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Organophosphates (OPs) and carbamates as insecticides, nematicides, fungicides, and herbicides are constantly increasing. Their neurotoxic nature requires careful usage, and misuse can lead to fatalities. OPs classified as 'Class 1′ toxic compounds irreversibly inhibit cholinesterases due to their molecular structure resembling the natural acetylcholine substrate, leading to toxic events in the human brain. Monitoring such chemicals is relevant for agricultural applications and essential for the military sector to ensure the safety of personnel and civilian populations. State-of-the-art analytical detection methods require time-consuming pre-treatments and costly reagents and face challenges associated with pesticide properties like thermal lability, low volatility, and high polarity, which can compromise analysis performance. Advanced systems like electrophoresis or liquid chromatography are used to address these, but these are not well suited for field analysis. Miniaturized colorimetric assays are becoming more popular for various portable devices and kits (i.e., metabolic or blood cell assays) due to their ease of use and practicality. Here, we aimed to establish and optimize a straight-forward paper-based microfluidic acetylcholine esterase inhibition assay for mobile organophosphate detection, laying the groundwork for future microdevice modules to be used in environmental monitoring, public health, and CBRN applications. • Characterization of a microfluidic paper-based acetylcholine inhibition assay parameters for quantitative malathion detection. • Transfer of the optimized protocol to a single-step multiplexed microfluidic device with prestored enzyme and chromogen reservoirs. • Proof-of-concept microdevice study on the inhibitory potential of the organophosphate malathion. [ABSTRACT FROM AUTHOR]

The development of deployable biosensors that monitor the cumulative dose of toxic pesticides is essential to enable monitoring of soil and water exposure in populated areas. Liquid crystal elastomers (LCEs) offer unique potential as cumulative dose biosensors due to their ability to store chemical information within the polymer network that can later be decoded in the form of quantifiable shape changes. Here, we present an LCE-based biosensor for the detection of the organophosphorus pesticide malathion through the immobilization of the hydrolytic enzyme pig liver esterase (PLE). Exposure to malathion was detected via shape change of the LCE from a flat ribbon to a helical structure. Quantification of the helical pitch provided a label free readout that correlated directly with the cumulative dose of malathion and enabled detection of successive doses independent of dosage timing or dilution. The cumulative dose was chemically encoded in the LCE and could be decoded by hydration, even after successive drying and rehydration steps. Importantly, the signal from the LCE was largely insensitive to sensing conditions and to interference from various chemicals. The combined results illustrate the utility of biocatalytic LCEs for monitoring harmful pollutants while allowing continuous and cumulative dose sensing in real-world conditions. [Display omitted] • LCE-based biosensor for malathion detection using pig liver esterase. • Label-free shape-change readout by measuring the ribbon helical pitch. • Malathion cumulative dose is chemically encoded in LCE. • Output can be rapidly encoded/decoded by drying/hydration of LCE. [ABSTRACT FROM AUTHOR]

The combination of electrochemiluminescence (ECL) and molecularly imprinted polymer (MIP) techniques offers distinct for detecting organophosphorus pesticides (OPs). Herein, a novel flake-like nanocomposites Au@Cu:ZIF-8 was successfully synthesized, as to design a molecularly imprinted electrochemiluminescence (MIP-ECL) sensor for the detection of malathion (MAL). The doped Cu2+ as a co-reaction promoter facilitated the generation of the active intermediate SO 4 •− for the cathodic reaction system with K 2 S 2 O 8 as the co-reactant, while AuNPs were used as an excellent catalyst, further enhancing the ECL strength of the overall reaction system. Subsequently, MIP film was formed by the electropolymerization of Benzo[1,2-b:4,5-b′]dithiophene-4,8-dione as a functional monomer and MAL as a template molecule on the electrode surface. Confirmation of this process was achieved through molecular docking technique, which indicated that template molecule and functional monomer were tightly bound through non covalent bonds. The ECL signal was controlled by the elution and incubation of MAL by the MIP, thus establishing a novel method for MAL detection. The sensor showed a good linear relationship in the range of 10 pg/mL to 0.1 μg/mL with a detection limit of 0.18 pg/mL (S/N = 3). Furthermore, the recoveries of MAL detection in apple, cabbage and tomato samples ranged from 91.94% to 104.50%, indicating that the sensor offers potential applications for trace analysis of OPs in food and agricultural products. [Display omitted] • A molecularly imprinted electrochemiluminescence sensor for the detection of malathion was developed. • Co-reaction promoter and noble metal nanoparticles increased sensitivity of sensor. • Interactions between template molecules and functional monomers were verified by molecular docking technique. • Molecularly imprinted polymer exhibited excellent selectivity for malathion. • The linear detection range was 10 pg/mL to 0.1 μg/mL with a detection limit of 0.18 pg/mL. [ABSTRACT FROM AUTHOR]

