A wearable electrode based on copper nanoparticles for rapid determination of paraquat.

The application of copper-based nanoparticles synthesized via green synthesis and their integration with a wearable electrode is reported for designing a flexible catalytic electrode on a glove for onsite electroanalysis of paraquat. A copper precursor and an orange extract from Citrus reticulata are used to synthesize an economical electrocatalytic material for supporting the selective and sensitive detection of paraquat. The electrode yields multidimensional fingerprints due to two redox couples in a square wave voltammogram, corresponding to the presence of paraquat. The developed lab-on-a-finger sensor provides the fast electroanalysis of paraquat within 10 s, covering a wide range from 0.50 to 1000 µM, with a low detection limit down to 0.31 µM and high selectivity. It is also possible to use this sensor at a fast scan rate as high as 6 V s-1 (< 0.5 s for a scan). This wearable glove sensor allows the user to directly touch and analyze samples, such as surfaces of vegetables and fruits, to screen the contamination. It is envisioned that these glove-embedded sensors can be applied to the on-site analysis of food contamination and environments.

A highly selective and sensitive CdS fluorescent quantum dot for the simultaneous detection of multiple pesticides.

The abuse of pesticides has introduced a large number of residues in soil and drinking water, which can then enter the food chain and the human body. Monitoring pesticide residues and developing simple and fast detection systems for pesticide residues is urgently needed. In this study, we presented one-pot prepared CdS fluorescent quantum dots (QDs) and explored their sensing application for organic pesticides. The CdS QDs can sensitively and selectively detect three different pesticides, dichlorvos (DDVP), paraquat, and glufosinate-ammonium, through different fluorescence responses. Paraquat can effectively quench the fluorescence of the QDs and DDVP can cause remarkable fluorescent enhancement. Glufosinate-ammonium can induce both 150 nm fluorescent blueshifting and 30-fold fluorescent enhancement. The probe exhibited low detection limits for the three pesticides: 1.44 µM for paraquat, 0.23 mM for DDVP, and 49.8 µM for glufosinate-ammonium. Furthermore, based on the results, we utilized the powerful functions of smartphones to establish a concentration-gray value standard curve through RGB values and gray values to realize the qualitative detection and quantitative analysis of DDVP. It is believed that this work presents a new platform for the simultaneous detection of multiple pesticides using a single QDs probe. The present on-site method using a smartphone is of great potential for water monitoring in rural areas.

Gold nanoparticle functionalized nanopipette sensors for electrochemical paraquat detection.

A sensitive nanopipette sensor is established through a unique design of host-guest recognition, which could be further enhanced by the introduction of gold nanoparticles (Au NPs). Generally, the nanopipette is conjugated with caboxylatopillar[5]arenes (CP[5]) or carboxylated leaning pillar[6]arene (CLP[6]) to generate recognition sites. After the addition of pesticide molecules, they would be captured by CP[5] (or CLP[6]), resulting in a significant electronegativity change on the nanopipette's inner surface, which could be determined by the ionic current change. The CP[5]-modified nanopipette exhibited reliable selectivity for paraquat, while the CLP[6]-modified nanopipette showed an ability of detection for both paraquat and diquat. The addition of Au NPs improved the selectivity and sensitivity of the CP[5]-Au NP-modified nanopipette for paraquat sensing. After optimization by lowering the size of the Au NPs, CP[5]-Au NPs (3 nm)-modified nanopipettes achieved lower detection limits of 0.034 nM for paraquat. Furthermore, in real sample analysis, this sensor demonstrates exceptional sensitivity and selectivity. This study provides a new strategy to develop nanopipette sensors for practical small molecule detection. The gold nanoparticles enhanced quartz nanopipette sensor based on host-guest interaction was firstly established, which could achieve an excellent limit of detection of 3.4 × 10-11 mol/L for paraquat.

Highly Sensitive Fluorescent Probe for Detection of Paraquat Based on Nanocrystals.

