Novel colorimetric aptasensor based on MOF-derived materials and its applications for organophosphorus pesticides determination

Cu-NC single-atom nanozymes with peroxidase-like activity for colorimetric detection of d-penicillamine

Most conventional nanozymes have poor specificity and low activity, and designing high-performance nanozymes remains a challenge. In contrast, single-atom nanozymes have high atom utilization and high reactivity. Here, we prepared Cu single-atom nanozymes (Cu-NC) with excellent peroxidase-like activity by high-temperature pyrolysis using Cu as a transition metal source. The introduction of Cu formed the Cu-Nx active site, which accelerated charge transfer between the reactants and the active site and was the key for improving the activity. With Cu-NC as a catalyst, H2O2 rapidly oxidized 3,3',5,5'-tetramethylbenzidine (TMB) to oxTMB, and the solution turned blue with strong absorption at 652 nm. Because d-penicillamine (D-PA) can reduce oxTMB or react with reactive oxygen species radicals to inhibit the color reaction, we built a colorimetric sensing platform around Cu-NC for the determination of D-PA and successfully used it for the determination of D-PA in urine samples. This work provides new ideas for the design of high-performance nanozymes and the detection of D-PA in real environments.

Identification of phoxim and omethoate using α-hemolysin nanopore and aptamers

Contamination with pesticides has inflicted substantial harm on human health; therefore, developing rapid, ultra-sensitive, and non-labelling simultaneous detection methods for multiple pesticides is necessary. In this study, we demonstrated that α-hemolysin (α-HL) nanopore sensor can detect and discriminate organophosphorus pesticides of phoxim and omethoate in a single nanopore without requiring labels of the probes or purification of the pesticides in real samples. Aptamers specifically recognise and bind pesticides to obtain pesticide-aptamer complexes that produce characteristic current signals while passing through the nanopore. Phoxim and omethoate were accurately distinguished by a portable instrument within minutes, and their detection sensitivity was up to the femtomole level, whether detected alone or simultaneously. The detection limits of phoxim and omethoate were 8.13 × 10-16 M and 4.16 × 10-15 M. The recoveries of phoxim and omethoate from pear, tomato, and cucumber samples were 82.0-107.0 % and 81.9-118.3 % respectively, with coefficient of variable below 8.0 %.

A microfluidic paper-based fluorescent sensor integrated with a smartphone platform for rapid on-site detection of omethoate pesticide

A novel approach combing a fluorescent microfluidic paper strip with a portable smartphone-based sensing platform is developed for rapid and sensitive detection of omethoate pesticide. The detection mechanism of the microfluidic paper strip is based on the fluorescence quenching of graphene oxide (GO) toward the cyanine 3 (Cy3)-labeled aptamer (Cy3-APT). Upon exposure to omethoate, the Cy3-APT detaches from the surface of GO, resulting in considerable fluorescence recovery, which can be visualized through the smartphone-based sensing platform. The images are analyzed through a self-developed app embedded with a pretrained convolutional neural network model, achieving a high regression coefficient of 0.9964 at an omethoate concentration range of 0-750 nM. The smartphone-based platform enables rapid on-site detection of omethoate pesticide in real samples within 10 min, with results comparable to those obtained using standard methods. In short, the proposed microfluidic paper-based fluorescent sensor combined with the smartphone-based sensing platform enhances the detection performance toward organophosphorus pesticides.

Colorimetric aptasensor for tobramycin based on a highly stabilized aptamer-enhanced enzyme-mimicking activity of iron oxide/graphene oxide nanospheres

Antibiotic contaminants in food are associated with detrimental health issues, and thus, the design of rapid and reliable detection methods to monitor them is in high demand. Although colorimetric aptamer sensing methods can achieve accurate and quick visual read-out analysis, they still have morphological defects that affect the detection efficiency and stability of the aptasensor. Hence, a simple and highly selective iron oxide/graphene oxide (Fe3O4/GO) nanospheres was developed and modified with an aptamer as nanozymes for colorimetric detection of tobramycin (Tob). Due to the electrostatic and π-π stacking interaction between the aptamer and the spherical Fe3O4/GOs nanozyme, the catalytic activity of the nanozyme was enhanced by the robust affinity between the aptamer and the 3,3',5,5'-tetramethylbenzidine (TMB) substrate. However, the presence of Tob could obstruct the catalytic activity through the specific binding of aptamer to Tob and the detachment of aptamer from the surface of the Fe3O4/GO, causing a low catalytic activity. Based on this strategy, a visual and quantitative detection for Tob was achieved with a detection limit of 70.7 nM. The proposed aptasensor demonstrated high selectivity, ease of operation, and potential application in food samples with satisfactory recoveries of 98.4-108.5 %. Therefore, this proposed method has great prospects for monitoring food safety and could be applied for sensing varied antibiotics by just switching the target-specific aptamer.

Nanozyme coating-gated multifunctional COF composite based dual-ratio enhanced dual-mode sensor for highly sensitive and reliable detection of organophosphorus pesticides in real samples

The reliable detection of organophosphorus pesticides (OPs) in complex matrices remains an enormous challenge due to inevitable interference of sample matrices and testing factors. To address this issue, we designed a nanozyme-coated mesoporous COF with guest molecule loading, and successfully used it to construct a dual-ratio dual-mode sensor through target-regulated signal generation. The multifunctional COF-based composite (MB/COF@MnO2, MCM) featured high loading of methylene blue (MB), oxidase-like MnO2 coatings as gatekeepers, and specific recognition of thiocholine (TCh). TCh, a regulator produced from acetylcholinesterase (AChE)-catalyzed hydrolysis of acetylthiocholine, could decompose MnO2 coatings, triggering the release of abundant MB and oxidation of few o-phenylenediamine (OPD). OPs, strong inhibitors of AChE, could restrain TCh production and MnO2 decomposition, thereby controlling the release of less MB and oxidation of more OPD. This regulation boosted the dual-ratio dual-mode assay of OPs by using the released MB and oxidized OPD in the solution as testing signals, measured by both fluorescent and electrochemical methods. Experimental results demonstrated the sensitive detection of dichlorvos with LODs of 0.083 and 0.026 ng/mL via the fluorescent/electrochemical mode, respectively. This study represented a creative endeavor to develop dual-ratio dual-mode sensors for OPs detection in complex samples, offering high sensitivity, excellent selectivity, and good reliability.

Nucleic acid-functionalized nanoscale porous carbon-based electrochemical genosensor for detection of Nocardia spp. in real samples

In this study, a porous carbon derived from a metal-organic framework (PCMOF) as a target-responsive material functionalized with Nocardia particular antisense ssDNA oligonucleotide (ssDNA capture probe) was developed to construct a simple genosensor based on biogatekeeper strategy for sensitive detection of Nocardia in complex biological samples. The PCMOF with suitable pores volume was used to encapsulate electroactive dye methylene blue (MB), and the ssDNA capture probe was used as a gatekeeper to cap PCMOF. Without the presence of Nocardia target, the electrochemical signal of trapped MB was high. Upon adding the target, the hybridization of ssDNA capture probe and target led to the formation of a probe-target double-stranded (dsDNA) structure which dissociated from PCMOF and allowed MB molecules to be released. Therefore, the electrochemical signal of the genosensor decreased. The detection of Nocardia was accomplished by observing variations in the MB peak current intensity in a dose-dependent manner. For this genosensor, a linearity range from 10-18 to 10-7 M for synthetic ssDNA target and 10 to 108 copies/mL for two standard isolates, Nocardia farcinica PTCC 1309 and Nocardia brasiliensis ATCC 19296 as well as for clinical isolates (identified as Nocardia otitidiscaviarum) was observed, respectively. The detection limit (DL) values were 0.54 aM for synthetic ssDNA target and 5, 7, and 4 copies/mL for N. farcinica, N. brasiliensis, and N. otitidiscaviarum, respectively. This genosensor was also characterized by good specificity, reproducibility, and stability.

