Ratiometric fluorescent hydrogel for point-of-care monitoring of organophosphorus pesticide degradation

Peroxidase-mimetic carbon dot based nanozyme hydrogel colorimetric sensor for visual trichlorfon detection

Organophosphorus pesticide residues pose considerable threats to the environment and public health and have become a global concern. This paper reports the development of a visual sensing platform for the detection of trichlorfon based on a carbon-based nanozyme (abbreviated as Fe-CDs) with peroxidase-mimetic catalytic activity in conjunction with acetylcholinesterase (AChE). The peroxide-mimetic enzyme activity of Fe-CDs can be inhibited by sulfhydryl (-SH) compounds, and AChE can decompose thiocholine (ATCh) to produce -SH-containing thiocholine (TCh), leading to the inability of Fe-CDs to oxidise 3,3',5,5'-tetramethylbenzidine (TMB) to turn the solution blue, while trichlorfon can inhibit the activity of AChE, thereby recovering the blue colour. This platform achieves sensitive detection of trichlorfon with a linear range of 200-50,000 pM and a detection limit of 157.57 pM and has been successfully applied to the detection of trichlorfon in Chinese cabbage. In addition, encapsulating Fe-CDs, ATCh and TMB in sodium alginate hydrogels and using a smartphone and colour analysis software, a colorimetric hydrogel portable kit is developed, realising the simple and rapid detection of the trichlorfon residue in real samples. This study provides a direct, simple and rapid strategy for the detection of trichlorfon in agricultural products and offers a potential on-site detection tool for food safety monitoring.

Fluorescent Sodium Alginate Hydrogel-Carbon Dots Sensor for Detecting Perfluorooctanoic Acid in Potable Water

Per- and polyfluoroalkyl substances (PFASs), especially perfluorooctanoic acid (PFOA), are emerging environmental and health concerns due to their persistence, resistance to degradation, and bioaccumulation. In this study, we developed a sensitive and selective detection platform based on a sodium alginate (SA) hydrogel modified with nitrogen and fluorinated carbon dots (N,F-CDs) to enhance the detection of PFOA in natural and engineered water systems. The SA hydrogel-N,F-CD composite exhibited strong fluorescence at 480 nm after optimization, achieving a detection limit as low as 0.001 ppt. The sensor was characterized by using Scanning Electron Microscopy (SEM), Fourier-Transform Infrared Spectroscopy (FT-IR), Powder X-ray Diffraction (PXRD), X-ray Photoelectron Spectroscopy (XPS), and zeta potential spectroscopy, revealing its structural integrity, functional groups, and the surface charge of the SA hydrogel-N,F-CDs network. Sensitivity assessments demonstrated a linear fluorescence response to PFOA concentrations ranging from 1 to 66 ppq. Selectivity tests confirmed the sensor's ability to distinguish PFOA from other perfluorinated compounds, with minimal interference from other substances. The practical applicability of the sensor was validated using spiked recovery experiments with tap water samples from various locations, achieving recovery rates between 94% and 106.6%. This sensor offers a reliable, efficient, and highly sensitive platform for the detection of PFAS, demonstrating its potential for real-world PFAS-monitoring applications.

A ratiometric fluorescence and visual sensor based on conjugated polymer nanoparticles@MnO2 probe for organophosphorus pesticides detection

Organophosphorus (OPs) pesticide residues pose significant threats to human health and the environment. To tackle this issue, we synthesized water-soluble fluorescent conjugated polymer nanoparticles (WSCPNs), which offer high fluorescence intensity, simple preparation methods, and ease of functionalization, making them ideal candidates for fluorescent sensing applications. These WSCPNs were subsequently used to prepare a WSCPNs@MnO2 probe via in situ synthesis, resulting in efficient fluorescence resonance energy transfer between WSCPNs and MnO₂. This system effectively oxidizes non-fluorescent o-Phenylenediamine (OPD) into 2,3-diaminophenazine (DAP). In the absence of OPs, acetylthiocholine (ATCh) is catalyzed by acetylcholinesterase (AChE) to produce thiocholine (TCh), which reduces MnO₂ on the surface of the probe, restoring the fluorescence intensity. When OPs are present, AChE's catalytic pathway is inhibited, limiting the recovery of fluorescence intensity in WSCPNs. The remaining MnO₂ can further oxidize OPD to DAP, allowing quantitative analysis by monitoring changes in fluorescence signal ratios, achieving a detection limit of 0.0139 ng/mL. Additionally, color changes can be captured and analyzed using a smartphone, facilitating fluorescence visualization for OPs detection, achieving a detection limit of 0.025 ng/mL. This method exhibits excellent anti-interference capabilities and has been successfully applied to detect organophosphorus pesticides in leaves and soil, demonstrating the effectiveness of our ratiometric fluorescence and fluorescence visualization dual-mode sensing platform for monitoring OPs.

