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The undesirable enzymatic activity of nanozymes under near neutral pH condition and the traditional single signal output always restrict the analytical application of nanozyme-based biosensors. Herein, graphitic carbon nitride nanosheets supported palladium nanosheets composite (Pd/g-C3N4) with both oxidase-like activity and fluorescent property is synthesized. Notably, Pd/g-C3N4 exhibits enhanced oxidase-like activity compared to Pd NSs under pH 7.4. By combining Pd/g-C3N4 with o-phenylenediamine (OPD), a ratiometric fluorescence assay for acetylcholinesterase (AChE) activity detection is developed. Pd/g-C3N4 can catalyze oxidation of nonfluorescent OPD to fluorescent oxidized OPD (oxOPD, Em = 565 nm), which can quench fluorescence of g-C3N4 supporter (Em = 441 nm) through fluorescence resonance energy transfer (FRET). However, in presence of AChE, acetylthiocholine can be hydrolyzed into thiocholine, which will block the oxidase-like activity of Pd/g-C3N4 and then hamper the FRET process. This ratiometric fluorescence assay is also viable to screen AChE inhibitor. This work will guide design of ratiometric fluorescence assay based on nanozymes with improved enzymatic activity.

Acetylcholinesterase (AChE) plays crucial roles in the nervous system, and thus the reliable assay of its activity is of great significance for the diagnosis of nervous diseases. In this work, we report a fluorescent sensing platform with silicon quantum dots (Si-QDs) as a fluorescence oscillator and nano iron oxyhydroxide (α-, β-, and γ-FeOOH) as a quencher for the assay of AChE. FeOOH with α-, β-, and γ-crystal forms quenches the fluorescence of Si-QDs at λex/λem = 350/438 nm, which is retrieved in the presence of AChE and its substrate acetylthiocholine (ATCh) to provide an off-on strategy with a high signal/noise ratio. It is interesting that the sensitivity of AChE sensing is closely related to the crystal forms of FeOOH, with the highest sensitivity by adopting α-FeOOH as the quencher. A linear calibration is achieved within 0.02-1.4 U/L along with a limit of detection of 0.016 U/L. The sensing strategy was demonstrated by the AChE assay in human blood, plasma, and hemocytes.

In this paper, a new fluorescence analysis method was proposed to detect parathion-methyl (PM) based on platinum nanoparticles (PtNPs) and 4-amino-3-hydroxy-1-naphthalenesulfonic acid (AHNSA) as fluorescent probe. AHNSA with high fluorescence could combine with PtNPs by electrostatic attraction, bringing out fluorescence quenching of AHNSA. Acetylthiocholine (ATCh) was hydrolyzed by acetylcholinesterase (AChE) to produce thiocholine, which could induce the aggregation of PtNPs by electrostatic attraction and restore the fluorescence intensity of AHNSA. However, in the presence of PM, the catalytic activity of AChE is inhibited, leading to the quenching of fluorescence of AHNSA again. Under the optimal conditions, the linear range of parathion-methyl (PM) detection was 0.26–53.3 ng/mL (R2 = 0.994), and the limit of detection was 0.17 ng/mL (S/N = 3). In addition, this method has been successfully used for the determination of PM in water and food samples.

Summary Amyloid fibrils are one of the hallmarks of Alzheimer's disease (AD), although a causative link between plaque-forming amyloid fibrils and AD pathology remains to be clarified. This study demonstrates, for the first time for a naturally occurring amyloid, that fibrils comprising the 42-residue amyloid-β peptide (Aβ42) exhibit significant catalytic properties. Aβ42 fibrils catalyzed the hydrolysis of the model ester para-nitrophenyl acetate (pNPA) and of acetylthiocholine, a surrogate for the neurotransmitter acetylcholine. Aβ42 fibrils also catalyzed oxidation of the prominent neurotransmitters dopamine and adrenaline. Importantly, the catalytic activity was specifically manifested by mature Aβ42 fibrils and not the peptide monomers or oligomeric Aβ42, the putative neurotoxic species. Furthermore, maximal catalytic activity was recorded by the full-length Aβ42 fibrils, whereas fibrillar assemblies comprising Aβ42 subdomains were significantly less catalytic. The catalytic activity of Aβ fibrils could exhibit insidious roles in AD pathophysiology.