Research progress and applications of iron-based nanozymes in colorimetric sensing of agricultural pollutants

Natural enzymes are highly valued for their efficient specificity and catalytic activity. However, their poor stability, environmental sensitivity, and costly preparation restrict their practical applications. Nanozymes are nanomaterials with superior catalytic properties that compensate for natural enzyme deficiencies. As one of the earliest developed nanozymes, iron-based nanozymes have diverse morphological structures and different simulated catalytic properties, showing promising potential for agricultural pollutant sensing. Compared with traditional detection methods, the colorimetric method based on nanozymes has the characteristics of simplicity, rapidity, and visualization, which can be used for immediate and rapid on-site detection. In this review, the catalytic types of iron-based nanozymes, such as peroxidase-like, oxidase-like, catalase-like, and superoxide dismutase-like activities, and the corresponding catalytic mechanisms are presented. The classification of iron-based nanozymes based on various structures is then discussed. Furthermore, this review focuses on the current status of iron-based nanozymes for the colorimetric detection of common agricultural pollutants, including heavy metal ions, nonmetal ions, pesticides, and pharmaceutical and personal care products. Finally, the current research status and development direction of iron-based nanozymes in sensing applications are summarized and prospected.

A novel fluorescent and photothermal probe based on nanozyme-mediated cascade reaction for detecting organophosphorus pesticide residues

In this study, a nanozyme (ZIF-Co-Cys) with high oxidase-like catalytic activity was prepared, and a ratiometric fluorescent/photothermal dual-mode probe was constructed for organophosphorus pesticides (OPs) detection based on the competitive effect of ZIF-Co-Cys and the enzymatic reaction product of acid phosphatase (ACP) on o-phenylenediamine and the inhibition effect of OPs on ACP activity. Using dimethyl dichloroviny phosphate (DDVP) as the model, both the fluorescence intensity ratio and the temperature change of the probe solution exhibited an excellent correlation with OPs concentration. The detection limits were 1.64 ng/mL and 0.084 ng/mL, respectively. Additionally, the detection of DDVP residues in real samples verified the outstanding anti-interference and accuracy of the probe. This work not only provided a complementary dual-mode method for the accurate and rapid detection of OPs residues in complex samples, but also supplied a new insight into the design of a multi-mode sensing platform based on the cascade reaction of nanozyme.

Novel ratiometric electrochemical aptasensor based on broad-spectrum aptamer recognition for simultaneous detection of penicillin antibiotics in milk

To effectively monitor multi-residues of penicillin antibiotics (PENs) in milk, we developed a novel ratiometric electrochemical aptasensor enabling simultaneous detection of PENs. The aptasensor employed a broad-spectrum aptamer as a recognition element, niobium carbide functionalized with methylene blue (Nb2C-MB) as a reference signal generator, and a ferrocene-labeled aptamer (Fc-Apt) as an output signal. Electrodes were modified with Fe-N-C doped carbon nanotubes (Fe-N-C-CNTs) to amplify detection signals further. During detection, Fc-Apt binding to PENs decreased Fc current intensity (IFc) and increased MB current intensity (IMB). The simultaneous detection of PENs was achieved using IMB/IFc as a quantitative signal. Under optimal conditions, a good linear relationship between IMB/IFc and antibiotic concentration was observed, indicating the aptasensor had a robustness. The limits of detection of aptasensor for four penicillin antibiotics and their mixed targets were 0.093-0.191 nM. This work provides a new approach to multi-residue detection of the same class of antibiotics.

CdTe@ZnS quantum dots for rapid detection of organophosphorus pesticide in agricultural products

Organophosphorus pesticides (OPPs) constitute the most widely employed class of pesticides. However, the prevalent use of OPPs, while advantageous, raises concerns due to their toxicity, posing serious threats to food safety. Chemical sensors utilizing quantum dots (QDs) demonstrate promising applications in rapidly detecting OPPs residues, thereby facilitating efficient inspection of agricultural products. In this study, we employ an aqueous synthesis approach to prepare low toxic CdTe@ZnS QDs with stable fluorescence properties. To mitigate the risk of imprecise measurements stemming from the inherent susceptibility of fluorescence to quenching, we have adopted the principle of fluorescence resonance energy transfer (FRET) for the construction of the turn-on quantum dot sensor. With a detection limit for chlorpyrifos as low as 10 ppb (10 μg/L), the QDs sensor exhibits notable resistance to interference from various pesticides. Application of this system to detect organophosphorothioate pesticides in apples produced results consistent with those obtained from high-performance liquid chromatography (HPLC) detection, affirming the promising application prospects of this sensing system for the rapid detection of OPPs residues.

Unveiling the scope and perspectives of MOF-derived materials for cutting-edge applications

Although synthesis and design of MOFs are crucial factors to the successful implementation of targeted applications, there is still lack of knowledge among researchers about the synthesis of MOFs and their derived composites for practical applications. For example, many researchers manipulate study results, and it has become quite difficult to quit this habit specifically among the young researchers Undoubtedly, MOFs have become an excellent class of compounds but there are many challenges associated with their improvement to attain diverse applications. It has been noted that MOF-derived materials have gained considerable interest owing to their unique chemical properties. These compounds have exhibited excellent potential in various sectors such as energy, catalysis, sensing and environmental applications. It is worth mentioning that most of the researchers rely on commercially available MOFs for use as precursor supports, but it is an unethical and wrong practice because it prevents the exploration of the hidden diversity of similar materials. The reported studies have significant gaps and flaws, they do not have enough details about the exact parameters used for the synthesis of MOFs and their derived materials. For example, many young researchers claim that MOF-based materials cannot be synthesized as per the reported instructions for large-scale implementation. In this regard, current article provides a comprehensive review of the most recent advancements in the design of MOF-derived materials. The methodologies and applications have been evaluated together with their advantages and drawbacks. Additionally, this review suggests important precautions and solutions to overcome the drawbacks associated with their preparation. Applications of MOF-derived materials in the fields of energy, catalysis, sensing and environment have been discussed. No doubt, these materials have become excellent class but there are still many challenges ahead to specify it for the targeted applications.

Glutathione‑iron hybrid nanozyme-based colorimetric sensor for specific and stable detection of thiram pesticide on fruit juices

Given the potential dangers of thiram to food safety, constructing a facile sensor is significantly critical. Herein, we presented a colorimetric sensor based on glutathione‑iron hybrid (GSH-Fe) nanozyme for specific and stable detection of thiram. The GSH-Fe nanozyme exhibits good peroxidase-mimicking activity with comparable Michaelis constant (Km = 0.551 mM) to the natural enzyme. Thiram pesticides can specifically limit the catalytic activity of GSH-Fe nanozyme via surface passivation, causing the change of colorimetric signal. It is worth mentioning that the platform was used to prepare a portable hydrogel kit for rapid qualitative monitoring of thiram. Coupling with an image-processing algorithm, the colorimetric image of the hydrogel reactor is converted into the data information for accurate quantification of thiram with a detection limit of 0.3 μg mL-1. The sensing system has good selectivity and high stability, with recovery rates in fruit juice samples ranging from 92.4% to 106.9%.

