Ultra-highly sensitive organophosphorus biosensor based on chitosan/tin disulfide and British housefly acetylcholinesterase

Highly sensitive turn-on electrochemical sensing of organophosphorus pesticides by integration of homogeneous reaction and heterogeneous catalytic signal amplification

Enzyme-inhibited electrochemical sensor is a promising strategy for detecting organophosphorus pesticides (OPs). However, the poor stability of enzymes and the high oxidation potential of thiocholine signal probe limit their potential applications. To address this issue, an indirect strategy was proposed for highly sensitive and reliable detection of chlorpyrifos by integrating homogeneous reaction and heterogeneous catalysis. In the homogeneous reaction, Hg2+ with low oxidation potential was employed as signal probe for chlorpyrifos detection since its electroactivity can be inhibited by thiocholine, which was the hydrolysate of acetylthiocholine catalyzed by acetylcholinesterase. Additionally, Co,N-doped hollow porous carbon nanocage@carbon nanotubes (Co,N-HPNC@CNT) derived from ZIF-8@ZIF-67 was utilized as high-performance electrode material to amplify the stripping voltammetry signal of Hg2+. Thanks to their synergistic effect, the sensor exhibited outstanding sensing performance, excellent stability and good anti-interference ability. This strategy paves the way for the development of high-performance OP sensors and their application in food safety.

Selective and stable visible-light-prompted scavenger-free photoelectrochemical strategy based on a ternary ErVO4/P@g-C3N4/SnS2 nanocomposite for the detection of lead ions in different water samples

Lead ions (Pb2+) are heavy metal environmental pollutants that can significantly impact biological health. In this study, the synthesis of a ternary nanocomposite, ErVO4/P@g-C3N4/SnS2, was achieved using a combination of hydrothermal synthesis and mechanical grinding. The as-fabricated photoelectrochemical (PEC) sensor was found to be an ideal substrate for Pb2+ detection with high sensitivity and reliability. The ErVO4/P@g-C3N4/SnS2/FTO was selected as the substrate because of its remarkable and reliable photocurrent response. The Pb2+ sensor exhibited a low detection limit of 0.1 pM and a broad linear range of 0.002-0.2 nM. Moreover, the sensor exhibited outstanding stability, selectivity, and reproducibility. In real-time applications, it exhibited stable recovery and a low relative standard deviation, ensuring reliable and accurate measurements. The as-prepared PEC sensor was highly stable for the detection of Pb2+ in different water samples. This promising characteristic highlights its significant potential for use in the detection of environmental pollutants.

Nanoassemblies of acetylcholinesterase and β-lactamase immobilized on magnetic nanoparticles as biosensors to detect pollutants in water

The use of enzymes immobilized on magnetic nanoparticles to detect contaminants in aqueous samples has gained interest, since it allows the magnetic control, concentration and reuse of the enzymes. In this work, the detection of trace amounts of organophosphate pesticides (chlorpyrifos) and antibiotics (penicillin G) in water was attained by developing a nanoassembly formed by either inorganic or biomimetic magnetic nanoparticles used as substrates to immobilize acetylcholinesterase (AChE) and β-lactamase (BL). Other than the substrate, the optimization of the nanoassembly was done by testing enzyme immobilization both through electrostatic interaction (also reinforced with glutaraldehyde) and covalent bonds (by carbodiimide chemistry). Temperature (25 °C), ionic strength (150 mM NaCl) and pH (7) were set to ensure enzymatic stability and to allow both the nanoparticles and the enzymes to present ionic charges that would allow electrostatic interaction. Under these conditions, the enzyme load on the nanoparticles was ⁓0.1 mg enzyme per mg nanoparticles, and the preserved activity after immobilization was 50-60% of the specific activity of the free enzyme, being covalent bonding the one which yielded better results. Covalent nanoassemblies could detect trace concentrations of pollutants down to 1.43 nM chlorpyrifos and 0.28 nM penicillin G. They even permitted the quantification of 14.3 μM chlorpyrifos and 2.8 μM penicillin G. Also, immobilization conferred higher stability to AChE (⁓94% activity after 20 days storage at 4 °C) and allowed to reuse the BL up to 12 cycles.

