Sensitive determination of thiamethoxam, imidacloprid and acetamiprid in environmental water samples with solid-phase extraction packed with multiwalled carbon nanotubes prior to high-performance liquid chromatography

Remediation of acetamiprid pesticide from contaminated water by antibacterial biosorbent based on carboxymethyl tragacanth-grafted-poly(3-aminophenol) decorated with ZnO@Fe3O4

Pesticides can have harmful impacts on the environment and living organisms. Thus, removing them from polluted water is crucial. In this study, a bionanocomposite of carboxymethyl tragacanth-grafted-poly(3-aminophenol)/zinc oxide@iron oxide (CMT-g-P3AP/ZnO@Fe3O4) synthesized by in situ copolymerization as an efficient adsorbent to eliminate the acetamiprid pesticide from polluted water. The CMT-g-P3AP/ZnO@Fe3O4 magnetic nanocomposite was analyzed utilizing various techniques including FTIR, EDX, FESEM, XRD, BET, CHNSO, and TGA. The results displayed that the resulting nanocomposite with maximum adsorption capacity (Qmax) successfully removed the acetamiprid pesticide from polluted water under optimal conditions such as pH of 7.00, 5.00 mg of adsorbent, 20.0 min duration, and 400 mg/L acetamiprid concentration. According to the linear Langmuir isotherm, the Qmax of the biosorbent was 833 mg/g. The experimental adsorption data fitted well with Temkin's nonlinear isotherm model. The adsorption kinetic data were closely related to the Weber-Morris intraparticle diffusion nonlinear model. After three repetitive cycles, CMT-g-P3AP/ZnO@Fe3O4 can be outstandingly renewed and recycled without significant reduction in its adsorption efficacy, as evidenced by the adsorption-desorption experiments. In addition, the CMT-g-P3AP/ZnO@Fe3O4 displayed the good antibacterial activity against E. coli and S. aureus.

Assessing the greenification potential of cyclodextrin-based molecularly imprinted polymers for pesticides detection

Cyclodextrins, with their unparalleled attributes of eco-friendliness, natural abundance, versatile utility, and facile functionalization, make a paramount contribution to the field of molecular imprinting. Leveraging the unique properties of cyclodextrins in molecularly imprinted polymers synthesis has revolutionized the performance of molecularly imprinted polymers, resulting in enhanced adsorption selectivity, capacity, and rapid extraction of pesticides, while also circumventing conventional limitations. As the concern for food quality and safety continues to grow, the need for standard analytical methods to detect pesticides in food and environmental samples has become paramount. Cyclodextrins, being non-toxic and biodegradable, present an attractive option for greener reagents in imprinting polymers that can also ensure environmental safety post-application. This review provides a comprehensive summary of the significance of cyclodextrins in molecular imprinting for pesticide detection in food and environmental samples. The recent advancements in the synthesis and application of molecularly imprinted polymers using cyclodextrins have been critically analyzed. Furthermore, the current limitations have been meticulously examined, and potential opportunities for greenification with cyclodextrin applications in this field have been discussed. By harnessing the advantages of cyclodextrins in molecular imprinting, it is possible to develop highly selective and efficient methods for detecting pesticides in food and environmental samples while also addressing the challenges of sustainability and environmental impact.

Determination of Neonicotinoid Insecticides in Environmental Water by the Enrichment of MIL-53 Mixed Matrix Membrane Coupled with High Performance Liquid Chromatography

Metal organic framework based mixed matrix membranes (MOF-MMMs) were synthesized and applied for dispersive membrane extraction (DME) of four neonicotinoid insecticides (nitenpyram, thiacloprid, imidacloprid, and acetamiprid) in environmental water, combined with high performance liquid chromatography (HPLC) for determination. Several experimental conditions were optimized in detail, involving dosage percentage of MOF, extraction time, sample pH, salinity, type and volume of eluent, and elution time. High sensitivity with limits of detection and quantification were achieved as 0.013-0.064 μg L^-1 and 0.038-0.190 μg L^-1, respectively, and good precision with relative standard deviations were obtained as 3.07-12.78%. The proposed method has been successfully applied to determine four neonicotinoid insecticides in tap water, surface water, and seawater, satisfactory recoveries of spiked water samples were between 72.50 and 117.98%. Additionally, the MOF-MMMs showed good reusability with the extraction efficiencies almost remaining stable after 14 cycles. The MOF-MMMs based DME followed by the HPLC method can be a promising utility for the determination of neonicotinoid insecticides in environmental water samples, with high sensitivity and convenient operation.

