Concentrations Of Paraoxon Research Articles

Reduction and Degradation of Paraoxon in Water Using Zero-Valent Iron Nanoparticles

Paraoxon is an emerging organophosphate pollutant that is commonly used as a pesticide and a drug, hence increasing the risk of contamination of water supplies. Its intensive use for vector control has led to pollutions in soil and water. Paraoxon is very toxic, with an LD50 of 2 to 30 mg/kg in rats. It can be metabolized in the body from parathion; thus, exposure can lead to serious health effects. In this study, zero valent iron (Fe°/ZVI NPs) nanoparticles were synthesized and investigated for the degradation of Paraoxon, a chemical warfare agent and insecticide, in an aqueous solution. The effects of solution pH, initial pollutant concentration, ZVI NPs dosage and contact time on mineralization efficiency were examined. Batch experiments demonstrated that 15 mg L−1 of Paraoxon was mineralized at degradation efficiencies of 75.9%, 63.9% and 48.9% after three-hour treatment with 6.0, 4.0 and 2.0% w/v Fe°, respectively. The calculated kinetic rate constant kobs was 0.4791 h−1, 0.4519 h−1 and 0.4175 h−1 after treating 10, 15 and 20 mg L−1 of Paraoxon solution with 6.0% w/v Fe, respectively. The degradation dynamics were described by the first-order kinetic law as evidenced by rate constants independent of the initial Paraoxon concentration. The degradation efficiency was strongly dependent on pH, increasing with a decrease in pH, with maximum removal at pH 4. p-nitrophenol was detected as a degradation product, suggesting cleavage of the O-P bond and hydrolysis as possible reaction processes. This study showed that Fe° particles have the potential for degrading Paraoxon.

Aqueous suspensions of Fuller’s earth potentiate the adsorption capacities of paraoxon and improve skin decontamination properties

Fuller’s earth (FE) is a phyllosilicate used as a powder for household or skin decontamination due to its adsorbent properties. Recent studies have shown that water suspensions exhibit similar adsorbent capacities. FE is heterogeneous due to its composition of elementary clay aggregates and heavy metal particles. Here, FE toxicity was assessed in vitro on skin cells and in vivo on Danio rerio embryos. Among the suspensions tested (5%, 9.1% and 15% w/w), only the highest one shows weak toxicity. Suspensions were tested for ex vivo dermal decontamination into pig ear skin and human abdominal skin using diffusion cells and paraoxon as organophosphorus contaminant. After 24 h of diffusion, no difference was observed in the paraoxon concentration in the receptor compartment whether the decontamination was carried out with FE in powder or in suspension form. In presence of FE suspensions, we observed the disappearance of paraoxon from the stratum corneum, the reservoir compartment, independently of the suspensions’ concentration. We suggest that water potentiates the absorbing capacities of FE powder by intercalating between clay lamellas leading to the appearance of new adsorption zones and swelling. These data support the use of FE aqueous suspensions as a safe tool for organophosphorus skin decontamination.

Dual-Signal Readout By Hybrid Nanoflowers for Point-of-Care Ultrasensitive Detection of Organophosphorus Pesticide