Advanced visual sensing techniques for on-site detection of pesticide residue in water environments

Pesticide usage has increased to fulfil agricultural demand. Pesticides such as organophosphorus pesticides (OPPs) are ubiquitous in world food production. Their widespread usage has unavoidable detrimental consequences for humans, wildlife, water, and soil environments. Hence, the development of more convenient and efficient pesticide residue (PR) detection methods is of paramount importance. Visual detecting approaches have acquired a lot of interest among different sensing systems due to inherent advantages in terms of simplicity, speed, sensitivity, and eco-friendliness. Furthermore, various detections have been proven to enable real-life PR surveillance in environment water. Fluorometric (FL), colourimetric (CL), and enzyme-inhibition (EI) techniques have emerged as viable options. These sensing technologies do not need complex operating processes or specialist equipment, and the simple colour change allows for visual monitoring of the sensing result. Visual sensing techniques for on-site detection of PR in water environments are discussed in this paper. This paper further reviews prior research on the integration of CL, FL, and EI-based techniques with nanoparticles (NPs), quantum dots (QDs), and metal-organic frameworks (MOFs). Smartphone detection technologies for PRs are also reviewed. Finally, conventional methods and nanoparticle (NPs) based strategies for the detection of PRs are compared.

A Sandwich-Type Electrochemical Immunosensor for Insulin Detection Based on Au-Adhered Cu5 Zn8 Hollow Porous Carbon Nanocubes and AuNP Deposited Nitrogen-Doped Holey Graphene

Rapid, accurate, and sensitive insulin detection is crucial for managing and treating diabetes. A simple sandwich-type electrochemical immunosensor is engineered using gold nanoparticle (AuNP)-adhered metal-organic framework-derived copper-zinc hollow porous carbon nanocubes (Au@Cu₅ Zn₈ /HPCNC) and AuNP-deposited nitrogen-doped holey graphene (NHG) are used as a dual functional label and sensing platform. The results show that identical morphology and size of Au@Cu₅ Zn₈ /HPCNC enhance the electrocatalytic active sites, conductivity, and surface area to immobilize the detection antibodies (Ab₂ ). In addition, AuNP/NHG has the requisite biocompatibility and electrical conductivity, which facilitates electron transport and increases the surface area of the capture antibody (Ab₁ ). Significantly, Cu₅ Zn₈ /HPCNC exhibits necessary catalytic activity and sensitivity for the electrochemical reduction of H₂ O₂ using (i-t) amperometry and improves the electrochemical response in differential pulse voltammetry. Under optimal conditions, the immunosensor for insulin demonstrates a wide linear range with a low detection limit and viable specificity, stability, and reproducibility. The platform's practicality is evaluated by detecting insulin in human serum samples. All these characteristics indicate that the Cu₅ Zn₈ /HPCNC-based biosensing strategy may be used for the point-of-care assay of diverse biomarkers.

A novel construct of an electrochemical acetylcholinesterase biosensor for the investigation of malathion sensitivity to three different insect species using a NiCr2O4/g-C3N4 composite integrated pencil graphite electrode

Herein, an electrochemical biosensor has been prepared to assess the sensitivity of an organophosphate insecticide, malathion, to acetylcholinesterase (AChE) enzyme of three insects including Apis mellifera (honeybee), Tribolium castaneum (red flour beetle), and Zootermopsis nevadensis (dampwood termite). A composite of nickel chromite (NiCr2O4) and graphitic carbon nitride (g-C3N4) was prepared and characterized for its morphological, chemical and electrical properties. The NiCr2O4/g-C3N4 composite integrated pencil graphite electrodes were used to covalently immobilize insect AChE enzymes and amperometric response of bioelectrodes was determined through cyclic voltammetry. The prepared bioelectrodes exhibited high enzyme immobilization efficiency and electro-catalytic performance. The integrated bioelectrodes could efficiently detect malathion induced inhibition of insects' AChEs. The linear ranges for malathion were found to be 0.1-1.6 μM, 1-40 nM and 2-100 nM, and LODs were 2 nM, 0.86 nM and 2.3 nM for A. mellifera, T. castaneum, and Z. nevadensis, respectively. Additionally, the biosensing platform developed using A. mellifera AChE was found highly sensitive and effective for malathion recoveries from spiked wheat flour samples with high recovery rates. Moreover, the proposed method was adequately reproducible and selective. The results revealed that A. mellifera AChE is less sensitive to inhibition by malathion as compared to T. castaneum, and Z. nevadensis AChE. The experimental results were validated through computational docking of malathion with insect AChEs and the results were in correspondence to experimental outcomes. The proposed method can be a plausible alternate to conventional analytical methods to assess the pesticide sensitivity and toxicity of various compounds against insect enzymes.

