Gas chromatography with flame photometric detection of 31 organophosphorus pesticide residues in Alpinia oxyphylla dried fruits

Ultrasensitive detection of acephate based on carbon quantum dot-mediated fluorescence inner filter effects

Acephate is an organophosphorus pesticide (OP) that is widely used to control insects in agricultural fields such as in vegetables and fruits. Toxic OPs can enter human and animal bodies and eventually lead to chronic or acute poisoning. However, traditional enzyme inhibition and colorimetric methods for OPs detection usually require complicated detection procedures and prolonged time and have low detection sensitivity. High-sensitivity monitoring of trace levels of acephate residues is of great significance to food safety and human health. Here, we developed a simple method for ultrasensitive quantitative detection of acephate based on the carbon quantum dot (CQD)-mediated fluorescence inner filter effect (IFE). In this method, the fluorescence from CQDs at 460 nm is quenched by 2,3-diaminophenazine (DAP) and the resulting fluorescence from DAP at 558 nm is through an IFE mechanism between CQDs and DAP, producing ratiometric responses. The ratiometric signal I558/I460 was found to exhibit a linear relationship with the concentration of acephate. The detection limit of this method was 0.052 ppb, which is far lower than the standards for acephate from China and EU in food safety administration. The ratiometric fluorescence sensor was further validated by testing spiked samples of tap water and pear, indicating its great potential for sensitive detection of trace OPs in complex matrixes of real samples.

An efficient multi-enzyme cascade platform based on mesoporous metal-organic frameworks for the detection of organophosphorus and glucose

An efficient colorimetric detection platform based on multi-enzyme cascade has been developed for detection of organophosphorus. Firstly, the dual-enzyme platform was prepared and applied for sensitive glucose detection (detection limit 0.32 μM). And then three enzymes, including acetylcholinesterase, horseradish peroxidase and choline oxidase were encapsulated in cruciate flower-like zeolitic imidazolate framework-8 (CF-ZIF-8) through one-step co-precipitation to construct detection platform with acetylcholine chloride as substrate. The acephate inhibited the activity of acetylcholinesterase, obstructed the cascade reaction and reduced the production of H₂O₂, resulting in the changes of color intensity for the colorimetric detection. With suitable size and porous structure, CF-ZIF-8 provided a good microenvironment for guaranteeing the activity and spatial proximity of enzymes. The multi-enzyme platform displayed great performances with the detection limit of 0.23 nM for acephate. It was applied to the detection of acephate in Chinese cabbage and romaine, verifying the practicability of this platform.

A novel label-free electrochemiluminescence aptasensor using a tetrahedral DNA nanostructure as a scaffold for ultrasensitive detection of organophosphorus pesticides in a luminol-H2O2 system

In this work, a new type of Au-tetrahedral DNA nanostructure (Au-TDN) was originally proposed and successfully applied in an electrochemiluminescence aptasensor to detect organophosphorus pesticides (Ops). The aptamers modified with -SH could be covalently bonded with gold nanoparticles (AuNPs) to form a tetrahedron structure, and there were independent probes at each vertex of the tetrahedron, which could increase the probability of specific binding with Ops. The originally designed structure could not only maintain a stable tetrahedral configuration, but also combined with the target to improve the sensitivity of the sensor. Meanwhile, silver nanoparticles (AgNPs) could catalyze the chemical reaction between luminol and H₂O₂ to generate a variety of intermediates called reactive oxygen species (ROS) for signal enhancement. Factors that had important influences on the aptasensor, such as the concentration of Au-TDN, the incubation time, and the pH value of the buffer, were optimized in this trial. According to the final results, the limit of detection (LOD) of 3 pg mL^-1 (S/N = 3) for methyl parathion, the LOD of 0.3 pg mL^-1 (S/N = 3) for parathion and the LOD of 0.03 pg mL^-1 (S/N = 3) for phoxim were obtained, respectively. Moreover, the novel tetrahedral structure could be replaced by different types of aptamers to expand its application range and lay a foundation for the development of portable rapid detection devices for pesticide residues.

