Development of a Luminescent Dinuclear Ir(III) Complex for Ultrasensitive Determination of Pesticides

Three-dimensional polymer phenylethnylcopper/nitrogen doped graphene aerogel electrode coupled with Fe3O4 NPs nanozyme: Toward sensitive and robust photoelectrochemical detection of glyphosate in agricultural matrix

BACKGROUND

Presently, glyphosate (Gly) is the most extensively used herbicide globally, Nevertheless, its excessive usage has increased its accumulation in off-target locations, and aroused concerns for food and environmental safety. Commonly used detection methods, such as high-performance liquid chromatography and gas chromatography, have limitations due to expensive instruments, complex pre-processing steps, and inadequate sensitivity. Therefore, a facile, sensitive, and reliable Gly detection method should be developed.

RESULTS

A photoelectrochemical (PEC) sensor consisting of a three-dimensional polymer phenylethnylcopper/nitrogen-doped graphene aerogel (PPhECu/3DNGA) electrode coupled with Fe3O4 NPs nanozyme was constructed for sensitive detection of Gly. The microscopic 3D network of electrodes offered fast transfer routes for photo-generated electrons and a large surface area for nanozyme loading, allowing high signal output and analytical sensitivity. Furthermore, the use of peroxidase-mimicking Fe3O4 NPs instead of natural enzyme improved the stability of the sensor against ambient temperature changes. Based on the inhibitory effect of Gly on the catalytic activity Fe3O4 NPs, the protocol achieved Gly detection in the range of 5 × 10-10 to 1 × 10-4 mol L-1. Additionally, feasibility of the detection was confirmed in real agricultural matrix including tea, maize seedlings, maize seeds and soil.

SIGNIFICANCE

This work achieved facile, sensitive and reliable analysis towards Gly, and it was expected to inspire the design and utilization of 3D architectures in monitoring agricultural chemicals in food and environmental matrix.

Simple and sensitive fluorescence sensing of methyl parathion based on the inner filter effect of p-nitrophenol on nitrogen-doped titanium carbide quantum dots

It is of great significance to develop an effective method for methyl parathion (MP) detection. Herein, a novel nitrogen-doped titanium carbide quantum dots (N-Ti3 C2 QDs) was prepared and used to construct a simple and sensitive fluorescence sensing platform of MP by making use of inner filter effect (IFE). The prepared N-Ti3 C2 QDs can exhibit strong blue fluorescence at 434 nm. Meanwhile, MP could hydrolyze to produce p-nitrophenol (p-NP) under alkaline conditions, which showed a characteristic ultraviolet-visible (UV-visible) absorption peak at 405 nm, resulting in the fluorescence of N-Ti3 C2 QDs is effectively quenched by p-NP. In addition, the investigation of time-resolved fluorescence decays indicated that the corresponding quenching mechanism of p-NP on N-Ti3 C2 QDs is due to the IFE. After optimizing the conditions, the as-developed fluorescence sensing platform displayed wide detection range (0.1-30 μg mL-1 ) and low detection limit (0.036 μg mL-1 ) for MP, and it was also successfully applied for MP analysis in real water samples, thus it is expected that this simple, sensitive and enzyme-free sensing platform shows great applications.

Portable Sensor Array for On-Site Detection and Discrimination of Pesticides and Herbicides Using Multivariate Analysis

Modern agricultural practice relies heavily on pesticides and herbicides to increase crop productivity, and consequently, their residues have a negative impact on the environment and public health. Thus, keeping these issues in account, herein we developed an azodye-based chromogenic sensor array for the detection and discrimination of pesticides and herbicides in food and soil samples, utilizing machine learning approaches such as hierarchical clustering analysis, principal component analysis, linear discriminant analysis (LDA), and partial least square regression (PLSR). The azodye-based sensor array was developed in combination with various metal ions owing to their different photophysical properties, which led to distinct patterns toward various pesticides and herbicides. The obtained distinct patterns were recognized and processed through automated multivariate analysis, which enables the selective and sensitive identification and discrimination of various target analytes. Further, the qualitative and quantitative determination of target analytes were performed using LDA and PLSR; the results obtained show a linear correlation with varied concentrations of target analytes with R2 values from 0.89 to 0.96, the limit of detection from 5.3 to 11.8 ppm with a linear working range from 1 to 30 μM toward analytes under investigation. Further, the developed sensor array was successfully utilized for the discrimination of a binary mixture of pesticide (chlorpyrifos) and herbicide (glyphosate).