Single-step microwave synthesis of a novel ternary nanocomposite as an efficient luminophore and boron nitride quantum dots as a new coreactant for a cathodic ECL monitoring of chlorpyrifos

In this study, a novel and innovative enzyme-free electrochemiluminescence (ECL) pesticide probe based on a ternary nanocomposite, CuS/CQDs/g-C₃N₄NS, was demonstrated for the accurate monitoring of chlorpyrifos. Boron nitride quantum dots were introduced as a new and effective coreactant in comparison with other coreactants, such as hydrogen peroxide, peroxydisulfate, and tripropylamine, in the negative potential range for the first time. The nanocomposite as a promoted luminophore was synthesized by a one-pot microwave route. Carbon quantum dots and copper sulfide nanostructures were truly incorporated on the porous graphitized carbon nitride, which displayed a good cooperative effect on the signal improvement. CuS as a co-reaction accelerator and CQDs with a superior luminescence effect produced more radical species, and thus, the ECL signal was amplified. Upon increasing the appropriate concentration of this coreactant in electrolyte media, the signal intensity of the nanocomposite increases. A low detection limit of 3.0 × 10^-16 M and a wide range from 2.0 × 10^-15 to 7.0 × 10^-9 M were gained. Also, the fabricated pesticide sensor presented excellent repeatability for 20 consecutive optical signals, with a RSD of about 1.4%. Owing to its high proficiency, the developed sensor was applied as a new probe for chlorpyrifos analysis in water and fruit samples.

MnO2/DNAzyme-mediated ratiometric fluorescence assay of acetylcholinesterase

A ratiometric fluorescent probe (MnO2/DNAzyme) is constructed. In the presence of AChE, the product thiocholine reduces MnO2 to Mn2+. The released H1 strands hybridizes with H2 strands to activate DNAzyme and cause cleavage of DNA-F signal probe.

Recent advancements in the detection of organophosphate pesticides: a review

Organophosphorus pesticides (OPPs) are generally utilized for the protection of crops from pests. Because the use of OPPs in various agricultural operations has expanded dramatically, precise monitoring of their concentration levels has become the critical issue, which will help in the protection of ecological systems and food supply. However, the World Health Organization (WHO) has classified them as extremely dangerous chemical compounds. Taking their immense use and toxicity into consideration, the development of easy, rapid and highly sensitive techniques is necessary. Despite the fact that there are numerous conventional ways for detecting OPPs, the development of portable sensors is required to make routine analysis considerably more convenient. Some of these advanced techniques include colorimetric sensors, fluorescence sensors, molecular imprinted polymer-based sensors, and surface plasmon resonance-based sensors. This review article specifically focuses on the colorimetric, fluorescence and electrochemical sensors. In this article, the sensing strategies of these developed sensors, analytical conditions and their respective limit of detection are compiled.

A pendant droplet-based sensor for the detection of acetylcholinesterase and its inhibitors

In this work, a pendant droplet-based sensor is developed for the rapid and label-free detection of acetylcholinesterase (AChE) and its inhibitors. The detection limit of AChE reaches 0.17 mU mL^-1. The pIC₅₀ values of AChE inhibitors such as neostigmine, rivastigmine and galantamine are determined to be 0.45 μM, 0.64 μM and 4.93 μM, respectively.

Colorimetric detection of chlorpyrifos in peach based on cobalt-graphene nanohybrid with excellent oxidase-like activity and reusability

Cobalt nanocrystal has been widely used as nano-enzyme for sensing and catalysis due to its high stability and low cost, but poor catalytic activity limits its applications in bioanalysis. The study reports one strategy for synthesis of cobalt-graphene nanohybrid. Histidine-functionalized graphene quantum dot (His-GQD) was bound to graphene sheet via π-π stacking and then combined with cobalt ions in the presence of cetyltrimethylammonium chloride to form stable complex and finally reduced under nitrogen to obtain Co-His-GQD-G. The as-synthesized nanohybrid offers well-defined three-dimensional structure and quasi-superparamagnetism. The cobalt nanoparticles were well dispersed on graphene sheets. The unique structure improves oxidase-like activity of Co-His-GQD-G. Further, Co-His-GQD-G was used as the nanozyme for colorimetric detection of chlorpyrifos. Co-His-GQD-G catalyzes oxidization of 3,3',5,5'-tetramethylbenzidine into blue product. Thiocholine produced by hydrolysis of acetylthiocholine under catalysis of acetylcholinesterase inhibits catalytic activity of Co-His-GQD-G and leads to a reduced oxidization rate. Chlorpyrifos inhibits activity of acetylcholinesterase and brings an enhanced absorbance of blue product. The absorbance at 652 nm linearly increases with increasing chlorpyrifos concentration in the range of 2-20 ng mL^-1 with detection limit of 0.57 ng mL^-1 (S/N = 3). The method was successfully applied in determination of chlorpyrifos in peach by preparing Co-His-GQD-G magnetic gel sheet.