Introduction At present precise tracking of pesticide has become very important for safeguarding the environment and food resources owing to their very high toxicity [1]. The development of sensitive and convenient sensors for the sensitive detection of pesticides is imperative to overcome practical limitations encountered in conventional methodologies, which require skilled manpower at the expense of high cost and low portability [2–3]. However, there are increasing bottlenecks in terms of poor stability caused by recognition unit and false positive result induced by single-modal readout, especially the bad performance in on spot monitoring. Herein, taking advantage of all-in-one enzyme-inorganic hybrid nanoflowers (ACC-HNFs) to fabricate high-performance artificial enzyme cascade system, we newly designed a ultrasensitive and affordable lab-on-paper device that incorporated disposable screen-printed carbon electrode (SPCE) and colorimetric test strips, which brought about the dual-modal readout (electrochemical and colorimetric signal) for on-site monitoring of pesticide, achieving an “on-demand” tuning of the detection performance. Method Typically, 200 mmol L– 1 PBS (pH 8.0) contained AChE (1.0 U mL−1) and ChO (2.0 U mL−1) was added to deionized water, then 200 mmol L– 1 CuSO4 was added to the mixture, followed by incubation at 4.0 °C for 18 h. Finally, ACC-HNFs were obtained. ACC-HNFs modified paper was directly added into the detection zone. Then, ACh, TMB, and stop solution was added into different regions in sequence. After paraoxon was introduced into detection zone, region Ⅰ, Ⅱ, and Ⅲ of the detection zone was folded and the fold of each region was maintained for 30 min, then a discernible colorimetric signal was observed with naked eyes in the hollow region. Meanwhile, the entire paper was folded above the electrodes, and the generated electrons can be better connected to the working electrode through the hollow region. All electrochemical measurement processes were performed at room temperature and each measurement was performed in a new disposable SPCE. Before the analysis of the paraoxon, parameters, such as ACh concentration, ACC-HNFs concentration, and incubation time, were further optimized. Amperometric i-t curves were recorded at +100 mV during 30 s. The detection mechanism of this dual-modal biosensor is based on inhibiting the activity of AChE, thus the inhibition rate (I%) can be expressed as a linear relationship with the concentration of paraoxon. I% was analyzed by the following relation:I% = (I no inhibitor – I inhibitor) / (Ino inhibitor ) ×100%Where I no inhibitor and I inhibitor represented the response of ACC-HNFs-TMB and ACC-HNFs-TMB-OPs system, respectively. Results and Conclusions Using paraoxon as a model analyte, the ACC-HNFs-based lab-on-paper platform could reach a limit of detection down to the picogram/mL level (0.06 pg mL−1), which is over 10-fold lower than that of conventional electrochemical assay. This proposed platform possesses the following advantages: (1) In the artificial enzyme cascade system, ACC-HNFs exhibited high catalytic activity by integrating nanozyme and natural enzyme, which remarkably amplified detection signal. (2) This approach integrates electrochemistry and colorimetric patterns into one system for “on-demand” detecting pesticide. The two groups of results can mutually authenticate, which can effectively avoid false positive and negative detection. (3) This portable lab-on-paper device dispenses with complex sample pretreatment or sophisticated instruments, which makes it suitable for on-site monitoring. We anticipated that the meticulous design of ACC-HNFs provided a versatile approach for constructing artificial enzyme as a recognizer and amplifier to fill the gap in constructing robust artificial enzyme systems, making it practically functional for on-site applications in the contamination monitoring and biological diagnosis, just through changing the building blocks.

A comparison of the antidotal effects of three oximes against an organophosphate on chick skeletal muscle

Background: One of the most toxic effects of organophosphorus poisoning (OP) is the paralysis of skeletal muscles. The oximes are a group of available antidotes. This study investigated the effects of different concentrations of paraoxon on the function of skeletal muscle and reversal or prevention of these effects by three different oximes (i.e., pralidoxime, obidoxime, and HI-6). Materials and Methods: This study was conducted based on the chicken biventer cervices (CBC) nerve-muscle preparation and the use of twitch tension recording technique. The twitches of the CBC were evoked by stimulating the motor nerve at 0.1 Hz with pulses of 0.2 msec duration and a voltage greater than that required to produce the maximum response. Moreover, twitches and contractures were recorded isotonically using Grass Biosystems. Results: Paraoxon at 0.1 µM induced a significant increase (more than 100%) in the twitch amplitude, while higher concentrations (0.3 and 1µM) induced partial or total contracture. Therefore, paraoxon at a concentration of 0.1 µ M was used to examine the capability of oximes to prevent or reverse its effects. Pralidoxime, obidoxime, and HI-6 dose-dependently prevented (when it was used as pre-treatment, 20 min before or at the same time of administration of the toxin) and reversed (when it was used as post-treatment, 20 min after the administration of the toxin) the effect of paraoxon. Conclusion: In conclusion, these results revealed that oximes were very useful in the prevention and reversal of the OP toxic effects on the skeletal muscle. Moreover, it was suggested that oximes were more effective when used as pre-treatment. Pralidoxime was more potent than obidoxime and HI-6. The HI-6, which is a newer oxime, was unexpectedly less effective than the other two.