Highlights • The electrodeposition synthesis of PDA-AuNPs improved the biocompatibility and electrical conductivity of the sensor. • The combination of dual-signal design and Exo I amplification made the biosensor highly sensitive to malathion. • The proposed sensor showed a wide linear range from 0.5 to 600 ng/L malathion. Abstract A highly sensitive dual-signal aptamer sensor based on polydopamine-gold nanoparticles (PDA-AuNPs) and exonuclease I (Exo I) was developed for detection of malathion. Compared with traditional sensing elements, aptamer has many advantages, such as high affinity, superior specificity, strong stability and easy modification. The electrodeposition synthesis of PDA-AuNPs gave excellent biocompatibility and electrical conductivity on the sensor. With the addition of malathion, the specific interaction between malathion and its aptamer forced the aptamer to detach from the electrode surface and induced the capture probe to form a hairpin structure on the electrode surface. Exo I was added to motivate the autocatalytic target cycling which remarkably increased the current change of electrochemical signal over 2 times. Therefore, the promising strategy gave rise to an optional dual-signal current readout in both the signal-on of Fc and the signal-off of Tn. In this work, the prepared biosensor exhibited high sensitivity to malathion via the combination of dual-signal design and autocatalytic target cycling amplification. Under the optimized conditions, the proposed sensor showed a wide linear range from 0.5 to 600 ng/L malathion. It also exhibited excellent specificity, acceptable repeatability and good stability. The application of real samples obtained satisfactory recovery results, demonstrating a promising potential in food safety analysis. [ABSTRACT FROM AUTHOR]

A non-enzymatic electrochemical sensor based on bimetallic Cu-Co metal-organic gel (MOG) modified glassy carbon electrode (GCE) was reported to achieve super-sensitive malathion detection. Phytic acid-based Cu-Co bimetallic MOG (PA-Cu-Co composite) is a kind of three-dimensional porous material and has a large surface area and superior conductivity due to crosslinked network structure and bimetal composition. The obtained PA-Cu-Co/GCE sensor can easily bond malathion due to the good affinity between Cu element and sulfur groups of malathion, leading to an inhibited redox signal of Cu element in presence of malathion. The electrode reaction was a typical adsorption controlled process. The introduction of Co element not only greatly improves the electron transfer ability but increases surface area and active sites of sensor interface for high affinity of malathion, thus endowing PA-Cu-Co composite with outstanding sensitivity and selectivity. Under optimized operating conditions, the enzyme-free PA-Cu-Co/GCE malathion sensor exhibits good stability and excellent detection performance, with a wide linear range to malathion of 0.5 pM to 5 μM and low detection limit of 0.3 pM. Furthermore, the PA-Cu-Co/GCE sensor showed good recovery in real samples detection, implicating the potential applicability of PA-Cu-Co/GCE sensor in sensitive and selective detection of organophosphorus pesticides (OPs). • 3D porous Cu-Co MOGs. • Large surface area and abundant active sites. • LOD is 0.3 pM. [ABSTRACT FROM AUTHOR]

The high residual nature of organophosphorus pesticides poses a potential risk to the environment and human health through bioaccumulation. Herein, by using Fe 3 O 4 nanoclusters (NCs) as the nucleation center and polyvinyl pyrrolidone as the stabilization layer, Cu-based metal-organic frameworks (Cu-MOFs) were directly grown around Fe 3 O 4 NCs to form core-shell Fe 3 O 4 @Cu-MOFs composites (FCF). Then, the fluorescence properties of FCF were used to construct a fluorescence biosensor for the detection of organophosphorus pesticide residues in vegetables. The bi-enzyme function between acetylcholinesterase and choline oxidase can produce hydrogen peroxide, which can oxidize ferrous ions to ferric ions thus influencing the fluorescence of FCF. Based on the ability of malathion pesticides to inhibit acetylcholinesterase activity, the biosensor demonstrated a linear relationship between the fluorescence intensity and the concentration of the malathion in the range of 5 ng/mL to 50 μg/mL with a detection limit of 4.2 ng/mL. Furthermore, the FCF was combined with agarose gels to realize the visualization detection of malathion. This novel fluorescent nanocomposite offers promising applications for the visual detection of malathion and in situ imaging of vegetables, establishing a new pathway to develop high-performance fluorescent materials for environmental and food safety. • Fe 3 O 4 @Cu-MOFs nanocomposites were synthesized by "bottle-around-ship" strategy. • Fe 3 O 4 @Cu-MOFs nanocomposites exhibited a stable and enhanced fluorescence. • The portable and visual detection of malathion pesticides was realized. • In-situ imaging of pesticide residues on fresh vegetables was performed. [ABSTRACT FROM AUTHOR]