Multimodal biosensing systems based on metal nanoparticles

Biosensors are currently among the most commonly used devices for analysing biomarkers and play an important role in environmental detection, food safety, and disease diagnosis. Researchers have developed multimodal biosensors instead of single-modal biosensors to meet increasing sensitivity, accuracy, and stability requirements. Metal nanoparticles (MNPs) are beneficial for preparing core probes for multimodal biosensors because of their excellent physical and chemical properties, such as easy regulation and modification, and because they can integrate diverse sensing strategies. This review mainly summarizes the excellent physicochemical properties of MNPs applied as biosensing probes and the principles of commonly used MNP-based multimodal sensing strategies. Recent applications and possible improvements of multimodal biosensors based on MNPs are also described, among which on-site inspection and sensitive detection are particularly important. The current challenges and prospects for multimodal biosensors based on MNPs may provide readers with a new perspective on this field.

Universal organophosphate pesticides detection by peptide based fluorescent probes

In practical applications, the rapid and efficient detection of universal organophosphorus pesticides (OPs) can assist inspectors in quickly identifying the presence of OPs in samples. However, this presents a challenge for most well-established methods, typically designed to detect only a specific type of organophosphorus molecule at a time. In this proof-of-concept study, we draw inspiration from the structural similarities among OPs to develop innovative peptide-based fluorescence probes for the first time, which could efficiently detect a broad range of OPs within a mere 3 min. Analysis of fluorescence curve fitting reveals a clear linear correlation between the fluorescent intensity of the peptide probes and the concentration of OPs. Additionally, the selectivity analysis indicates that these peptide fluorescent probes exhibit an excellent response to various OPs while maintaining sufficient selectivity for detecting other pesticide types. Accurate sample analysis has also highlighted the potential of these peptide probes as practical tools for the rapid detection of OPs in actual vegetable samples. In summary, this proof-of-concept study presents an innovative approach to designing and developing ultrafast, universally peptide-based OP probes. These custom-designed peptide probes may facilitate rapid sample screening and offer initial quantification for OPs, potentially saving valuable time and effort in practical OP detection.

Preparation of Hybrid Magnetic Nanoparticles for Sensitive and Rapid Detection of Phorate Residue in Celery Using SERS Immunochromatography Assay

Extensive use of pesticides in agricultural production has been causing serious health threats to humans and animals. Among them, phorate is a highly toxic organophosphorus insecticide that has been widely used in planting. Due to its harmful effects on human and animal health, it has been restricted for use in many countries. Analytical methods for the rapid and sensitive detection of phorate residues in agricultural products are urgently needed. In this study, a new method was developed by combining surface-enhanced Raman spectroscopy (SERS) and immunochromatography assay (ICA). Hybrid magnetic Fe3O4@Au@DTNB-Ab nanoprobes were prepared by modifying and growing Au nanoseeds on an Fe3O4 core. SERS activity of the nanoprobe was optimized by adjusting the concentration of the Au precursor. A rapid and sensitive assay was established by replacing the traditional colloidal gold-based ICA with hybrid SERS nanoprobes for SERS-ICA. After optimizing parameters including coating antibody concentrations and the composition and pH of the buffer solution, the limit of detection (LOD) for phorate could reach 1 ng/mL, with a linear range of 5~100 ng/mL. This LOD is remarkably lower than the maximum residue limit in vegetables and fruits set by the Chinese government. The feasibility of this method was further examined by conducting a spiking test with celery as the real sample. The result demonstrated that this method could serve as a promising platform for rapid and sensitive detection of phorate in agricultural products.

Sensing the invisible: Ultrasensitive and selective colorimetric detection of E. coli O157:H7 based on masking the peroxidase-mimetic activity of aptamer-modified Au/Fe3O4

Escherichia coli O157:H7 (E. coli O157:H7) emerges as a significantly worrisome pathogen associated with foodborne illnesses, emphasizing the imperative for creating precise detection tools. In this investigation, we developed a sensitive colorimetric biosensor for detecting E. coli O157:H7. It was constructed using a nanozyme comprised of Au@Fe3O4 NPs, which was fabricated and subsequently modified with an aptamer (Apt). The nanozyme harnesses its inherent peroxidase-like activity to facilitate the transformation of reduced TMB into its oxidized form in the presence of H2O2, resulting in a noticeable shift to a blue color. However, the presence of E. coli O157:H7 effectively diminished the absorbance of oxidized TMB. Consequently, the normalized absorbance at 652 nm demonstrates a linear decrease corresponding to concentrations of E. coli O157:H7 within the range of 101 to 108 CFU mL-1 with a low limit of detection (LOD, S/N = 3) of 3 CFU mL-1.

Colorimetric array sensor based on bimetallic nitrogen-doped carbon-based nanozyme material to detect multiple antioxidants

Copper-cobalt bimetallic nitrogen-doped carbon-based nanoenzymatic materials (CuCo@NC) were synthesized using a one-step pyrolysis process. A three-channel colorimetric sensor array was constructed for the detection of seven antioxidants, including cysteine (Cys), uric acid (UA), tea polyphenols (TP), lysine (Lys), ascorbic acid (AA), glutathione (GSH), and dopamine (DA). CuCo@NC with peroxidase activity was used to catalyze the oxidation of TMB by H2O2 at three different ratios of metal sites. The ability of various antioxidants to reduce the oxidation products of TMB (ox TMB) varied, leading to distinct absorbance changes. Linear discriminant analysis (LDA) results showed that the sensor array was capable of detecting seven antioxidants in buffer and serum samples. It could successfully discriminate antioxidants with a minimum concentration of 10 nM. Thus, multifunctional sensor arrays based on CuCo@NC bimetallic nanoenzymes not only offer a promising strategy for identifying various antioxidants but also expand their applications in medical diagnostics and environmental analysis of food.

Chlorpyrifos-induced suppression of the antioxidative defense system leads to cytotoxicity and genotoxicity in macrophages

Chlorpyrifos, widely used for pest control, is known to have various harmful effects, although its toxic effects in macrophages and the mechanisms underlying its toxicity remain unclear. The present study investigated the toxic effects of chlorypyrifos in a macrophage cell line. Here, we found that chlorpyrifos induced cytotoxicity and genotoxicity in RAW264.7 macrophages. Moreover, chlorpyrifos induced intracellular ROS production, subsequently leading to lipid peroxidation. Chlorpyrifos reduced the activation of antioxidative enzymes including superoxide dismutase, catalase, and glutathione peroxidase. Chlorpyrifos upregulated HO-1 expression and activated the Keap1-Nrf2 pathway, as indicated by enhanced Nrf2 phosphorylation and Keap1 degradation. Chlorpyrifos exerted effects on the following in a dose-dependent manner: cytotoxicity, genotoxicity, lipid peroxidation, intracellular ROS production, antioxidative enzyme activity reduction, HO-1 expression, Nrf2 phosphorylation, and Keap1 degradation. Notably, N-acetyl-L-cysteine successfully inhibited chlorpyrifos-induced intracellular ROS generation, cytotoxicity, and genotoxicity. Thus, chlorpyrifos may induce cytotoxicity and genotoxicity by promoting intracellular ROS production and suppressing the antioxidative defense system activation in macrophages.

