selective and rapid response toward BChE. In this study, we developed a novel near-infrared fluorescent probe (Chy-1) for the detection of BChE activity. An excellent sensitivity, good biocompatibility, and lower limit of detection (LOD) of 0.12 ng/mL made the probe extremely specific for BChE, which was successfully used in biological imaging. What is more, Chy-1 can not only clearly distinguish tumor from normal cells but also forms a clear boundary between the normal and cancer tissues due to the obvious difference in fluorescence intensity produced via in situ spraying. Most important of all, Chy-1 was also successfully applied to track the BChE activity in AD mouse models. Based on this research, the novel probe may be a powerful tool for clinical diagnosis and therapy of tumor and neurodegenerative diseases.

Exposure Routes and Health Risks Associated with Pesticide Application

Pesticides play an important role in agricultural development. However, pesticide application can result in both acute and chronic human toxicities, and the adverse effects of pesticides on the environment and human health remain a serious problem. There is therefore a need to discuss the application methods for pesticides, the routes of pesticide exposure, and the health risks posed by pesticide application. The health problems related to pesticide application and exposure in developing countries are of particular concern. The purpose of this paper is to provide scientific information for policymakers in order to allow the development of proper pesticide application technics and methods to minimize pesticide exposure and the adverse health effects on both applicators and communities. Studies indicate that there are four main pesticide application methods, including hydraulic spraying, backpack spraying, basal trunk spraying, and aerial spraying. Pesticide application methods are mainly selected by considering the habits of target pests, the characteristics of target sites, and the properties of pesticides. Humans are directly exposed to pesticides in occupational, agricultural, and household activities and are indirectly exposed to pesticides via environmental media, including air, water, soil, and food. Human exposure to pesticides occurs mainly through dermal, oral, and respiratory routes. People who are directly and/or indirectly exposed to pesticides may contract acute toxicity effects and chronic diseases. Although no segment of the general population is completely protected against exposure to pesticides and their potentially serious health effects, a disproportionate burden is shouldered by people in developing countries. Both deterministic and probabilistic human health risk assessments have their advantages and disadvantages and both types of methods should be comprehensively implemented in research on exposure and human health risk assessment. Equipment for appropriate pesticide application is important for application efficiency to minimize the loss of spray solution as well as reduce pesticide residuals in the environment and adverse human health effects due to over-spraying and residues. Policymakers should implement various useful measures, such as integrated pest management (IPM) laws that prohibit the use of pesticides with high risks and the development of a national implementation plan (NIP) to reduce the adverse effects of pesticides on the environment and on human health.

Ratiometric imaging of butyrylcholinesterase activity in mice with nonalcoholic fatty liver using an AIE-based fluorescent probe

Butyrylcholinesterase (BChE) is an essential human biomarker which is related to liver and neurodegenerative diseases. It is of great significance to develop a fluorescent probe that can image BChE in vitro and in vivo. Unfortunately, most fluorescent probes that are based on a single change in fluorescence intensity are susceptible to environmental interference. Therefore, we reported an easily available ratiometric fluorescent probe, TB-BChE, with aggregation-induced emission (AIE) characteristics for ratiometric imaging of BChE. TB-BChE demonstrated excellent sensitivity (LOD = 39.24 ng mL^-1) and specificity for BChE. Moreover, we have successfully studied the ratiometric imaging of TB-BChE to BChE in a nonalcoholic fatty liver disease model. These results indicated that TB-BChE is expected to become a powerful analysis tool for butyrylcholinesterase research in basic medicine and clinical applications.

Redox-regulated synthesis of fluorescent polydopamine nanoparticles for detection of butyrylcholinesterase activity

Butyrylcholinesterase (BChE) is an enzyme which is relevant to a variety of diseases, and often serve as a common biomarker of health. In this work, a novel fluorescence sensor based on redox-regulated synthesis of polydopamine nanoparticles (PDANPs) has been developed for simple and sensitive sensing BChE activity. A facile and rapid one-step approach for the preparation of fluorescent PDANPs uses potassium permanganate to oxidize dopamine. We demonstrated that the fluorescence intensity of PDANPs is dependent on the dose of potassium permanganate. Butyrylcholinesterase catalyzes the hydrolysis of butyrylthiocholine iodide (BTCh) to produce thiolcholine (TCh) which in a redox reaction with potassium permanganate prevents the formation of fluorescent PDANP. As a result, the activity of BChE can be determined in line with changes in the fluorescence of PDANPs. Based on this finding, a convenient and label-free fluorescence sensor for BChE activity was established via redox-control of the fluorescence intensity of PDANPs. A dynamic response range for BChE is acquired within 0.5 ∼ 200 U/L along with a detection limit of 0.047 U/L. Importantly, the proposed method achieves practical application toward BChE in human sera. Moreover, its satisfying performance for screening of inhibitors was also proved. Hence, the proposed sensor holds great potential for cholinesterase-related biomedical investigation.

