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

An acylaminoacyl-peptide hydrolase-activated fluorescent probe for ultrasensitive detection of pesticide residue

Due to increasing threats to global public health and widespread environmental pollution issues caused by improper and excessive application of pesticides, the detection of pesticide residues is important in securing food safety and responding to public health. However, conventional methods for pesticide residues detection were usually labor- and time-consuming, making the acquisition of efficient tools for rapid and sensitive detection of pesticide residues an urgent need. Enzyme-targeted organic fluorescent probes, which displayed high simplicity and sensitivity, have shown great potential in enzyme inhibition-based pesticide residues detection and related bioimaging. Among these, fluorescent probes-based biosensors for pesticide targeted serine hydrolyses such as carboxylesterases and cholinesterases have been widely developed. Acylaminoacyl-peptidase hydrolase (APEH), a serine hydrolase with typical α/β fold structure, is a promising protein target for pesticides such as organophosphorus (OPs) and carbamate. However, no fluorescent probe targeting APEH has been reported for pesticide detection or related research. To address this, an enzyme-activated fluorescent probe (named as RH-AcA) with high sensitivity (limit of detection = 3.7 mU/mL), binding affinity (Km = 6.49 ± 0.29 μM) and high specificity toward APEH was constructed whilst inhibitory efficacy of different pesticides toward APEH in living cells and zebrafish was first visualized. Most importantly, APEH-inhibition-based pesticide residues detection was first achieved using RH-AcA, revealing significantly higher detection sensitivity toward OPs compared to esterase-based fluorescent probes This demonstrated APEH is a promising non-esterase target for enzyme-inhibition-based pesticide residues detection, and RH-AcA could serve as an ultrasensitive and practical tool for pesticides detection and related bioimaging.

A near-infrared fluorescent probe based on purine for glyphosate detection in real sample, living cells and zebrafish

In this study, we developed a novel NIR purine-based fluorescent probe, EPNA, that operates on an on-off-on fluorescence mechanism. EPNA exhibits high selectivity for Cu2+ ions, with fluorescence quenching and a detection limit of 129.2 nM. Job's plot and Density Functional Theory (DFT) calculation confirm the formation of a stable 1:1 complex between EPNA and Cu2+. The EPNA-Cu2+ complex is highly sensitive to glyphosate, with fluorescence restoration upon exposure to glyphosate, achieving a detection limit of 157.4 nM. The detection of Cu2+ and glyphosate by the probe EPNA can also be observed with the naked eye under visible light, offering an easy and intuitive method for detection. The probe successfully detects glyphosate in environmental samples, living cells and zebrafish. Key advantages of the EPNA-Cu2+ system include low detection limits, exceptional selectivity, rapid response times (30 s for Cu2+ and 20 s for glyphosate), and strong resistance to interference, making it an efficient tool for glyphosate detection.

Colorimetric - Fluorescence - Photothermal tri-mode sensor array combining the machine learning method for the selective identification of sulfonylurea pesticides

Though cholinesterase-based method could detect two types of pesticides (organophosphorus and carbamate), they had weak sensing on sulfonylurea pesticides. In our previous work, the peroxidase-like reaction system of nanozyme - H2O2 - TMB showed selective detection of sulfonylurea pesticides, but the single-signal output sensing platform was easily affected by complex matrix background, cross-contamination and human error. Therefore, this work used colorimetric, photothermal, and fluorescent signals of the nanozyme reaction as sensing units for the detection of pesticides. This is the first time that photothermal signals have been used to construct a sensor array. When the concentration of interfering substances was 25 times that of pesticides, the method was still unaffected and had excellent selectivity and anti-interference performance. Meanwhile, a concentration-independent differentiation mode was established based on the K-nearest neighbor (KNN) algorithm. The pesticides were detected and distinguished with 100% accuracy. This work contributed to the detection of sulfonylurea pesticides in complex environmental/food matrices, bridging the gap of existing pesticide detection methods and providing an effective method for food safety detection.