A new N,O-rich covalent organic framework (COFDHNDA-BTH) was synthesized by an amine-aldehyde condensation reaction between 2,6-dialdehyde-1,5-dihydroxynaphthalene (DHNDA) and 1,3,5-phenyltriformylhydrazine (BTH) for carbaryl detection. The free NH, OH, and C=O groups of COFDHNDA-BTH not only covalently couples with acetylcholinesterase (AChE) into the pores of COFDHNDA-BTH, but also greatly improves the catalytic activity of AChE in the constrained environment of COFDHNDA-BTH’s pore. Under the catalysis of AChE, the acetylthiocholine (ATCl) was decomposed into positively charged thiocholine (TCl), which was captured on the COFDHNDA-BTH modified electrode. The positive charges of TCl can attract anionic probe [Fe(CN)6]3−/4− on the COFDHNDA-BTH-modified electrode to show a good oxidation peak at 0.25 V (versus a saturated calomel electrode). The carbaryl detection can inhibit the activity of AChE, resulting in the decrease in the oxidation peak. Therefore, a turn-off electrochemical carbaryl biosensor based on a flexible carbon paper electrode loaded with COFDHNDA-BTH and AChE was constructed using the oxidation peak of an anionic probe [Fe(CN)6]3−/4− as the detection signal. The detection limit was 0.16 μM (S/N = 3), and the linear range was 0.48~35.0 μM. The sensor has good selectivity, repeatability, and stability, and has a good application prospect in pesticide detection.

The bifunctional moderator is urgently needed in the field of ratiometric electrochemiluminescence (ECL) sensing since it can mediate simultaneously two ECL signals to conveniently realize their opposite change trend. This work designed a novel dual-signal combined nanoprobe with carboxyl-functionalized poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-{2,1',3}-thiadazole)] nanoparticles (c-PFBT NPs) as the anodic ECL probe and L-cysteine capped CdS quantum dots (L-CdS QDs) as the cathodic ECL probe, which performed a dual-signal output capability without any additional coreactants. More importantly, hydrogen peroxide (H2O2) produced in situ by enzyme-catalyzed reaction was developed as a bifunctional moderator for simultaneously regulating two signals. The dual-signal combined nanoprobe (c-PFBT NPs@CdS QDs) served as the matrix to immobilize acetylcholinesterase (AChE) and choline oxidase for organophosphorus (OPs) analysis. In the absence of OPs, H2O2 was produced by catalyzing the substrate acetylthiocholine (ATCl) with enzymes and it quenched the anodic ECL signal from c-PFBT NPs and simultaneously promoted the cathodic ECL signal from L-CdS QDs. When OPs was present, the activity of AChE was inhibited, the anodic signal would increase, and the cathodic signal would accordingly decrease. The integration of the bifunctional moderator H2O2 and dual-signal combined nanoprobe c-PFBT NPs@CdS QDs not only provides an attractive ECL platform for enzymatic sensing involving the generation or consumption of H2O2 but also paves a new pathway for other ratiometric ECL systems involving enzyme catalytic amplification for detecting antigens, antibodies, DNA, RNA, etc.

A water-soluble and sensitive fluorescent probe N,N′-bis[tris-(2-aminoethyl)amine]-3,4,9,10-perylenetetracarboxylic diimide (PTRIS) was synthesized and, in combination with polydopamine (PDA), utilised in the detection of acetylcholinesterase (AChE) activity. PDA is spontaneously polymerized from dopamine (DA) in aerobic and alkaline solutions. The excellent absorption of PDA results in the aggregation of PTRIS around PDA as well as π–π stacking between them, which consequently quenched the fluorescence of PTRIS due to aggregation induced quenching (AIQ) in 9 min. The hydrolysis product of acetylthiocholine (ATCh) catalyzed by AChE, thiocholine (TCh), was proved to inhibit the polymerization of DA, therefore the free monomeric PTRIS retained its strong fluorescence intensity. The fluorescence was switched off and on depending on the activity of AChE. According to the change of fluorescence intensity at 550 nm, the detection limit of AChE was quantified as 0.02 mU mL−1. It was also proved that this probe possessed excellent selectivity for AChE. Tacrine and the organophosphate pesticide diazinon were further evaluated for inhibitor screening. The half-maximal inhibitory concentration value of tacrine and diazinon was calculated to be 1.4 and 1.6 μM respectively, revealing potential applications for inhibition and pesticide detecting.

A self-enhanced electrochemical luminescence (ECL) composite material g-C

Most of the fluorescence sensors require choline oxidase or quenchers to detect organophosphorus pesticides (OPs) based on a single hydrolysate and suffer from high cost, complex procedures, weak stability, and low sensitivity. Here, we proposed a brand-new fluorescence strategy for highly sensitive detection of OPs based on both hydrolysate-response disulfide bond-functionalized gold nanoclusters (S-S-AuNCs) without additional substances. S-S-AuNCs were synthesized via a facile one-step redox reaction and emitted bright red light with ultrasmall size and high water dispersion. Interestingly, S-S-AuNCs displayed a unique response to thiol compounds and low pH values and were thus pioneered as a high-efficiency sensor for OPs based on acetylcholinesterase (AChE)-catalyzed hydrolysis of acetylthiocholine into thiocholine and CH3COOH and OP inhibition of AChE activity. Further, S-S-AuNCs were employed to monitor the residue, distribution, and metabolization of methidathion in pakchoi with acceptable results. We believe that this work supplies a simpler and more highly sensitive approach for OP assay than the known ones and opens a new avenue to development of multistimulus-responsive and high-performance fluorescence substances.