A novel electrochemical biosensor was constructed by anchoring acetylcholine esterase (AChE) onto the core-shell nanostructured composite of hollow carbon spheres coated with needle-like polyaniline (denoted by HCS@PANI), and used for rapid determination of malathion, which was established based on the chemisorption/desorption process of AChE used as an indicator. The uniformly distributed HCS was wrapped with the needle-like PANI nanowires to form the HCS@PANI nanocomposite, which not only exhibits high specific surface area and chemical functionality but also possesses strong electrochemical activity. After AChE was adsorbed onto the HCS@PANI nanocomposite, the electrochemical catalysis of AChE/HCS@PANI-based biosensor towards acetylthiocholine chloride (ATCl) was inhibited in the presence of malathion, which was applied to detect malathion, and the biosensor exhibited a low detection limit of 0.16 ng mL −1 within a linear range from 1.0 ng mL −1 to 10 μg mL −1 of the malathion concentration. Also, the results suggested that the developed electrochemical biosensor showed high selectivity, good reproducibility, and applicability for malathion detection, indicating that the proposed method using the HCS@PANI nanocomposite as the sensitive layer for the AChE immobilization and catalysis of ATCl has potential application in high-sensitive pesticide determinations. [ABSTRACT FROM AUTHOR]

This paper reports a new assay platform that performed in polar organic solutions for ultrasensitive and highly selective detection of isocarbophos pesticide. The sensing system just contains hemin molecules and random ssDNAs. Free hemin molecules have a strong absorption peak at Soret band in polar organic solvents, and they can assemble into few small particles with random ssDNAs via their special π–π stacking interaction. However, the subsequent addition of isocarbophos into above sensing system can aggregate hemin molecules to form many larger particles, which result in a great decrease in absorbance value of sensing solution. UV/Vis absorption spectra and scanning probe microscope (SPM) were used to characterize hemin aggregation. Additionally, the effects of some parameters like type of solvents, hemin amount and random ssDNAs on the sensing platform were also investigated. The present assay platform has a detection limit as low as 0.2 μg/L, a dynamic range of 0.5–500 μg/L, and high selectivity over other competitive pesticides. Moreover, the assay platform also displays excellent stability and accuracy in the detection of spiked real samples, suggesting that such sensing platform will play an important role in biological and environmental detection. [ABSTRACT FROM AUTHOR]

Nanozymes have drawn lot of attention as they overcome the limitations of natural enzymes and present a more robust alternative. Herein, the potential of Gold nanorods (GNRs) as nanozyme or enzyme mimetics is investigated. The detailed catalytic parameters of GNRs are studied and compared with other gold nanostructures (+ve and −ve nanoparticles) and horseradish peroxidase (HRP). Gold nanorods of 2.8 aspect ratio were synthesized and demonstrated to have 2.5 times higher peroxidase activity than HRP and +ve gold nanoparticles. GNRs are found to be robust enzyme mimetics displaying stability over a wide range of pH and temperature. Proof of concept is demonstrated for developing a simple, colorimetric inhibition assay for malathion using GNRs as nanozyme. The assay shows an inverse relationship between GNRs catalytic activity and malathion concentration. The sensitivity of the assay is 1.78 μg/mL and the assay is specific with <0.01% cross-reaction with organosphosphates and metal salts. The study presents the intrinsic catalytic potential of GNRs for the first time and its subsequent use thereof for developing an assay for malathion. [ABSTRACT FROM AUTHOR]