Glyphosate as a Food Contaminant: Main Sources, Detection Levels, and Implications for Human and Public Health

Glyphosate is a broad-spectrum pesticide that has become the most widely used herbicide globally. However, concerns have risen regarding its potential health impacts due to food contamination. Studies have detected glyphosate in human blood and urine samples, indicating human exposure and its persistence in the organism. A growing body of literature has reported the health risks concerning glyphosate exposure, suggesting that the daily intake of contaminated food and water poses a public health concern. Furthermore, countries with high glyphosate usage and lenient regulations regarding food and water contamination may face more severe consequences. In this context, in this review, we examined the literature regarding food contamination by glyphosate, discussed its detection methods, and highlighted its risks to human health.

Efficient detection of flusilazole by an electrochemical sensor derived from MOF MIL-53(Fe) for food safety

Flusilazole is a triazole fungicide with residues that are potentially toxic to humans. It enters the human body mainly through food, although its bactericidal activity is substantial. In this study, an electrochemical sensor Fe/Fe2O3@C with a core-shell structure was constructed to efficiently detect flusilazole by annealing MIL-53(Fe) which was prepared by a simple solvothermal method. Transmission electron microscopy and scanning electron microscopy were used to characterize the apparent morphology of MIL-53(Fe) and Fe/Fe2O3@C, and their structures were further characterized by X-ray photoelectron spectroscopy, Raman spectroscopy, powder X-ray diffraction, and the mapping of elements by energy dispersive spectroscopy. The electrochemical behavior of Fe/Fe2O3@C in the detection of flusilazole was evaluated by differential pulse voltammetry under optimal conditions. The results of the study indicate that the Fe/Fe2O3@C electrochemical sensor displayed excellent detection capabilities for flusilazole, where the sensor exhibited a wide detection range from 1.00 × 10-4 to 1.00 × 10-12 mol/L with an incredibly low LOD of 593 fM, making it highly sensitive to trace amounts of flusilazole. Moreover, Fe/Fe2O3@C demonstrated superior reproducibility, stability, and resistance to interference, highlighting its reliability in practical applications. The sensor was also successfully utilized to quantitatively detect flusilazole in various real samples, which suggests that Fe/Fe2O3@C has broad-spectrum environmental resistance and can effectively and rapidly detect flusilazole residues in different types of food items and environmental matrices. The study also delved into the mechanism of Fe/Fe2O3@C for the detection of flusilazole, providing a deeper understanding of the functionality of this sensor. Overall, these findings emphasize the practical significance of Fe/Fe2O3@C as an electrochemical sensor, showcasing its potential for real-world applications in food safety and environmental monitoring.

Metal-Organic Framework-Enabled Sustainable Agrotechnologies: An Overview of Fundamentals and Agricultural Applications

With aggravated abiotic and biotic stresses from increasing climate change, metal-organic frameworks (MOFs) have emerged as versatile toolboxes for developing environmentally friendly agrotechnologies aligned with agricultural practices and safety. Herein, we have explored MOF-based agrotechnologies, focusing on their intrinsic properties, such as structural and catalytic characteristics. Briefly, MOFs possess a sponge-like porous structure that can be easily stimulated by the external environment, facilitating the controlled release of agrochemicals, thus enabling precise delivery of agrochemicals. Additionally, MOFs offer the ability to remove or degrade certain pollutants by capturing them within their pores, facilitating the development of MOF-based remediation technologies for agricultural environments. Furthermore, the metal-organic hybrid nature of MOFs grants them abundant catalytic activities, encompassing photocatalysis, enzyme-mimicking catalysis, and electrocatalysis, allowing for the integration of MOFs into degradation and sensing agrotechnologies. Finally, the future challenges that MOFs face in agrotechnologies were proposed to promote the development of sustainable agriculture practices.

A dual-mode biosensor featuring single-atom Fe nanozyme for multi-pesticide detection in vegetables

The single-atom iron nanozyme (SA-Fe-NZ) exhibits high catalytic activity and excellent electron transfer efficiency in biosensors. However, the binding of bioreceptors to the surface of SA-Fe-NZ results in a decrease in the catalytic activity of the nanozyme due to its toxic effects. We utilized the toxic effects and excellent electrochemical properties of the SA-Fe-NZ to successfully construct a smartphone-assisted dual-mode biosensor. The complex formed by the binding of organophosphorus pesticides (OPs) to the aptamer exhibited toxic effects and inhibited the catalytic activity of the nanozyme, preventing the colorimetric substrate from being catalyzed. Simultaneously, the aptamers labeled with electrochemical signal molecules approached the electrode surface, causing a change in the electrochemical signal. The results demonstrated that the constructed broad-spectrum aptamer biosensor exhibited a low limit of detection of 3.55 fM and a wide linear range of 10-13-10-2 M, allowing for qualitative and quantitative detection of multiple OPs in vegetables.

UiOL@AIEgens-assisted lateral flow immunosensor for the ultrasensitive dual-modal point-of-care detection of aflatoxin B1

Aflatoxin B1 (AFB1) contamination in food has attracted worldwide attention. The sensitive detection of AFB1 is vital for ensuring food quality and safety. This study developed an ultrasensitive signal-enhanced lateral flow immunosensor (LFIS) based on the functionalized zirconium metal-organic framework (MOF) of a UiO linker enriched with abundant aggregation-induced emission luminogen (UiOL@AIEgens) probes for the rapid dual-modal point-of-care (POC) determination of AFB1. Using UiO MOFs with numerous active sites as the carrier facilitated abundant AIEgens enrichment on the surface. After coupling with enough anti-AFB1 monoclonal antibodies (mAbs), the green-emissive UiOL@AIEgens-mAbs probes with high specificity and remarkably-enhanced fluorescence responses were obtained to competitively capture target AFB1 in the standard or sample solution and AFB1 antigen immobilized on the test (T) line of the POC LFIS. Under optimum conditions, the LFIS was capable of visual qualitative and smartphone-assisted dual-modal determination of target AFB1 within 7 min. Detection occurred in a range of 0.01-5 ng/mL at an ultra-low detection limit of 0.003 ng/mL, which was 300- and 600-fold lower than traditional immunoassays and the maximum limit set by the European Union, respectively. Moreover, the feasibility and robustness of the LFIS platform were assessed by detecting AFB1 in maize and lotus seed samples with average recoveries of 94.3-109.0%. The developed UiOL@AIEgens-based POC LFIS can be used for ultrasensitive, reliable, on-site detection in food. This study provides a new method for the real-time monitoring of AFB1 and other harmful contaminants in food and more complex matrices.

Fluorescent aptasensor mediated with multiple ssDNA for sensitive detection of acetamiprid in vegetables based on magnetic Fe3O4/C-assisted separation

Acetamiprid (ACE) is a highly effective broad-spectrum insecticide, and its widespread use is potentially harmful to human health and environmental safety. In this study, magnetic Fe3O4/carbon (Fe3O4/C), a derivative of metal-organic framework MIL-101 (Fe), was synthesized by a two-step calcination method. And a fluorescent sensing strategy was developed for the efficient and sensitive detection of ACE using Fe3O4/C and multiple complementary single-stranded DNA (ssDNA). By using aptamer with multiple complementary ssDNA, the immunity of interference of the aptasensor was improved, and the aptasensor showed high selectivity and sensitivity. When ACE was present, the aptamer (Apt) combined with ACE. The complementary strand of Apt (Cs1) combined with two short complementary strands of Cs1, fluorophore 6-carboxyfluorescein-labeled complementary strand (Cs2-FAM) and the other strand Cs3. The three strands formed a double-stranded structure, and fluorescence would not be quenched by Fe3O4/C. In the absence of ACE, Cs2-FAM would be in a single-chain state and would be adsorbed by Fe3O4/C, and the fluorescence of FAM would be quenched by Fe3O4/C via photoelectron transfer. This aptasensor sensitively detected ACE over a linear concentration range of 10-1000 nM with a limit of detection of 3.41 nM. The recoveries of ACE spiked in cabbage and celery samples ranged from 89.49% to 110.76% with high accuracy.

