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).

A colorimetric smartphone-based platform for pesticides detection using Fe-N/C single-atom nanozyme as oxidase mimetics

In this study, a novel highly sensitive colorimetric platform has been designed for malathion assay based on Fe-N/C SAzyme. The as-synthesized SAzyme can directly oxidize 3,3´,5,5´-tetramethylbenzidine (TMB) to generate blue colored oxidized TMB. L-ascorbic acid-2-phosphate (AA2P), a substrate of acid phosphatase (ACP), could be hydrolyzed to AA, thereafter inhibit the oxidization reaction of TMB, leading to a conspicuous blue color fading. With the addition of malathion hindered the ACP activity and limited the AA production, resulting in the recovery of the catalytic activity of single-atom nanozyme. Under optimized operational conditions, a novel colorimetric assay has been designed for malathion detection with LOD of 0.42 nM. Besides, quantification of malathion in environmental and food samples was achieved based on the proposed strategy. In addition, the successfully integrated paper/smartphone sensor provided sensitive, and rapid, reliable detection of malathion with a LOD of 1 nM.

Selective Inhibition toward Dual Enzyme-like Activities of Iridium Nanozymes for a Specific Colorimetric Assay of Malathion without Enzymes

A colorimetric assay based on an enzyme-inhibition strategy is promising for the on-site detection of pesticide residues. Due to the high cost and low stability of enzymes, nanozymes (nanomaterials with enzyme-like activities) are widely developed as substitutes of enzymes. However, the inhibition of pesticides toward enzymes and nanozymes generally lacks selectivity. It is of great significance and challenge to design a specific pesticide assay based on an activity-inhibition strategy. Here, we discovered that iridium nanoparticles possess both peroxidase-like and oxidase-like activities under the same conditions, and their catalytic mechanisms are different. The synergistic effect of dual enzyme-like activities enhanced the colorimetric signal. Interestingly, the dual enzyme-mimicking activities could be simultaneously inhibited, and the inhibition effect exhibited high selectivity toward malathion. Considering the popularity and the hazards of malathion, a malathion assay method based on activity inhibition was established without enzymes and a redundant process. The synergistic effect of the selective inhibition of dual enzyme-like activities enhanced the selectivity and sensitivity. The proposed assay strategy opens up an avenue for specific assay of various pesticides.

Non-biological fluorescent chemosensors for pesticides detection

The ongoing poisoning of agricultural products has pushed the security problem to become an important issue. Among them, exceeding the standard rate of pesticide residues is the main factor influencing the quality and security of agricultural products. Moreover, the abuse of pesticides has introduced a large amount of residues in soil and drinking water, which will enter the food chain to the human body, leading to neurological disorders and cancer. Therefore, great efforts have been devoted to developing fluorescent sensors for detecting pesticide in a facile, quickly, sensitive, selective, accurate manner, which exhibit greater advantages than some traditional methods. In this review, we mainly focus on summarizing the non-biological fluorescent probes for organic pesticides detection with the detection limit of micromole to nanomole, including organic functional small molecules, calixarenes and pillararenes, metal organic framework systems, and nanomaterials. Meanwhile, we described the different sensing mechanisms for pesticides detection of these mentioned fluorescent sensors, the detection limit of each pesticide, the application in detecting actual samples, as well as their respective advantages and development prospects associated with present non-biological fluorescent sensors.

Role of Zr6 Metal Nodes in Zr-Based Metal-Organic Frameworks for Catalytic Detoxification of Pesticides

Pesticides are chemicals widely used for agricultural industry, despite their negative impact on health and environment. Although various methods have been developed for pesticide degradation to remedy such adverse effects, conventional materials often take hours to days for complete decomposition and are difficult to recycle. Here, we demonstrate the rapid degradation of organophosphate pesticides with a Zr-based metal-organic framework (MOF), showing complete degradation within 15 min. MOFs with different active site structures (Zr node connectivity and geometry) were compared, and a porphyrin-based MOF with six-connected Zr nodes showed remarkable degradation efficiency with half-lives of a few minutes. Such a high efficiency was further confirmed in a simple flow system for several cycles. This study reveals that MOFs can be highly potent heterogeneous catalysts for organophosphate pesticide degradation, suggesting that coordination geometry of the Zr node significantly influences the catalytic activity.

Porous Graphene Oxide-Metal Ion Composite for Selective Sensing of Organophosphate Gases

Organophosphates are used as agricultural pesticides and also encountered as toxic nerve agents in chemical warfare. Accordingly, development of sensors for detecting and monitoring organophosphate vapors is highly sought after. We present a new capacitive gas sensor exhibiting remarkable specificity and sensitivity toward the organophosphate nerve gas simulants triethyl-phosphate (TEP) and dimethyl methyl phosphate and the pesticide dichlorvos. Specifically, the capacitive sensor comprises a composite porous graphene oxide matrix intercalating cobalt or nickel ions, prepared through a simple freeze-drying procedure. We demonstrate that the porous graphene oxide/metal ion electrode undergoes fast capacitance changes only upon exposure to organophosphate vapors. Moreover, the sensor exhibits extraordinary sensitivity upon interactions with TEP. Detailed mechanistic analyses, carried out in comparison to porous graphene oxide coupled to other transition metal ions, reveal that the remarkable sensing properties of the Co²⁺ or Ni²⁺/porous graphene oxide systems likely arise from the distinct mode of metal ion incorporation into the graphene oxide host matrix and substitution of metal-complexed water ligands with organophosphate molecules. The new metal ion/porous graphene oxide capacitive sensor may be employed for alerting and monitoring organophosphate gases in different environments.

Hybrid 3,4-dihydropyrimidin-2-(thi)ones as dual-functional bioactive molecules: fluorescent probes and cytotoxic agents to cancer cells

A series of new hybrid fluorescent Biginelli compounds, including a Monastrol derivative, were designed and synthesized with good yields.