Iron/manganese-zeolitic imidazolate framework (Fe/Mn-ZIF) nanozyme combined with acetylcholinesterase for colorimetric rapid detection of organophosphorus pesticides

Organophosphorus pesticides (OPs) are extensively utilized in agricultural production, but they pose significant threats to environment and organisms. This study aims to develop a novel method for the rapid and efficient detection of OPs. Initially, an iron/manganese zeolitic imidazolate framework (Fe/Mn-ZIF) with excellent oxidase-like activity was synthesised. The catalytic performance was evaluated, and the main factors influencing catalytic activity were investigated. Subsequently, a combined acetylcholinesterase assay was employed to detect three OPs. The specificity and recyclability of Fe/Mn-ZIF were also studied. The proposed colorimetric strategy demonstrated strong linear relationships: 0.1-2 mg/L for trichlorfon, 0.2-14 mg/L for glyphosate, and 0.4-10 mg/L for glufosinate, with the low detection limits of 0.024, 0.080, and 0.121 mg/L (3 S/N) respectively. Good recoveries were observed in real sample detection. This work lays a foundation for enhancing the catalytic performance of Fe/Mn-ZIF, which holds promise for biosensing applications.

Nanozyme-mediated ratiometric fluorescence hydrogel for on-site detection of sulfite in food

In this work, a ratiometric fluorescence hydrogel nanosensor was developed by integrating a composite consisting of o-phenylenediamine (OPD), manganese dioxide nanoflakes (MnO2 NFs), and N-doped carbon dots (N-CDs) into an agarose hydrogel for sulfite detection. MnO2 NFs demonstrated intense oxidase-like activity, facilitating the conversion of non-fluorescent OPD into yellow-emissive 2,3-diaminophenazine (DAP). As a result, a significant emission peak belongs to DAP, alongside the fluorescence quenching of N-CDs through FRET. Upon interaction with sulfite, MnO2 NFs lost their oxidase-like function. This process decreased the fluorescence of DAP and restored the blue fluorescence of N-CDs, producing a typical ratiometric response, ranging from 3 nM ∼ 400 μM, with a detection limit (LOD) of 3.79 nM. Employing a smartphone, the fluorescence color change demonstrated by the hydrogel sensor was translated into quantitative data (LOD: 8.44 nM). This hydrogel sensor offers an affordable, portable, and user-friendly solution for sulfite detection and food safety monitoring.

Polysaccharide Hydrogel-Assisted Biosensing Platforms for Point-of-Care Use

Point-of-care (POC) use is one of the essential goals of biosensing platforms. Because the increasing demand for testing cannot be met by a centralized laboratory-based strategy, rapid and frequent testing at the right time and place will be key to increasing health and safety. To date, however, there are still difficulties in developing a simple and affordable, as well as sensitive and effective, platform that enables POC use. In terms of materials, hydrogels, a unique family of water-absorbing biocompatible polymers, have emerged as promising components for the development of biosensors. Combinations of hydrogels have various additional applications, such as in hydrophilic coatings, nanoscale filtration, stimuli-responsive materials, signal enhancement, and biodegradation. In this review, we highlight the recent efforts to develop hydrogel-assisted biosensing platforms for POC use, especially focusing on polysaccharide hydrogels like agarose, alginate, chitosan, and so on. We first discuss the pros and cons of polysaccharide hydrogels in practical applications and then introduce case studies that test different formats, such as paper-based analytical devices (PADs), microfluidic devices, and independent platforms. We believe the analysis in the present review provides essential information for the development of biosensing platforms for POC use in resource-limited settings.