Detection of arsenate in colored grains using an interference-free dual-signal ratiometric HEC sensor

The design of novel homogeneous electrochemical (HEC) sensors with dual-signal ratiometric response holds great potential for highly sensitive and reliable detection of arsenic in food matrices. Herein, COF-based hybrids were prepared by integrating methylene blue (MB) signals and MnO2 nanozyme coatings, possessing the advantages of high signal loading, oxidase-mimicking activity, and ascorbic acid (AA)-specific recognition to realize ratiometric HEC detection of arsenate. The hydrolysate AA, produced from ALP-catalyzed AAP hydrolysis, could decompose MnO2 coatings into Mn2+, and regulate MB release and o-phenylenediamine oxidation to 2,3-diaminophenazine (DAP). Furthermore, arsenate specifically inhibited ALP, subsequently restraining AA formation and MnO2 decomposition. Consequently, a decreased MB current and an increased DAP current with opposite responses were regulated by arsenate compared with those without arsenate. Thus, this dual-signal ratiometric HEC sensor achieved sensitive detection of arsenate, with a LOD of 0.509 ppb. It was successfully applied to reliable detection of arsenate in complex food matrices.

A Near-Infrared Fluorescent Probe for Visualization of Acetylcholinesterase Flux in the Acute Epileptic Mice Brain

Neurotransmitter imbalance is an important pathological basis for epilepsy seizures. Acetylcholinesterase (AChE) as a key hydrolase in the cholinergic system directly affects the metabolism of neurotransmitter. Unfortunately, owing to the lack of reliable in situ imaging tools in the brain, the association between AChE and epilepsy has not been fully elucidated yet. Here, we rationally designed a near-infrared (NIR) fluorescent probe (QXMC) by employing N,N-dimethyl carbamyl as an AChE sensing group in the quinolinium-xanthene NIR skeleton. QXMC exhibited high sensitivity, excellent selectivity, and ultrafast response time (within 0.5 s) toward AChE. Moreover, QXMC can sensitively monitor the fluctuations of AChE activity in the neuronal cells and zebrafish during the apoptosis or oxidative stress process. Significantly, using QXMC with superb blood-brain barrier (BBB) permeability, for the first time, we discovered a down-regulated AChE level in the acute epileptic mice brain through noninvasive NIR in vivo imaging. Moreover, the visualization of therapeutic evaluation of epilepsy has also been achieved by monitoring AChE with QXMC. This work demonstrated the great potential of QXMC as an effective imaging tool for epilepsy diagnosis, therapeutic evaluation, and pathogenesis study.

A novel dicyanoisophorone-based fluorescent probe for rapid detection of acetylcholinesterase in biological systems

Acetylcholinesterase (AChE) plays a vital role in various neurological diseases including brain disorders, neurotransmission alterations, and cancer. Developing effective methods to image AChE in biological samples is essential for understanding its mechanisms in biosystems. Here, we introduce a novel fluorescent probe CNA, that enables detection of AChE at 520 nm with rapid response time of 60 s and a detection limit of 0.014 U/mL. We successfully applied CNA to image endogenous and exogenous AChE in PC12 cells and in living mice. These findings highlight the potential of CNA as an effective method to study the physiological and pathological roles of AChE in complex living systems.