An enzyme-free electrochemiluminescence sensing probe based on ternary nanocomposite for ultrasensitive determination of chlorpyrifos

Herein, an innovative enzyme free electrochemiluminescence chlorpyrifos sensor was reported based on the incorporation of ternary nanocomposite (ruthenium nanobeads/silver nanoparticles/graphene oxide) on the surface of glassy carbon electrode. The silver nanoparticles as a robust signal enhancing agent were well deposited on the modified graphene oxide/glassy carbon electrode and exhibited supreme electrocatalytic proficiency. Then, Ru(bipy)₃²⁺ species in bead-like nanoparticles were uniformly anchored on the surface of the modified electrode with the help of chitosan, as a good crosslinking agent. Boron nitride quantum dots as a new coreactant species showed the excellent proficiency for signal enhancement of the fabricated electrode. The fabricated electrode was successfully used as an ultra-sensitive sensor for trace analysis of chlorpyrifos by ECL technique. The wide linear range and the low detection limit were obtained from 5.0 × 10^-15 to 4.2 × 10^-9 M and 6.5 × 10^-16 M, respectively.

Removal of a cationic dye from aqueous solution by a porous adsorbent templated from eco-friendly Pickering MIPEs using chitosan-modified semi-coke particles

Porous materials prepared from high internal phase emulsions have been attracting much attention in recent years, but two major defects related to the high consumption of organic solvent and surfactants are always difficult to solve.

Double-enzymes-mediated fluorescent assay for sensitive determination of organophosphorus pesticides based on the quenching of upconversion nanoparticles by Fe3

Herein, a new double-enzymes-modulated fluorescent assay based on the quenching of upconversion nanoparticles (UCNPs) by Fe³⁺ was constructed for sensitive determination of OPs. OPs can inhibit the activity of acetylcholinesterase to reduce the production of choline and further lead to the lack of H₂O₂ in the presence of choline oxidase. Therefore, Fe²⁺ cannot be converted into Fe³⁺, resulting in "turn-on" fluorescence of UCNPs. Under optimal conditions, an excellent linear correlation between the inhibition efficiency and the logarithm of the chlorpyrifos concentration was achieved with a detection limit (LOD) of 6.7 ng/mL in the range of 20-2000 ng/mL. The recovery for chlorpyrifos in apples and cucumbers was 89.5-97.1%. The results were consistent with those obtained by GC-MS. Overall, the integration of UCNPs into the double-enzymes-mediated Fe³⁺/Fe²⁺ conversion endows this method with desirable rapidity, sensitivity, selectivity, stability, operational simplicity, and strong anti-interference capability, holding great potential in the application of food safety.

Design of A Low-Cost and Disposable Paper-Based Immunosensor for the Rapid and Sensitive Detection of Aflatoxin B1

We report a paper-based electrochemical immunosensor made with sustainable materials to detect aflatoxin B1 (AFB1), a highly toxic, carcinogenic mycotoxin found in food. The immunosensor was prepared with a waterproof paper substrate and low-cost graphite-based conductive ink through a simple cut-printing method. The working electrode was functionalized with a drop-cast film of multiwalled carbon nanotubes (MWCNT)/chitosan on which a layer of anti-AFB1 monoclonal antibodies was immobilized covalently. The architecture of the immunosensor was confirmed with polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) and electrochemical impedance spectroscopy (EIS), including the effective immobilization of the active layer of anti-AFB1. With EIS as the principle of detection, the immunosensor could detect AFB1 in the range from 1 to 30 ng·mL−1, and detection limit of 0.62 ng·mL−1. This sensitivity is sufficient to detect AFB1 in food according to regulatory agencies. The immunosensor exhibited good repeatability, reproducibility, stability, and selectivity in experiments with a possible interferent. Furthermore, detection of AFB1 in maize flour samples yielded recovery of 97–99%, in a demonstration of the possible use of the paper-based immunosensor to detect AFB1 using extraction solutions from food samples.