Paper-based multicolor sensor for on-site quantitative detection of organophosphate pesticides based on acetylcholinesterase-mediated paper-based Au3+-etching of gold nanobipyramids and CIELab color space

On-site quantitative detection of organophosphorus pesticides (OPs) is crucial for safeguarding food and public safety. This study presents a novel acetylcholinesterase (AChE)-mediated paper-based Au3+-etching of gold nanobipyramids (AuNBPs) system. The system employs a long-term storable AuNBPs-deposited nylon membrane embedded within a portable and temperature-controlled paper-based analytical device. This system, coupled with a colorimeter-based quantitative method, enables the development of a practical paper-based multicolor sensor (PMS) for on-site quantitative detection of three common OPs (paraoxon, dichlorvos, and trichlorfon). In the absence of OPs, AChE hydrolyzes acetylthiocholine to thiocholine, which reduces Au3+ to Au+. The presence of OPs inhibits AChE activity, thereby preserving Au3+ to etch AuNBPs on nylon membranes, accompanied by multicolor changes. These color changes can be simply quantified by measuring the a∗ parameter of the CIELab color space using a portable colorimeter. Under optimal conditions, the PMS displayed eight OPs-corresponding color changes with a minimum detectable concentration of 1.0-10 μg/L (visual observation) and limits of detection of 0.8-7.2 μg/L (colorimeter) and 0.2-3.4 μg/L (UV-vis spectrometry). The PMS successfully determined the OPs in vegetable and rice samples with recoveries of 89.0-109 % and RSDs (n = 5) of <6 %. These results were consistent with those obtained using the HPLC-MS method. The PMS demonstrates excellent portability, AuNBPs stability, detection sensitivity, and reproducibility, making it a promising tool for the on-site quantitative detection of OPs residues in food. Furthermore, the paper-based etching system coupled with the colorimeter-based quantitative method provides a valuable reference to develop practical PMSs for various targets in diverse fields.

Organophosphorus Pesticides Management Strategies: Prohibition and Restriction Multi-Category Multi-Class Models, Environmental Transformation Risks, and Special Attention List

Organophosphorus pesticides (OPs) have become one of the most widely used pesticides in Chinese agriculture; however, methods to identify potential restrictions on OPs molecules are lacking. Therefore, this study retrieved the OPs restriction list and constructed eight multi-class, multi-category machine learning models for OPs restrictions. Among these, the random forest (RF) model demonstrated excellent predictive performance, as it was successfully validated and applied. Potential environmental transformation products of OPs were obtained using EAWAG-BBD software, while toxicity indicators for the parent OPs and their transformation products were predicted with ADMETlab 3.0 software. This study found that unrestricted OPs, such as phorate, parathion, and chlorpyrifos, exhibited a high probability of toxicity. Additionally, the environmental transformation products of OPs posed similar comprehensive toxicity risks as the parent compounds. A special attention list for OPs was created based on the toxicity risks of unrestricted parent OPs and their transformation products, using standard deviation classification. Phorate and parathion were identified as OPs requiring special attention. This paper aims to provide an effective method for identifying the potential restriction levels of OPs and to propose an evaluation system that comprehensively considers the health risk, thereby supporting the improvement and optimization of management and usage strategies for OPs.

Lamellar Ti3C2 MXene composite decorated with platinum-doped MoS2 nanosheets as electrochemical sensing functional platform for highly sensitive analysis of organophosphorus pesticides