Dual Monitoring of Blood Acetylcholinesterase Content and Catalytic Activity Utilizing Fluorometry-Integrated Surface Plasmon Resonance

Acetylcholinesterase inhibitors (AChEIs), particularly donepezil, are commonly used to treat mild-to-moderate Alzheimer's disease (AD). However, drug accumulation during long-term use could change AChE activity and content, leading to peripheral side effects and prompting medication discontinuation. However, there are a lack of methods to simultaneously determine the content and catalytic activity of AChE. By using phosphatidylinositol-specific phospholipase C to strip AChE from erythrocyte surfaces, we developed a novel method combining surface plasmon resonance and fluorescence detection for the simultaneous detection of AChE content and activity, producing stable, reliable, and accurate results. The established determination range spans from 263.37 ng/mL to 3000 ng/mL (4.05 nM to 46.15 nM) for concentration, and from 39.02 mU/mL to 1000 mU/mL for activity. Compared to traditional methods, this approach simplifies operations, reduces detection time, expands the dynamic range, and lowers detection limits, potentially advancing AChE-related research and supporting clinical diagnostics and drug development.

A fluorescence biosensor for organophosphorus pesticide detection with a portable fluorescence device-based smartphone

An innovative fluorescence biosensor was successfully developed to detect organophosphorus pesticide (OPs) by utilizing smartphone technology. The assay relied on the enzymatic activity of alkaline phosphatase (ALP), which facilitated the conversion of L-ascorbic acid 2-phosphate sesquimagnesium salt hydrate (AAP) into L-ascorbic acid (AA). The AA that generated was then reactedwith o-phenylenediamine (OPD) to yield a fluorescent marker identified as 3-(1,2-dihydroxyethyl)furo[3,4-b]quinoxalin-1(3H)-one (DFQ). A novel bandpass approach was specifically developed for a smartphone that was integrated with a customized portable fluorescence device to measure the fluorescence emission of DFQ. The device has a unique application that converts the fluorescence intensity into an RGB signal. In the presence of OPs, malathion was chosen as the representative of the OPs substance; the enzymatic activity of the ALP was inhibited, resulting in a decrease in fluorescence intensity, which was proportional to the concentration of malathion. Smartphones can be used to measure fluorescence emission, offering a calibration sensitivity more than 70 times higher than that of conventional spectrofluorometer. The recently developed methodology can be employed to identify malathion within the concentration range of 0.1-1 ppm, with a detection limit of 0.05 ppm. The practical applicability of the method was established using vegetable samples, and the acquired results were in good agreement with those obtained using the standard HPLC approach. This innovative method provides both portability and accuracy, while also exhibiting a notable degree of sensitivity in detecting traceamounts of OPs.

Recent advances in the analytical methods for quantitative determination of antioxidants in food matrices

Antioxidants are crucial in reducing oxidative stress and enhancing health, necessitating precise quantification in food matrices. Advanced techniques such as biosensors and nanosensors offer high sensitivity and specificity, enabling real-time monitoring and accurate antioxidant quantification in complex food systems. These technologies herald a new era in food analysis, improving food quality and safety through sophisticated detection methods. Their application facilitates comprehensive antioxidant profiling, driving innovation in food technology to meet the rising demand for nutritional optimization and food integrity. These are complemented by electrochemical techniques, spectroscopy, and chromatography. Electrochemical methods provide rapid response times, spectroscopy offers versatile chemical composition analysis, and chromatography excels in precise separation and quantification. Collectively, these methodologies establish a comprehensive framework for food analysis, essential for improving food quality, safety, and nutritional value. Future research should aim to refine these analytical methods, promising significant advancements in food and nutritional science.

Unique hemispherical coordination-drivened pesticide residue probes: Enhanced stability in linear recognition for trifluralin

Trifluralin (TRL) is an effective and persistent herbicide, but its extensive and prolonged use has increasingly posed ecological and environmental health risks, making the development of convenient and rapid TRL detection methods essential for environmental protection and food safety. In the present research, a novel fluorescent probe was designed and developed, Zn-χ-L, for the rapid and selective detection of TRL in complex environments. The sensor demonstrates excellent sensitivity and stability, while also exhibiting significant resistance to interference from other pesticides and metal ions. Moreover, Zn-χ-L exhibited stable performance across various solvents and showed resistance to interference from other pesticides and metal ions. Molecular docking and theoretical calculations indicate that the unique recognition of TRL molecules by Zn-χ-L is related to its specific hemispheric structural feature, which forms strong coordination interactions between Zn-χ-L and TRL through coordination bonds, π-π stacking, and halogen bonds. This special conformation not only enables the formation of coordination bonds but also establishes multiple π-π stacking and halogen bonding interactions between Zn-χ-L and TRL, leading to efficient charge transfer and exceptional probe performance.