A comprehensive review on the pretreatment and detection methods of neonicotinoid insecticides in food and environmental samples

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The metabolism and residue status of neonicotinoids were briefly summarized in this work.

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Sample pretreatment techniques for the analysis of neonicotinoids were critically discussed.

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The commonly used detection methods for neonicotinoids residues were also pointed out.

In recent years, the residues of neonicotinoid insecticide in food and environmental samples have attracted extensive attention. Neonicotinoids have many adverse effects on human health, such as cancer, chronic disease, birth defects, and infertility. They have substantial toxicity to some non-target organisms (especially bees). Hence, monitoring the residues of neonicotinoid insecticides in foodstuffs is necessary to guarantee public health and ecological stability. This review aims to summarize and assess the metabolic features, residue status, sample pretreatment methods (solid-phase extraction (SPE), Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS), and some novel pretreatment methods), and detection methods (instrument detection, immunoassay, and some innovative detection methods) for neonicotinoid insecticide residues in food and environmental samples. This review provides detailed references and discussion for the analysis of neonicotinoid insecticide residues, which can effectively promote the establishment of innovative detection methods for neonicotinoid insecticide residues.

Biochemical and histopathological investigation of the protective effects of melatonin and vitamin E against the damage caused by acetamiprid in Balb-c mouse testicles at light and electron microscopic level

The protective effects of melatonin (Mel) and vitamin E (Vit E) against the negative effects of acetamiprid (Acmp) on testicles, reproductive hormones, and oxidative stress parameters were investigated in the present study. A total of 50 Balb-c male mice were used in 7 groups; 6 mice in the control groups (distilled water, corn oil, ethanol), and 8 in other groups (Acmp, Acmp + Mel, Acmp + Vit E, Acmp + Vit E + Mel). After the experiment, which lasted 21 days, hematoxylin eosin (H&E), periodic acid Schiff (PAS), and caspase-3 immunohistochemical (IHC) staining was performed on the testicular tissues. Also, the tissues were examined ultrastructurally with the transmission electron microscopy (TEM). In the Acmp group, there were decreased seminiferous tubule diameter and epithelial thickness, epithelial degeneration, decreased spermatozoa in the lumen, decreased PAS-positive staining in the seminiferous epithelial basement membrane, edema in the interstitial area, and hydropic degeneration in Leydig cells. Caspase-3 immunoreactivity was higher than in the other groups. TEM examination showed degeneration in tubule cells, lysosomal accumulation in cells of the spermatogenic line, vacuolizations with myelin figures, and necrosis. Hydropic degeneration, electron-dense lipid vacuoles, and chromatolysis were evident in the Leydig cell cytoplasm. In Sertoli cells, electron-dense lysosomal deposits were noted. In biochemical terms, there were decreased tissue glutathione (GSH) and total antioxidant status (TAS), and increased malondialdehyde (MDA) and total oxidant status (TOS). Plasma luteinizing hormone (LH), follicular stimulating hormone (FSH), and testosterone levels were decreased. In the groups with melatonin, vitamin E, and both were applied together, tissue damage, and apoptotic cell death were reduced at both light microscopic and ultrastructural levels. In biochemical terms, there were decreased oxidative parameters and increased hormonal parameters. It was found that vitamin E was more effective in decreasing oxidative parameters and increasing antioxidative parameters when compared to melatonin, and hormonal parameters increased at a higher level in the Acmp + Vit E group than in all groups. As a result, it was found that exposure to Acmp caused damage to testicular tissue, induced oxidative stress in testicles, and decreased plasma LH, FSH, and testosterone levels, and although vitamin E is more effective than melatonin in preventing this damage, both are effective.