Paraquat is one of the most toxic materials widely applied in agriculture in most countries. In the present study, a simple, innovative and inexpensive nano biosensor which is based on a thioglycolic acid (TGA) - CdTe@CdS core-shell nanocrystals (NCs) to detect paraquat, is suggested. The NCs based biosensor shows a linear working range of 10-100 nM, and limited detection of 3.5 nM. The proposed sensor that has been well used for the detection and determination of paraquat in natural water samples is collected from corn field and a canal located near to the corn field yielding recoveries as high as 98%. According to our findings, the developed biosensor shows reproducibility and high sensitivity to determine paraquat in natural water samples in which the amount of paraquat has low levels. The suggested method is efficiently applied to paraquat determination in the samples of natural water that are collected from a tap water and a canal located near to the cornfield.

Filamentous fungi with high paraquat-degrading activity isolated from contaminated agricultural soils in northern Thailand.

The contamination of paraquat (1,1'-dimethyl-4,4'-bipyridylium dichloride) herbicide from the farming area has become a public concern in many countries. This herbicide harms to human health and negatively effects the soil fertility. Several methods have been introduced for the remediation of paraquat. In this study, 20 isolates of the paraquat-tolerant fungi were isolated from the contaminated soil samples in northern Thailand. We found that isolate PRPY-2 and PFCM-1 exhibited the highest degradation activity of paraquat on synthetic liquid medium. About 80 and 68% of paraquat were removed by PRPY-2 and PFCM-1 respectively after 15 days of cultivation. Based on the morphological characteristic and molecular analysis, the fungal isolate PRPY-2 and PFCM-1 were identified as Aspergillus tamarii and Cunninghamella sp. respectively. The biosorption of paraquat on these fungal mycelia was also investigated. It was found that only 8-10% of paraquat could be detected on their mycelia, while 24-46% of paraquat was degraded by fungal mycelia. This is the first report on paraquat degrading ability by A. tamarii and Cunninghamella sp. It is demonstrated that these filamentous fungi are promising microorganisms available for remediation of paraquat contaminated environment.

Aptasensor for paraquat detection by gold nanoparticle colorimetric method.

This study aimed to develop an aptasensor for paraquat detection by gold nanoparticles. The specific aptamer for paraquat was selected by using the SELEX process via capillary electrophoresis. Sixty-three aptamer candidates were amplified by asymmetric PCR and screened for paraquat binding using gold nanoparticles (AuNPs). Aggregation of AuNPs was specifically induced by desorption of paraquat binding aptamers from the surface of AuNPs as a result of aptamer-target interaction leading to the color change from red to purple. Aptamer 77F with the following sequence: 5'-AGGCTTACACCTGAAAAGCGGCTTAATTTACACTACTGTAT-3' was selected as a highly specific aptamer for paraquat. The detection limit of paraquat was 0.267 µg/mL by colorimetry and 1.573 µg/mL by the quartz crystal microbalance (QCM) technique. This aptamer showed specificity for paraquat by colorimetry. Dimethyl phophite, diethyl phophite and O,O diethyl thiophosphate potassium salt did not react by colorimetry but, exhibited a weak nonspecific reaction by QCM. This is first time that an aptasensor was used for detection of paraquat based on QCM. However, the aptasensor based on the colorimetric method simply uses a generation of a signal that can be detected by the naked eye. This technique is rapid, low cost easy to use and suitable for on-site detection of herbicide residue.

[Liquid chromatography-tandem mass spectrometry method for the determination of paraquat and diquat in plasma and urine].