Dual-emitting Iridium nanorods combining dual-regulating coreaction accelerator Ag nanoparticles for electrochemiluminescence ratio determination of amyloid-β oligomers

Iridium(III) complexes have been developed as eminent electrochemiluminescence (ECL) luminophores, but their current applications are only limited to anodic ECL emission because of weak cathodic ECL emission. This work explored poly(styrene-co-maleicanhydride) (PSMA) as functional reagent to modulate iridium(III) complexes to simultaneously emit bipolar ECL signals. The prepared iridium(III) nanorods (Ir NRs) were detected strong bipolar ECL emissions at +0.9 V and -2.0 V with N,N-diisopropylethylenediamine (DPEA) and persulfate (S₂O₈^2-) as coreactant, respectively. Meanwhile, Ag nanoparticles (Ag NPs) were developed as dual-regulating coreaction accelerator to boost the bipolar emissions of Ir NRs simultaneously. The dual-emitting Ir NRs coupled with dual-regulating coreaction accelerator Ag NPs facilitated the construction of mono-luminophore-based ECL ratio strategy for detecting amyloid-β oligomers (AβO). When the target AβO appeared, the Mg²⁺-dependent DNAzyme-powered biped walkers were unlocked to cleave single-stranded S1 immobilized on the surface of magnetic beads (MBs), resulting in the production of massive single-stranded ST. Then, the output ST cleaved hairpin H1 captured by Ir NRs modified electrode to produce numerous single strands, which could initiate the hybridization chain reaction (HCR) between Ag NPs-labeled H2 and Ag NPs-labeled H3 to introduce abundant Ag NPs onto the electrode surface. Due to the enhancement effect of Ag NPs on the bipolar ECL emissions from Ir NRs, the ECL ratio detection of AβO was achieved with the detection limit of 0.62 pM. The unique dual-emitting properties of Ir NRs coupled with dual-regulating effect of Ag NPs provided an interesting mono-luminophore-based ECL ratio sensing platform for biological analysis.

Nonenzymatic Target-Driven DNA Nanomachine for Monitoring Malathion Contamination in Living Cells and Bioaccumulation in Foods

Intensive applications of toxic malathion pesticides bring a vital threat to the environment and health. Hence, a credible and sensitive strategy is urgently needed for the respective detection of malathion. In this work, an aptamer-based nonenzymatic autonomous DNA walking machine was fabricated for monitoring trace malathion contamination in cells and foods. Along with the machine walking driven by malathion-triggered reaction entropy, multiple fluorescent signal outputs were thermodynamically generated for signal amplification. The proposed stable DNA nanomachine achieved satisfactory results with a detection limit of 81.9 pg L^-1 for testing malathion, which could be applied to actual samples including apple juice, paddy water, and paddy soil. Furthermore, the high stability, sensitivity, and biocompatibility of the nanomachine enabled monitoring of the malathion contamination in living cells and bioaccumulation in lettuce without additional purification. Consequently, with these excellent performances, it is strongly anticipated that the DNA walking machine has tremendous potential to be extended to general platforms against pesticides to avoid malathion-contaminated agricultural production for environmental safety and human health.