Precisely detecting organophosphorus pesticides (OPs) is paramount in upholding human safety and environmental preservation, especially in food safety. Herein, an electrochemical acetylcholinesterase (AChE) sensing platform entrapped in chitosan (Chit) on the glassy carbon electrodes (GCEs) decorated with Pt/MoS2/Ti3C2 MXene (Pt/MoS2/TM) was constructed for the detection of chlorpyrifos. It is worth noting that Pt/MoS2/TM possesses good biocompatibility, remarkable electrical conductivity, environmental stability and large specific surface area. Besides, the heterostructure formed by the composite of TM and MoS2 improves the conductivity and maintains the original structure, which is conducive to improving the electrochemical property. The coordination effect between the individual components enables the even distribution of functional components and enhances the electrochemical performance of the biosensor (AChE-Chit/Pt/MoS2/TM). Under optimal efficiency and sensitivity, the AChE-Chit/Pt/MoS2/TM/GCE sensing platform exerts comparable analytical performance and a wide concentration range of chlorpyrifos from 10-12 to 10-6 M as well as a low limit of detection (4.71 × 10-13 M). Furthermore, the biosensor is utilized to detect OPs concerning three kinds of fruits and vegetables with good feasibility and recoveries (94.81% to 104.0%). This work would provide a new scheme to develop high-sensitivity sensors based on the two-dimensional nanosheet/laminar hybrid structure for practical applications in environmental monitoring and agricultural product detection.

Rapid Detection of Methyl Parathion Based on SiONPs-Eu3+ Dual-Emitting Fluoroprobe and Its On-Site Application

Herein, we pioneered an innovative methodology for the rapid identification and quantitation of methyl parathion (MP) residues, overcoming the drawbacks of existing methods such as poor selectivity, high costs, and intricate operational procedures. A dual-emitting fluoroprobe SiONPs-Eu3+ was engineered based on silica oxide nanoparticles (SiONPs) conjugated with Eu3+, and the synthetic conditions were meticulously optimized to ensure exceptional sensitivity and selectivity to 4-nitrophenol (4-NP), one of the MP hydrolytic products. Upon excitation at 317 nm, the blue fluorescence of SiONPs at 400 nm was quenched, while the red fluorescence of Eu3+ at 616 nm remained nearly unchanged, constituting a ratiometric fluorescent change that significantly enhanced the detection stability. The fluoroprobe rapidly detected 4-NP at concentrations below 80 μM within 10 s and gave a limit of detection (LOD) as low as 0.16 μM, markedly lower than the allowable residue limit of MP in China food safety standards. Also, it exhibited excellent anti-interference properties in complex matrices, remaining unaffected by common amino acids, cations, and pesticides. The underlying mechanism of the fluoroprobe was elucidated through time-dependent density functional theory (TD-DFT) calculations. Under optimized hydrolysis conditions, the detection of MP in real rice samples was successfully achieved. Furthermore, the self-developed and dual-channel portable device was conducive to on-site fluorescence detection of 4-NP, offering enhanced stability in contrast to traditional photography-based methods.

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.

A novel phosphotriesterase hybrid nanoflower-hydrogel sensor equipped with a smartphone detector for real-time on-site monitoring of organophosphorus pesticides

Designing efficient and rapid methods for the detection of organophosphorus pesticides (OPs) residue is a prerequisite to mitigate their negative health impacts. In this study, we propose the concept of an enzyme catalysis system-based hydrogel kit integrated with a smartphone detector for in-field screening of OPs. Here, we rapidly prepared phosphotriesterase hybrid nanoflowers (PTE-HNFs) using a self-assembly strategy by adding external energy and embedded the nanocomposite in sodium alginate (SA) hydrogel to construct a target-responsive hydrogel kit. The color response of the kit is induced by catalyzing methyl parathion (MP) to produce p-nitrophenol. For on-site quantification, the color variations of the portable kit are converted into digital information through a smartphone, which exhibits an applicable linear range towards OPs. The hydrogel sensing platform demonstrates a wide linear range (1-150 μM) and low detection limit (0.15 μM) for MP while maintaining high reliability, excellent long-term stability, and ease of operation. Overall, the PTE-HNFs-based SA hydrogel kit provides a useful strategy for simple and sensitive detection of MP and holds great potential for applications in detecting OPs in food and environmental water.