Single-atom Ce-N-C nanozyme bioactive paper with a 3D-printed platform for rapid detection of organophosphorus and carbamate pesticide residues

Rapid detection of pesticide residues based on enzyme mimics has recently attracted much interest. However, most nanozymes have low activity. Herein, a "single-atom Ce-N-C nanozyme" (SACe-N-C nanozyme) was rationally devised and verified to mimic peroxidase (POD-like) with superior activity. Based on its high POD-like activities and cascaded catalytic reactions with acetylcholinesterase (AChE), we constructed a bioactive paper for the detection of pesticide residues, which offered a portable approach to monitor fruits and vegetables within 30 min. More importantly, a 3D printed platform was integrated on the basis of SACe-N-C bioactive paper to achieve on-site portable testing of omethoate, methamidophos, carbofuran, and carbosulfan, showing limits of detection (LODs) of 55.83, 71.51, 81.81, and 74.98 ng/mL, respectively. The recovery rates were 84.09-104.68%. This study provided new insight into the design of novel single-atom nanozymes for cascaded catalytic detection and other rapid detection applications with high efficiency and low cost.

Ultrasensitive detection of butyrylcholinesterase activity based on self-polymerization modulated fluorescence of sulfur quantum dots

Butyrylcholinesterase (BChE) is an important clinical diagnosing index for liver dysfunction and organophosphate toxicity. However, the current assays for BChE activity are suffering from the relative poor detection sensitivity. In this work, an ultrasensitive fluorescence assay for BChE activity was developed based on the self-polymerization modulated fluorescence of sulfur quantum dots (S-dots). The luminescence of S-dots can be quenched by the self-polymerized dopamine. The hydrolysate of substrates, thiocholine, under the catalysis of BChE can reduce dopamine, which results in the inhibition of self-polymerization and the fluorescence recovery of S-dots. BChE can be quantitatively detected by recording the recovered fluorescence of S-dots, and a linear relationship is observed between the ratio of fluorescence and the concentration of BChE in the range from 0.01 to 10 U/L. A limit of detection as low as 0.0069 U/L calculated, which is the lowest number so far. The assay also shows excellent selectivity towards various interference species and acetylcholinesterase. These features allowed the direct detection of BChE activity in human serum, demonstrating the great practical applications of our assay.

A turn on fluorescent assay for real time determination of β-galactosidase and its application in living cell imaging

In recent years, fluorescent probes based on chemical reactions have been widely investigated as a powerful and noninvasive method for the diagnosis of diseases. β-Galactosidase (β-gal), a typical lysosomal glycosidase, over expressed in senescent cells and primary ovarian cancer cells, which has been considered as an important biomarker cell senescence and primary ovarian cancers. Fluorescent probes for the determination of β-gal provide an excellent choice for visualization of cell senescence. In this work, a turn on fluorescent probe (HBT-gal) for β-gal activity was developed based on the enzymatic hydrolysis of glycosidic bonds. HBT-gal showed little fluorescence in aqueous buffer excited at 415 nm, while emitted green fluorescence centered at ∼ 492 nm upon incubated with β-gal. The sensing scheme showed high selectivity and sensitivity for β-gal activity with a limit of detection calculated as low as 0.19 mU/mL. Moreover, HBT-gal was successfully applied to image β-gal activity in senescent Hep G2 cells treated with H₂O₂. Therefore, probe HBT-gal demonstrated a potential usage for the determination of cell senescence using β-gal as a biomarker.

Electrochemically-promoted synthesis of benzo[b]thiophene-1,1-dioxides via strained quaternary spirocyclization

We report an approach for the synthesis of benzothiophene motifs under electrochemical conditions by the reaction of sulfonhydrazides with internal alkynes. Upon the formation of a quaternary spirocyclization intermediate by the selective ipso-addition instead of an ortho-attack, the S-migration process was rationalized to lead to the products. Computational studies revealed the selectivity and the compatibility of drug molecules showcased the potential application of the protocols.

We report an approach for the synthesis of benzothiophene motifs under electrochemical conditions by the reaction of sulfonhydrazides with internal alkynes.

