Real time monitoring of nerve agent mimics: Novel solid state emitter for enhanced precision and reliability

Chemical nerve agents are hazardous compounds that terrorists can exploit to pose a significant threat to public safety and national security. The nucleophilic behaviour of these agents enables their interaction with acetyl cholinesterase in the body, leading to paralysis and potentially fatal consequences. Therefore, developing robust and efficient detection methods for these agents is crucial for preventing their misuse. In this manuscript, (E)-12-(1-hydrazineylideneethyl)benzo[f]pyrido[1,2-a]indole-6,11-dione (HBID) is developed as a novel colorimetric and fluorometric probe for the detection of specific chemical nerve agent simulants in both liquid and vapor phase. HBID reacts rapidly with diethyl chlorophosphate (DCP), a common nerve agent simulant, leading to a significant increase in the fluorescence intensity. Under optimized conditions, HBID exhibits high sensitivity, good recyclability, fast response and low limit of detection (0.092 µM). NMR and mass spectral studies suggest that the reaction involves the nucleophilic addition of HBID to DCP, forming a phosphate ester. Additionally, the developed sensor demonstrates viscosity-sensitive AIE phenomena thus greatly expanding its potential applications in biological systems. This sensitivity enables precise detection and visualization of viscosity changes within cellular environments, making the sensor an invaluable tool for studying complex biological processes. The developed probe also detects pH within biologically relevant range (4-6). In practical applications, the probe-treated strips efficiently detected DCP vapor in real time, showing a noticeable fluorescence response. Further, the probe has a strong potential to detect the presence of DCP in the soil samples.

Enzyme-free ratiometric fluorescence and colorimetric dual-signal determination of glyphosate based on copper nanoclusters (ZIF/CuNCs) combined with blue carbon dots (bCDs)

A novel ratio fluorescent and colorimetric dual-signal sensing platform for detecting glyphosate based on blue carbon dots (bCDs) combined with ZIF/CuNCs nanomaterials that encapsulate copper nanoclusters (CuNCs) in a metal-organic framework (MOF). In principle, the immobilization of Cu2+ in ZIF/CuNCs results in complexation with imidazole in ZIF, leading to fluorescence quenching of ZIF/CuNCs, while the reference fluorophore bCDs remains unaffected. In addition, the colorimetric sensing strategy was based on the efficient peroxidase-like activity of bCDs binding to Cu2+, catalyzing H2O2 to generate OH. Under this condition, TMB could be oxidized to form blue oxTMB. However, when glyphosate was involved in the system, the fluorescence of ZIF/CuNCs was restored upon due to the strong chelation between Cu2+ and glyphosate, while the peroxidase-like activity of bCDs/Cu2+ decreased and resulted in the generation of fewer oxTMB, accompanied by a lighter blue color. The sensing platform was successfully applied to the determination of glyphosate in real samples of lake water and cabbage, demonstrating reliable and sensitive performance in practical applications.

Sensing of organophosphorus pesticides by fluorescent complexes based on purine-hydrazone receptor and copper (II) and its application in living-cells imaging

In this study, we used purine hydrazone derivatives and coumarin aldehyde to synthesize a novel fluorescent sensor (EDTP) by Schiff base reaction, which exhibited significant selective fluorescence quenching of Cu²⁺, and a distinct change from brilliant yellow to red is present along with the solution color. The detection limit of EDTP for Cu²⁺ was 109.52 nM. Job's plot experiment, density flooding theory (DFT) and ¹H NMR titration experiments revealed the possible binding mechanism of EDTP to Cu²⁺, the probe EDTP could achieve highly detection of Cu²⁺ through forming a 1:1 complex. Additionally, this new fluorescent sensor EDTP-Cu²⁺ can be further applied in the rapid and selective detection of pesticide residues in solutions. When the EDTP-Cu²⁺ system was subsequently exposed to organophosphorus pesticides (glyphosate and glufosinate-ammonium), it was observed that the fluorescence was recovered and accompanied by a red to yellow color change. This may be attributed to the strong chelation of glyphosate and glufosinate-ammonium with Cu²⁺, leading to the dissociation of the EDTP-Cu²⁺ system and thus triggering the fluorescence recovery effect. The detection limits of the EDTP-Cu²⁺ system is 2.48 nM for glyphosate and 17.23 nM for glufosinate-ammonium, respectively. Finally, the developed sensor system has been successfully utilized image glyphosate and glufosinate-ammonium fluorescence in living cells. Purine fluorescence probes are a potential fluorescent probe for the detection of metal ions and pesticides due to their good characteristics. This study opens up a new way for the detection of fluorescent probes in pesticides.