Development of dispersive solid-phase microextraction coupled with high-pressure liquid chromatography for the preconcentration and determination of the selected neonicotinoid insecticides

Neonicotinoid insecticides have raised a lot of societal concerns due to their environmental ubiquity and unique mode of action. Therefore, it is of great research interest to monitor their occurrence in the environmental waters. However, these compounds exist at low concentrations that is below instrument detection limits. This study reports the applicability of magnetic poly (3 aminobenzoic acid)-based activated carbon (Fe3O4@PABA/AC) composite as an adsorbent in dispersive magnetic solid-phase microextraction (d-MSPME) of neonicotinoid insecticides from wastewater and river water samples. The as-synthesized adsorbent was characterized and confirmed by Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, Brunauer–Emmett–Teller and X-ray diffraction spectroscopy. The analytes of interest were detected and quantified by high-performance liquid chromatography coupled with diode array detector (HPLC–DAD). The parameters affecting the extraction and preconcentration processes, such as pH, extraction time, mass of adsorbent, desorption time and eluent volume, were optimized using fractional factorial design and central composite design. Under optimum conditions, the limits of detection and quantification were in the ranges of 0.41–0.82 µg L−1 and 1.4–2.7 µg L−1, respectively. The linearity ranged from 1.4–700 µg L−1 with correlation of determination (R2) values varied between 0.9933 and 0.9987. The intra-day and inter-day precisions were 0.35–0.75% and 1.7–5.5%, respectively. The spike recovery experiments were conducted to evaluate the accuracy of the d-MSPME analytical method in real samples, and the percentage recoveries ranged from 86.7 to 99.2%. Therefore, this method shows great potential applicability in preconcentrating the pollutants from the environment.

Simultaneous determination of acetamiprid and 6-chloronicotinic acid in environmental samples by using ion chromatography hyphenated to online photoinduced fluorescence detector

This study aims to introduce a simple, sensitive, and cost-effective method for the simultaneous determination of acetamiprid and its main metabolite 6-chloronicotinic acid in environmental samples by using a nonsuppressed ion chromatography hyphenated with an online postcolumn photoinduced fluorescence detection system. The fluorescence detector wavelengths λ_ex /λ_em  = 257/382 nm was set for up to 6.0 min for acetamiprid, while λ_ex /λ_em  = 231/370 nm programmed for 6-chloronicotinic acid for the rest of the analysis time. Both samples were treated by applying miniaturized quick, easy, cheap, effective, rugged, and safe method before the separation of analytes on an IonPac^® AS11-HC column by pumping 40 mM NaOH having minuscule content of acetonitrile (5%, v/v) as an eluent. Both intrinsically nonfluorescent analytes were turned-on by online postcolumn photoinduced derivatization, avoiding the need for complex chemical derivatization or addition of a postcolumn extra pump. The developed method was appraised for the analysis of environmental samples, exhibiting excellent linearity (0.050-10 μg/mL) with a correlation coefficient greater than 0.9993 for both analytes. Whereas, obtained limit of detection (0.025-0.0072 μg/mL), recoveries (98.02-116.00%), and inter- and intraday precision (≤3.02 %) were satisfactory for both compounds in environmental samples.

Reproductive effects of subchronic exposure to acetamiprid in male rats

Acetamiprid, a selective agonist of nicotinic acetylcholine recetors, is one of the most widely used neonicotinoids. There is limited data about toxicity of acetamiprid on male reproductive system. Therefore, the study aimed to investigate the reproductive toxic potential of acetamiprid in male rats orally treated with acetamiprid with low (12.5 mg/kg) medium (25 mg/kg) or high dose (35 mg/kg) for 90 days. According to our results, sperm concentration and plasma testosterone levels decreased in dose dependent manner. Gonadotropin-releasing hormone (GnRH), follicle-stimulating hormeone (FSH), luteinizing hormone (LH) levels increased at low and medium dose groups and acetamiprid caused lipid peroxidation and glutathione (GSH) depletion in the testes. Histologic examinations revealed that acetamiprid induced apoptosis in medium and high dose groups and proliferation index dramatically decreased in high dose group. In conclusion, acetamiprid caused toxicity on male reproductive system in the high dose. The mechanism of the toxic effect may be associated with oxidative stress, hormonal disruptions and apoptosis.