A highly sensitive and selective method was developed for both UV–vis spectrophotometric and fluorimetric determination of organophosphorus pesticides (OPs). This method used silver nanoparticles (AgNPs) modified with graphitic carbon nitride (g-C3N4). The AgNPs reduced the fluorescence intensity of g-C3N4. Acetylthiocholine (ATCh) could be catalytically hydrolyzed by acetylcholinesterase (AChE) to form thiocholine, which induces aggregation of the AgNPs. This aggregation led to the recovery of the blue fluorescence of g-C3N4, with excitation/emission peaks at 310/460 nm. This fluorescence intensity could be reduced again in the presence of OPs because of the inhibitory effect of OPs on the activity of AChE. The degree of reduction was found to be proportional to the concentration of OPs, and the limit of fluorometric detection was 0.0324 μg/L (S/N = 3). In addition, the absorption of the g-C3N4/AgNPs at 390 nm decreased because of the aggregation of the AgNPs, but was recovered in presence of OPs because of the inhibition of enzyme activity by OPs. This method was successfully applied to the analysis of parathion-methyl in real samples., Graphical abstract Image 1, Highlights • A g-C3N4/AgNPs sensor could be used for the determination of organophosphorus pesticides (OPs). • The method exhibits ultra-sensitivity and high-selectivity toward OPs. • Double-signal OPs probe was developed with low cost, simple interpretation and easy handling.

Inhibition kinetics assays were conducted with 16 commercial organophosphate (OP) pesticides or their metabolites on acetylcholinesterase (AChE) in erythrocyte “ghost” preparations from 18 individual humans (both sexes; adults, juveniles, and cord blood samples; mixed races/ethnicities) and pooled samples from adult rats (both sexes). A well-established spectrophotometric assay using acetylthiocholine as substrate and a chromogen was employed. The kinetic parameters bimolecular rate constant (ki), dissociation constant (KI), and phosphorylation constant (kp) were calculated for each compound. As expected, a wide range of potencies were displayed among the tested compounds. Statistical analysis of the resultant data indicated no differences in sex, age, or race/ethnicity among the human samples that are unexpected based on chance (4.2% statistically significant out of 48 parameters calculated) and no differences between the sexes in rats. The bimolecular rate constants for 10 of the compounds were not statistically different between rats and humans. The data indicate that, consistent with the high level of conservation of AChE among species and the fact that AChE at different locations within a species arises from the same gene, the inhibition kinetic parameters calculated from rat erythrocyte ghost preparations should be useful in estimating potencies of OP compounds on target AChE in humans. Additionally, the data indicate that differences in sensitivities among individual humans were not apparent.

Traditional peroxidase-like nanozyme-based sensors suffer from self-decomposition and high toxicity of H2O2, as well as the interference of color from nanozymes themselves and testing samples. In this work, we adopt nanozymes (two-dimension (2D) MnO2 sheets, manganese dioxide nanosheets (MnNS)) with oxidase-like and peroxidase-like properties as advanced catalysts to develop a novel homogeneous electrochemical sensor for organophosphate pesticides (OPs) using dissolved O2 as a coreactant without the interference of H2O2 and color. Owing to the large surface area and unique catalytic activity of MnNS, a large amount of tetramethylbenzidine (TMB) is catalyzed oxidation, leading to a significantly declined differential pulse voltammetry (DPV) current. Obviously, MnNS display an excellent response to thiocholine, deriving from the catalyzing hydrolysis of acetylthiocholine (ATCh) by acetylcholinesterase (AChE), which switches a homogeneous electrochemical OP detection process based on the depressing AChE activity with a limit of detection (LOD) of 0.025 ng mL-1. The as-proposed strategy on using nanozymes with oxidase-like and peroxidase-like properties to develop a homogeneous electrochemical sensor will provide a new pathway for improving the performance of nanozyme-based sensors, and the established MnNS-based homogeneous electrochemical sensor will find more applications for OP residue determination in food samples.

Currently, pesticide residues increasingly lead to health problems. Acetylcholinesterase enzyme (AChE) plays a role in detoxification processes due to their ability to scavenge organophosphates. Thus, this enzyme has been selected for the detection of pesticides. Herein, this study describes the preparation and application of appropriate new immobilized spheres that could be used for the detection of organophosphorus pesticide residues. That is a simple colorimetric enzymatic assay for the practical discovery of N-(Mercaptomethyl) phthalimide S-(O, O-dimethylphosphorodithioate) from organophosphorus pesticides (OPs) widely used in the treatment of sugar beet, apple, nut, corn, and tobacco. The process is based on the immobilization of acetylcholinesterase onto tryptophan FMPS-Trp, (FMPS-Trp)Pd(II), and (FMPS-Trp)Pt(II) functionalized spheres. Spectroscopic and microscopic techniques were used in the characterization of the spheres where scanning electron microscopy (SEM) is an essential tool. The (FMPS-Trp)Pt(II)-AChE showed a good affinity to acetylthiocholine chloride (ATCl) and was found to have the ability to catalyze the hydrolysis of ATCl with an apparent Michaelis-Menten constant value of 288 mM. The developed colorimetric process showed good qualitative analytical performance for Phosmet (OPs) detection as low as 10(-7) M. [GRAPHICS] . Gazi University Research FundGazi University [05/2014-02] This work was supported by the Gazi University Research Fund (05/2014-02). WOS:000612292300001 2-s2.0-85099954280