Ultrathin C3N4 nanosheets-based oxidase-like 2D fluorescence nanozyme for dual-mode detection of organophosphorus pesticides

Engineering efficient dual-mode portable sensor with built-in cross reference correction is of great significance for onsite reliable and precise detection of organophosphorus pesticides (OPs) and evading the false-positive outputs, especially in emergency case. Currently, most nanozyme-based sensors for OPs monitoring primarily replied on the peroxidase-like activity, which involved unstable and toxic H₂O₂. In this scenario, a hybrid oxidase-like 2D fluorescence nanozyme (PtPdNPs@g-C₃N₄) was yielded by in situ growing PtPdNPs in the ultrathin two-dimensional (2D) graphitic carbon nitride (g-C₃N₄) nanosheet. When acetylcholinesterase (AChE) hydrolyzed acetylthiocholine (ATCh) to thiocholine (TCh), it ablated O₂^-• from the dissolved O₂ catalyzed by PtPdNPs@g-C₃N₄'s oxidase-like activity, hampering the oxidation of o-phenylenediamine (OPD) into 2,3-diaminophenothiazine (DAP). Consequently, with the increasing concentration of OPs which inhibited the blocking effect by inactivating AChE, the produced DAP caused an apparent color change and a dual-color ratiometric fluorescence change in the response system. Through integrating into a smartphone, a H₂O₂-free 2D nanozyme-based onsite colorimetric and fluorescence dual-mode visual imaging sensor for OPs was proposed with acceptable results in real samples, which holds vast promise for further development of commercial point-of-care testing platform in early warning and controlling of OPs pollution for safeguarding environmental health and food safety.

Engineering an Ag/Au bimetallic nanoparticle-based acetylcholinesterase SERS biosensor for in situ sensitive detection of organophosphorus pesticide residues in food

Developing simple, efficient, and inexpensive method for trace amount organophosphorus pesticides' (OPs) detection with high sensitivity and specificity is of significant importance for guaranteeing food safety. Herein, an Ag/Au bimetallic nanoparticle-based acetylcholinesterase (AChE) surface-enhanced Raman scattering (SERS) biosensor was constructed for in situ simple and sensitive detection of pesticide residues in food. The principle of this biosensor exploited 4-mercaptophenylboronic acid (4-MPBA)-modified Ag/Au bimetallic nanoprobes as SERS signal probe to improve sensitivity and stability. The combination of AChE and choline oxidase (CHO) can hydrolyze acetylcholine (ATCh) to generate H₂O₂. The product of H₂O₂ selectively oxidizes the boronate ester of 4-MPBA, decreasing the Raman intensity of the B-O symmetric stretching. In the presence of OPs, it could inhibit the production of H₂O₂ by destroying the AChE activity, so the reduction of the SERS signal was also alleviated. Based on the principle, an Ag/Au bimetallic nanoparticle-based AChE SERS sensor was established without any complicated pretreatments. Benefiting from the synergistic effects of Ag/Au bimetallic hybrids, a linear detection range from 5×10^-9 to 5×10^-4 M was achieved with a limit of detection down to 1.7×10^-9 M using parathion-methyl (PM) as the representative model of OPs. Moreover, the SERS biosensor uses readily available reagents and is simple to implement. Importantly, the proposed SERS biosensor was used to quantitatively analyze OP residues in apple peels. The levels of OPs detected in real samples by this method were consistent with those obtained using gas chromatography-mass spectrometry (GC-MS), suggesting the proposed assay has great potential applications for OPs in situ detection in food safety fields.

Recent Advances in the Recognition Elements of Sensors to Detect Pyrethroids in Food: A Review

The presence of pyrethroids in food and the environment due to their excessive use and extensive application in the agriculture industry represents a significant threat to public health. Therefore, the determination of the presence of pyrethroids in foods by simple, rapid, and sensitive methods is warranted. Herein, recognition methods for pyrethroids based on electrochemical and optical biosensors from the last five years are reviewed, including surface-enhanced Raman scattering (SERS), surface plasmon resonance (SPR), chemiluminescence, biochemical, fluorescence, and colorimetric methods. In addition, recognition elements used for pyrethroid detection, including enzymes, antigens/antibodies, aptamers, and molecular-imprinted polymers, are classified and discussed based on the bioreceptor types. The current research status, the advantages and disadvantages of existing methods, and future development trends are discussed. The research progress of rapid pyrethroid detection in our laboratory is also presented.