Synthesis of molecularly imprinted polymer modified magnetic particles for chiral separation of tryptophan enantiomers in aqueous medium

Molecularly imprinted polymers coated magnetic particles (Fe₃O₄@MIPs) were prepared and used as adsorbents in solid phase extraction for efficient enantioseparation of racemic tryptophan (Trp) in aqueous medium. The amino-modified magnetic particles (Fe₃O₄-NH₂) were first synthesized by one-pot hydrothermal method. Then the template molecules (L-Trp) were assembled on the surface of Fe₃O₄-NH₂. Finally, Fe₃O₄@MIPs were prepared via a sol-gel method using L-Trp@Fe₃O₄-NH₂ complex as matrix, 3-aminopropyltriethoxylsilane and n-octyltriethoxysilane as functional monomers. The as-prepared Fe₃O₄@MIPs were spherical with an average diameter about 149 ± 6.0 nm. The thickness of MIPs layer was approximately 3.5 ± 2.3 nm. The adsorption isotherms data of Fe₃O₄@MIPs toward L-Trp and D-Trp were well described by the Langmuir model. The maximum adsorption capacities of Fe₃O₄@MIPs for L-Trp and D-Trp were calculated to be 17.2 ± 0.34 mg/g and 7.2 ± 0.19 mg/g, respectively. The material exhibited good selectivity toward L-Trp with imprinting factor of 5.6. Excitingly, the enantiomeric excess (ee) of Trp in supernatant after adsorption of racemic Trp by Fe₃O₄@MIPs was as high as 100%. The result suggests that the imprinted caves in Fe₃O₄@MIPs are highly matched with L-Trp molecule in space structure and spatial arrangement of active functional groups. The work also demonstrates that sol-gel technology has great potential in preparation of MIPs for chiral separation.

Protective effects of melatonin and vitamin E in acetamiprid-induced nephrotoxicity

Investigation of probable toxic effects of acetamiprid (ACMP) on kidney and comparative analysis of the probable protective effects of vitamin E and melatonin were conducted in the present study. The ethics committee approval was obtained from Inonu University Medical Faculty Ethics Committee. Fifty Balb-c mice were randomly assigned to control, corn oil, ethyl alcohol, ACMP, ACMP + melatonin, ACMP + vitamin E, and ACMP + melatonin + vitamin E groups. At the end of the experiments, rat kidney tissues were incised under anesthesia. Blood samples and kidney tissues were examined. After 21 days of ACMP administration, it was observed that malondialdehyde (MDA), total oxidant status (TOS), BUN, creatinine, IL-6, IL-1β, and TNF-α levels, histopathological damage, and Caspase-3 immunoreactivity scores increased, and glutathione (GSH), superoxide dismutase (SOD), catalase (CAT), and total antioxidant status (TAS) levels decreased, and histopathological damages were observed. Melatonin and vitamin E administration led to improvements in oxidative stress parameters, renal functions, inflammatory markers, and histopathological findings. ACMP administration led to nephrotoxicity in rat kidney tissues. Although melatonin and vitamin E administrations were effective on ACMP nephrotoxicity separately, co-administration of both was quite effective. Concomitant use of melatonin and vitamin E could be effective on prevention of toxicity.

Health risk assessment of neonicotinoid insecticide residues in pistachio using a QuEChERS-based method in combination with HPLC-UV

There is an increasing need to address the potential risks arising from combined exposures to multiple residues from pesticides in the diet. Pesticide residue-related pollution is a problem that arises because of the increased use of pesticides in agriculture to meet the growing demands of food production. In this study, pesticide residue data were obtained based on an optimized extraction method. For this purpose, we established a method based on quick, easy, cheap, effective, rugged, and safe (QuEChERS) extraction for simultaneous determination of imidacloprid (IMI) and acetamiprid (ACT) in pistachio nuts. The parameters influencing the QuEChERS method were the sample-to-water ratio and adsorbent amounts. As a result, both were optimized to improve the recovery of the analytes as well as the clean-up efficiency of the pistachio matrix. Our results indicated that a freeze-out step and use of primary and secondary amines as an adsorbent led to much cleaner chromatograms with lower baseline drift, without using graphitized carbon black and C₁₈ -based adsorbent, which reduced both cost and time of analysis. Following extraction, the pesticide residues were separated and quantified by reverse-phase HPLC. For validation purposes, recovery studies were carried out using a concentration range from 20 to 2500 μg/L at nine levels. The suitable linearity, precision, and accuracy were obtained with HPLC-UV with recoveries of 70.37%-89.80% for IMI and 81.05%-113.57% for ACT, with relative standard deviations <12%. The validated method was successfully applied to the analysis of pistachio samples collected from a field trial to estimate maximum residue limits. There was no significant health risk for consumers via pistachio consumption.

