Fabricated Electrochemical Sensory Platform Based on the Boron Nitride Ternary Nanocomposite Film Electrode for Paraquat Detection

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.

Copper nanoparticle-decorated nitrogen-doped carbon nanosheets for electrochemical determination of paraquat

A new strategy to prepare copper (Cu) nanoparticles anchored in nitrogen-doped carbon nanosheets (Cu@CN) has been designed and the nanomaterial applied to the determination of paraquat (PQ). The nanocomposite materials were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and several other techniques. We found that the Cu nanoparticles are uniformly distributed on the carbon materials, providing abundant active sites for electrochemical detection. The electrochemical behavior of the Cu@CN-based PQ sensor was investigated by square-wave voltammetry (SWV). Cu@CN exhibited excellent electrochemical activity and PQ detection performance. The Cu@CN-modified glassy carbon electrode (Cu@CN/GCE) exhibited excellent stability, favorable sensitivity, and high selectivity under optimized conditions (enrichment voltage -0.1 V and enrichment time 400 s) of the SWV test. The detection range reached 0.50 nM to 12.00 μM, and the limit of detection was 0.43 nM with high sensitivity of 18 μA·μM^-1·cm^-2. The detection limit is 9 times better than that of the high-performance liquid chromatography method. The Cu@CN electrochemical sensor demonstrated excellent sensitivity and selectivity also in environmental water and fruit samples enabling its use in practical, rapid trace-level detection of PQ in environmental samples.

Fluorescent and Colorimetric Ionic Probe Based on Fluorescein for the Rapid and On-Site Detection of Paraquat in Vegetables and the Environment

Detection of pesticide paraquat (PQ) is of considerable significance to ensure food safety, and its rapid and on-site detection is still a challenge. Aimed at the ion characteristics of PQ, an "enrichment and detection" strategy was proposed to improve the sensitivity through electrostatic attractions, and the ion characteristic of probes was adopted to increase the portability through avoiding aggregation-caused quenching effects in the paper strips. Herein, a novel anion-functionalized ionic liquid (IL) probe with a large conjugated plane and rich π-electrons ([Fluo][P₆₆₆₁₄]₂) was designed as a fluorescent and colorimetric dual-channel probe to sensitively and rapidly detect trace amounts of PQ in vegetables and the environment. The proposed probe exhibited good linearity with a detection limit of 64.0 nM in the PQ concentration range of 0.3-7.0 μM (fluorometry) and 0.1 μM in that of 0.1-8.0 μM (colorimetry), respectively. In addition, it displayed a rapid fluorescence quenching response from green to dark (<5 s) and excellent anti-interference (among 23 other pesticides) due to dual effects of electrostatic attraction and π-π stacking. Most importantly, the lipophilic IL probe could be applied in real vegetables and environmental samples with a satisfying recovery rate of 98-103% and assembled into a handy paper strip that achieved the visual semiquantitative detection of PQ. This ionic probe provides a feasible approach for rapidly and conveniently detecting PQ for ensuring agricultural and food safety and opens a new avenue to detect ion-responsive analytes in real complex samples by an "enrichment and detection" strategy.

Electrochemical sensor for ultrasensitive detection of paraquat based on metal-organic frameworks and para-sulfonatocalix[4]arene-AuNPs composite

The widespread occurrence of pesticides in surface water, groundwater, soil, and food has received increasing attention towards environmental safety. Paraquat (PQ) is world widely used as a rapid sterilant herbicide and is highly toxic to humans. A simple, rapid, sensitive, and on-site detection method for the water environment to detection of PQ is urgently required. Here, we prepared a zeolite imidazole skeleton-8 (ZIF-8) and para-sulfonylcalix[4]arene (pSC₄) coated gold nanoparticles composite (pSC₄-AuNPs@ZIF-8) by one-step method. An electrochemical biosensor assay for PQ was established based on pSC₄-AuNPs@ZIF-8 modified glassy carbon electrode through host-guest recognition of PQ and pSC₄. Under the optimal conditions, recoveries of targets determination results were 92.7%-103% (n = 3), respectively. The quantity PQ detection limit was found to be 0.49 pM. Therefore, the signal amplification strategy based on pSC₄-AuNPs@ZIF-8 has potential value in detecting trace pollutants in the water environment.

Highly Sensitive Electrochemical Detection of Paraquat in Environmental Water Samples Using a Vertically Ordered Mesoporous Silica Film and a Nanocarbon Composite

Herein, we demonstrate a sensitive and rapid electrochemical method for the detection of paraquat (PQ) using a glassy carbon electrode (GCE) modified with vertically ordered mesoporous silica films (VMSF) and a nanocarbon composite. The three-dimensional graphene-carbon nanotube (3DG-CNT) nanocarbon composite has a 3D network structure, a large electroactive area and oxygen-containing groups, promoting electron transfer between PQ and the underlying electrode and providing a suitable microenvironment for the stable growth of VMSF. This VMSF/3DG-CNT nanocomposite film could be prepared on the GCE's surface by a two-step electrochemical method with good controllability and convenience. Owing to the synergistic effect of the electrocatalytic ability of 3DG-CNT and the electrostatically enriched capacity of VMSF, the proposed VMSF/3DG-CNT/GCE has superior analytical sensitivity compared with the bare GCE. Furthermore, VMSF has excellent anti-fouling ability that makes the fabricated sensor exhibit satisfactory performance for direct analysis of PQ in environmental water samples.