Three-dimensional DNA biomimetic networks (B-3D Net)-based ratiometric fluorescence platform for cancer-related gene biosensing

Efficient detection of cancer-related nucleic acids is pivotal for early cancer diagnosis. This study introduces a target induced three-dimensional DNA biomimetic networks (B-3D Net)-based ratiometric fluorescence platform using manganese dioxide nanosheets (MnO2 NS)/o-phenylenediamine in combination with hybridization chain reaction to detect cancer-related genes (p53 gene). The incorporation of multiple signals within the B-3D networks can significantly enhance catalytic activity and amplify the output signals, enabling a high sensitivity. Compared with traditional ratio fluorescence platforms, there is no demand to synthesize fluorescent nanoprobes due to the in-situ formation of fluorescence species, which is simple and cost-effective. The corresponding assay demonstrated exceptional sensitivity (with a detection limit as low as 2 fM), selectivity, reproducibility, and accuracy, which mitigates disturbances caused by instrument errors, an inaccurate probe count, and the microenvironment. Furthermore, the ease and straightforwardness of discerning changes in fluorescent brightness and colour by the naked eye are evident. Using the relevant software, a linear relationship between fluorescent images using a smartphone and target concentration was obtained. Hence, the novel ratiometric sensing system will demonstrate new opportunities on determination of target DNA samples in complex biological environments.

Rapid analysis of dichlorvos via releasing the phosphate core

Monitoring the residual dichlorvos (O,O-dimethyl-O-2,2-dichlorovinylphosphate, DDVP) in food has received extensive attention owing to its large consumption in agriculture. However, the previous sensing methods are not time-efficient enough due to the long incubation time for enzyme inhibition (tens of minutes to hours) or bottlenecked by the complicated procedures for senor fabrication. Herein, a novel sensing strategy is proposed based on the hydrolysis of DDVP into PO43-. By using alkaline phosphatase for hydrolysis, a certain portion of DDVP was transformed to PO43- within only 8 min. Then, the released PO43- was detected by a fluorescent terbium metal-organic framework (Tb-MOF). The coordination of the naked P-O groups to the metal nodes of the Tb-MOF disturbed the antenna effects of its ligands. Thus, DDVP was quantified by the decrease of the fluorescence of Tb ions. Based on this method, DDVP residues on plum surfaces were collected by swabs and successfully detected. The recovery of DDVP was determined in the range from 105 % to 115 %, demonstrating the quantification accuracy of this method. The detection limit reached 4.7 μM, which was lower than the restricted amount in fruit set by the National Standard of China. The present method provides an efficient and user-friendly way for the detection of DDVP and many other organophosphorus pesticides in food.

Insights into Translational and Biomedical Applications of Hydrogels as Versatile Drug Delivery Systems

Hydrogels are a network of crosslinked polymers which can hold a huge amount of water in their matrix. These might be soft, flexible, and porous resembling living tissues. The incorporation of different biocompatible materials and nanostructures into the hydrogels has led to emergence of multifunctional hydrogels with advanced properties. There are broad applications of hydrogels such as tissue culture, drug delivery, tissue engineering, implantation, water purification, and dressings. Besides these, it can be utilized in the field of medical surgery, in biosensors, targeted drug delivery, and drug release. Similarly, hyaluronic acid hydrogels have vast applications in biomedicines such as cell delivery, drug delivery, molecule delivery, micropatterning in cellular biology for tissue engineering, diagnosis and screening of diseases, tissue repair and stem cell microencapsulation in case of inflammation, angiogenesis, and other biological developmental processes. The properties like swellability, de-swellability, biodegradability, biocompatibility, and inert nature of the hydrogels in contact with body fluids, blood, and tissues make its tremendous application in the field of modern biomedicines nowadays. Various modifications in hydrogel formulations have widened their therapeutic applicability. These include 3D printing, conjugation, thiolation, multiple anchoring, and reduction. Various hydrogel formulations are also capable of dual drug delivery, dental surgery, medicinal implants, bone diseases, and gene and stem cells delivery. The presented review summarizes the unique properties of hydrogels along with their methods of preparation and significant biomedical applications as well as different types of commercial products available in the market and the regulatory guidance.