Comparison of two different nickel oxide films for electrochemical reduction of imidacloprid

A nickel oxide (NiO) thin film was successfully prepared on Ni foil via a sol–gel method and a reduced state nickel oxide (r-NiO) thin film was obtained by etching NiO with hydrazine hydrate solution.

Dynamics and dietary risk assessment of thiamethoxam in wheat, lettuce and tomato using field experiments and computational simulation

Thiamethoxam is a widely used pesticide applied to different field crops. To inform risk assessment for this pesticide across relevant crops, we usually rely on field trials, which require time, costs and energy. For providing reliable data across crops and reduce experimental efforts, field trials should be complemented with dynamic modelling. In the present work, we hence focused on combining field trials with dynamic modelling to simulate mass evolutions of the pesticide-plant-system for thiamethoxam applied to wheat, lettuce and tomato as three major food crops. Field trials were conducted with QuEChERS (quick, easy, cheap, effective, rugged and safe) liquid chromatography-mass spectrometry, which gave consistent maximum residue concentrations for thiamethoxam in wheat, lettuce and tomato. We used these residues to evaluate the related dietary risk of humans consuming these food crops. Our results indicated that thiamethoxam did not provide any unacceptable dietary risk for humans across these three food crops, which is in line with findings from previous studies. Results for the studied crops could be extrapolated to other crops and with that, our study constitutes a cost- and time-efficient way of providing reliable input for risk assessment of pesticides across crops, which is relevant for both practitioners and regulators.

Determination of imidacloprid and its relevant metabolites in tomato using modified QuEChERS combined with ultrahigh-pressure liquid chromatography/Orbitrap tandem mass spectrometry

BACKGROUND

Red tomato processing is one of the leading industries in Xinjiang, but also the largest export industry. In the process of tomato planting, imidacloprid (IMI) is often used to kill aphids, which poses the risk of pesticide residue. However, as daily consumables, pesticide residue on tomatoes may cause a potential threat to human health. Therefore the aims of this research were to study the residue dynamics of IMI pesticides in tomatoes by monitoring field experiments and to investigate the fate of IMI and its metabolites under Xinjiang field conditions.

RESULTS

In the field trials, three different doses of IMI were sprayed on tomato during the fruit setting stage. Degradation of IMI and residue behaviors of its metabolites at different stages were systemically traced and evaluated by ultrahigh-performance liquid chromatography coupled with tandem mass spectrometry (UHPLC/Q-Orbitrap MS). An accurate mass tool was used as the main method to identify the IMI metabolites. The improved method showed high efficiency in detecting IMI and 6-chlorinated nicotinic acid (6-CNA), being able to determine hazardous pesticides at trace levels. The fate of IMI in field tomato was investigated over 28 days. The metabolic mechanism of IMI in tomato is: OH products in the early stage and carbonyl products in the late stage.

CONCLUSION

Under natural conditions, pesticides in tomatoes will gradually decrease with time. In this process, olefin IMI is produced, but it is almost completely metabolized after 28 days. Therefore even 10 times the recommended dose of IMI pesticide will not endanger human health. © 2019 Society of Chemical Industry.