Objective: To establish a LC-MS/MS method for determination of paraquat and diquat in plasma and urine samples. Methods: Plasma is precipitated by acetonitrile then diluent with phosphate buffer (pH=7) , urine is diluent with phosphate buffer (pH=7) , then diluent samples extracted with Oasis WCX solid-phase extraction column. Samples were analyzed using LC-MS/MS in multiple reaction monitoring (MRM) mode. The analytical column was XBridge®BEH-HILIC (100 mm×2.1 mm×2.5 µm) and the mobile phase were 100 mmol ammonium formate add 0.5% formic acid and acetonitrile. Paraquat was quantified by internal standard method and diquat by external standard method. Results: The calibration curves of paraquat and diquat were linear in the concentration range of 10.0~120.0 µg/L, the correlation coefficient (r) were 0.9985~0.9994. The limit of detection of paraquat in plasma and urine were 1.98 µg/L and 1.00 µg/L, respectively, the recovery rate were 100.2%~107.3%, the RSD were 1.6%~3.3%. The limit of detection of diquat in plasma and urine were 1.80 µg/L and 2.77 µg/L, respectively, the recovery rate were 85.3%~93.1%, the RSD were 1.8%~5.5%. Conclusion: This method is sensitive and accurate, and can simultaneously determine paraquat and diquat in plasma and urine.

A balsam pear-shaped CuO SERS substrate with highly chemical enhancement for pesticide residue detection.

Simple and traditional hydrothermal fabrication of a novel balsam pear-shaped CuO with high SERS enhancement is presented. XRD (X-ray diffraction), SEM (scanning electronic microscopy), TEM (transmission electron microscope), HRTEM (high-resolution transmission electron microscope), UV-Vis, and Raman are adopted to ensure that this balsam pear-shaped CuO with dense nanoparticle protuberance is successfully prepared. The LOD of this CuO SERS substrate is 4.79 µg L-1 with R6G as molecular probe. By using DFT (density functional theory) calculation and FDTD (finite difference time domainmethod) simulation, both EM (electromagnetic enhancement) and CM (chemical enhancement) mechanisms are investigated, and the results show that these two-enhancement mechanisms can coexist in this balsam pear-shaped CuO. Finally, the prepared substrate has been applied for the determination of trace levels of paraquat in solution , and results show that its LOD for paraquat is 275 µg L-1 (optimum Raman band: 1646 cm-1 Raman shift), which is better than the government standard in China. A dexterous and facile way for fabrication of CuO SERS-active substrates with low cost and high performance, quite promising in detection of chemically hazardous substances and pesticide residue is provided. Graphical abstract.

Nanofibrillar cellulose/Au@Ag nanoparticle nanocomposite as a SERS substrate for detection of paraquat and thiram in lettuce.

A nanocomposite based on nanofibrillar cellulose (NFC) coated with gold-silver (core-shell) nanoparticles (Au@Ag NPs) was developed as a novel surface-enhanced Raman spectroscopy (SERS) substrate. SERS performance of NFC/Au@Ag NP nanocomposite was tested by 4-mercaptobenzoic acid. The cellulose nanofibril network was a suitable platform that allowed Au@Ag NPs to be evenly distributed and stabilized over the substrate, providing more SERS hotspots for the measurement. Two pesticides, thiram and paraquat, were successfully detected either individually or as a mixture in lettuce by SERS coupled with the nanocomposite. Strong Raman scattering signals for both thiram and paraquat were obtained within a Raman shift range of 400-2000 cm-1 and a Raman intensity ~ 8 times higher than those acquired by NFC/Au NP nanocomposite. Characteristic peaks were clearly observable in all SERS spectra even at a low concentration of 10 µg/L of pesticides. Limit of detection values of 71 and 46 µg/L were obtained for thiram and paraquat, respectively. Satisfactory SERS performance, reproducibility, and sensitivity of NFC/Au@Ag NP nanocomposite validate its applicability for real-world analysis to monitor pesticides and other contaminants in complex food matrices within a short acquisition time. Graphical abstract.

Glassy carbon electrode modified with carbon black and cross-linked alginate film: a new voltammetric electrode for paraquat determination.