Chemiluminescence sensors based on molecularly imprinted polymers for the determination of organophosphorus in milk

As a food adapted to all kinds of people, milk has a high nutritional value. Because milk is a complex biological matrix, detecting illegal compounds is often difficult. As a common pesticide, organophosphorus (OP) residues caused by nonstandard use may be ignored, which is a threat to milk quality. In this study, using coumaphos as template molecule, the synthesized molecularly imprinted polymer (MIP) can specifically recognize 7 kinds of OP. Then, the MIP was used as an identification element to prepare a chemiluminescence sensor on a 96-well microplate for the determination of OP residues in milk samples. Due to the 4-(imidazol-1-yl)phenol-enhanced luminol-H₂O₂ system, the sensitivity of the system is very high; the detection limits of 7 OP including coumaphos, fenthion, chlorpyrifos, parathion, diazinon, fenchlorphos, and fenitrothion were 1 to 3 pg/mL, and the half maximal inhibitory concentrations were 1 to 20 ng/mL. The intraday recoveries of 7 OP were in the range of 86.1 to 86.5%, and the interday recoveries were in the range of 83.6 to 94.2%. Furthermore, the sensor can be reused up to 5 times. Therefore, the MIP-based chemiluminescence sensor can be used as a routine tool to detect OP residues in milk samples.

Synthesis of metal-organic framework @molecularly imprinted polymer adsorbents for solid phase extraction of organophosphorus pesticides from agricultural products

The novel core-shell structural zeolitic imidazolate framework-8 @molecularly imprinted polymers were successfully synthesized by surface imprinting technique and used as adsorbents for solid-phase extraction of organophosphorus pesticides. The obtained hybrid composites were characterized by scanning electron microscopy, transmission electron microscopy and Fourier-transform infrared, and their adsorbing and recognition performance were evaluated by binding experiments. The results showed that zeolitic imidazolate framework-8 @molecularly imprinted polymers presented a typically core-shell structure with molecularly imprinted shell (about 50 nm) homogeneously polymerized on the surface of zeolitic imidazolate framework-8 core, and exhibited specific recognition towards organophosphorus pesticides with fast adsorption capacity. The adsorption and desorption conditions including sample loading solvent, sample pH, washing and elution solvent were optimized. Under optimum conditions, the solid-phase extraction based on zeolitic imidazolate framework-8 @molecularly imprinted polymers combined with high liquid chromatography-tandem mass spectrometry method for determining organophosphorus pesticides was established and exhibited good linearity (R² ≥ 0.9927) in the range of 1-200 µg/L. With spiked at three different concentration levels in agricultural products (cauliflower, radish, pear, muskmelon), the recoveries ranged from 82.5% to 123.0% with relative standard deviations lower than 8.24%. The developed method was sensitive, convenient and efficient. More importantly, this study could provide a promising strategy for designing new adsorbents with extremely fast mass transfer rate for other potential trace contaminants.

A BCNO QDs-MnO2 nanosheets based fluorescence "off-on-off" and colorimetric sensor with smartphone detector for the detection of organophosphorus pesticides