Quantum Dots-Based Immunochromatographic Strip for Rapid and Sensitive Detection of Acetamiprid in Agricultural Products

In this study, a rapid and sensitive immunochromatographic strip (ICS) assay, based on quantum dots (QDs), was developed for the qualitative and quantitative detection of acetamiprid in agricultural samples. Acetamiprid-ovalbumin conjugates (ACE-OVA) and goat anti-mouse IgG were sprayed onto a nitrocellulose membrane as a test and control line. Two kinds of anti-acetamiprid monoclonal antibodies (mAb) obtained in our lab were characterized by the ELISA and surface plasmon resonance assay. The competitive immunoassay was established using a QDs-mAb conjugate probe. The visual detection limit of acetamiprid for a qualitative threshold was set as 1 ng/mL to the naked eye. In the quantitative test, the fluorescence intensity was measured by a portable strip reader and a standard curve was obtained with a linear range from 0.098 to 25 ng/mL, and the half maximal inhibitory concentration of 1.12 ng/mL. The developed method showed no evident cross-reactivities with other neonicotinoid insecticides except for thiacloprid (36.68%). The accuracy and precision of the developed QDs-ICS were further evaluated. Results showed that the average recoveries ranged from 78.38 to 126.97% in agricultural samples. Moreover, to test blind tea samples, the QDs-ICS showed comparable reliability and a high correlation with ultra-performance liquid chromatography-tandem mass spectrometry. The whole sample detection could be accomplished within 1 h. In brief, our data clearly manifested that QDs-ICS was quite qualified for the rapid and sensitive screening of acetamiprid residues in an agricultural product analysis and paves the way to point-of-care testing for other analytes.

Preconcentration of Trace Neonicotinoid Insecticide Residues Using Vortex-Assisted Dispersive Micro Solid-Phase Extraction with Montmorillonite as an Efficient Sorbent

In this work, we investigated montmorillonite for adsorption of neonicotinoid insecticides in vortex-assisted dispersive micro-solid phase extraction (VA-d-μ-SPE). High-performance liquid chromatography with photodiode array detection was used for quantification and determination of neonicotinoid insecticide residues, including thiamethoxam, clothianidin, imidacloprid, acetamiprid, and thiacloprid. In this method, the solid sorbent was dispersed into the aqueous sample solution and vortex agitation was performed to accelerate the extraction process. Finally, the solution was filtered from the solid sorbent with a membrane filter. The parameters affecting the extraction efficiency of the proposed method were optimized, such as amount of sorbent, sample volume, salt addition, type and volume of extraction solvent, and vortex time. The adsorbing results show that montmorillonite could be reused at least 4 times and be used as an effective adsorbent for rapid extraction/preconcentration of neonicotinoid insecticide residues. Under optimum conditions, linear dynamic ranges were achieved between 0.5 and 1000 ng mL^-1 with a correlation of determination (R²) greater than 0.99. Limit of detection (LOD) ranged from 0.005 to 0.065 ng mL^-1, while limit of quantification (LOQ) ranged from 0.008 to 0.263 ng mL^-1. The enrichment factor (EF) ranged from 8 to 176-fold. The results demonstrated that the proposed method not only provided a more simple and sensitive method, but also can be used as a powerful alternative method for the simultaneous determination of insecticide residues in natural surface water and fruit juice samples.

Ringer tablet-based ionic liquid phase microextraction: Application in extraction and preconcentration of neonicotinoid insecticides from fruit juice and vegetable samples

An efficient, reliable, sensitive, rapid, and green analytical method for the extraction and determination of neonicotinoid insecticides in aqueous samples has been developed using ionic liquid phase microextraction coupled with high performance liquid chromatography-diode array detector. In this method, a few microliters of 1-hexyl-3-methylimidazolium hexafluorophosphate (as an extractant) is added onto a ringer tablet and it is transferred into a conical test tube containing aqueous phase of the analytes. By manually shaking, the ringer tablet is dissolved and the extractant is released into the aqueous phase as very tiny droplets to provide a cloudy solution. After centrifuging the extracted analytes into ionic liquid are collected at the bottom of a conical test tube. Under the optimum extraction conditions, the method showed low limits of detection and quantification between 0.12 and 0.33 and 0.41 and 1.11ngmL(-1), respectively. Extraction recoveries and enrichment factors were from 66% to 84% and 655% to 843%, respectively. Finally different aqueous samples were successfully analyzed using the proposed method.