A new electrode based on glassy carbon modified with an alginate film cross-linked with glutaraldehyde containing immobilized carbon black particles was successfully developed and applied for the determination of paraquat (PQ), a herbicide widely used for broadleaf weed control. Different polysaccharides (alginate, cellulose, pectin, starch, and chitosan) were investigated for the immobilization process, and alginate presented the highest chemical modifier potential for PQ determination. Additionally, the influence of chemical cross-linking agents (glutaraldehyde and epichlorohydrin) on the morphology, electrochemical response, and film stability was investigated. All experimental conditions were optimized, including the supporting electrolyte conditions (composition, pH, and concentration) and square wave voltammetry technical parameters. Under the optimized experimental conditions, the PQ analytical curve was linear from 0.4 to 2.0 mg L-1 and the limits of detection and quantification were 0.06 and 0.19 mg L-1, respectively. The proposed electrode is easy to obtain, stable, selective, sensitive, and low cost and was successfully applied for PQ determination in environmental and beverage samples. Graphical abstract.

Rapid and sensitive surface-enhanced Raman spectroscopy (SERS) method combined with gold nanoparticles for determination of paraquat in apple juice.

BACKGROUND: Paraquat, a highly efficient herbicide, is widely used in agricultural practices throughout the world. However, paraquat residues in food pose a threat to human health. In order to develop a rapid and sensitive method, surface-enhanced Raman spectroscopy (SERS) coupled with gold nanoparticles was applied to analysis of paraquat in apple juice. RESULTS: Natural organic compounds (sugars and organic acids) in apple juice interfered with SERS measurement. Sample preparation was needed. Paraquat could be detected at concentrations as low as 0.02 and 0.1 µg mL- 1 with the weak cation-exchange solid-phase extraction (WCX-SPE) method and dilution method for sample preparation, respectively. For quantitative analysis, the R2 cv of the partial least-squares regression model with the dilution method (0.939) was not as good as with the WCX-SPE method (0.984), but the dilution method is much less costly, simpler and time saving. Satisfactory recovery values were obtained ranging from 94.73% to 114.81%, with the exception of 56.55% for the lowest concentration. CONCLUSION: This work showed that SERS combined with gold nanoparticles could determine paraquat in apple juice. As a simple, rapid and ultrasensitive method, it has great practical potential for detection of other contaminants in a variety of foods. © 2018 Society of Chemical Industry.

Ion-pair switchable-hydrophilicity solvent-based homogeneous liquid-liquid microextraction for the determination of paraquat in environmental and biological samples before high-performance liquid chromatography.

An approach involving ion-pair switchable-hydrophilicity solvent-based homogeneous liquid-liquid microextraction coupled to high-performance liquid chromatography has been applied for the preconcentration and separation of paraquat in a real sample. A mixture of triethylamine and water was used as the switchable-hydrophilicity solvent. The pH was regulated using carbon dioxide; hence the ratio of the ionized and non-ionized form of triethylamine could control the optimum conditions. Sodium dodecyl sulfate was utilized as an ion-pairing agent. The ion-associate complex formed between the cationic paraquat and sodium dodecyl sulfate was extracted into triethylamine. The separation of the two phases was carried out by the addition of sodium hydroxide, which changed the ionization state of triethylamine. The effects of some important parameters on the extraction recovery were investigated. Under the optimum conditions (500 µL of the extraction solvent, 1 mg sodium dodecyl sulfate, 2.0 mL of 10 mol/L sodium hydroxide, and pH 4), the limit of detection and the limit of quantification were 0.2 and 0.5 µg/L, respectively, with preconcentration factor of 74. The precision (RSD, n = 10) was  <5%. The recovery of the analyte in environmental and biological samples was in the range of 90.0-92.3%.

Whirling agitated single drop microextraction technique for the simultaneous analysis of Paraquat and Maneb in tissue samples of treated mice.

A new microextraction technique, whirling agitated single drop microextraction, has been proposed for the simultaneous analysis of Paraquat and Maneb in tissue samples before liquid chromatography with tandem mass spectrometry. This technique is based on the idea that the escalatory motion of the sample solution along with the extraction solvent increases the movement of molecules into the extraction solvent. In this technique, a simple handheld rotator was utilized to rapidly agitate the biphasic extraction system for the instantaneous extraction of targeted analytes. After extraction, the extracted phase was directly solidified by cooling in crushed ice and easily collected using a micro-spatula. The method showed good performance by achieving sensitive detection limits at 4.81 ng g(-1) (Paraquat) and 9.12 ng g(-1) (Maneb). Mean recoveries and enrichment factors were obtained >91.21% and up to 114 that ensured the preconcentration capacity of the method. The method precision was verified by evaluating intraday variation (n = 10) ≤4.57 (Paraquat) and ≤4.68 (Maneb) in terms of percent relative standard deviation. Additionally, method efficacy was assured by obtaining very little matrix interferences (≤3.11%). Moreover, the method suitability was also checked with its application on tissue samples of intraperitoneally treated mice with Paraquat and Maneb.