The construction of dual-emissive ratiometric fluorescent probes based on fluorescent nanoparticles for the detection of metal ions and small molecules

With the rapid development of fluorescent nanoparticles (FNPs), such as CDs, QDs, and MOFs, the construction of FNP-based probes has played a key role in improving chemical sensors. Ratiometric fluorescent probes exhibit distinct advantages, such as resistance to environmental interference and achieving visualization. Thus, FNP-based dual-emission ratiometric fluorescent probes (DRFPs) have rapidly developed in the field of metal ion and small molecule detection in the past few years. In this review, firstly we introduce the fluorescence sensing mechanisms; then, we focus on the strategies for the fabrication of DRFPs, including hybrid FNPs, single FNPs with intrinsic dual emission and target-induced new emission, and DRFPs based on auxiliary nanoparticles. In the section on hybrid FNPs, methods to assemble two types of FNPs, such as chemical bonding, electrostatic interaction, core satellite or core-shell structures, coordination, and encapsulation, are introduced. In the section on single FNPs with intrinsic dual emission, methods for the design of dual-emission CDs, QDs, and MOFs are discussed. Regarding target-induced new emission, sensitization, coordination, hydrogen bonding, and chemical reaction induced new emissions are discussed. Furthermore, in the section on DRFPs based on auxiliary nanoparticles, auxiliary nanomaterials with the inner filter effect and enzyme mimicking activity are discussed. Finally, the existing challenges and an outlook on the future of DRFP are presented. We sincerely hope that this review will contribute to the quick understanding and exploration of DRFPs by researchers.

Eu-MOF based fluorescence probe for ratiometric and visualization detection of Cu2

Water contamination caused by heavy metals represents an urgent global issue. Cu2+, a potential trace heavy metal pollutant, can accumulate in the human body through the food chain, leading to excessive levels that give rise to diverse health complications. Hence, in this investigation, a novel and efficacious fluorescent probe named Eu-BTB was developed for the detection of Cu2+, employing 1,3,5-triphenyl(4-carboxyphenyl) (H3BTB) as the ligand and Eu3+ as the metallic framework. The probe demonstrates exceptional fluorescence characteristics. The interaction between the probe ligand BTB and Eu3+ triggers an antenna effect, heightening the emission efficiency of Eu3+ while preserving its intrinsic emission. The introduction of Cu2+ competes with BTB for binding, thus quelling the antenna effect and inducing a fluorescence alteration. Within the concentration range of 0.05-10 μM, the fluorescence intensity-to-Cu2+ concentration ratio exhibits a robust linear correlation, with a remarkably low detection limit of 10 nM and a rapid response time of 3 min. The fluorescent probe has been effectively deployed for the detection of copper ions in water across diverse environmental conditions, with the obtained outcomes being validated via the conventional approach of inductively coupled plasma mass spectrometry (ICP-MS). The Eu-BTB probe showcases the advantages of simplicity, swiftness, and broad applicability, thus affirming its potential for the prompt and accurate detection of Cu2+ in diverse environmental water samples.

Enzyme-mediated Ru@UiO-66@MnO2 NSs/thiamine-based ratiometric fluorescence sensor for visual detection of organophosphorus pesticide residues

In view of the potential hazards of organophosphorus pesticides (OPs), this paper constructed a ratiometric fluorescent probe utilizing a functionalized metal-organic framework to detect OPs. Ru(bpy)3Cl2 was encapsulated inside UiO-66 as a reference signal, and MnO2 nanosheets (MnO2 NSs) were grown on the surface to obtain Ru@UiO-66@MnO2 NSs. Acetylcholinesterase catalyzed the decomposition of acetylcholine into reductive thiocholine, which consumed MnO2 NSs, thus restoring the Ru@UiO-66 fluorescence. Due to the enzymatic inhibition of OPs and the redox reaction between MnO2 NSs and thiamine, this probe emitted blue fluorescence in the presence of OPs. The probe achieved linear responses to dichlorvos and chlorpyrifos with LODs of 9.99 × 10-6 μg mL-1 and 9.99 × 10-5 μg mL-1. The probe exhibited a satisfactory recovery rate for OPs in green tea. Furthermore, a hydrogel detection platform was developed by embedding the probe into sodium alginate. Overall, this work provides a visual approach to detect OPs in agricultural products.