A Label-Free Electrochemical Aptasensor Based on Zn/Fe Bimetallic MOF Derived Nanoporous Carbon for Ultra-Sensitive and Selective Determination of Paraquat in Vegetables

Paraquat (PQ) has high acute toxicity, even at low concentrations. For most people, the main pathway of exposure to PQ is through the diet. Therefore, the development of simple and efficient methods for PQ testing is critical for ensuring food safety. In this study, a new electrochemical detection strategy for paraquat is proposed based on the specific binding of PQ to its nucleic acid aptamer. Firstly, the Zn/Fe bimetallic ZIF derived nanoporous carbon (Zn/Fe-ZIF-NPC) and nickel hexacyanoferrate nanoparticles (NiHCF-NPs) were sequentially modified onto the glassy carbon electrode (GCE). NiHCF-NPs served as the signal probes, while Zn/Fe-ZIF-NPC facilitated electron transfer and effectively enhanced the sensing signal of NiHCF-NPs. Au nanoparticles (AuNPs) were then electrodeposited on the NiHCF-NPs/Zn/Fe-ZIF-NPC/GCE and then the thiolated aptamer was assembled on the AuNPs/NiHCF-NPs/Zn/Fe-ZIF-NPC/GCE via Au-S bonding. When incubated with PQ, the formation of PQ–aptamer complexes delayed the interfacial electron transport reaction of NiHCF-NPs, which caused a decrease in the current signals. As a result, simple and highly sensitive detection of PQ can be readily achieved by detecting the signal changes. A linear range was obtained from 0.001 to 100 mg/L with a detection limit as low as 0.34 μg/L. Due to the recognition specificity of the aptamer to its target molecule, the proposed method has excellent anti-interference ability. The prepared electrochemical aptasensor was successfully used for PQ assay in lettuce, cabbage and agriculture irrigation water samples with recoveries ranging from 96.20% to 104.02%, demonstrating the validity and practicality of the proposed method for PQ detection in real samples.

A copper-based metal-organic framework/reduced graphene oxide-modified electrode for electrochemical detection of paraquat

An electrochemical device using copper-based metalorganic franmeworks (MOF) associated with reduced graphene oxide to improve the charge transfer, stability, and adherence of the structures on the surface of the electrodes was developed. The syntheses of these materials were confirmed using scanning electron microscopy, thermogravimetric analysis, X-ray diffraction, Fourier transform infrared and Raman spectroscopy. For the first time, this type of sensor was applied to a systematic study to understand the action mechanism of MOFs and reduced graphene oxide in the electrochemical detection of paraquat pesticide. Under optimized conditions, paraquat was detected in standard solutions by differential pulse voltammetry (- 0.8 to - 0.3 V vs Ag/AgCl), achieving a linear response range between 0.30 and 5.00 μmol L^-1. The limits of detection and quantification were 50.0 nmol L^-1 and 150.0 nmol L^-1, respectively. We assessed the accuracy of the proposed device to determine paraquat in water and human blood serum samples by recovery study, obtaining recovery values ranging from 98 to 104%. Furthermore, the selectivity of the proposed electrode for paraquat detection was evaluated against various interferences, demonstrating their promising application in environmental analysis.

Hydrothermally constructed AgWO4-rGO nanocomposites as an electrode enhancer for ultrasensitive electrochemical detection of hazardous herbicide crisquat

The advancements in electrode materials with high efficiency has been prioritized to effectively monitor the presence of harmful pesticides concerning the environment. In such a way, we hydrothermally constructed a hybrid AgWO₄-rGO nanocomposites for the rapid electrochemical detection of crisquat (CQT). The structural, compositional, morphological and topographical characterization for AgWO₄-rGO nanocomposites is thoroughly performed to understand its electrocatalytic properties. The AgWO₄-rGO nanocomposites are used as an electrode enhancer (rGO@AgWO₄/GCE) for the electrochemical investigations towards CQT detection. The results indicated that the rGO@AgWO₄/GCE possessed an excellent catalytic activity with a wide linear detection range 1-1108 μM coupled with an ultrasensitive limit of detection (LOD) 0.0661 μM for electrochemical CQT detection. The rGO@AgWO₄/GCE CQT sensor also expressed remarkable sensitivity of 0.6306 μAμM^-1cm^-2 in addition to good selectivity and reproducibility. Furthermore, the commercial CQT, river water, tap water and washed vegetable water are used as a representative for real world analysis using rGO@AgWO₄/GCE and results are highly appreciable for the real time CQT detection. Our work proposes a novel hybrid rGO@AgWO₄ nanocomposites reinforced electrodes for ultra-trace level CQT detection with good reliability and can be advocated for real time detection of pesticides.