This work will show, for the first time, the absorptive silica-supported polyaniline (PANI) molybdenum trioxide (MoO 3) semiconductor hybrid coating onto the optical fiber realizing the concept of lossy mode resonance (LMR) incorporated with molecular imprinting (MIP)-based sensors. The unique optical absorptive and imprinting (IP) properties and possessing a proper refractive index, introducing a versatile optical transducer, were assessed in the detection of Malathion (MAL) to address the rising concern of pesticide residue in crops. The accurate structural and morphological characterization confirmed the rough crystalline and spherical particles for a ternary composite of PANI, SiO 2 , and MoO 3 onto an optical fiber curved surface while spectroscopic analysis confirms the formation of imprinting polymer and desirable absorbance characteristics. The experimental and numerical sensing studies revealed that the proposed sensing probe allows the rapid adsorption/desorption of MAL to the sensing films and highly permeable coating under studying the effective parameters influence. The optimized probe exhibits an excellent performance with the maximum sensitivity of within 14–224 µM with the linearity coefficient of R2 = 0.99 possessing a low limit of detection of 9.1 nM. Additionally, this sensor selectively detects. in the presence of other real species and also showed good recovery in the various corps samples. [Display omitted] • The absorptive MoO 3/ PANI hybrid was successfully coated onto the optical fiber. • This work is realizing the concept of LMR incorporated with MIP-based sensors. • Operating fabrication parameters were fully optimized to detect Malathion. • An excellent performance obtained within 14–224 µM and R2 = 0.99 with LOD 9.1 nM. • This work could be further extended to detect other pesticides in aqueous media. [ABSTRACT FROM AUTHOR]

This study establishes an incredibly simple method for trace detection of malathion (MLT) by using spherical Ag nanoparticles (Ag NPs) based on surface enhanced Raman scatting (SERS). MLT was rapidly hydrolyzed through β-elimination reaction under alkaline condition, then provided a favorable ionic environment for SERS detection by using Lewis acids (LAs), leading to a 305 times maximum additional enhancement, and a limit of detection (LOD) as low as 0.1 ppb was achieved. The different alkaline hydrolysis pathways of MLT and other dithiophosphate organophosphorus molecules was clarified, and the conversion of molecular binding states on nano-surface were determined. The method was successfully applied in various tea samples, a LOD as low as 0.05 ppm was obtained. Due to the complex variation of characteristic peaks intensity, multivariate analysis method was used for quantitative analysis and a high determination coefficient (R2 =0.9573) and good dynamic range of 0.1–5 ppm were obtained. [Display omitted] • SERS sensitivity of MLT in alkaline hydrolysis condition was improved by using Lewis acids. • The alkaline hydrolysis of MLT followed β-elimination reaction rather than S N 2 reaction. • The characteristic peaks intensities were influenced by the binding model on the nano-surface. • Malathion in tea was detected within 5 min with a LOD of 0.05 ppm. • MVA was more suitable for quantitative analysis in multiple characteristic peaks. [ABSTRACT FROM AUTHOR]

Detection and discrimination of several organophosphorus pesticides in water using a colorimetric probe array containing twelve dyes has been achieved. A clear discrimination for malathion, leptophos, dichlorvos, dibrom and diazinon was observed. The array was used to determine the concentration of diazinon in orange leaves. [ABSTRACT FROM AUTHOR]

Abstract: A new electrochemical sensor based on hybrid nanocomposite consisting of copper oxide nanowires (CuO NWs) and single-walled carbon nanotubes (SWCNTs) was first developed for the detection of organophosphorus pesticides (OPs). The surface morphology, chemical composition and crystal structure of the hybrid nanocomposite were studied by SEM and XRD. The hybrid nanocomposite was highly stable and possessed special affinity for malathion, thus providing the basis for facile electrochemical quantification of malathion. The electrochemical behavior of the hybrid nanocomposites based sensor and its application for pesticides determination were first evaluated through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Under optimized operational conditions, differential pulse voltammetry (DPV) was further employed for malathion detection, which shows a wide dynamic range with a limit of detection as low as 0.1ppb (0.3nM), good selectivity against other common pesticides, inorganic ions and sugars, as well as good stability and reproducibility. Its application for malathion-spiked liquid garlic samples was also demonstrated. These features implicate the potential applicability of CuO NWs–SWCNTs hybrid nanocomposites in sensitive and selective detection of organophosphorus pesticides. [Copyright &y& Elsevier]