Recent advances and perspectives of enzyme-based optical biosensing for organophosphorus pesticides detection

The overuse or abuse of organophosphorus pesticides (OPs) can bring about severe contamination problems in foodstuff and the environment, which will seriously threaten human health and the ecosystem's cycle. Hence, it is in high demand to establish sensitive, portable, specific, and cost-effective methods for monitoring OPs to control food safety, protect the ecosystem, and prevent disease. The optical biosensor with enzyme as bio-recognition elements has been an effective alternative for OPs detection. Herein, we firstly introduce various enzymes, sensing mechanisms, advantages and disadvantages used as bio-recognition elements in optical sensing for OPs detection. Then, we review various optical biosensing strategies based on enzymes as recognition elements that were ingeniously designed and successfully utilized for OPs detection, with a particular emphasis on photoluminescence (PL), chemiluminescence (CL), electrochemiluminescence (ECL), and colorimetric (CM) biosensing strategies. We not only highlight the state-of-art developments and the construction strategies of the enzyme-based optical biosensing method but also summarize the existing deficiencies, current challenges, and the future perspectives of OPs detection.

Recent Advances on Detection of Insecticides Using Optical Sensors

Insecticides are enormously important to industry requirements and market demands in agriculture. Despite their usefulness, these insecticides can pose a dangerous risk to the safety of food, environment and all living things through various mechanisms of action. Concern about the environmental impact of repeated use of insecticides has prompted many researchers to develop rapid, economical, uncomplicated and user-friendly analytical method for the detection of insecticides. In this regards, optical sensors are considered as favorable methods for insecticides analysis because of their special features including rapid detection time, low cost, easy to use and high selectivity and sensitivity. In this review, current progresses of incorporation between recognition elements and optical sensors for insecticide detection are discussed and evaluated well, by categorizing it based on insecticide chemical classes, including the range of detection and limit of detection. Additionally, this review aims to provide powerful insights to researchers for the future development of optical sensors in the detection of insecticides.

An Overview on the Mechanisms and Applications of Enzyme Inhibition-Based Methods for Determination of Organophosphate and Carbamate Pesticides

Acetylcholinesterase inactivating compounds, such as organophosphate (OP) and carbamate (CM) pesticides, are widely used in agriculture to ensure sustainable production of food and feed. As a consequence of their applications, they would result in neurotoxicity, even death. In this essence, the development of enzyme inhibition methods still shows great significance as rapid detection techniques for on-site large-scale screening of OPs and CMs. Initially, mechanisms and applications of various enzyme-inhibition-based methods and devices, including optical colorimetric assay, fluorometric assays, electrochemical biosensors, rapid test card, and microfluidic device, are highlighted in the present overview. Further, to enhance the enzyme sensitivity for detection; alternative enzyme sources or high yield enrichment methods (such as abzyme, artificial enzyme, and recombinant enzyme), as well as enzyme reactivation and identification, are also addressed in this comprehensive overview.

A dual-mode nanoprobe for the determination of parathion methyl based on graphene quantum dots modified silver nanoparticles

We developed a highly sensitive and selective method for double-signal analysis (fluorescence and ultraviolet-visible spectrophotometry) of organophosphorus pesticides (OPs), based on reversible quenching of graphene quantum dots (GQDs; fluorophores) with silver nanoparticles (AgNPs; absorbers). We used acetylcholinesterase to catalytically convert acetylthiocholine into thiocholine. In turn, by competitive binding to the AgNPs, the produced thiocholine displaces AgNPs from the GQDs and thus induces fluorescence recovery. However, OP analytes inhibit the activity of acetylcholinesterase and, in so doing, retain the silver-graphene nanoparticle complex and fluorescence quenching. The degree of quenching is proportional to the concentration of OPs; the detection limit is as low as 0.017 μg/L. The ultraviolet-visible absorption of GQDs/AgNPs at 390 nm decreases-because of AgNP aggregation that occurs after desorption from the GQDs-and the absorbance is linearly proportional to the OP concentration. Our system has good selectivity to substances that are commonly present in water and vegetables. We successfully applied our method to OP analysis in water, apple, and carrot samples.

Research progress in the development of organic small molecule fluorescent probes for detecting H2O2

Hydrogen peroxide (H2O2), as an important signaling molecule during biological metabolism, is a key member of the reactive oxygen species (ROS) family. The excess of H2O2 will lead to oxidative stress, which is a crucial factor in the production of various ROS-related diseases. In order to study the diverse biological roles of H2O2 in cells and animal tissues, many methods have been developed to detect H2O2. Recently, fluorescence imaging has attracted more and more attention because of its high sensitivity, simple operation, experimental feasibility, and real-time online monitoring. Based on the response group, this study will review the research progress on hydrogen peroxide and summarizes the mechanisms, actualities and prospects of fluorescent probes for H2O2.

Ligand exchange reactions on citrate-gold nanoparticles for a parallel colorimetric assay of six pesticides

A rapid parallel colorimetric method was developed for identification of six pesticides (acephate, phenthoate, profenofos, acetamiprid, chlorothalonil and cartap) via ligand exchange reactions on citrate-gold nanoparticles.