Herein, combined with a pervasive smartphone installed with a color recognition app, dual-responsive CDs@Eu/GMP ICPs were designed as a red-to-blue paper-based colorimetric sensor for the point-of-use analysis of cerebral acetylcholinesterase (AChE) upon Cd2+ exposure. Blue-emitting CDs with multi-functional groups as guests were encapsulated into the network of Eu/GMP ICPs to obtain CDs@Eu/GMP ICPs with the sensitized red fluorescence of Eu3+. With the presence of thiocholine (TCh), derived from acetylthiocholine (ATCh) hydrolyzed by AChE, the coordination environment of the CDs@Eu/GMP ICPs was interrupted, leading to the collapse of the CDs@Eu/GMP ICP network and the corresponding release of guest CDs into the surrounding environment. Consequently, the sensitized red fluorescence of Eu3+ decreased and the blue fluorescence of the CDs increased. This obvious red-to-blue fluorescent color changes of CDs@Eu/GMP ICPs on test paper could then be integrated with the smartphone for point-of-use analysis of cerebral AChE upon Cd2+ exposure, which not only offers a new analytical platform for a better understanding of the environmental risk of Alzheimer's Dementia (AD), but also holds great potential in the early diagnosis of AD even at the asymptomatic stage with the decrease in CSF AChE as an early biomarker.

In this study, we have developed a sensitive approach to measure organophosphorus pesticides (OPs) using graphitic-phase C

Organophosphorus pesticides (OPs) are extensively used worldwide as agrochemicals; however, excess use may threaten the health of humans. Thus, it is an urgent need to develop a sensitive method for determination of OPs. Herein, a simple and sensitive split-type electrochemical method was developed by using MnO2 nanoflower-electron mediator as a signal transduction element. The MnO2 nanoflower-electron mediator was synthesized and shows an excellent electrochemical signal attributed to the high specific surface area of MnO2 nanoflower. Meanwhile, the inhibition of OPs on butyrylcholinesterase (BChE) was carried out in the homogeneous system. In the absence of target molecule, a large number of thiocholines (TCh) were yielded from hydrolysis of acetylthiocholine (ATCh) by BChE. The MnO2 nanoflower was cracked, and subsequently, multiple electron mediator molecules were released from the platform after treated with TCh, thus decreasing the electrochemical response. Furthermore, the inhibition of OPs on BChE resulted in the reduced generation of TCh, thus inducing the recovery of electrochemical signal. Under the optimal experimental, dichlorvos can be detected in a wide range of 10−6–10−10 M, with a detection limit of 3 × 10−10 M. Moreover, the assay was successfully used to analyze dichlorvos in cucumber juice and pear juice, showing a great promising potential for detecting organophosphorus pesticides in complex samples.

Ratiometric fluorescent sensors are powerful tools for quantitative analyses. However, gold nano-clusters (AuNCs) as typical fluorophores in ratiometric sensors have some disadvantages, such as low luminous efficiency. In this study, a highly sensitive ratiometric fluorescence sensor was fabricated by the combination of AuNCs and fluorescein (FL), and the photonic crystals (PhCs) were used to selectively enhance the fluorescence intensity of AuNCs. This fluorescence sensor was used for the sensitive detection of acetylcholinesterase (AChE) and its inhibitor paraoxon. AChE can catalyze the hydrolysis of acetylthiocholine (ATCh) to form thiocholine (TCh), which can induce the fluorescence quenching of AuNCs while having no obvious influence on the fluorescence intensity of FL. AChE can be determined in the range from 0.1 to 25 mU mL-1 with a limit of detection (LOD) of 0.027 mU mL-1, and paraoxon can be determined in the range of 0.06 to 60 ng mL-1 with a LOD 0.025 ng mL-1. This method, as a new way to selectively improve the fluorescence signal of one of the fluorophores in the ratiometric sensor, would be a promising strategy for the sensitive determination of AChE and its inhibitor.