A colorimetric sensing platform with smartphone for organophosphorus pesticides detection based on PANI-MnO2 nanozyme

Organophosphorus pesticides (OPs) are of great concern due to its potential harms on human health and the environment. Herein, a budget-friendly, rapid and convenient colorimetric sensing platform is developed for detection of OPs in the environmental and food samples. The sensing element, PANI-MnO2 nanozyme with excellent oxidase mimetic activity is synthesized at room temperature, which is able to directly oxidize 3,3,5,5-tetramethylbenzidine (TMB) to generate blue colored oxidized TMB (OxTMB) within 2 min. Ascorbic acid (AA) can inhibit the oxidization reaction of TMB, consequently causing the blue color fading. Ascorbic acid 2-phosphate (AAP) could be hydrolyzed to produce AA by alkaline phosphatase (ALP). In the presence of OPs can effectively decrease ALP activity, resulting in the recovery of catalytic activity of PANI-MnO2. Therefore, sensitive and selective OPs detection is achieved. Under the optimal conditions, excellent detection performance in term of glyphosate as a model is achieved with a linear range from 0.50 to 50 μM, the detection limit is 0.39 μM (S/N = 3). The utility of method is further improved by combining a portable smartphone platform with a color picking application. The colorimetric platform achieves instrument-free detection of OPs and overcomes the uneven color distribution of traditional paper-based chip, providing an alternative strategy for the qualitative discernment and semi-quantitative analysis of OPs on-site.

Phytotoxicity of radionuclides: A review of sources, impacts and remediation strategies

Various anthropogenic activities and natural sources contribute to the presence of radioactive materials in the environment, posing a serious threat to phytotoxicity. Contamination of soil and water by radioactive isotopes degrades the environmental quality and biodiversity. They persist in soils for a considerable amount of time and disturb the fauna and flora of any affected area. Hence, their removal from the contaminated medium is inevitable to prevent their entry into the food chain and the organisms at higher levels of the food chain. Physicochemical methods for radioactive element remediation are effective; however, they are not eco-friendly, can be expensive and impractical for large-scale remediation. Contrastingly, different bioremediation approaches, such as phytoremediation using appropriate plant species for removing the radionuclides from the polluted sites, and microbe-based remediation, represent promising alternatives for cleanup. In this review, sources of radionuclides in soil as well as their hazardous impacts on plants are discussed. Moreover, various conventional physicochemical approaches used for remediation discussed in detail. Similarly, the effectiveness and superiority of various bioremediation approaches, such as phytoremediation and microbe-based remediation, over traditional approaches have been explained in detail. In the end, future perspectives related to enhancing the efficiency of the phytoremediation process have been elaborated.

Pt@AuNF nanozyme and horseradish peroxidase-based lateral flow immunoassay dual enzymes signal amplification strategy for sensitive detection of zearalenone

Lateral flow immunoassay (LFIA) has been employed extensively for the rapid, accurate, and portable detection of foodborne toxins. Here, the platinum gold nanoflower core-shell (Pt@AuNF) nanozyme with excellent optical properties, good catalytic ability and controllable reaction conditions were prepared to effectively improve the performance of lateral flow immunoassay (LFIA) strips. The Pt@AuNF nanozyme and horseradish peroxidase (HRP) combined with monoclonal antibody were used as signal probes based on the dual enzymes catalytic signal amplification strategy to detect Zearalenone sensitively. Dual enzymes catalyze the decomposition of hydrogen peroxide into hydroxyl radicals, and under the influence of hydroxyl radicals, colorless 3,3',5,5' -tetramethylbenzidine (TMB) is oxidized to blue ox-TMB, which is superimposed on the strips for signal amplification to broaden the detection range. The limit of detection (LOD) of the Pt@AuNF-HRP labeled LFIA strips after signal amplification was 0.052 ng/mL, and the detection range was 0.052-7.21 ng/mL. Compared with the Pt@AuNF labeled strips, while reducing the probes amount by half to achieve antibody conservation, the detection range was expanded by 5-fold based on achieving improved sensitivity. The study provided a meaningful reference for expanding the detection range based on immunoassay.

An advanced ratiometric molecularly imprinted sensor based on metal ion reoxidation for indirect and ultrasensitive glyphosate detection in fruit

An indirect and ultrasensitive ratiometric molecularly imprinted (MIP) sensor, based on metal ion reoxidation, is introduced for glyphosate (GLY) determination in fruit. As high-performance signal amplification substrates, carbon nanotubes (MWCNTs) and gold nanoparticles (AuNPs) are conveniently modified on GCE. The artificial antibody-MIP membrane, presents typical three-dimensional structure to GLY template. Built-in reference methylene blue (MB) is directly electropolymerized on MWCNTs-Au/GCE. Particularly, Cu2+ and GLY interestingly form chelate complex, and the Cu2+ (ICu) in Cu(Ⅱ)-GLY-complex can be reoxidized, and indirectly quantizes GLY. The reference signal (IMB) presents noteworthy stability with different GLY levels, and the ratiometric readout (ICu/IMB) is recognized as a more trustworthy indicator to quantize GLY. Proposed sensor presents broad range as 1.73 ∼ 400 ng/mL, and limit of detection is well found as 0.24 ng/mL (S/N = 3). Finally, as-fabricated method is verified with standard HPLC in real-fruit-sample, and the errors and recovery rates are calculated as 3.4% ∼ 6.7% and 94.4% ∼ 104.6%, respectively.

A novel electrochemical aptasensor based on core-shell nanomaterial labeling for simultaneous detection of acetamiprid and malathion

At present, due to the coexistence of multiple pesticides in vegetables and the enhanced toxicity, a simultaneous detection method for multiple pesticides is urgently needed. In this work, two types of core-shell nanomaterials, Ag-Au core-shell nanoparticles (Ag@Au NPs) and Cu2O-Au core-shell nanoparticles (Cu2O@Au NPs), were synthesized and labeled with acetamiprid aptamer and malathion aptamer to prepare two novel electroactive signal probes, respectively. The two probes were hybridized on the surface of the electrode by the principle of base complementary pairing between the aptamers and the thiolated DNA oligonucleotide sequences, and a dual-signal electrochemical aptasensor for the simultaneous detection of acetamiprid and malathion was established by modified glassy carbon electrode (GCE). The limits of detection (LOD) were calculated to be 43.7 pg mL-1 for acetamiprid and 63.4 pg mL-1 for malathion. The aptasensor determined acetamiprid and malathion in spinach and rape with the recovery rates of 88.9%-112.5% and 98.0%-114.1%, respectively.