Validity of geographically modeled environmental exposure estimates.

Geographic modeling is increasingly being used to estimate long-term environmental exposures in epidemiologic studies of chronic disease outcomes. However, without validation against measured environmental concentrations, personal exposure levels, or biologic doses, these models cannot be assumed a priori to be accurate. This article discusses three examples of epidemiologic associations involving exposures estimated using geographic modeling, and identifies important issues that affect geographically modeled exposure assessment in these areas. In air pollution epidemiology, geographic models of fine particulate matter levels have frequently been validated against measured environmental levels, but comparisons between ambient and personal exposure levels have shown only moderate correlations. Estimating exposure to magnetic fields by using geographically modeled distances is problematic because the error is larger at short distances, where field levels can vary substantially. Geographic models of environmental exposure to pesticides, including paraquat, have seldom been validated against environmental or personal levels, and validation studies have yielded inconsistent and typically modest results. In general, the exposure misclassification resulting from geographic models of environmental exposures can be differential and can result in bias away from the null even if non-differential. Therefore, geographic exposure models must be rigorously constructed and validated if they are to be relied upon to produce credible scientific results to inform epidemiologic research. To our knowledge, such models have not yet successfully predicted an association between an environmental exposure and a chronic disease outcome that has eventually been established as causal, and may not be capable of doing so in the absence of thorough validation.

ZIF-67 based CoS2 self-assembled on graphitic carbon nitride microtubular for sensitive electrochemical detection of paraquat in fruits.

Paraquat (PQ) is a widely used and harmful herbicide that must be detected in the environment. This study reports a novel composite (CoS2-GCN) prepared by assembling cobalt disulfide (CoS2) derived from metal-organic frameworks (MOFs) on graphitic carbon nitride (GCN). An electrochemical sensor (CoS2-GCN/ glassy carbon electrode (GCE)) was successfully prepared by modifying CoS2-GCN onto a GCE to sensitively detect PQ. Different concentrations of PQ were detected using square-wave voltammetry, and the CoS2-GCN/GCE electrochemical sensor showed remarkable response signals for PQ in the range of 20 - 1000 nM and 1 - 13 µM, with a detection limit of 4.13 nM (S/N = 3). The CoS2-GCN/GCE electrochemical sensor exhibited high stability, reproducibility, and immunity to interference, which were attributed to the synergistic effects of CoS2 and GCN. In addition, the CoS2-GCN/GCE electrochemical sensor showed high applicability for the analysis of fruit samples. Therefore, the proposed sensor has potential applications in PQ detection.

A SERS-based point-of-care testing approach for efficient determination of diquat and paraquat residues using a flexible silver flower-coated melamine sponge.

Diquat (DQ) and paraquat (PQ) residues in food are potential hazards to consumers' health. Point-of-care testing (POCT) of them remains challenging. Based on surface-enhanced Raman spectroscopy (SERS) technology, we developed a POCT strategy for DQ and PQ on apple surface and in apple juice. A point-of-use composite was fabricated using a piece of porous melamine sponge (MS) modified with silver nanoflowers (AgNFs), combining the specificity of the SERS fingerprint and the excellent adsorption capacity of MS. Using this dual-functional AgNFs@MS, the on-site determination of the DQ and PQ residues was completed within 3 min without pretreatment. Clear trends were observed between SERS intensity and logarithmic concentrations, with r values from 0.962 to 0.984. The limit of detection of DQ and PQ were 0.14-0.70 ppb in apple juice and on apple surface. This study provides a new point-of-use alternative for rapidly detecting DQ and PQ residues in nonlaboratory settings.