This work demonstrates a new strategy for sensing cerebrospinal acetylcholinesterase (AChE) as a cholinergic biomarker for brain dysfunction based on graphene quantum dot (GQD)-functionalized lanthanide infinite coordination polymer (Ln-ICP) nanoparticles. The ICPs used in this work were comprised of two components, i.e. a supramolecular Ln-ICP host formed by the coordination between the GMP ligand and central metal ion Tb3+, and guest GQDs with abundant functional groups, which were utilized as antenna ligands to further sensitize the fluorescence of Tb/GMP. Upon excitation at 300 nm, the obtained GQD@Tb/GMP ICP nanoparticles exhibited enhanced green fluorescence from Tb/GMP. With the addition of Cu2+, the competitive coordination between Cu2+ and GQDs weakened the antenna effect, leading to a decrease in the fluorescence of GQD@Tb/GMP ICPs. However, in the presence of thiocholine (TCh), a thiol-containing compound hydrolyzed from acetylthiocholine (ATCh) by AChE, a stronger coordination interaction between Cu2+ and TCh occurred, resulting in the restoration of the fluorescence of GQD@Tb/GMP ICPs. Using the method established herein, the cerebrospinal AChE fluctuation of rats with acute organophosphorus pesticide (OP) poisoning or chronic Alzheimer's disease (AD) could be monitored. This study essentially provides a novel approach to realize the direct monitoring of a biomarker for brain dysfunction by regulating the competitive coordination interaction reversibly, which is critical in the early diagnosis and therapy of brain diseases.

A feasible and sensitive colorimetric platform was established for the assay of acetylcholinesterase (AChE) activity and evaluation of its inhibitor screening, based upon the light-accelerating oxidase-mimicking activity of black phosphorus quantum dots (BP QDs). The BP QDs were synthesized through a thermal exfoliation method and characterized using various techniques. The BP QDs exhibit oxidase-mimicking catalytic activity on dissolved oxygen-mediating oxidation of 3,3',5,5'-tetramethylbenzidine, a typical substrate of oxidase. This results in a transformation of 3,3',5,5'-tetramethylbenzidine into its blue oxidized product, which has a visible absorption peak at 652 nm. The exposure of 365 nm light irradiation significantly accelerates the oxidase-mimicking activity of the BP QDs and speeds up the reaction efficiency. AChE can specifically catalyze the decomposition of its substrate acetylthiocholine chloride to thiocholine. Thiocholine has reducing capacity and can thus reduce the oxidase-mimicking activity of the BP QDs. As a result, the oxidation of 3,3',5,5'-tetramethylbenzidine is hindered and the blue solution becomes paler. This gives a linear response for AChE ranging from 0.5 to 10.0 mU mL-1 and a detection limit of 0.17 mU mL-1. The assay was successfully applied to evaluate inhibitor screening with neostigmine as the model.

Butyrylcholinesterase (BChE) activity is an important index for a variety of diseases. In this work, a "turn-on" assay is proposed based on controlling the inner filter effect (IFE) of MnO2 nanosheets (NSs) on sulfur nanodots (S-dots). The fluorescence of S-dots is effectively quenched by the MnO2 NSs, due to the wide overlap of the emission spectrum of S-dots and absorption spectrum of MnO2 NSs, together with the superior light absorption capability of MnO2 NSs. BChE can catalyze acetylthiocholine and produce thiocholine, which effectively decomposes the MnO2 NSs into Mn2+, resulting in the disappearance of the IFE and recovery of fluorescence of S-dots. Two-stage linear relationships between the ratio of fluorescence intensity and concentration of BChE are observed from 0.05 to 10 and from 10 to 500 U L-1. A limit of detection of 0.035 U L-1 is achieved, which is the best performance so far. The as-proposed assay is robust enough for practical detection in human serum, and it can avoid interference from its sister enzyme (acetylcholinesterase) and glutathione at the micromolar level. The presented results provide a clue for the functionalization of S-dots, and offer a powerful tool as an analytic technique for nanomedicine and environmental science.

Analytical methods for detecting organophosphorus pesticides (OPs) with high sensitivity as well as on-site screening are urgently required to guarantee food safety and protect ecosystems. Herein, we developed a Ce(III)-driven self-assembled strategy to fabricate nanocomposites (CeGONRs) by a facile method. We used multiple characterization techniques and revealed that CeGONRs form a 3D porous structure and possess high surface-to-volume ratios, mixed valence, and multiple catalytic sites. We have also demonstrated that high-performance CeGONRs have nanozyme catalytic ability and revealed their synergistic catalytic mechanism. As a proof of concept, we investigated the excellent catalytic property of the CeGONRs by catalyzing the oxidation of a 3,3′,5,5′-tetramethylbenzidine (TMB) substrate to produce a blue color. Furthermore, based on the acetylcholinesterase (AChE) enzyme inhibition method, upon the addition of AChE and acetylthiocholine (ATCh), the blue becomes colorless; OPs inhibited the activity of AChE, and prevented the generation of thiocholine (TCh), accompanied by no color change. The CeGONR nanozyme-based sensing platform was used successfully for the colorimetric detection of OPs. OPs were detected at 3.43 ng mL−1 (0.0034 ppb) and the linear range was from 0.012 to 3.50 μg mL−1. The corresponding LOD for chlorpyrifos was measured to be lower than 2 ppb that is below the maximum residue limit (MRL) adopted by the national food safety standard of China. The color change was observable by the naked eye and successfully applied to paper-based disposable test strip screening for OPs; satisfactory results were also obtained using cabbage samples. The rational design of CeGONRs sheds light on the catalytic mechanism and provides a versatile approach for constructing artificial enzymes that can be potentially used for a rapid, on-site, paper-based visual screening of a large number of samples.