A deep learning-enabled smartphone platform for rapid and sensitive colorimetric detection of dimethoate pesticide

A novel deep learning-enabled smartphone platform is developed to assist a colorimetric aptamer biosensor for fast and highly sensitive detection of dimethoate. The colorimetric determination of dimethoate is based on the specific binding of dimethoate and aptamer, which leads to the aggregation of AuNPs in high-concentration NaCl solution, resulting in an obvious color change from red to blue. This color change provides sufficient data for self-learning enabled by a convolutional neural network (CNN) model, which is established to predict dimethoate concentration based on images acquired from a smartphone. To enhance user-friendliness for non-experts, the CNN model is then embedded into a smartphone app, enabling offline detection of dimethoate pesticide in real environments within just 15 min using a pre-configured colorimetric probe. The developed platform exhibits superior performance, achieving a regression coefficient of 0.9992 in the concentration range of 0-10 μM. Moreover, the app's performance is found to be consistent with the ELISA kit. These remarkable findings demonstrate the potential of combining colorimetric biosensors with smartphone-based deep learning methods for the development of portable and affordable tools for pesticide detection.

Portable multichannel detection instrument based on time-resolved fluorescence immunochromatographic test strip for on-site detecting pesticide residues in vegetables

In this work, a portable multichannel detection instrument based on time-resolved fluorescence immunochromatographic test strip (TRFIS) was proposed for on-site detecting pesticide residues in vegetables. Its hardware consisted of a silicon photodiode and excitation light source array, a mainboard of the lower machine with STMicroelectronics 32 (STM32) and a linear stepping motor. While detecting, cardboard with 6-channel TRFIS was pulled into the cassette by the stepping motor. The peak area of the test (T) line and control (C) line of each TRFIS was sampled and calculated by software, then the concentration of the detected pesticide was obtained according to the ratio of the T to C value. This instrument could sample 6-channel TRFIS within 30 s simultaneously, and it exhibited excellent accuracy with a 2.5% average coefficient of variation for each channel (n = 12). In addition, the TRFIS was constructed by using europium oxide time-resolved fluorescent microspheres to label the monoclonal antibody against acetamiprid and form a fluorescent probe, which was fixed on the binding pad. The TRFIS was used for the detection of acetamiprid in celery cabbage, cauliflower and baby cabbage. This instrument was used to complete the qualitative and quantitative analysis of the TRFIS, so as to enhance the practical application of the detection method. This TRFIS possessed excellent linearity ranging from 0.25 mg kg-1 to 1.75 mg kg-1 for the detection of acetamiprid, and the limit of detection were 0.056-0.074 mg kg-1 in the different vegetable matrix. The platform combines the accuracy and portability of traditional test strips with the highly sensitive and efficient fluorescence intensity recognition function of detection equipment, which shows a great application prospect of multi-channel rapid detection of small molecule pollutants in the field.

Fluorescent nanostructured carbon dot-aptasensor for chlorpyrifos detection: Elucidating the interaction mechanism for an environmentally hazardous pollutant

Chlorpyrifos (CPF) is a commonly used insecticide found in many water sources and is related to several health and environmental effects. Biosensors based on aptamers (single-stranded nucleic acid oligonucleotides) are promising alternatives to achieve the detection of CPF and other pesticides in natural waters. However, several challenges need to be addressed to promote the real application of functional aptasensing devices. In this work, an ssDNA aptamer (S1) is combined with carbon quantum dots (CD) and graphene oxide (GO) to produce a stable fluorescent aptasensor characterized through spectrophotometric and electrophoretic techniques. For a deeper understanding of the system, the mechanism of molecular interaction was studied through docking modeling using free bioinformatic tools like HDOCK, showing that the stem-loops and the higher guanine (G) content are crucial for better interaction. The model also suggests the possibility of generating a truncated aptamer to improve the binding affinity. The biosensor was evaluated for CPF detection, showing a low LOD of 0.01 μg L-1 and good specificity in tap water, even compared to other organophosphates pesticides (OPs) like profenofos. Finally, the recovery of the proposed aptasensor was evaluated in some natural water using spiked samples and compared with UPLC MS-MS chromatography as the gold standard, showing a good recovery above 2.85 nM and evidencing the need of protecting ssDNA aptamers from an erratic interaction with the aromatic groups of dissolved organic matter (humic substances). This work paves the way for a better aptasensors design and the on-site implementation of novel devices for environmental monitoring.

Magnetic-assisted exciton-plasmon interactions modulated Bi2S3 nanorods@MoS2 nanosheets heterojunction: towards a split-type photoelectrochemical sensing of profenofos

A split-type photoelectrochemical (PEC) sensor was designed for the detection of profenofos (PFF) depending on the magnetic-assisted exciton-plasmon interactions (EPI) between the semiconductor substrate and Au NPs. The core-shell Bi2S3 nanorods@MoS2 nanosheets (Bi2S3 NRs@MoS2 NSs) heterostructure nanomaterial with fascinating performance was synthesized and used as the photovoltaic conversion substrate and signal molecules absorption platform. The PEC sensor is operated by co-incubating with the released Au NPs-cDNA from the surface of magnetic beads, originating from the target-triggered DNA double-stranded structure opening event. Due to the strong EPI effects, the photocurrent of Bi2S3 NRs@MoS2 NSs decreased and varied with the PFF concentrations. The proposed PEC sensor exhibited outstanding analytical performances, including a wide linear range (1.0 pg mL-1~1.0 μg mL-1), low detection limitation (0.23 pg mL-1, at 3 σ/m), excellent specificity, high stability, and applicability. Overall, this work provides a new signal strategy for PEC biosensors and extends its application in environmental analysis.

Bio-barcode assay: A useful technology for ultrasensitive and logic-controlled specific detection in food safety: A review

Food safety is one of the greatest public health challenges. Developing ultrasensitive detection methods for analytes at ultra-trace levels is, therefore, essential. In recent years, the bio-barcode assay (BCA) has emerged as an effective ultrasensitive detection strategy that is based on the indirect amplification of various DNA probes. This review systematically summarizes the progress of fluorescence, PCR, and colorimetry-based BCA methods for the detection of various contaminants, including pathogenic bacteria, toxins, pesticides, antibiotics, and other chemical substances in food in over 120 research papers. Current challenges, including long experimental times and strict storage conditions, and the prospects for the application of BCA in biomedicine and environmental analyses, have also been discussed herein.

Facile colorimetric smartphone-based biosensor for rapid detection of organophosphorus pesticides residues in environment using the aptamer-enhanced oxidase activity of octahedral Ag2O particles

The long-term and excessive use of organophosphorus pesticides (OPs) leads to hazardous residues in the environment, which threatens human health to a considerable extent. Colorimetric methods can quickly and readily identify pesticide residue, but they still have various challenges in accuracy and stability. Herein, a smartphone-assisted and non-enzymatic colorimetric biosensor was constructed for rapid monitoring of multiple OPs based on the enhanced effect of aptamer on the catalytic ability of octahedral Ag₂O. It was demonstrated that the aptamer sequence could enhance the affinity of colloidal Ag₂O to chromogenic substrates, and accelerate the generation of oxygen radicals such as superoxide radical (·O₂^-) and singlet oxygen (¹O₂) from dissolved oxygen, thereby significantly increasing the oxidase activity of octahedral Ag₂O. The color change of the solution can be easily converted to the corresponding RGB values by a smartphone for quantitative and rapid detection of multiple OPs. Hence, the smartphone-based and visual biosensor of multiple OPs was acquired with limit of detection of 10 μg L^-1, 28 μg L^-1 and 40 μg L^-1 for isocarbophos, profenofos and omethoate, respectively. The colorimetric biosensor also exhibited good recoveries in several environmental and biological samples, showing that it may have broad application prospects for detecting OPs residues.