Nanozyme coating-gated multifunctional COF composite based dual-ratio enhanced dual-mode sensor for highly sensitive and reliable detection of organophosphorus pesticides in real samples

The reliable detection of organophosphorus pesticides (OPs) in complex matrices remains an enormous challenge due to inevitable interference of sample matrices and testing factors. To address this issue, we designed a nanozyme-coated mesoporous COF with guest molecule loading, and successfully used it to construct a dual-ratio dual-mode sensor through target-regulated signal generation. The multifunctional COF-based composite (MB/COF@MnO2, MCM) featured high loading of methylene blue (MB), oxidase-like MnO2 coatings as gatekeepers, and specific recognition of thiocholine (TCh). TCh, a regulator produced from acetylcholinesterase (AChE)-catalyzed hydrolysis of acetylthiocholine, could decompose MnO2 coatings, triggering the release of abundant MB and oxidation of few o-phenylenediamine (OPD). OPs, strong inhibitors of AChE, could restrain TCh production and MnO2 decomposition, thereby controlling the release of less MB and oxidation of more OPD. This regulation boosted the dual-ratio dual-mode assay of OPs by using the released MB and oxidized OPD in the solution as testing signals, measured by both fluorescent and electrochemical methods. Experimental results demonstrated the sensitive detection of dichlorvos with LODs of 0.083 and 0.026 ng/mL via the fluorescent/electrochemical mode, respectively. This study represented a creative endeavor to develop dual-ratio dual-mode sensors for OPs detection in complex samples, offering high sensitivity, excellent selectivity, and good reliability.

A highly specific two-photon fluorescent probe for real-time monitoring of acetylcholinesterase in neurogenic disorders in vivo

Acetylcholinesterase (AChE) hydrolyses choline into thiocholine, which is essential for cholinergic neurons to revert to their resting state following activation. Abnormal changes in AChE activity can directly affect nervous system function. Thus, the specific detection of AChE activity is urgently needed for elucidating the function of the nervous system and diagnosing AChE-related diseases. Current methods for detecting AChE activity have several limitations, including strong background interference and poor tissue penetration. Thus, we designed and synthesized a two-photon (TP) excited fluorescent probe, WZ-AChE, for the specific detection of AChE. Briefly, a carbamate bond was chosen to specifically recognize AChE, which can also be cleaved by AChE. The product, WZ, released strong deep red fluorescence signal under TP excitation at 800 nm. Our results showed that WZ-AChE can detect AChE activity in PC12 cells with both superior sensitivity and selectivity. In addition, we successfully applied WZ-AChE to a C. elegans Parkinson's disease (PD) model and a mouse model of depression. The findings revealed that AChE activity was greater in both disease models than in the control group. To summarize, a novel tool was created to investigate the mechanisms underlying PD and depression.

Real time monitoring of nerve agent mimics: Novel solid state emitter for enhanced precision and reliability