Common homogeneous electrochemical (HEC) sensors usually suffer from the drawbacks of high background signal, low signal-to-noise ratio, and even false positive results due to the preaddition of electroactive substances. Thus, it is necessary to develop novel HEC sensors based on in situ generation of electroactive substances to overcome these shortcomings, which, however, is underexplored. In this work, two-dimensional (2D) nanozymes, i.e., cobalt-doped 2D Ti

Gold nanoclusters (Au NCs) with luminescence property are emerging as promising candidates in fluorescent methods for monitoring contaminants, but low luminescence efficiency hampers their extensive applications. Herein, GSH-Au NCs@ZIF-8 was designed by encapsulating GSH-Au NCs with AIE effect into metal-organic frameworks, achieving high luminescence efficiency and good stability through the confinement effect of ZIF-8. Accordingly, a fluorescent sensing platform was constructed for the sensitive detection of copper ions (Cu

Ti3C2 MQDs were synthesized using an effective fluorine-free method with excitation/emission maxima at 390/490 nm and a fluorescence quantum yield of 11.78%. In contrast to the traditional, hazardous, and time-consuming process of HF pretreatment, our fluorine-free method is safe and simple. Acetylcholinesterase (AChE) could catalyze the hydrolysis of acetylthiocholine (ATCh) to produce thiocholine which was further reacted with Ehrman's reagent and decomposed to form a yellow product 2-nitro-5-thiobenate anion (TNB). Due to the obvious overlap between the excitation spectrum of Ti3C2 MQDs and the absorption spectrum of TNB, AChE catalyzed the hydrolysis of substrate DTNB/ATCh to form TNB, which can effectively quench the fluorescence of Ti3C2 MQDs through the inner filter effect (IFE). However, the presence of organophosphorus (OPs) inhibited the activity of AChE, leading to a less expressed IFE and increasing recovery of fluorescence. This was used for the quantification of OPs with a detection limit of 0.20 μg·L-1. Moreover, with the constant increase of AChE activity, the color of the reaction system changed visibly from colorless to yellow, and then from yellow to colorless with further continuous addition of OPs. A colorimetric detection with a paper-based sensor of AChE activity and OP concentration was also fabricated by analyzing changes in RGB value using a smartphone APP. In this work, we proposed an effective fluorescence/colorimetric two-mode detection method, which opened a new horizon to detect other targets.

A novel ratiometric fluorescence strategy for detection of acetylcholestinerase (AChE) is proposed based on carbon nitride quantum dots (g-CNQD) and the complex (PA) formed between phenylboronic acid (PBA) and alizarin red S (ARS). PA showed fluorescence at 598 nm and quenched the fluorescence of g-CNQD at 438 nm. Through UV–visible absorption, fluorescence, and fluorescence lifetime measurements, the quenching effect was demonstrated as inner filter effect (IFE). When Cu2+ was added, the coordination of ARS and Cu2+ decreased the fluorescence of PA at 598 nm and recovered that of g-CNQD at 438 nm. In the presence of AChE it catalyzed the hydrolysis of acetylthiocholine (ATCh) to produce thiocholine (TCh) which competed with ARS for binding to Cu2+; thus, the fluorescence at 598 nm increased and that at 438 nm decreased again. Under the mediation of Cu2+, the fluorescence ratio F598/F438 of PA-CNQD probe had good linear relationship with AChE concentration in the range 0.5–15 mU/mL with a detection limit of 0.36 mU/mL. The method was successfully applied to the determination of AChE in human serum and the screening of inhibitors.

Substrate competition for human acetylcholinesterase (AChE) and human butyrylcholinesterase (BChE) was studies under steady-state conditions using wide range of substrate concentrations. Competing couples of substates were acetyl-(thio)esters. Phenyl acetate (PhA) was the reporter substrate and competitor were either acetylcholine (ACh) or acetylthiocholine (ATC). The common point between investigated substrates is that the acyl moiety is acetate, i.e. same deacylation rate constant for reporter and competitor substrate. Steady-state kinetics of cholinesterase-catalyzed hydrolysis of PhA in the presence of ACh or ATC revealed 3 phases of inhibition as concentration of competitor increased: a) competitive inhibition, b) partially mixed inhibition, c) partially uncompetitive inhibition for AChE and partially uncompetitive activation for BChE. This sequence reflects binding of competitor in the active centrer at low concentration and on the peripheral anionic site (PAS) at high concentration. In particular, it showed that binding of a competing ligand on PAS may affect the catalytic behavior of AChE and BChE in an opposite way, i.e. inhibition of AChE and activation of BChE, regardless the nature of the reporter substrate. For both enzymes, progress curves for hydrolysis of PhA at very low concentration (≪Km) in the presence of increasing concentration of ATC showed that: a) the competing substrate and the reporter substrate are hydrolyzed at the same time, b) complete hydrolysis of PhA cannot be reached above 1 mM competing substrate. This likely results from accumulation of hydrolysis products (P) of competing substrate and/or accumulation of acetylated enzyme·P complex that inhibit hydrolysis of the reporter substrate.