Integrating Intelligent Logic Gate Dual-Nanozyme Cascade Fluorescence Capillary Imprinted Sensors for Ultrasensitive Simultaneous Detection of 2,4-Dichlorophenoxyacetic Acid and 2,4-Dichlorophenol

Herein, a dual-nanozyme cascade catalysis triemission fluorescence capillary imprinted sensor integrated with intelligent logic gates was constructed for simultaneous detection of 2,4-dichlorophenoxyacetic acid (2,4-DA) and 2,4-dichlorophenol (2,4-DCP). The novel nanozyme fluorescence organic framework (Bi, Co-MOF) was grafted on the surface of Fe3O4 modified with histidine to form a nanozyme composite (FBM) with dual-enzyme activity, which was imprinted with 2,4-DA to prepare a fluorescence molecularly imprinted polymer (FBM@MIP). Carbon dots (CDs) coupling with FBM@MIP (FBM@MIP/CDs) was inhaled into a capillary to construct a dual-nanozyme capillary imprinted sensor directly. The FBM@MIP/CDs capillary sensor realized to detect 2,4-DA and 2,4-DCP simultaneously within a linear concentration range of 1.0 × 10-12-1.2 × 10-9 M and 1.0 × 10-12-4.8 × 10-9 M with the detection limit of 0.75 and 0.68 pM, respectively. Interestingly, a smartphone-assisted portable capillary fluorescence intelligent sensing platform was developed that can detect 2,4-DA and 2,4-DCP visually without tedious operations such as soaking and drying. Combined with a smartphone, the linear relationships between RGB ratios and concentrations of 2,4-DA and 2,4-DCP were established with the detection limit of 0.93 and 0.81 pM, respectively. The integrated logic gates provided a promising way for intelligent sensing of multiple targets simultaneously, which provided a new strategy for ultrasensitive simultaneous detection of multiple pollutants with a microvolume (18 μL/time) in complex environments.

Introducing Mn into ZIF-8 nanozyme for enhancing its catalytic activities and adding specific recognizer for detection of organophosphorus pesticides

In order to design and establish a highly efficient and selective nanozyme-based sensing platform for the UV-vis detection of organophosphorus pesticides (OPs), Mn was introduced into ZIF-8 nanozyme for enhancing its catalytic activities and adding specific recognizer. The Mn-doped ZIF-8 (Mn-ZIF-8) nanocomposites were synthesized with a very facile one-pot method by heating the mixture of ZnO, 2-methylimidazole (Hmin) and Mn(CH3COO)2·4H2O in a solvent-free system at 180 °C for 8 h. The Mn-ZIF-8 nanocomposite showed a higher peroxidase activity and an additional thiocholine (TCh)-degradable property compared to the pristine ZIF-8. OPs could inhibit acetylcholinesterase (AChE) to catalyze the hydrolysis of acetylthiocholine (ATCh) to produce TCh, thus blocking the degradation of Mn-ZIF-8 and protecting the catalysis of the oxidation of colorless 3,3',5,5'-tetramethylbenzydine (TMB) to blue oxidized TMB (ox-TMB). Accordingly, a detection method for OPs with high sensitivity and selectivity was designed and established on the basis of the Mn-ZIF-8 nanozyme with a linear range of 0.1-20 nM and a limit of detection (LOD) as low as 54 pM.

A smartphone-based fluorospectrophotometer and ratiometric fluorescence nanoprobe for on-site quantitation of pesticide residue

Cost-effective and user-friendly quantitation at points-of-need plays an important role in food safety inspection, environmental monitoring, and biomedical analysis. This study reports a stand-alone smartphone-based fluorospectrophotometer (the SBS) installed with a custom-designed application (the SBS-App) for on-site quantitation of pesticide using a ratiometric sensing scheme. The SBS can collect fluorescence emission spectra in the wavelength range of 380-760 nm within 5 s. A ratiometric fluorescence probe is facilely prepared by directly mixing the blue-emissive carbon nanodots (the Fe3+-specific fluorometric indicator) and red-emissive quantum dots (the internal standard) at a ratio of 11.6 (w/w). Based on the acetylcholinesterase/choline oxidase dual enzyme-mediated cascade catalytic reactions of Fe2+/Fe3+ transformation, a ratiometric fluorescence sensing scheme is developed. The practicability of the SBS is validated by on-site quantitation of chlorpyrifos in apple and cabbage with a comparable accuracy to the GC-MS method, offering a scalable solution to establish a cost-effective surveillance system for pesticide pollution.