Chemical nerve agents are hazardous compounds that terrorists can exploit to pose a significant threat to public safety and national security. The nucleophilic behaviour of these agents enables their interaction with acetyl cholinesterase in the body, leading to paralysis and potentially fatal consequences. Therefore, developing robust and efficient detection methods for these agents is crucial for preventing their misuse. In this manuscript, (E)-12-(1-hydrazineylideneethyl)benzo[f]pyrido[1,2-a]indole-6,11-dione (HBID) is developed as a novel colorimetric and fluorometric probe for the detection of specific chemical nerve agent simulants in both liquid and vapor phase. HBID reacts rapidly with diethyl chlorophosphate (DCP), a common nerve agent simulant, leading to a significant increase in the fluorescence intensity. Under optimized conditions, HBID exhibits high sensitivity, good recyclability, fast response and low limit of detection (0.092 µM). NMR and mass spectral studies suggest that the reaction involves the nucleophilic addition of HBID to DCP, forming a phosphate ester. Additionally, the developed sensor demonstrates viscosity-sensitive AIE phenomena thus greatly expanding its potential applications in biological systems. This sensitivity enables precise detection and visualization of viscosity changes within cellular environments, making the sensor an invaluable tool for studying complex biological processes. The developed probe also detects pH within biologically relevant range (4-6). In practical applications, the probe-treated strips efficiently detected DCP vapor in real time, showing a noticeable fluorescence response. Further, the probe has a strong potential to detect the presence of DCP in the soil samples.

Advancing abiotic stress monitoring in plants with a wearable non-destructive real-time salicylic acid laser-induced-graphene sensor

Drought and salinity stresses present significant challenges that exert a severe impact on crop productivity worldwide. Understanding the dynamics of salicylic acid (SA), a vital phytohormone involved in stress response, can provide valuable insights into the mechanisms of plant adaptation to cope with these challenging conditions. This paper describes and tests a sensor system that enables real-time and non-invasive monitoring of SA content in avocado plants exposed to drought and salinity. By using a reverse iontophoretic system in conjunction with a laser-induced graphene electrode, we demonstrated a sensor with high sensitivity (82.3 nA/[μmol L-1⋅cm-2]), low limit of detection (LOD, 8.2 μmol L-1), and fast sampling response (20 s). Significant differences were observed between the dynamics of SA accumulation in response to drought versus those of salt stress. SA response under drought stress conditions proved to be faster and more intense than under salt stress conditions. These different patterns shed light on the specific adaptive strategies that avocado plants employ to cope with different types of environmental stressors. A notable advantage of the proposed technology is the minimal interference with other plant metabolites, which allows for precise SA detection independent of any interfering factors. In addition, the system features a short extraction time that enables an efficient and rapid analysis of SA content.

Trace Amount of Bi-Doped Core-Shell Pd@Pt Mesoporous Nanospheres with Specifically Enhanced Peroxidase-Like Activity Enable Sensitive and Accurate Detection of Acetylcholinesterase and Organophosphorus Nerve Agents

The urgent need for sensitive and accurate assays to monitor acetylcholinesterase (AChE) activity and organophosphorus pesticides (OPs) arises from the imperative to safeguard human health and protect the ecosystem. Due to its cost-effectiveness, ease of operation, and rapid response, nanozyme-based colorimetry has been widely utilized in the determination of AChE activity and OPs. However, the rational design of nanozymes with high activity and specificity remains a great challenge. Herein, trace amount of Bi-doped core-shell Pd@Pt mesoporous nanospheres (Pd@PtBi2) have been successfully synthesized, exhibiting good peroxidase-like activity and specificity. With the incorporation of trace bismuth, there is a more than 4-fold enhancement in the peroxidase-like performance of Pd@PtBi2 compared to that of Pd@Pt. Besides, no significant improvement of oxidase-like and catalase-like activities of Pd@PtBi2 was found, which prevents interference from O2 and undesirable consumption of substrate H2O2. Based on the blocking impact of thiocholine, a colorimetric detection platform utilizing Pd@PtBi2 was constructed to monitor AChE activity with sensitivity and selectivity. Given the inhibition of OPs on AChE activity, a biosensor was further developed by integrating Pd@PtBi2 with AChE to detect OPs, capitalizing on the cascade amplification strategy. The OP biosensor achieved a detection limit as low as 0.06 ng mL-1, exhibiting high sensitivity and anti-interference ability. This work is promising for the construction of nanozymes with high activity and specificity, as well as the development of nanozyme-based colorimetric biosensors.