A facile, economic, and portable test kit based on target-responsive hydrogel with smartphone detection was fabricated for the accurate determination of dichlorvos in tap water and food samples. Carbon dots (CDs) and CdTe quantum dots (QDs) embedded hydrogel were employed as indicator, and fluorescence of CdTe QDs (645 nm) was dynamically quenched by Cu2+ while that of CDs (490 nm) were non-response for Cu2+, em erging a typical ratiometric fluorescence signal. Acetylcholinesterase hydrolyzed acetylthiocholine to generate thiocholine that bound with Cu2+ strongly via S-Cu-S bond. Dichlorvos as competitive inhibitor for acetylcholinesterase prevented the generation of thiocholine, which blocked the formation of Cu-thiocholine complex and changed the ratiometric fluorescence signal. The signal of the test kit, which was recorded by smartphone’s camera, was transduced by ImageJ software into the color parameter that was linearly proportional to the logarithm of dichlorvos concentration. This portable test kit showed wide linear range of 1 to 40 ppb and low detection limit of 0.38 ppb for dichlorvos. This test kit exhibited rapid sample-to-answer detection time (50 min) of dichlorvos in tap water and food samples, and the recoveries were in the range 81.3 to 111% with relative standard deviations of less than 9.1%.

In this study, a simple colorimetric method was established to detect copper ion (Cu2+), sulfathiazole (ST), and glucose based on the acetylcholinesterase (AChE)-like activity of zeolitic imidazolate framework-8 (ZIF-8). The AChE-like activity of ZIF-8 can hydrolyze acetylthiocholine chloride (ATCh) to thiocholine (TCh), which will further react with 5,5′-dithiobis (2-nitrobenzoic acid) (DTNB) to generate 2-nitro-5-thiobenzoic acid (TNB) that has a maximum absorption peak at 405 nm. The effects of different reaction conditions (buffer pH, the volume of ZIF-8, reaction temperature and time, and ATCh concentration) were investigated. Under the optimized conditions, the value of the Michaelis-Menten constant (Km) is measured to be 0.83 mM, which shows a high affinity toward the substrate (ATCh). Meanwhile, the ZIF-8 has good storage stability, which can maintain more than 80.0% of its initial activity after 30 days of storage at room temperature, and the relative standard deviation (RSD) of batch-to-batch (n = 3) is 5.1%. The linear dependences are obtained based on the AChE-like activity of ZIF-8 for the detection of Cu2+, ST, and glucose in the ranges of 0.021–1.34 and 5.38–689.66 µM, 43.10–517.24 µM, and 0.0054–1.40 mM, respectively. The limit of detections (LODs) are calculated to be 20.00 nM, 9.25 µM, and 5.24 µM, respectively. Moreover, the sample spiked recoveries of Cu2+ in lake water, ST in milk, and glucose in strawberry samples were measured, and the results are in the range of 98.4–115.4% with the RSD (n = 3) lower than 3.3%. In addition, the method shows high selectivity in the real sample analysis.

Sensors based on colorimetry, fluorescence, and electrochemistry have been widely employed to detect acetylcholinesterase and its inhibitors, however, there are only a minority of strategies for AChE detection based on photothermal method. This work reports a versatile dual-mode colorimetric and photothermal biosensing platform for acetylcholinesterase (AChE) detection and its inhibitor (paraoxon-ethyl, a model of AChE inhibitors) monitor based on Fe-N-C/H

Background Cocaine is a commonly abused drug and there is no approved medication specifically to treat its addiction or overdose. Bacterial cocaine esterase (CocE)-derived RBP-8000 is currently under clinical development for cocaine overdose treatment. It is proven to be effective for human use to accelerate cocaine metabolism into physiologically inactive products. Besides cocaine, RBP-8000 may hydrolyze the neurotransmitter acetylcholine (ACh), however, no study has reported its cholinesterase activity. The present study aims to examine RBP-8000′s cholinesterase activity and substrate selectivity to address the potential concern that this enzyme therapy might produce cholinergic side-effects. Methods Both computational modeling and experimental kinetic analysis were carried out to characterize the potential cholinesterase activity of RBP-8000. Substrates interacting with RBP-8000 were modeled for their enzyme-substrate binding complexes. In vitro enzymatic kinetic parameters were measured using Ellman’s colorimetric assay and analyzed by Michaelis–Menten kinetics. Results It is the first demonstration that RBP-8000 catalyzes the hydrolysis of acetylthiocholine (ATC). However, its catalytic efficiency (kcat/KM) against ATC is 1000-fold and 5000-fold lower than it against cocaine at 25 °C and 37 °C, respectively, suggesting RBP-8000 has the desired substrate selectivity for cocaine over ACh. Conclusion Given the fact that clinically relevant dose of RBP-8000 displays insignificant cholinesterase activity relative to endogenous cholinesterases in human, administration of RBP-8000 is unlikely to produce any significant cholinergic side-effects. This study provides supplemental evidences in support of further development of RBP-8000 towards a clinically used pharmacotherapy for cocaine overdose.