A turn on fluorescent assay for γ-glutamyltransferase activity and its application in biological imaging

γ-glutamyltransferase (GGT) is widely presented in living cells and overexpressed in many tumor tissues. Therefore, it is generally considered as an important biomarker for the detection of tumor, especially for liver cancer. Accurate determination of its activity is helpful for early diagnosis and treatment of related diseases. In this work, a "turn on" fluorescent probe NSA-GGT for the detection of GGT activity based on glutamine bond was designed and synthesized by employing dansylamino as fluorophore. The probe shows good water solubility and can be well dispersed in aqueous buffer. After incubated with GGT in phosphate buffer, the fluorescence of NSA-GGT centered at ∼523 nm increased over 25-fold. This sensing pattern exhibits an intriguing sensing sensitivity for GGT, and has good performance on intracellular GGT staining, serving as a promising candidate for GGT measurement. Subsequent biological experiments showed that probe NSA-GGT could also be used for fluorescent imaging of GGT activity in living cells and animal tissues.

A Dual-Control Strategy by Phosphate Ions and Local Microviscosity for Tracking Adenosine Triphosphate Metabolism in Mitochondria and Cellular Activity Dynamically

Adenosine triphosphate (ATP) acts as the main energy source for growth and development in organisms, and the disorder reflects the mitochondrial damage to a large extent. Therefore, an efficient tool for the evaluation of the ATP metabolic level is important to track mitochondrial health, providing an additional perspective for an in-depth long-term study on living activities. Herein, a twisted intramolecular charge transfer (TICT) framework is utilized to build up a sensitive receptor, Mito-VP, with a negligible background to target mitochondrial ATP metabolism by monitoring the phosphate ion (Pi) level upon ATP hydrolysis under the overall consideration of the structural and functional features of mitochondria. The responsive fluorescence could be lighted on under the dual control of Pi and local microviscosity, and the two steps of ATP hydrolysis could be captured through fluorescence. In addition to the well-behaved mitochondrial targeting, the energy metabolism at cellular and organism levels has been clarified via mitosis and zebrafish development, respectively.

Ratiometric sensing of butyrylcholinesterase activity based on the MnO2 nanosheet-modulated fluorescence of sulfur quantum dots and o-phenylenediamine

Butyrylcholinesterase (BChE) can modulate the expression level of cholinesterase, which emerges as an important clinical diagnose index. However, the currently reported assays for BChE are suffering from the problem of interferences. A ratiometric fluorescence assay was developed based on the MnO₂ nanosheet (NS)-modulated fluorescence of sulfur quantum dots (S-dots) and o-phenylenediamine (OPD). MnO₂ NS can not only quench the fluorescence of blue emissive S-dots, but also enhance the yellow emissive OPD by catalyzing its oxidation reactions. Upon introducing BChE and substrate into the system, their hydrolysate can reduce MnO₂ into Mn²⁺, leading to the fluorescence recovery of S-dots and failure of OPD oxidation. BChE activity can be quantitatively detected by recording the change of fluorescence signals in the blue and yellow regions. A linear relationship is observed between the ratio of F₄₃₅/F₅₆₀ and the concentration of BChE in the range 30 to 500 U/L, and a limit of detection of 17.8 U/L has been calculated. The ratiometric fluorescence assay shows an excellent selectivity to acetylcholinesterase and tolerance to various other species. The method developed  provides good detection performances in human serum medium and for screening of  inhibitors.

AND-Logic Strategy for Accurate Analysis of Alzheimer's Disease via Fluorescent Probe Lighted Up by Two Specific Biomarkers

Alzheimer's disease (AD) has become a global threat to the elderly health with a short survival time after diagnosis. Due to the asymptomatic stage during the early development, patients are usually diagnosed at the middle or late stage. Therefore, an efficient tool for AD early diagnosis deserves considerable attention, which could make a significant contribution to the treatment intervention. A fluorescent probe has been widely applied for detecting and visualizing species of interest in vitro and in vivo, and the proper reaction between the probe and analytes is responsible for the fluorescence change to provide a lighting-on or ratiometric responsive pattern with satisfactory sensing behavior. In this work, we report the first attempt to build up an AND-logic probe P2 for AD accuracy diagnosis taking butyrylcholinesterase (BChE) and reactive oxygen species (ROSs) as dual targets. Upon the co-stimulation by these two factors through enzymatic hydrolysis and redox reaction, the NIR emission could be readily turned on. This AND sensing pattern avoided the false-positive response effectively, and other diseases sharing one biomarker could hardly induce a NIR fluorescence response. The sensing assay has also been confirmed to be feasible in vitro and in vivo with good sensibility and selectivity. It is worth mentioning that the probe structure has been optimized in terms of the linkage length. This study shows that probe P2 with a connecting arm of medium length (one methylene, n = 1) has superior sensing performance, promising to provide a reference for the relative structure design.