In this work, boron carbon oxynitride quantum dots (BCNO QDs) were prepared by a one-step hydrothermal process of ethanolamine and boric acid. BCNO QDs exhibited blue fluorescence with the optimal excitation/emission fluorescence peak at 335 and 420 nm, respectively. As an efficient fluorescence quencher, manganese dioxide (MnO₂) nanosheets can effectively quench the fluorescence of BCNO QDs via the inner filter effect (IFE). Acetylcholinesterase (AChE) catalyzes the hydrolysis of acetylcholine (ATCh) to produce thiocholine (TCh). TCh can reductively degrade MnO₂ nanosheets to generate Mn²⁺, thereby recovering the fluorescence of BCNO QDs. Organophosphorus pesticides (OPs) can inhibit the activity of AChE enzymes, thereby preventing the production of TCh and the decomposition of MnO₂ nanosheets, resulting in the fluorescence "turn-off". Therefore, the concentration of OPs can be detected by measuring the fluorescence intensity change of AChE-ATCh-MnO₂-BCNO-QDs system. Under optimal experimental conditions, the dynamic detection range of paraoxon is 0.1-250 ng mL^-1, and the detection limit is 0.03 ng mL^-1. Meanwhile, the reaction system also showed concentration-dependent visual color changes from colorless to brownish. Furthermore, we prepared a portable BCNO QDs test paper. By using a smartphone to identify the RGB values of the reaction solution and the corresponding test paper, we carried out the digital image chromaticity analysis, which can shorten the detection time and reduce the detection cost, and provide an effective solution for the rapid detection of OPs on site.

Applications of covalent organic frameworks and their composites in the extraction of pesticides from different samples

Pesticides are used extensively in a wide range of applications and due to their high rate of consumption, they are ubiquitous in the different media and samples like environment, water sources, air, soil, biological materials, wastes (liquids, solids or sludges), vegetables and fruits, where they can persist for long periods. Pesticides often have hazardous side effects and can cause a range of harmful diseases like Parkinson, Alzheimer, asthma, depression and anxiety, cancer, etc, even at low concentrations. To this end, extraction, pre-concentration and determination of pesticides from various samples presents significant challenges caused by sample complexity and the low concentrations of them in many samples. Often, direct extraction and determination of pesticides are impossible due to their low concentrations and the complexity of samples. The main goals of sample preparation are removing interfering species, pre-concentrating target analyte/s and converting the analytes into more stable forms (when needed). The most popular approach is solid-phase extraction due to its simplicity, efficiency, ease of operation and low cost. This method is based on using a wide variety of materials, among which covalent organic frameworks (COFs) can be identified as an emerging class of highly versatile materials exhibiting advantageous properties, such as a porous and crystalline structure, pre-designable structure, high physical and chemical stability, ease of modification, high surface area and high adsorption capacity. The present review will cover recent developments in synthesis and applications of COFs and their composites for extraction of pesticides, different synthesis approaches of COFs, possible mechanisms for interaction of COFs-based adsorbents with pesticides and finally, future prospects and challenges in the fabrication and utilization of COFs and their composites for extraction of pesticides.

[Progress of sample preparation and analytical methods of dried fruit foods]

坚果、果脯等干果类食品含有丰富的营养成分,深受国内外广大消费者的喜爱。但这些食品在果实生产、加工、储运时会使用农药或产生霉变等,造成干果中农药、重金属、霉菌毒素或添加剂等有害成分残留,甚至超过国家限量要求,带来严重的食品安全问题。因此,加强干果类食品的质量监督具有重要的经济和社会意义。但干果类食品基质复杂,有害物质种类多,结构和性质差异大,含量低,其分析检测需要快速高效的样品前处理技术和准确灵敏的分析检测方法。该文主要综述了近十年来干果类食品中有害物质的样品前处理及分析检测方法研究进展。其中样品前处理方法主要包括各种场辅助萃取法、相分离法和衍生化萃取方法等。场辅助萃取法主要是借助超声波和微波场等外场(协同)作用加快干果中有害物质的溶出速度,提高其萃取效率。相分离法,包括固相(微)萃取、分散固相萃取和液相(微)萃取法等,具有溶剂消耗少、分离富集效率高的优势,是干果样品分析中较常使用的前处理方法。该文还重点介绍了干果中各类有害成分分析检测技术,主要包括色谱、原子光谱、无机质谱、电化学分析等常规实验室方法,以及一些适用于现场分析的快速检测技术,并以此为基础,展望了干果类食品中有害物质分析检测技术的发展趋势。

Organic-Molecule-Based Fluorescent Chemosensor for Nerve Agents and Organophosphorus Pesticides