Colorimetric and fluorescent dual detection of paraquat and diquat based on an anionic polythiophene derivative.

We have developed a colorimetric and fluorescent dual-response probe for the detection of paraquat and diquat in aqueous solutions based on an anionic polythiophene derivative. The detection limit of this approach can be as low as 10(-9) M by fluorescence measurements.

An electrochemical magneto immunosensor (EMIS) for the determination of paraquat residues in potato samples.

An electrochemical magneto immunosensor for the detection of low concentrations of paraquat (PQ) in food samples has been developed and its performance evaluated in a complex sample such as potato extracts. The immunosensor presented uses immunoreagents specifically developed for the recognition of paraquat, a magnetic graphite-epoxy composite (m-GEC) electrode and biofunctionalized magnetic micro-particles (PQ1-BSAMP) that allow reduction of the potential interferences caused by the matrix components. The amperometric signal is provided by an enzymatic probe prepared by covalently linking an enzyme to the specific antibodies (Ab198-cc-HRP). The use of hydroquinone, as mediator, allows recording of the signal at a low potential, which also contributes to reducing the background noise potentially caused by the sample matrix. The immunocomplexes formed on top of the modified MP are easily captured by the m-GEC, which acts simultaneously as transducer. PQ can be detected at concentrations as low as 0.18 ± 0.09 µg L(-1). Combined with an efficient extraction procedure, PQ residues can be directly detected and accurately quantified in potato extracts without additional clean-up or purification steps, with a limit of detection (90% of the maximum signal) of 2.18 ± 2.08 µg kg(-1), far below the maximum residue level (20 µg kg(-1)) established by the EC. The immunosensor presented here is suitable for on-site analysis. Combined with the use of magnetic racks, multiple samples can be run simultaneously in a reasonable time.

Determination of paraquat in water samples using a sensitive fluorescent probe titration method.

Paraquat (PQ), a nonselective herbicide, is non-fluorescent in aqueous solutions. Thus, its determination through direct fluorescent methods is not feasible. The supramolecular inclusion interaction of PQ with cucurbit[7]uril was studied by a fluorescent probe titration method. Significant quenching of the fluorescence intensity of the cucurbit[7]uril-coptisine fluorescent probe was observed with the addition of PQ. A new fluorescent probe titration method with high selectivity and sensitivity at the ng/mL level was developed to determine PQ in aqueous solutions with good precision and accuracy based on the significant quenching of the supramolecular complex fluorescence intensity. The proposed method was successfully used in the determination of PQ in lake water, tap water, well water, and ditch water in an agricultural area, with recoveries of 96.73% to 105.77%. The fluorescence quenching values (deltaF) showed a good linear relationship with PQ concentrations from 1.0 x 10(-8) to 1.2 x 10(-5) mol/L with a detection limit of 3.35 x 10(-9) mol/L. In addition, the interaction models of the supramolecular complexes formed between the host and the guest were established using theoretical calculations. The interaction mechanism between the cucurbit[7]uril and PQ was confirmed by 1H NMR spectroscopy.

3D electrochemical device obtained by additive manufacturing for sequential determination of paraquat and carbendazim in food samples.

Pesticides are heavily employed compounds protecting crops, however, these compounds can be extremely harmful to human health. Once the monitoring of pesticides in foods is of great importance, in this work we propose a ready-to-use electrochemical sensor made with 3D printing technology, capable of detecting paraquat and carbendazim in sequential analysis. The proposed electrodes are lab-made and of easy obtention, composed of graphite on a polylactic acid matrix, and provided great results for the analysis of paraquat and carbendazim in honey, milk, juice, and water samples. The sequential analysis of paraquat and carbendazim was proposed, providing optimal analysis of both compounds individually when both are present in a mixture. Limits of detection of 0.01 and 0.03 µmol/L for paraquat and carbendazim, respectively. Recovery tests attested to the suitability of the method, ranging from 94.5 to 113.7 %, and the suitability of 3D printing for environmental and food samples analysis.