Malathion is widely applied in agriculture as one of organophosphorus pesticides (OPs) and easily causes a number of health and environmental problems. Traditional methods for analyzing malathion residues have failed to meet the current requirements of detection. To address this challenge, we designed a colorimetric-based single particle detection (SPD) method to quantify malathion using MnO 2 -coated gold nanoparticles (GNP@MnO 2 NPs) as the probe. In the existence of alkaline phosphatase (ALP), p-aminophenyl phosphate (p-APP) can be hydrolyzed to p-aminophenol (p-AP), which employs as a reductant to induce MnO 2 to Mn2+ and make the gold core exposure. With the dark field optical microscopy (DFM), the color change of the probe can be readily observed at the single particle level. However, malathion is able to inhibit the activity of ALP and makes the color of the probe remain. Thus, the content of malathion can be accurately quantified by monitoring the changes in color and scattering intensity of the probe. The linear range of this assay is 0.001–0.1 ng/mL and the limit of detection (LOD) is as low as 0.82 pg/mL. In addition, degradation of malathion can be achieved due to the interaction between malathion and ALP. Therefore, this strategy offers new insights on the design of an ultrasensitive assay for OPs detection and degradation in the future. • A colorimetric-based single particle detection method was developed to quantify malathion. • This assay was achieved by the inhibition of ALP activity with malathion. • The detection limit can reach 0.82 pg/mL. [ABSTRACT FROM AUTHOR]

Malathion is widely applied in agriculture as one of organophosphorus pesticides (OPs) and easily causes a number of health and environmental problems. Traditional methods for analyzing malathion residues have failed to meet the current requirements of detection. To address this challenge, we designed a colorimetric-based single particle detection (SPD) method to quantify malathion using MnO 2 -coated gold nanoparticles (GNP@MnO 2 NPs) as the probe. In the existence of alkaline phosphatase (ALP), p-aminophenyl phosphate (p-APP) can be hydrolyzed to p-aminophenol (p-AP), which employs as a reductant to induce MnO 2 to Mn2+ and make the gold core exposure. With the dark field optical microscopy (DFM), the color change of the probe can be readily observed at the single particle level. However, malathion is able to inhibit the activity of ALP and makes the color of the probe remain. Thus, the content of malathion can be accurately quantified by monitoring the changes in color and scattering intensity of the probe. The linear range of this assay is 0.001–0.1 ng/mL and the limit of detection (LOD) is as low as 0.82 pg/mL. In addition, degradation of malathion can be achieved due to the interaction between malathion and ALP. Therefore, this strategy offers new insights on the design of an ultrasensitive assay for OPs detection and degradation in the future. • A colorimetric-based single particle detection method was developed to quantify malathion. • This assay was achieved by the inhibition of ALP activity with malathion. • The detection limit can reach 0.82 pg/mL. [ABSTRACT FROM AUTHOR]

Abstract: We report on a novel approach for the detection of toxic organophosphorus (OP) compounds using electrochemical and fluorescence spectroscopy. An electrochemical sensor device that employs gold (Au) interdigitated electrodes (IDT) on a glass substrate was used for the electrical impedance spectroscopy (EIS) of various OP compounds. Picomolar level detection of ethion, malathion, parathion and fenthion was made possible through EIS performed in the presence of benzodipyrido [3,2-a:2′3′-c] phenazine (BDPPZ). Quantitative detection of ethion, malathion, parathion and fenthion, based on different optical signals produced in the emission spectra, was obtained through fluorescence titration spectroscopy for concentrations as low as 1pM, 1nM, 1μM and 10μM, respectively. [Copyright &y& Elsevier]

Abstract: A facile, one-step synthesis of nanocomposites using multiwalled carbon nanotube coating gold nanoparticles (MWCNTs-Au) was presented. Scanning electron microscopy and UV–vis spectroscopy confirmed that more than 97% of gold nanoparticles have been loaded on the surface of carbon nanotubes without congregation. The formed MWCNTs-Au nanocomposites offered an extremely hydrophilic surface for biomolecule adhesion, leading to a stable acetylcholinesterase (AChE) biosensor. Due to the excellent conductivity of the nanocomposites, the immobilized AChE showed favorable affinity to acetylthiocholine (ATCl) and could catalyze the hydrolysis of ATCl with a value of 268μM to form thiocholine, which was then oxidized to produce a detectable and fast response. Based on the inhibition of organophosphates (OPs) on the enzymatic activity of AChE, the magnitude of peak current from thiocholine on the biosensor is a simple and effective way to biomonitoring of OPs exposure. Using malathion as a model compound, the inhibition of malathion was proportional to its concentration ranging from 1.0 to 1000ngmL−1 and from 2 to 15μgmL−1, with a detection limit 0.6ngmL−1. The developed biosensor exhibited good reproducibility and acceptable stability, thus providing a new promising tool for analysis of enzyme inhibitors. [Copyright &y& Elsevier]