Organophosphorus (OP) compounds are typically a broad class of compounds that possess various uses such as insecticides, pesticides, etc. One of the most evil utilizations of these compounds is as chemical warfare agents, which pose a greater threat than biological weapons because of their ease of access. OP compounds are highly toxic compounds that cause irreversible inhibition of enzyme acetylcholinesterase, which is essential for hydrolysis of neurotransmitter acetylcholine, leading to series of neurological disorders and even death. Due to the extensive use of these organophosphorus compounds in agriculture, there is an increase in the environmental burden of these toxic chemicals, with severe environmental consequences. Hence, the rapid and sensitive, selective, real-time detection of OP compounds is very much required in terms of environmental protection, health, and survival. Several techniques have been developed over a few decades to easily detect them, but still, numerous challenges and problems remain to be solved. Major advancement has been observed in the development of sensors using the spectroscopic technique over recent years because of the advantages offered over other techniques, which we focus on in the presented review.

New frontiers and prospects of metal-organic frameworks for removal, determination, and sensing of pesticides

Pesticides have been widely used in agriculture to control, reduce, and kill insects. Humans are also being using pesticides to control insidious animals in daily life. By these practices, a huge volume of pesticides is introduced to the environment. Despite broad-spectrum applicability, pesticides also have hazardous effects on both humans and animals at high and low concentrations. Long-term exposure to pesticides can cause different diseases, like leukemia, lymphoma, and cancers of the brain, breasts, prostate, testis, and ovaries. Reproductive disorders from pesticides include birth defects, stillbirth, spontaneous abortion, sterility, and infertility. Therefore, the application of determination and treatment methods for pre-concentration and removal of these toxic materials from the environment appears a vital concern. To date, different materials and approaches have been employed for these purposes. Among these approaches, multifunctional metal-organic frameworks (MOFs)-assisted adsorption and determination processes have always been in the spotlight. These facts are due to exclusive properties of MOFs in terms of the crystallinity, large surface area, high chemical, and physical stability, and controllable structure as well as unique features of adsorption and determination process in terms of simple, easy, cheap, available method and ability to use in large and industrial scales. In the present work, we illustrate the exceptional features of MOFs as well as the possible mechanism for the adsorption of pesticides by MOFs. The use of these fantastic materials for pre-concentration and removal of pesticides are extensively explored. In addition, the performance of MOFs was compared with other adsorbents. Finally, the new frontiers and prospects of MOFs for the determination, sensing, and removal of pesticides are presented.

Enhancement of Chemiluminescence Intensity of S2* in Non-premixed Hydrogen Microjet Flame in the Photometric Detector for Sulfur Detection

A transparent quartz rod (q) placed vertically on top of a non-premixed hydrogen microjet flame in a flame photometric detector (qFPD) was developed and evaluated for sulfur detection. The microjet flame burned around the quartz rod because of Coanda effect, forming an extended downstream flame zone with a relatively low temperature between 550 and 650 °C, which is favorable to the formation of S₂*. The emission intensity of S₂* and the signal-to-noise ratio (SNR) of sulfur response were enhanced 2.6- and 2.1-fold, respectively. It was found that the quartz rod of diameter 4 mm with a tip shape of semicircle placed 6 mm above the nozzle yielded the highest SNR. The limits of detection (LOD) for seven kinds of tested sulfur-containing compounds of qFPD were 0.3-0.5 pg S s^-1, which is 5-7 times better than that of commercially available FPD detectors (LOD: 1.6-2.8 pg S s^-1). The selectivity of sulfur over carbon was 10⁵ on qFPD when the SNR for the mass flow rate of S and C atoms was ∼3 times. It was the first time that a quartz rod was used vertically on top of a microjet hydrogen-rich flame in FPD to enhance the chemiluminescence of S₂* and improve the LOD down to 0.3-0.5 pg S s^-1.