Ready-to-use paraquat sensor using a graphene-screen printed electrode modified with a molecularly imprinted polymer coating on a platinum core

We propose the fabrication of a novel ready-to-use electrochemical sensor based on a screen-printed graphene paste electrode (SPGrE) modified with platinum nanoparticles and coated with a molecularly imprinted polymer (PtNPs@MIP) for sensitive and cost-effective detection of paraquat (PQ) herbicide. Successive coating of the PtNPs surface with SiO₂ and vinyl end-groups formed the PtNPs@MIP. Next, we terminated the vinyl groups with a molecularly imprinted polymer (MIP) shell. MIP was attached to the PtNPs cores using PQ as the template, methacrylic acid (MAA) as the monomer, ethylene glycol dimethacrylate (EGDMA) as the cross-linker, and 2,2'-azobisisobutyronitrile (AIBN) as the initiator. Coating the SPGrE surface with PtNPs@MIP furnished the PQ sensor. We studied the electrochemical mechanism of PQ on the MIP sensor using cyclic voltammetry (CV) experiments. The PQ oxidation current signal appears at -1.08 V and -0.71 V vs. Ag/AgCl using 0.1 M potassium sulfate solution. Quantitative analysis was performed by anodic stripping voltammetry (ASV) using a deposition potential of -1.4 V for 60 s and linear sweep voltammetric stripping. The MIP sensor provides linearity from 0.05 to 1000 μM (r² = 0.999), with a lower detection limit of 0.02 μM (at -0.71 V). The compact imprinted sensor gave a highly sensitive and selective signal toward PQ. The ready-to-use MIP sensor can provide an alternative approach to the determination of paraquat residue on vegetables and fruits for food safety applications.

Using Post-graphene 2D Materials to Detect and Remove Pesticides: Recent Advances and Future Recommendations

Detection and removal of pesticides have become increasingly imperative as the widespread production and use of pesticides severely contaminate soil and groundwater and cause serious problems to non-target species such as human and animals. Recently, new two-dimensional materials beyond graphene (e.g., transition metal dichalcogenides, layered double hydroxides), called post-graphene two-dimensional materials (pg-2DMs), have exhibited promising potentials in detecting and removing pesticides due to their unique physiochemical attributes such as high photocatalytic activity and large specific surface area. This review summarizes the recent advances of utilizing pg-2DMs to detect, degrade and adsorb pesticides (e.g., thiobencarb, methyl parathion, paraquat). The current gaps and future prospects of this field are discussed as well.

Silver Inkjet-Printed Electrode on Paper for Electrochemical Sensing of Paraquat

The use of fully printed electrochemical devices has gained more attention for the monitoring of clinical, food, and environmental analytes due to their low cost, great reproducibility, and versatility characteristics, serving as an important technology for commercial application. Therefore, a paper-based inkjet-printed electrochemical system is proposed as a cost-effective analytical detection tool for paraquat. Chromatographic paper was used as the printing substrate due its sustainable and disposable characteristics, and an inkjet-printing system deposited the conductive silver ink with no further modification on the paper surface, providing a three-electrode system. The printed electrodes were characterized with scanning electron microscopy, cyclic voltammetry, and chronopotentiometry. The proposed sensor exhibited a large surface area, providing a powerful tool for paraquat detection due to its higher analytical signal. For the detection of paraquat, square-wave voltammetry was used, and the results showed a linear response range of 3.0–100 μM and a detection limit of 0.80 µM, along with the high repeatability and disposability of the sensor. The prepared sensors were also sufficiently selective against interference, and high accuracy (recovery range = 96.7–113%) was obtained when applied to samples (water, human serum, and orange juice), showing the promising applicability of fully printed electrodes for electrochemical monitoring.

A label-free electrochemical sensor for ultrasensitive microRNA-21 analysis based on the poly(l-cysteine)/MoS2 sensing interface

The label-free detection of nucleic acids has attracted interest of scientists due to the fact that it is simple, fast and efficient. Herein, l-cysteine was electropolymerized on the molybdenum disulfide (MoS₂) surface to form a stable and electroactive poly(l-cysteine)-functionalized molybdenum disulfide (Pl-Cys/MoS₂) sensing interface. Taking microRNA-21 (miRNA-21) as an analytical model, a label-free electrochemical sensor was designed according to the properties of the Pl-Cys/MoS₂ sensing interface. Experimental data exhibited that the designed electrochemical sensor exhibited excellent sensitivity, selectivity and stability towards miRNA-21 detection in buffer and real samples. This study offers a methodology to construct a label-free sensing interface by combining MoS₂ nanosheets and electroactive molecules.

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.

The facile co-precipitation synthesis of strontium tungstate anchored on a boron nitride (SrWO4/BN) composite as a promising electrocatalyst for pharmaceutical drug analysis

Strontium tungstate/boron nitride (SrWO₄/BN) composite considered efficient electrocatalysts in the area of electrochemical sensors.