Sensitive and label-free chemiluminescence detection of malathion using exonuclease-assisted dual signal amplification and G-quadruplex/hemin DNAzyme

Malathion is one of the most commonly used organophosphorus pesticides that can cause serious harm to the ecological environment and human health. Herein, we demonstrated a label-free chemiluminescent aptasensor for the sensitive detection of malathion based on exonuclease-assisted dual signal amplification and G-quadruplex/hemin DNAzyme. Upon the addition of malathion, the aptamer probe specifically bound to the target to form a complex malathion-S3, leaving a duplex S1-S2. The complex malathion-S3 was digested by exonuclease I and the target was released. The released target was recycled to perform exonuclease I-assisted signal amplification. Furthermore, after treatment with exonuclease III, the duplex S1-S2 was converted into the secondary target ST. The secondary target ST interacted with the hairpin H1 to form a complex H1-ST, which was further digested by exonuclease III and released the secondary target. The released secondary target was recycled to perform exonuclease III-assisted signal amplification. After complete amplification, large numbers of G-quadruplex/hemin DNAzymes were generated. Under the optimal experimental conditions, the prepared aptasensor showed an excellent linear response to malathion with a detection limit of 0.47 pM. The relative standard deviations were in the range of 4.2-6.9%. Moreover, the aptasensor was successfully applied to detect malathion in spiked food and traditional Chinese medicine samples.

An OliGreen-responsive fluorescence sensor for sensitive detection of organophosphorus pesticide based on its specific selectivity towards T-Hg2+-T DNA structure

In this paper, it was found that OliGreen emitted much stronger fluorescence in rigid T-Hg²⁺-T DNA structure than that in the presence of poly T. Thus, an OliGreen-responsive label-free fluorescent sensor was proposed for sensitive detection of organophosphorus pesticides (OPs) by constructing T-Hg²⁺-T DNA structure. OliGreen emits strong fluorescence in T-Hg²⁺-T structures. The rigid DNA structure of T-Hg²⁺-T is prone to be destroyed by thiocholine (TCh) that hydrolyzed by acetylcholinesterase (AChE) because of the high affinity of TCh with Hg²⁺. As a result, T-Hg²⁺-T DNA structure broke down and the fluorescence intensity of OliGreen decreased greatly. With the inhibition of AChE by OPs, fluorescence intensity of OliGreen remained strong because of the rigid T-Hg²⁺-T DNA structure. Thus, a "turn-on" fluorescent sensor which avoids synthesis of nanomaterials and complex label procedures is proposed based on the fluorescence intensity of OliGreen. DDVP were detected with a wide linear range from 0.005 to 25.0 ng/mL and the detection limit was 2.9 pg/mL, which is more sensitive than previously reported methods.

Fluorescence sensor for organophosphorus pesticide detection based on the alkaline phosphatase-triggered reaction

The threat of organophosphorus pesticide (OPP) residue to food safety and human health has caused widespread concern. In this paper, a sensitive fluorescence sensor for OPP detection was constructed based on the alkaline phosphatase (ALP) -triggered in situ reaction. In this method, ALP catalyses the dephosphorylation of the substrate l-ascorbic acid 2-phosphate sesquimagnesium salt hydrate (AAP) to generate l-ascorbic acid (AA). AA instantly combines with o-phenylenediamine (OPD) to form 3-(1,2-dihydroxyethyl)furo[3,4-b]quinoxalin-1(3H)-one (DFQ), which contains a quinoxaline core skeleton fluorophore and emits a strong fluorescence intensity at 425 nm. The existence of OPPs inhibits the activity of ALP and the production of AA and DFQ. As a result, the fluorescence intensity obviously decreases. Under optimal conditions, the fluorescence intensity linearly depends on the logarithm of chlorpyrifos concentration over a wide range of 20 pg/mL ∼1000 ng/mL with a detection limit of 15.03 pg/mL (S/N = 3), which is lower than the previously reported values. The sensor with its satisfactory accuracy and precision has been successfully applied to the detection of chlorpyrifos in leeks and celery samples with recoveries of 94.5-106.7% and an inter-assay relative standard deviation (RSD) below 11.51%. OPPs can be semiquantitatively determined by the colour changes in ultraviolet light. The superiority of the sensor is due to its visual simplicity without complex fluorescence labelling procedures and costly instruments.