Naphthalene-based fluorescent probe for on-site detection of hydrazine in the environment

The widespread occurrence of hydrazine residues in the environment, including in water, soil, and organisms, is a potential health threat to humans. Therefore, the development of an efficient method for the detection of hydrazine in environmental samples is highly desirable although it poses a significant challenge. In this study, we designed and synthesized a series of naphthalene-based fluorescent dyes through structural engineering and developed a novel probe for hydrazine detection. The probe could provide a distinct fluorescence response toward hydrazine in aqueous solution with high sensitivity and selectivity. Moreover, paper-based test strips can be easily fabricated using this probe, enabling the portable on-site detection of hydrazine with the aid of a smartphone. Furthermore, we demonstrated that this probe is capable of recognizing hydrazine in various environmental samples, including water, soil, plants, and zebrafish embryos. This research provides a promising tool for the detection of hydrazine in the environment.

Advanced visual sensing techniques for on-site detection of pesticide residue in water environments

Pesticide usage has increased to fulfil agricultural demand. Pesticides such as organophosphorus pesticides (OPPs) are ubiquitous in world food production. Their widespread usage has unavoidable detrimental consequences for humans, wildlife, water, and soil environments. Hence, the development of more convenient and efficient pesticide residue (PR) detection methods is of paramount importance. Visual detecting approaches have acquired a lot of interest among different sensing systems due to inherent advantages in terms of simplicity, speed, sensitivity, and eco-friendliness. Furthermore, various detections have been proven to enable real-life PR surveillance in environment water. Fluorometric (FL), colourimetric (CL), and enzyme-inhibition (EI) techniques have emerged as viable options. These sensing technologies do not need complex operating processes or specialist equipment, and the simple colour change allows for visual monitoring of the sensing result. Visual sensing techniques for on-site detection of PR in water environments are discussed in this paper. This paper further reviews prior research on the integration of CL, FL, and EI-based techniques with nanoparticles (NPs), quantum dots (QDs), and metal-organic frameworks (MOFs). Smartphone detection technologies for PRs are also reviewed. Finally, conventional methods and nanoparticle (NPs) based strategies for the detection of PRs are compared.

Spherical Hydrogel Sensor Based on PB@Fe-COF@Au Nanoparticles with Triplet Peroxidase-like Activity and Multiple Capture Sites for Effective Detection of Organophosphorus Pesticides

The residues of organophosphorus pesticides (OPs) have drawn worldwide increasing attention because of their potential fatal effects on human health and ecological systems. It is of great significance to develop an efficient and portable method for in-field detection of OPs. Herein, a novel core-shell nanocomposite of prussian blue@Fe-covalent organic framework@Au (PB@Fe-COF@Au) was constructed. Fe²⁺ and Fe³⁺ in PB nanoparticle (PBNP) cores, Fe-porphyrin in COF shells, and AuNPs grown on shells all acted as peroxidase-like catalytic active sites, enabling PB@Fe-COF@Au to possess triplet peroxidase-like activity. A colorimetric, affordable, sensitive, and selective strategy was designed to detect OPs. Compared with previous reports, this sensor realized a wider linear range for chlorpyrifos of 10-800 ng mL^-1 with a relatively lower detection limit of 0.61 ng mL^-1, which was attributed to the overlapping triple catalytic sites of PB@Fe-COF@Au and triple response sites to OPs. The assay was successfully employed to detect chlorpyrifos in food and environmental samples. Moreover, to meet the demand of in-field detection for OPs, a spherical hydrogel method based on PB@Fe-COF@Au with visual, portable, and equipment-free features was fabricated. This work provides a new pathway to design and apply effective nanozymes for on-site monitoring of pesticides.