Aptamer contained triple-helix molecular switch for rapid fluorescent sensing of acetamiprid

In this study, an aptamer-based fluorescent sensing platform using triple-helix molecular switch (THMS) was developed for the pesticide screening represented by acetamiprid. The THMS was composed of two tailored DNA probes: a label-free central target specific aptamer sequence flanked by two arm segments acting as a recognition probe; a hairpin-shaped structure oligonucleotide serving as a signal transduction probe (STP), labeled with a fluorophore and a quencher at the 3' and 5'-end, respectively. In the absence of acetamiprid, complementary bindings of two arm segments of the aptamers with the loop sequence of STP enforce the formation of THMS with the "open" configuration of STP, and the fluorescence of THMS is on. In the presence of target acetamiprid, the aptamer-target binding results in the formation of a structured aptamer/target complex, which disassembles the THMS and releases the STP. The free STP is folded to a stem loop structure, and the fluorescence is quenched. The quenched fluorescence intensity was proportional to the concentration of acetamiprid in the range from 100 to 1200nM, with the limit of detection (LOD) as low as 9.12nM. In addition, this THMS-based method has been successfully used to test and quantify acetamiprid in Chinese cabbage with satisfactory recoveries, and the results were in full agreement with those from LC-MS. The aptamer-based THMS presents distinct advantages, including high stability, remarkable sensitivity, and preservation of the affinity and specificity of the original aptamer. Most importantly, this strategy is convenient and generalizable by virtue of altering the aptamer sequence without changing the triple-helix structure. So, it is expected that this aptamer-based fluorescent assay could be extensively applied in the field of food safety inspection.

Simultaneous determination of three neonicotinoid insecticide residues and their metabolite in cucumbers and soil by QuEChERS clean up and liquid chromatography with diode-array detection

A new method was developed for the simultaneous determination of three neonicotinoid insecticides with their metabolite in cucumbers and soil based on QuEChERS as a pretreatment procedure.

Aptamer-based fluorescent screening assay for acetamiprid via inner filter effect of gold nanoparticles on the fluorescence of CdTe quantum dots

This paper reports a novel aptamer-based fluorescent detection method for small molecules represented by acetamiprid based on the specific binding of aptamers with acetamiprid, and the inner filter effect (IFE) of gold nanoparticles (AuNPs) on the fluorescence of CdTe quantum dots (CdTe QDs). When CdTe QDs were mixed with AuNPs, the fluorescence of CdTe QDs was significantly quenched via IFE. The IFE efficiency could be readily modulated by the absorption and the aggregation state of AuNPs. The presence of salt could easily induce the aggregation of AuNPs, resulting in the fluorescence recovery of the quenched QDs. Acetamiprid-binding aptamer (ABA) could adsorb on the negatively charged AuNPs through the coordination interaction to protect AuNPs from salt-induced aggregation, so the fluorescence of CdTe QDs would be quenched by the IFE of AuNPs. However, the specific binding of ABA with acetamiprid could release the ABA from the surfaces of AuNPs and decrease the salt tolerance of AuNPs, so the IFE-decreased fluorescence of CdTe QDs was regained with the presence of acetamiprid, and the fluorescence enhancement efficiency was driven by the concentration of acetamiprid. Based on this principle, the aptamer-based fluorescent method for acetamiprid has been established and optimized. The assay exhibited excellent selectivity towards acetamiprid over its analogues and other pesticides which may coexist with acetamiprid. Under the optimum experiment conditions, the established method could be applied for the determination of acetamiprid with a wide linear range from 0.05 to 1.0 μM, and a low detection limit of 7.29 nM (3σ). Furthermore, this IFE-based method has been successfully utilized to detect acetamiprid in six types of vegetables, and the results were in full agreement with those from HPLC and LC-MS. The proposed method displays remarkable advantages of high sensitivity, rapid analysis, excellent selectivity, and would be suitable for the practical application of target screening in real samples.