A colorimetric aptasensor fabricated with group-specific split aptamers and complex nanozyme for enrofloxacin and ciprofloxacin determination

Developing simultaneous detection methods for multiple targets is crucial for the field of food analysis. Herein, enrofloxacin (ENR) and ciprofloxacin (CIP) were taken as model targets. For the first time, a strategy to generate group-specific split aptamers was established by revealing and splitting the critical binding domain, and the split aptamers were exploited to design a four-way DNA junction (4WJ) which could regulate the enzymatic activity of chitosan oligosaccharide (COS)-AuNPs nanozyme to develop a colorimetric aptasensor. A pair of split aptamers were obtained for ENR (K_d = 15.00 nM) and CIP (K_d = 4.870 nM). The mechanism of COS binding with double-stranded DNA in the 4WJ was elucidated. Under optimal conditions, the colorimetric aptasensor enabled a wide linear detection range of 1.4-1400 nM and a limit of detection (LOD) of 321.1 pM and 961.0 pM towards ENR and CIP, respectively, which exhibited excellent sensitivity, selectivity, and availability in detecting ENR/CIP in seafood. This study expands the general strategies for generating robust aptamers and nanozyme complex and provides a good reference for developing multi-target detection methods.

Organic ligands regulate the environmental impacts of metal-organic frameworks on nitrogen-fixing bacterium Azotobacter vinelandii

Metal-organic frameworks (MOFs) are rapidly developed materials with fantastic properties and wide applications. The increasing studies highlighted the potential threats of MOF materials to the environment. Comparing to the limited species of metal elements, the organic ligands have much higher diversity, but the influence of organic ligands on the environmental impacts of MOFs has not been revealed. Herein, we synthesized three Cu-MOFs with different organic ligands, namely Cu-BDC (1,4-terephthalic acid), Cu-IM (imidazole) and Cu-TATB (2,4,6-tris(4-carboxyphenyl)- 1,3,5-triazine), and evaluated their environmental toxicity to the nitrogen-fixing bacterium Azotobacter vinelandii. Cu-BDC inhibited the bacterial growth at lower concentrations than Cu-IM and Cu-TATB. The transcriptomes suggested the changes of membrane components by Cu-MOFs, consistent with the membrane leakage and cell wall damages. Cu-MOFs inhibited the nitrogen fixation activity through energy metabolism disturbance according to Gene Ontology functional annotation of ATP binding, Ca²⁺Mg²⁺-ATPase activity and ATP content. Only Cu-IM lowered the nitrogen fixation related nif genes, and affected the ribosome, purine metabolism and oxidative phosphorylation pathways. Otherwise, Cu-BDC and Cu-TATB mainly affected the flagellar assemblies and bacterial chemotaxis pathways. Our results collectively indicated that organic ligands regulated the environmental toxicity of MOFs through different metabolism pathways.

Smartphone-assisted sensor array constructed by copper-based laccase-like nanozymes for specific identification and discrimination of organophosphorus pesticides

Accurate pesticide identification is of great importance for regulating food safety. However, the discrimination between organophosphorus pesticides (OPs) and carbamate pesticides (CPs) is still a challenge for existing analytical methods based on cholinesterase inhibition. It mainly because of the similar inhibitory effect of OPs and CPs on cholinesterase. Herein, we found that OPs and CPs differentially affected nanozymes with laccase-like activity, which would be interfered by OPs in different degrees rather than CPs. Thus, we fabricated a nanozyme sensor array and successfully achieved the OPs identification and similar individual discrimination, ignoring the interference from CPs or other potential interferents (antibiotics, ions, other pesticides). On the basis of nanozyme sensor array, a portable method using smartphone was constructed and utilized to determine OPs in fruits and vegetables. This work would contribute to the development of portable sensors and the highly selective identification and discrimination of OPs in complex samples.

Malathion detection based on polydopamine enhanced oxidase-mimetic activity of palladium nanocubes

Nowadays, fabricating simple and efficient pesticide detection methods become a research focus due to the great threat pesticide residues posed to human health and environment. Herein, we constructed a high-efficiency and sensitive colorimetric detection platform for malathion detection based on polydopamine-dressed Pd nanocubes (PDA-Pd/NCs). The Pd/NCs coated with PDA exhibited excellent oxidase-like activity, which was attributed to the substrates accumulation and accelerated electron transfer induced by PDA. What's more, we successfully achieved sensitive detection of acid phosphatase (ACP) using 3,3',5,5'-tetramethylbenzidine (TMB) as the chromogenic substrate, relying on the satisfactory oxidase activity from PDA-Pd/NCs. However, the addition of malathion could inhibit the activity of ACP and limit the production of medium AA. Therefore, we constructed a colorimetric assay for malathion based on PDA-Pd/NCs + TMB + ACP system. The wide linear range (0-8 μM) and low detection limit (0.023 μM) indicate excellent analytical performance, which is superior to most malathion analysis methods previously reported. This work not only provides a new idea for dopamine coated nano-enzyme to improve its catalytic activity, but also creates a new tactics for the detection of pesticides such as malathion.

High-loading Cu single-atom nanozymes supported by carbon nitride with peroxidase-like activity for the colorimetric detection of tannic acid

The design of nanozymes with high metal atom loading is of great significance to improve enzyme activity and is also the key to furthering the construction of highly sensitive colorimetric sensors. In this work, a colorimetric sensor for the quantitative analysis of tannic acid (TA) was developed based on two-dimensional carbon nanosheet carbon nitride (CN)-supported Cu single-atom nanozymes (Cu/CN). Cu/CN was synthesized by supramolecular preorganization and calcination, with an ultrathin nanosheet structure and a high density of Cu active sites, with a Cu loading of up to 14.3 wt%. Benefiting from the above characteristics, Cu/CN exhibits peroxidase-mimicking activity and excellent catalytic performance. Therefore, a colorimetric sensor was constructed for the fast and sensitive quantitative analysis of TA with good linearity in the range of 0.09-3.2 μM and a low detection limit of 30 nM. Furthermore, the sensor was successfully applied to the analysis of TA in tea samples of different varieties. This work sheds new light on the design of nanozymes with a high density of active sites and the analysis of TA in real environments.

Aptamer recognition-promoted hybridization chain reaction for amplified label-free and enzyme-free fluorescence analysis of pesticide

Development of high-performance fluorescence sensors for pesticide is highly urgent but remains a grand challenge. It is due to that most of known fluorescence sensors detect pesticides based on enzyme-inhibited strategy, which requires high-price cholinesterase, suffers from serious interference of reductive materials, and can't difference pesticides with each other; the known aptamer-based fluorescence ones entail tool enzymes or nanomaterials to transducer/amplify the signal and demand signalers to be tagged in nucleic acid, which are expensive and intricate. Herein, we develop a novel aptamer-based fluorescence system for label-free, enzyme-free and highly sensitive detection of pesticide (profenofos) based on target-initiated hybridization chain reaction (HCR)-assisted signal amplification and specific intercalation of N-methylmesoporphyrin IX (NMM) in G-quadruplex DNA. Hairpin probe ON1 recognizes profenofos to generate profenofos@ON1 complex, which switches the HCR to yield multiple G-quadruplex DNA, consequently making large numbers of NMM be locked. In comparison with profenofos absence, a sharply improved fluorescence signal was recorded and it was dependent on profenofos dose. Hence, label-free, enzyme-free and highly sensitive detection of profenofos is achieved with limit of detection of 0.085 nM, which compared favorably with or superior to those of known fluorescence methods. Furthermore, the present method was applied to determine the profenofos residue in rice with agreeable result, and will provide more valuable information for guaranteeing the pesticide-related food safety.