Fluoride-Free 2D Niobium Carbide MXenes as Stable and Biocompatible Nanoplatforms for Electrochemical Biosensors with Ultrahigh Sensitivity

Recently, 2D niobium carbide MXene has drawn vast attention due to its merits of large surface area, good metallic conductivity, and tunable band gap, making it desirable for various applications. However, the usage of highly toxic fluoride-containing etchant and quite long etching time in the conventional synthesis route has greatly hindered further exploration of MXene, especially restricting its biomedical application. Herein, novel fluoride-free Nb2CT x nanosheets are prepared by a facile strategy of electrochemical etching (E-etching) exfoliation. Taking advantage of rapid aluminum clearance, excellent chemical stability, and biocompatibility from the MXene by E-etching, fluoride-free Nb2CT x /acetylcholinesterase-based biosensors are constructed for phosmet detection with the limit of detection down to 0.046 ng mL-1. The fabricated Nb2CT x -based biosensor is superior to the counterpart from hydrofluoric acid-etched Nb2CT x , indicating that fluoride-free MXene can enhance the enzyme activity and electron transfer in the biosensor. The results prove that the fluorine-free MXene shows promise for developing biosensors with high performance of ultrahigh sensitivity and selectivity. It is highly expected that the fluoride-free MXene as a stable and biocompatible nanoplatform has great potential to be expanded to many other biomedical fields.

Ultra-sensitive detection of malathion residues using FRET-based upconversion fluorescence sensor in food

Malathion is an organophosphorus pesticide which could remain in agricultural products and exert irreversible harmful effects on human health. Hence, strict monitoring of malathion contents is very significant. Here, a highly sensitive fluorescent aptasensor was developed for the determination of malathion, the system was based on a cationic polymer-mediated fluorescence 'turn-off'. In this system, malathion-specific aptamers were bound to cationic polymer through electrostatic interactions. To produce fluorescence resonance energy transfer (FRET), negatively charged upconversion fluorescent nanoparticles (UCNPs) and cationic-polymer encapsulated gold nanoparticles (GNPs) were combined. This combination resulted in fluorescence quenching, and the degree of quenching was correlated with the concentration of malathion. Under optimum conditions, the fluorescence intensities were observed to decrease linearly with the rising concentration of the malathion from 0.01 to 1 μM with a detection limit of 1.42 nM. Furthermore, the developed sensor possessed good selective recognition ability for malathion and was successfully used to detect malathion in adulterated tap water and matcha samples with high accuracy.

A new fluorescent technique for pesticide detection by using metal coordination polymer and nanozyme

Background

Chinese herbs have been widely used for thousands of years. In order to kill or control insects and fungus during the cultivation of herb plants, pesticides have played a significant role. More than 30 kinds of pesticides have been documented in the latest version of Chinese Pharmacopoeia. It is urgent to develop new analytical methods for pesticide detection.

Methods

A fluorescent detection system was established by using Cerium based fluorescent polymer and Sm-CeO₂. As a new doped nanozyme, Sm-CeO₂ exhibits OPH-like activity to hydrolyze OPP pesticide.

Results

The morphology of the prepared CFP and Sm-CeO₂ were characterized. The optimal conditions for CFP synthesis are CeCl₃ (16 mmol L⁻¹, 200 μL), ATP (4 mmol L⁻¹, 200 μL) and Tris buffer (5 mmol L⁻¹, 500 μL, pH 8.0). Sm-CeO₂ shows the best mimic activity to hydrolyze OPP pesticide at pH = 8.0. The results exhibit good linear relationship between fluorescent quenching effect and MP in the range of 2–50 μmol L⁻¹. Finally, this fluorescent technique was successfully applied in Poria cocos and Semen Coicis sample.

Conclusions

It is the first report on OPP detection by using CFP and doped nanozyme. The successful application in real sample indicates this method is a rapid, reliable strategy to detect OPP in Chinese herbs.