A simultaneous extraction method for organophosphate, pyrethroid, and neonicotinoid insecticides in aqueous samples

A method was developed for the extraction and analysis of 2 organophosphate, 8 pyrethroid, and 5 neonicotinoid insecticides from the same water sample. A salted liquid-liquid extraction (LLE) was optimized with a solid-phase extraction (SPE) step that separated the organophosphates (OPs) and pyrethroids from the neonicotinoids. Factors that were optimized included volume of solvent and amount of salt used in the LLE, homogenization time for the LLE, and type and volume of eluting solvent used for the SPE. The OPs and pyrethroids were quantified using gas chromatography-mass spectrometry, and the neonicotinoids were quantified using liquid chromatography-diode array detector. Results showed that the optimized method was accurate, precise, reproducible, and robust; recoveries in river water spiked with 100 ng L(-1) of each of the insecticides were all between 86 and 114 % with RSDs between 2 and 8 %. The method was also sensitive with method detection limits ranging from 0.1 to 27.2 ng L(-1) depending on compounds and matrices. The optimized method was thus appropriate for the simultaneous extraction of 15 widely applied insecticides from three different classes and was shown to provide valuable information on their environmental fate from field-collected aqueous samples.

Preparation, characterization and efficiency of nanoencapsulated imidacloprid under laboratory conditions

In this work, nano-imidacloprid was prepared by direct encapsulation with ABA triblock linear dendritic copolymers composed of poly(citric acid) (PCA) as A block and poly(ethylene glycol) (PEG) as B block. Nanocapsules of imidacloprid were characterized using spectroscopy, microscopy and thermal analysis. The encapsulation process was performed by self-assembly of PCA-PEG-PCA in the presence of imidacloprid in different solvents. Comparison of the TEM images of nano-imidacloprid prepared in ethanol and water showed that, during the first day, self-assemblies appeared as small particles with an average size of 10-20nm. Depending upon the type of solvent, the time and concentration, morphology and size of the nano-imidacloprid varied from fiber-like to globular to tubular from 10nm to several mm in size. Higher loading capacity and slower release rate of imidacloprid from nano-imidacloprid at optimum pH of Glyphodes pyloalis׳s gut (pH=10) compared to neutral pH confirmed the selective and controllable action of nano-imidacloprid. Results of bioassays on the model insect showed that by using the nanoform of imidacloprid, essential dosage of pesticide and environmental risk decreased significantly and indicated good performance for this formulation.

Liquid chromatography with diode array detection and tandem mass spectrometry for the determination of neonicotinoid insecticides in honey samples using dispersive liquid-liquid microextraction

The combination of solid-phase extraction with dispersive liquid-liquid microextraction (SPE-DLLME) is proposed for the determination of five neonicotinoid insecticides in honey. After a cleanup stage, the analytes were eluted using acetonitrile. DLLME was performed by injecting rapidly the acetonitrile extract into 10 mL of water containing a 10% (w/v) NaCl and 100 μL of CHCl3. The settled organic phase obtained after centrifugation was evaporated, reconstituted in acetonitrile (ACN), and submitted to liquid chromatography (LC) with photodiode array detection (DAD) and atmospheric pressure chemical ionization-ion trap-tandem mass spectrometry (APCI-IT-MS/MS). The matrix effect was evaluated, and quantification was carried out using external aqueous calibrations when using DAD, the matrix-matched calibration method was applied for MS/MS. Detection limits in the 0.2-1.0 and 0.02-0.13 ng/g ranges were obtained when using DAD and MS/MS, respectively. The SPE-DLLME-LC-APCI-IT-MS/MS method was applied for the analysis of different honey samples, and none was found to contain residues.

Next-generation sequencing-based transcriptome analysis of Cryptolaemus montrouzieri under insecticide stress reveals resistance-relevant genes in ladybirds

As the most efficient natural enemy of mealybugs, the ladybird Cryptolaemus montrouzieri Mulsant plays an important role in integrated pest management. We report here a profiling analysis of C. montrouzieri under insecticide stress to gain a deeper view of insecticide resistance in ladybirds. For transcriptome sequencing, more than 26 million sequencing reads were produced. These reads were assembled into 38,369 non-redundant transcripts (mean size=453 nt). 23,248 transcripts were annotated with their gene description. Using a tag-based DGE (Digital gene expression) system, over 5.7 million tags were sequenced in both the insecticide stress group and the control group, and mapped to 38,369 transcripts. We obtained 993 genes that were significantly up- or down-regulated under insecticide stress in the ladybird transcriptome. These results can contribute to in-depth research into the molecular mechanisms of resistance and enhance our current understanding of the effects of insecticides on natural enemies.