Highly Sensitive Fluorescence Detection of Three Organophosphorus Pesticides Based on Highly Bright DNA-Templated Silver Nanoclusters

It is still challenging to achieve simultaneous and sensitive detection of multiple organophosphorus pesticides (OPs). Herein, we optimized the ssDNA templates for the synthesis of silver nanoclusters (Ag NCs). For the first time, we found that the fluorescence intensity of T base-extended DNA-templated Ag NCs was over three times higher than the original C-riched DNA-templated Ag NCs. Moreover, a "turn-off" fluorescence sensor based on the brightest DNA-Ag NCs was constructed for the sensitive detection of dimethoate, ethion and phorate. Under strong alkaline conditions, the P-S bonds in three pesticides were broken, and the corresponding hydrolysates were obtained. The sulfhydryl groups in the hydrolyzed products formed Ag-S bonds with the silver atoms on the surface of Ag NCs, which resulted in the aggregation of Ag NCs, following the fluorescence quenching. The fluorescence sensor showed that the linear ranges were 0.1-4 ng/mL for dimethoate with a limit of detection (LOD) of 0.05 ng/mL, 0.3-2 µg/mL for ethion with a LOD of 30 ng/mL, and 0.03-0.25 µg/mL for phorate with a LOD of 3 ng/mL. Moreover, the developed method was successfully applied to the detection of dimethoate, ethion and phorate in lake water samples, indicating a potential application in OP detection.

A Co-based MOF as nanozyme with enhanced oxidase-like activity for highly sensitive and selective colorimetric differentiation of aminophenol isomers

Nanozyme with the merit of excellent and adjustable catalytic activity, outstanding stability and low cost is a promising alternative for natural enzymes widely applied in a variety of fields. In the present study, a new two-dimensional cobalt-based MOF nanocomposite designated as MVCM@β-CD was synthesized. Combined with the strategies of increasing the ratio of Co(Ⅲ)/Co(Ⅱ) and modifying with small molecule β-cyclodextrin (β-CD), MVCM@β-CD displayed remarkably enhanced oxidase-mimicking activity, which was attributed to synergistic effect from large surface area of two dimensional Co-MOF nanosheet, numerous exposed active sites, high-proportioned trivalence of cobalt and regulating action of β-cyclodextrin. The addition of aminophenol isomers inhibited the catalytic oxidation process, resulting in different color change of the solution and UV-Vis absorption behaviors, based on which a sensitive ratiometric colorimetry for m-aminophenol (m-Ap) and a simple colorimetric p-aminophenol (p-Ap) detection method were developed with the detection limit of 0.16 μM and 1.01 μM, respectively. This method realized the colorimetric differentiation of aminophenol isomers, which provided a simple, accurate and low-cost approach for visual discrimination without complicated instrument and procedure, especially appropriate for on-site detection.

Integration of Metallic Nanomaterials and Recognition Elements for the Specifically Monitoring of Pesticides in Electrochemical Sensing

Although all countries have been controlling the excessive use of pesticides, incidents of pesticide residues still existed. Electrochemical biosensors are extensively applied detection techniques to monitor pesticides with the help of different types of biorecognition components mainly including, antibodies, aptamers, enzymes (i.e., acetylcholinesterase, organophosphorus hydrolase, etc.), and synthetic molecularly imprinted polymers. Besides, the electrode materials mainly affected the sensitivity of electrochemical biosensors. Metallic nanomaterials with various structures and excellent electrical conductivity were desirable choice to construct electrochemical platforms to achieve the detection with high sensitivity and good specificity toward the target. This work reviewed the developed metallic materials including monometallic nanoparticles, bimetallic nanomaterials, metal atoms, metal oxides, metal molybdates, metal-organic frameworks, MXene, etc. Integration of recognition elements endowed the electrode materials with higher specificity toward the target pesticide. Besides, future challenges of metallic nanomaterials-based electrochemical biosensors for the detection of pesticides are also discussed and described.

New insights into the effects of chlorpyrifos on soil microbes: Carbon and nitrogen cycle related microbes in wheat/maize rotation agricultural field

Chlorpyrifos, a broad-spectrum organophosphorus insecticide, has been widely detected worldwide and is a potential neurotoxin and endocrine disruptor. Besides, chlorpyrifos has been proven that have a negative effect on soil microbes. In the present study, chlorpyrifos formulation (LORSBAN®, 45% emulsifiable concentrate) was applied in an agricultural field at the recommended dose (R dose, 270.0 and 337.5 g a.i. ha^-1 for wheat and maize respectively) and double recommended (DR) dose. Chlorpyrifos residue level and effect on soil microbes related to soil carbon and nitrogen cycle function were analyzed. Results showed that the half-lives of chlorpyrifos in wheat and maize field soil were 7.23-8.23 and 1.45-1.77 d, respectively. Application of chlorpyrifos at even DR dose did not result in unacceptable residual chlorpyrifos, where the final residual chlorpyrifos in wheat/maize (leaf, stem, and grain) was meet the requirement of the maximum residual limit (0.5 mg kg^-1 for wheat and 0.05 mg kg^-1 for maize) in China. Chlorpyrifos enhanced the activity of β-glucosidase by increasing the relative abundance of Sphingosinicella and promoted the carbon cycle in wheat field. The changes of cbbLR and cbbLG gene abundance also confirmed that chlorpyrifos could affect the import and export of soil carbon pool. The effect of chlorpyrifos on soil N cycle was determined by changes in the abundance of the bacterial genus Gemmatimonas, which is associated with denitrification. Further analysis of N-cycle functional genes and urease activity showed that chlorpyrifos inhibited nitrogen fixation in wheat field, but promoted nitrogen fixation in maize field. In general, bacterial abundance, urease, and AOA-amoA gene could be early warning markers of chlorpyrifos contamination. The results demonstrated the negative effects of chlorpyrifos on soil microbes especially on soil C and N cycle in actual agricultural field. It provides new insights about chlorpyrifos environmental pollution and its effect on soil ecosystems.

Electrochemical Aptasensor Based on Au Nanoparticles Decorated Porous Carbon Derived from Metal-Organic Frameworks for Ultrasensitive Detection of Chloramphenicol

A facile and sensitive electrochemical aptamer sensor (aptasensor) based on Au nanoparticles-decorated porous carbon (AuNPs/PC) composite was developed for the efficient determination of the antibiotic drug chloramphenicol (CAP). AuNPs modified metal-organic framework (AuNPs/ZIF-8) is applied as a precursor to synthesize the porous carbon with homogeneous AuNPs distribution through a direct carbonization step under nitrogen atmosphere. The as-synthesized AuNPs/PC exhibits high surface area and improved conductivity. Moreover, the loading AuNPs could enhance the attachment of the aptamers on the surface of electrode through the Au–S bond. When added to CAP, poorly conductive aptamer-CAP complexes are formed on the sensor surface, which increases the hindrance to electron transfer resulting in a decrease in electrochemical signal. Based on this mechanism, the developed CAP aptasensor represents a wide linear detection range of 0.1 pM to 100 nM with a low detection limit of 0.03 pM (S/N = 3). In addition, the proposed aptasensor was employed for the analysis of CAP in honey samples and provided satisfactory recovery.