Facile Removal of Phytochromes and Efficient Recovery of Pesticides Using Heteropore Covalent Organic Framework-Based Magnetic Nanospheres and Electrospun Films

Nontargeted analysis of food safety requires selective removal of interference matrices and highly efficient recovery of chemical hazards. Porous materials such as covalent organic frameworks (COFs) show great promise in selective adsorption of matrix molecules via size selectivity. Considering the complexity of interference matrices, we prepared crystalline heteropore COFs whose two kinds of pores have comparable sizes to those of several common phytochromes, main interference matrices in vegetable sample analysis. By controlling the growth of COFs on the surface of Fe3O4 nanoparticles or by utilizing a facile co-electrospinning method, heteropore COF-based magnetic nanospheres or electrospun nanofiber films were prepared, respectively. Both the nanospheres and the films maintain the dual-pore structures of COFs and show good stability and excellent reusability. Via simple magnetic separation or immersion operation, respectively, they were successfully used for the complete removal of phytochromes and highly efficient recovery of 15 pesticides from the extracts of four vegetable samples, and the recoveries are in the range of 83.10-114.00 and 60.52-107.35%, respectively. Film-based immersion operation gives better sample pretreatment performance than the film-based filtration one. This work highlights the great application potentials of heteropore COFs in sample pretreatment for nontargeted analysis, thus opening up a new way to achieve high-performance sample preparation in many fields such as food safety analysis, environment monitoring, and so on.

Induced fluorescent enhancement of protein-directed synthesized gold nanoclusters for selective and sensitive detection of flame retardants

Organophosphate flame retardants (OPFRs), typical toxic and hazardous pollutants, are called for new detection approaches to avoid laborious synthetic procedures and large and expensive instruments. Hence, a novel fluorescent probe was constructed for quantitative detection of OPFRs via heightening the fluorescence of acetylcholinesterase synthesized gold nanoclusters (AChE-AuNCs). The as-prepared AChE-AuNCs exhibited high fluorescence emission at about 398 nm with the average particle size of about 1.60 nm. When the AChE-AuNCs was applied to the proposed fluorescent detection, excellent sensitivity with wide linear range (50-1000 ng L^-1) and low detection limit (30 ng L^-1) for TClPP with the response time less than 1 h were achieved. The fluorescent probe could be extended to detect other three types of OPFRs (TEP, TPHP, and TBOEP) and the target pollutants could be detectable in the presence of halogenated flame retardants. The mechanism might be mainly contributed by the interaction between OPFRs and AChE-AuNCs restricting internal vibration consumption of their capping ligands. The proposed detection approach could be easily operated and was not involved with other intermediate products. Therefore, AChE-AuNCs could be a promising fluorescent probe for rapid, selective and sensitive detection of OPFRs and even in the practical application.

Ratiometric fluorescence sensor for organophosphorus pesticide detection based on opposite responses of two fluorescence reagents to MnO2 nanosheets

The detection of organophosphorus pesticides (OPs) has received considerable attention for their great harm to human beings. Herein, a novel ratiometric fluorescence biosensor was constructed for the determination of OPs by using Scopoletin (SC) and Amplex Red (AR) as probe pairs that have opposite responses to MnO₂ nanosheets (MnO₂ NS). MnO₂ NS possess peroxidase-like catalytic activity, which could quench the fluorescence of SC as well as enhance the fluorescence of the non-fluorescent substance AR by oxidation. In the absence of OPs, acetylcholinesterase (AChE) hydrolyzed acetylcholine chloride (ATCh) into choline (TCh) and acetate. TCh led the decomposition of MnO₂ NS to manganese ions (Mn²⁺), increasing signal of SC and decreasing signal of AR. In the presence of OPs, the activity of AChE was inhibited and the decomposition of MnO₂ NS was hindered, therefore the fluorescence intensity of SC was weak and the fluorescence intensity of AR had an obvious increase. Moreover, under the optimal conditions, the ratio of fluorescence intensity response recorded on the AR/SC increases with increasing the concentration of DDVP. The method has wider linear range of 5.0 pg/mL ∼500 ng/mL with a detection limit of 1.6 pg/mL, which is superior to previously reported methods. This strategy has also been applied to a visual observation based on the color change of the solution under UV light.