This paper presents a new probe for fluorescence detection of the acetylcholinesterase (AChE) activity based on molecularly imprinted polymer (MIP) coated carbon dots (C-dots) composite. The C-dots were hydrothermally synthesized with grafted silica surface and sealed with molecularly imprinted polymers in silica pores (MIP@C-dots) in situ. Removed the original template molecules, the MIP@C-dots composite exhibits quite high selectivity for acetylthiocholine (ACh). With AChE, its substrate ACh will be hydrolyzed into thiocholine and the fluorescence signals exhibit a dramatic decrease at 465 nm, Under optimal conditions, the fluorescent probe shows sensitive responses to AChE in the range of 0.01-0.6 mU/mL. The detection limits of AChE are as low as 3 µU/mL. These experiments results validate the novel fluorescent probe based on MIP@C-dots composite, paving a new way to evaluation of AChE activity and Screening inhibitors.

In this paper, we present a simple strategy to fabricate a sensitive fluorescence microfluidic sensor based on quantum dots (QDs) aerogel and acetylcholinesterase enzyme (AChE) for organophosphate pesticides (OPs) detection The detection is based on the change of fluorescence intensity of QDs aerogel, which will be partly quenched as a consequence of the hydrolytic reaction of acetylthiocholine (ATCh) catalyzed by the AChE, and then the fluorescence of QDs aerogel is recovered due to decreasing of the enzymatic activity in the presence of OPs. The QDs-AChE aerogel based microfluidic arrays sensor provided good sensitivity for rapid detection of OPs with a detection limit of 0.38 pM, while the detection range is from 10−5 to 10−12 M. Due to the result of random orientations of AChE in the 3D porous aerogel nano-structure, the sensor presents similar calibration curves to difference pesticides, which promises the ability of the sensor to monitor total OPs of mixture. This determination sensor shows a low detection limit, wide linear range, and highly accurate determination of total OPs and carbamate content. Finally, we show the proposed sensor can be used to monitor of simple OPs and mixture in spiked fruit samples. This novel QDs-AChE aerogel sensor has an extremely high sensitivity and large detection range, it is a promising tool for accurate, rapid and cost-effective detection of various OP residues on agricultural products.

Purpose Because of the bioaccumulation effect, organophosphorus pesticides cause long-term damage to mammals, even at small concentrations. The ability to perturb the phospholipid bilayer structure as well as the overstimulation of cholinergic receptors makes them hazardous to humans. Therefore, there is a need for a quick and inexpensive detection of organophosphorus pesticides for agricultural and household use. As organophosphorus pesticides are acetylcholinesterase (AChE) inhibitors, biosensors using this mechanism hold a great promise to meet these requirements with a fraction of reagents and time used for measurement comparing to laboratory methods. This study aims to manufacture AChE-coated, screen-printed carbon electrodes applicable in such amperometric biosensors. Design/methodology/approach AChE enzyme, known for catalytic activity for the hydrolysis of acetylthiocholine (ATCh), could be used to obtain electrochemically active thiocholine from acetylthiocholine chloride in aqueous solutions. Using Malathion’s inhibitory effect towards AChE, pesticides’ presence can be detected by reduction of anodic oxidation peaks of thiocholine in cyclic voltammetry. Findings The conducted research proved that it is possible to detect pesticides using low-cost, simple-to-manufacture screen-printed graphite (GR) electrodes with an enzymatic (AChE) coating. Investigated electrodes displayed significant catalytic activity to the hydrolysis of ATCh. Owing to inhibition effect of the enzyme, amperometric response of the samples decreased in pesticide-spiked solution, allowing determination of organophosphorus pesticides. Originality/value Printed electronics has grown significantly in recent years as well as research focused on carbon-based nanocomposites. Yet, the utilization of carbon nanocomposites in screen-printed electronics is still considered a novelty in the market. Biosensors have proved useful not only in laboratory conditions but also in home applications, as glucometers are a superior solution for glucose determination for personal use. Although pesticides could be detected accurately using chromatography, spectroscopy, spectrometry or spectrophotometry, the market lacks low-cost, disposable solutions for pesticide detection applicable for household use. With biosensing techniques and electric paths screen-printed with GR or graphene nanocomposites, this preliminary research focuses on meeting these needs.