A flame photometric detector with a silicon photodiode assembly for sulfur detection

A flame photometric detector with a silicon photodiode assembly instead of a photomultiplier tube for sulfur detection was developed and evaluated. The photosensitive area of photodiode, the optical design, and band-pass filters, were optimized. It was found that the optimal photosensitive area of the photodiode was 100 (mm)², and three focus lenses combined with a broad band-pass filter of 378/52 nm and a QB21 glass yielded the best result. This design fully utilized the wide emission spectrum of S₂*, the response characteristics of silicon photodiode, and effective absorption of strong emission spectrums of OH* at wavelength around 310 nm by QB21 glass. The limits of detection for nine kinds of sulfur containing compounds were between 5.8 × 10^-12 to 9.5 × 10^-12 g s^-1. This mode provided a linear response of 3 orders of magnitude for compounds being tested and a selectivity of sulfur over carbon of 10⁵. It is demonstrated for the first time that the overall performance of the flame photometric detector integrated with a silicon photodiode assembly work at room temperature was comparable to a conventional detector coupled with a photomultiplier tube, with advantages of short equilibration time, robust to electromagnetic interference and vibration, and low cost. The new detector can find wide application in gas chromatography and on-line monitoring instruments for sulfur measurement.

Voltammetric determination of organophosphorus pesticides using a hairpin aptamer immobilized in a graphene oxide-chitosan composite

An aptasensor is described for electrochemical determination of organophosphorus pesticides (OPPs), specifically of profenofos, phorate, isocarbophos, and omethoate. The method uses a hairpin aptamer as signalling donor. Its 5' and 3' ends were modified with amino groups and the redox probe ferrocene (Fc), respectively. A nanocomposite consisting of graphene oxide and chitosan (GO-chit) was used to immobilize the aptamer via formation of an amide link. Its good conductivity facilitates monitoring of the electrochemical responses. Upon addition of an OPP, it will be bound by the aptamer. This results in an opening of the hairpin structure. Thus, Fc is shifted away from the surface of the electrode. As a result, the impedance increases and the redox signal of Fc decreases. The electrochemical performance, binding capacity and response of the aptasensor for profenofos, phorate, isocarbophos and omethoate were studied. The limits of detection are as low as 0.01, 0.1, 0.01 and 0.1 nM, respectively. Graphical abstract Schematic representation of an electrochemical aptasensor prepared by immobilizing ferrocene (Fc) labeled hairpin aptamer (HP) on the surface of graphene oxide-chitosan (GO-chit) modified electrode, and its application to the determination of organophosphorus pesticides (OPPs) by voltammetry.

Up-Converting Nanoparticle-Based Immunochromatographic Strip for Multi-Residue Detection of Three Organophosphorus Pesticides in Food

Organophosphorus (OP) pesticides are widely used to control pests because of their high activity. This study described a rapid and sensitive lateral flow immunochromatographic (LFIC) assay based on up-converting nanoparticles (UCNPs) for multi-residue detection of three OP pesticides. The developed assay integrated novel fluorescent material UCNPs labeled with a broad-specific monoclonal antibody. Based on the competitive platform by immobilized antigen in the test zone, the optimized UCNPs-LFIC assay enabled sensitive detection for parathion, parathion-methyl, and fenitrothion with IC50 of 3.44, 3.98, and 12.49 ng/mL (R 2 ≥ 0.9776) within 40 min. The detectable ability ranged from 0.98 to 250 ng/mL. There was no cross-reactivity with fenthion, phoxim, isocarbophos, chlorpyrifos, or triazophos, even at a high concentration of 500 ng/mL. Matrix interference from various agricultural products was also studied in food sample detection. In the spiked test, recoveries of the three OP pesticides ranged from 67 to 120% and relative standard deviations were below 19.54%. These results indicated that the proposed strip assay can be an alternative screening tool for rapid detection of the three OP pesticides in food samples.