[Display omitted] • Introduce a sensing system for extract and colorimetric assay of malathion as a model of organophosphorus pesticide. • A new malathion colorimetric sensor based on Cu@Ag was developed. • The sensitivity of recognizer Cu@Ag nanoparticles toward malathion was improved in the presence of NaCl. • Recognition naked eye card for different concentration of malathion was designed. • The proposed method was applied for determination of malathion in real environmental samples. In this work, a system was developed for the extraction and colorimetric assay of malathion as a model of organophosphorus pesticide in the environmental sample matrixes. In this regard, graphene oxide (GO) was synthesized from sugar beet bagasse and applied to produce Fe 3 O 4 /GO adsorbent. Subsequently, the prepared adsorbent was employed for magnetic solid phase extraction (MSPE) of malathion. MSPE was performed by the investigation of the influence of some key independent variables including sorbent dosage, extraction time and pesticide concentration. The extraction experiments were designed by Central Composite Design (CCD) under Response Surface Methodology (RSM) by Design-Expert software. Then, the extracted malathion was quantified by colorimetric detection method using Cu@Ag nanoparticles in optimum colorimetric conditions (including reaction time: 45 min, pH of sensor: 7 and NaCl concentration: 0.1 M). Results revealed that the preconcentration process was successfully achieved in a sorbent dosage of 0.2 g/L, extraction time of 6.85 min and pesticide concentration of 250 μg/L. The colorimetric response of A570/A400 was linear in the range of 0.001–5 mg/L (R2 = 0.9925). The sensing mechanism of malathion was based on the aggregation of Cu@Ag nanoparticles in the presence of malathion. Moreover, the naked-eye detection was shown by obvious color change of Cu@Ag core-shell from brassy yellow to purple-grayish, which leads to design naked-eye recognition card for sensing malathion. The detection limit of this method was 0.014 mg/L. The method was successfully applied for the detection of malathion in the environmental samples. [ABSTRACT FROM AUTHOR]

Abstract: One-step electrochemical deposition of gold nanoparticles (AuNPs) in chitosan hydrogel onto a planar gold electrode was used to create a favorable surface for the attachment of the enzyme acetylcholinesterase (AChE). AChE exhibited high affinity to its substrate of acetylthiocholine chloride (ATCl) from calculated Michealis–Menten constant () of 0.309mM. Thiocholine, the product through AChE-catalyzed hydrolysis of ATCl, could be chemisorbed on the surface with an applied potential of −0.7V and then desorbed in KOH solution, giving a measurable peak current. When enzymatic activity was inhibited by organophosphate pesticides, the amount of chemisorpted thiocholine on the interface was anticipated to decrease. As a result, a simple method for rapid determination of malathion was established based on the chemisorption/desorption process of thiocholine used as an indicator. Under the optimal conditions, the decrease in response was proportional to the concentration of malathion from 0.1 to 20ngmL−1, with detection limit of 0.03ngmL−1 (0.1nM). The method based on one-step electrochemical deposition and chemisorption/desorption process of thiocholin has potential application in high-sensitive pesticide determinations. [Copyright &y& Elsevier]