A simple multi-residue method for determination of plant growth retardants in Ophiopogon japonicus and soil using ultra-performance liquid chromatography-tandem mass spectrometry

Plant growth retardants may play an important role in regulation of yield and quality of crops, fruits, and vegetables. Such compounds have begun to be used in the cultivation of traditional Chinese medicines (TCMs), especially for root medicines. Although the potential risks to human health of these compounds has attracted increasing attention, analytical methods for detection of plant growth retardants in TCMs remain poorly investigated. In this study, an effective and reliable method for simultaneous determination of 11 plant growth retardants in Ophiopogon japonicus and soil samples was developed by ultra-performance liquid chromatography-triple quadrupole tandem mass spectrometry (UPLC-QqQ-MS/MS). Extraction was conducted in acetonitrile containing 1.0% (v/v) acetic acid with ultrasonication. The octadecylsilyl (C₁₈) and MgSO₄ were used as the dispersive-solid phase extraction (d-SPE) sorbent and provided satisfactory recoveries for the analytes. The conditions of extraction and LC-MS/MS were optimized to achieve the highest recovery and sensitivity. Good linearity was achieved within a wide range with all correlation coefficients exceeding 0.9950. The recoveries of all analytes in O. japonicus and soil samples ranged from 57.37% (choline chloride) to 99.93% (trinexapac-ethyl) and from 54.37% (daminozide) to 94.82% (triadimenol), respectively. The limits of quantifications ranged from 0.03 to 3.54 μg/L. The proposed method was successfully applied to detect and quantify 11 plant growth retardants in empirical O. japonicus and soil samples. High frequency of paclobutrazol and choline chloride was found in O. japonicus samples. In addition, paclobutrazol showed a high residual concentration (>1100 μg/kg) in the soil of O. japonicus indigenous production.

A non-competitive surface plasmon resonance immunosensor for rapid detection of triazophos residue in environmental and agricultural samples

The wide application of an organophosphate pesticide triazophos raises concern on the environmental pollution and the potential risk to human health. Thus, it is crucial to regularly monitor triazophos residue in the environment and agro-products. Herein we described a non-competitive immunoassay for trace detection of triazophos using a direct surface plasmon resonance (SPR) biosensor. Two anti-triazophos monoclonal antibodies (mAbs) were immobilized on the sensor chip and characterized by SPR-based kinetic analysis. The mAb with relatively slow dissociation rate was used for direct immunosensing of triazophos. The biosensor assay showed a high specificity and a low detection limit of 0.096ngmL^-1 to triazophos, with the linear detection range of 0.98-8.29ngmL^-1. Under the optimal condition, the sensor chip could be regenerated for 160cycles at least. Moreover, the sensitive method was applied to determine triazophos in the spiked environmental water and agricultural products, as well as in unknown real-life samples (including Chinese cabbage, cucumber, and apple). Desirable results demonstrated that the newly-developed immunosensor could be used as a rapid, convenient, and reliable tool to regularly monitor triazophos and meet the detection requirement of its maximum residue limits.

Ultrasensitive electrochemical immuno-sensing platform based on gold nanoparticles triggering chlorpyrifos detection in fruits and vegetables

Chlorpyrifos (chl) is an organophosphate pesticide extensively used in agriculture and highly toxic for human health. Fluorine doped tin-oxide (FTO) based electrochemical nanosensor was developed for chlorpyrifos detection with gold nanoparticles (AuNPs) and anti-chlorpyrifos antibodies (chl-Ab). AuNPs provides high electrical conductivity and specific resistivity, thus increases the sensitivity of immunoassay. High electrical conductivity of AuNPs reveals that it promotes the redox reaction for better cyclic voltammetry. Based on the intrinsic conductive properties of FTO-AuNPs complex, chl-Ab was immobilized onto AuNPs surface. Under optimized conditions, the proposed FTO based nanosensor exhibited high sensitivity and stable response for the detection of chlorpyrifos, ranging from 1fM to 1µM with limit of detection (LOD) up to 10fM. The FTO-AuNPs sensor was successfully employed for the detection of chlorpyrifos in standard as well in real samples up to 10nM for apple and cabbage, 50nM for pomegranate. The proposed FTO-AuNPs nanosensor can be used as a quantitative tool for rapid, on-site detection of chlorpyrifos traces in real samples when miniaturized due to its excellent stability, sensitivity, and simplicity.