[Display omitted] • Improved oxidase-mimetic catalytic activity of Ag 3 PO 4 /UiO-66. • Malathion rapidly adsorbs onto Ag 3 PO 4 /UiO-66 surface and inhibits its activity. • Colorimetric sensing of malathion completely free from bioenzymes. • A chromogenic hydrogel-based smartphone sensing system for pesticide analysis. Detection of pesticide residues is important because it is related to food and environmental safety. Although lots of sensors have been developed and applied for pesticide analysis, most of them rely on the use of vulnerable bioenzymes, weakening the highlights of these sensors. Here we recommend a bioenzyme-free colorimetric assay of malathion, a typical organophosphorus pesticide, based on the analyte inducing the oxidase-mimicking activity loss of Ag 3 PO 4 /UiO-66. Compared to counterparts, the Ag 3 PO 4 /UiO-66 composite can provide enhanced oxidase-mimetic catalytic activity to trigger the 3,3′-tetramethylbenzidine chromogenic reaction with the participation of dissolved O 2. When malathion exists, it rapidly adsorbs onto the composite surface via their unique interactions and significantly shields the oxidase-like activity of Ag 3 PO 4 /UiO-66, thus affecting the catalytic chromogenic reaction. With such a principle, sensing of malathion in a wide linear range (0.0083–5.333 μg/mL) was realized with a detection limit 7.5 ng/mL. Given no biological elements were involved in the proposed assay, it exhibited robust and reliable performance in determining malathion in practical samples. Furthermore, a chromogenic hydrogel-based smartphone sensing system was developed for instrument-free on-site analysis of malathion. With good analytical performance and facile operation, our assay and device will find promising applications in phosphothionate pesticide determination. [ABSTRACT FROM AUTHOR]

• A photoelectrochemical sensor was proposed based on the biocatalysis induced formation of BiOBr/Bi 2 S 3 heterostructures. • Hemin/G-quadruplex structure and MnTMPyP based DNA intercalator were used to construct the HRP-mimicking DNA concatemer. • The reaction of BiOBr nanoflowers with H 2 S resulted in formation of BiOBr/Bi 2 S 3 heterostructures with enhanced photocurrent. • This strategy provided a new efficient signal transduction mechanism for photoelectrochemical sensing methods In this work, we present a highly sensitive photoelectrochemical (PEC) sensing platform for malathion (Mal) detection based on the biocatalysis-induced formation of BiOBr/Bi 2 S 3 semiconductor heterostructures (BIFBSH). Initially, a double-stranded DNA consisting of an initiator strand and the anti-Mal aptamer was immobilized on magnetic beads surface. The target Mal could competitively bind with its aptamer and liberate the initiator strand from the double-stranded DNA. Subsequently, the initiator strand triggered a hybridization chain reaction (HCR) to produce a long DNA concatemer containing the sequence of G-quadruplex structure. The DNA concatemer was then endowed with HRP-like activity via the formation of hemin/G-quadruplex complexes and binding with MnTMPyP. The HCR-synthesized HRP-mimicking DNA concatemer (HSHMDC) was employed to catalyze Na 2 S 2 O 3 conversion to H 2 S with the aid of H 2 O 2. The generated H 2 S could react with BiOBr nanoflowers (BiOBrNFs) modified on an indium tin oxide electrode, resulting in the in situ formation of BiOBr/Bi 2 S 3 heterostructures with enhanced photoelectric conversion efficiency. The BiOBr/Bi 2 S 3 heterostructures could generate a strong photocurrent signal to indicate Mal recognition. Under the optimal conditions, a wide linear range between the Mal concentration and photocurrent intensity (0.001–1000 ng mL−1) and a limit of detection (LOD) as low as 0.12 pg mL−1 were achieved. [ABSTRACT FROM AUTHOR]

• A dual-signal aptamer sensor for simultaneous detection of acetamiprid and malathion was established. • The prepared hollow copper-cobalt-MOF had good catalytic effect on the luminescence of luminol. • Luminol and g-C 3 N 4 generate ECL signals at different potentials for simultaneous detection of two pesticides. A novel hollow copper-cobalt MOF (Cu/Co-MOF) was synthesized by a template method and characterized by SEM, TEM, XRD, and XPS techniques. The hollow Cu/Co-MOF was used to load the luminol and significantly enhanced the ECL signal of the luminol by catalyzing H 2 O 2 to produce more O 2 −. Meanwhile, a dual-signal electroluminescence (ECL) aptasensor was established based on the ECL signal of luminol and graphite-like carbon nitride nanosheet (g-C 3 N 4). The dual-signal was observed at −1.5 and 0.6 V, corresponding to the luminescence signals of g-C 3 N 4 and luminol, respectively. This ECL aptasensor for simultaneous detection of acetamiprid and malathion showed good sensitivity with a linear range of 0.1 μM∼0.1 pM, detection limit of 0.015 pM, and 0.018 pM (S/N = 3), respectively. Furthermore, the aptasensor also exhibited reasonable specificity, repeatability, and stability. The prepared ECL aptasensor was applied for the detection of acetamiprid and malathion in apple and tomato samples. [ABSTRACT FROM AUTHOR]