Determination of six organophosphorus pesticides in water samples by three-dimensional graphene aerogel-based solid-phase extraction combined with gas chromatography/mass spectrometry

In the present study, a three-dimensional graphene aerogel (3D-GA), synthesised by chemical reduction of an aqueous solution of graphene oxides (GOs) with ethylenediaminethermal by a simple water bath method followed by freeze-drying treatment, was used for the solid-phase extraction (SPE) of six organophosphorus pesticides (OPPs) (i.e. trichlorfon, dimethoate, ethoprophos, parathion, fenitrothion and fenthion) from water samples. The target analytes were extracted using packed SPE cartridges and then eluted with tetrahydrofuran. The eluate was collected and dried with high-purity nitrogen gas at room temperature. After redissolving in acetone, the residue was analysed using gas chromatography/mass spectrometry (GC/MS). The proposed method demonstrated a good linearity between 0.5 and 500 μg L⁻¹ with the correlation coefficient of 0.9990–0.9998. The limits of detection (LODs) (S/N = 3) and the limits of quantification (LOQs) (S/N = 10) for the six OPPs pesticides were in the range of 0.12–0.58 μg L⁻¹ and 0.41–1.96 μg L⁻¹, respectively. The accuracy of the present method was evaluated by measuring the recovery of the spiked samples, which ranged from 93.8% to 104.2% with relative standard deviations (RSDs) of 1.1–5.6%. The established method was successfully applied to the determination of the target analytes in environmental water samples including tap water, river water, drinking water and lake water, demonstrating its great potential for the determination of OPPs in water.

3D graphene aerogel fabricated via chemical reduction followed by freeze-drying treatment was used as SPE sorbent to extract OPPs from water sample.

Sensitive and Selective Detection of Oxo-Form Organophosphorus Pesticides Based on CdSe/ZnS Quantum Dots

A rapid, sensitive and enzyme-based optical biosensor was applied for the determination of seven organophosphorus pesticides (OPPs), including the oxo forms (malaoxon, paraoxon, dibrom, and dichlorvos), the thio forms (malathion and parathion) and the mixed form (demeton) in Panax ginseng. The principal of the proposed method is that the fluorescence quenching effect of quantum dots (QDs) can be observed by enzyme-generated H₂O₂. The active centers of acetylcholinesterase (AChE) could be inhibited in the presence of pesticides, which caused decrease of the generated H₂O₂. Then, the inhibition efficiency of pesticide to AChE activity could be evaluated by measuring the fluorescence changes. Different from biosensors based on immobilized enzyme or self-assembling technique, the proposed biosensor demonstrated a good selectivity for the detection of oxo forms of OPPs. In the present study, the important experimental conditions of the proposed biosensor were investigated. Under the optimized conditions (incubation temperature, 35 °C; incubation time, 20 min; pH value, 8.0; detection time, 30 min; AChE concentration, 40.9 U/L; and choline oxidase (ChOx) concentration, 637.5 U/L), the limit of detection for the investigated oxo-form OPPs was no more than 0.05 μM, which suggested that the proposed method could be used for sensitive and selective determination of trace amounts of OPPs residues in real samples with complex matrices.

An ultrasensitive aptasensor for chlorpyrifos based on ordered mesoporous carbon/ferrocene hybrid multiwalled carbon nanotubes

In this study, we designed a novel and ultrasensitive aptamer sensor for the quantitative detection of chlorpyrifos.

A rapid immunomagnetic-bead-based immunoassay for triazophos analysis

Schematic illustration of a direct competitive immunomagnetic-bead-based enzyme-linked immunosorbent assay (IMB-ELISA) to detect the triazophos pesticides.