Simple colorimetric detection of organophosphorus pesticides using naturally occurring extracellular vesicles

Organophosphorus pesticides (OPs) are widely used in agriculture to eradicate insects. They, however, have raised public concern with respect to their potential impacts on human health. Here, a simple and sensitive colorimetric strategy was developed for the detection of OPs using acetylcholinesterase (AChE) in naturally occurring extracellular vesicles (EVs). To validate this strategy, the concentration of paraoxon as a representative OP was detected by measuring the colorimetric response in the dynamic range of 10−12–10−4 M, with a limit of detection (LOD) of 53.8 pM. Because EVs, which are composed of lipid bilayers, can provide a protective environment for AChE, the detection of OPs was highly reproducible without significant loss of AChE activity over a 30-day period. Furthermore, a spike-and-recovery experiment in human serum confirmed that despite impurities that may interfere with AChE activity, our EV-based AChE assay would be applicable for real samples in field detection. Importantly, our cost-effective, stable EV-based strategy enables a simple and sensitive OP detection without the expression/integration of AChE, formation of lipids, or encapsulation of AChE into liposomes. Thus, this strategy will offer new prospects for ensuring the safety of environmental and food samples with respect to contamination with various pesticides.

Dual-Signal Readout By Hybrid Nanoflowers for Point-of-Care Ultrasensitive Detection of Organophosphorus Pesticide

Introduction At present precise tracking of pesticide has become very important for safeguarding the environment and food resources owing to their very high toxicity [1]. The development of sensitive and convenient sensors for the sensitive detection of pesticides is imperative to overcome practical limitations encountered in conventional methodologies, which require skilled manpower at the expense of high cost and low portability [2–3]. However, there are increasing bottlenecks in terms of poor stability caused by recognition unit and false positive result induced by single-modal readout, especially the bad performance in on spot monitoring. Herein, taking advantage of all-in-one enzyme-inorganic hybrid nanoflowers (ACC-HNFs) to fabricate high-performance artificial enzyme cascade system, we newly designed a ultrasensitive and affordable lab-on-paper device that incorporated disposable screen-printed carbon electrode (SPCE) and colorimetric test strips (Scheme 1), which brought about the dual-modal readout (electrochemical and colorimetric signal) for on-site monitoring of pesticide, achieving an “on-demand” tuning of the detection performance. Method Typically, 200 mmol L– 1 PBS (pH 8.0) contained AChE (1.0 U mL−1) and ChO (2.0 U mL−1) was added to deionized water, then 200 mmol L– 1 CuSO4 was added to the mixture, followed by incubation at 4.0 °C for 18 h. Finally, ACC-HNFs were obtained. ACC-HNFs modified paper was directly added into the detection zone. Then, ACh, TMB, and stop solution was added into different regions in sequence. After paraoxon was introduced into detection zone, region Ⅰ, Ⅱ, and Ⅲ of the detection zone was folded and the fold of each region was maintained for 30 min, then a discernible colorimetric signal was observed with naked eyes in the hollow region. Meanwhile, the entire paper was folded above the electrodes, and the generated electrons can be better connected to the working electrode through the hollow region. All electrochemical measurement processes were performed at room temperature and each measurement was performed in a new disposable SPCE. Before the analysis of the paraoxon, parameters, such as ACh concentration, ACC-HNFs concentration, and incubation time, were further optimized. Amperometric i-t curves were recorded at +100 mV during 30 s. The detection mechanism of this dual-modal biosensor is based on inhibiting the activity of AChE, thus the inhibition rate (I%) can be expressed as a linear relationship with the concentration of paraoxon. I% was analyzed by the following relation:I% = (I no inhibitor – I inhibitor) / (I no inhibitor ) ×100%Where I no inhibitor and I inhibitor represented the response of ACC-HNFs-TMB and ACC-HNFs-TMB-OPs system, respectively. Results and Conclusions Using paraoxon as a model analyte, the ACC-HNFs-based lab-on-paper platform could reach a limit of detection down to the picogram/mL level (0.06 pg mL−1), which is over 10-fold lower than that of conventional electrochemical assay. This proposed platform possesses the following advantages: (1) In the artificial enzyme cascade system, ACC-HNFs exhibited high catalytic activity by integrating nanozyme and natural enzyme, which remarkably amplified detection signal. (2) This approach integrates electrochemistry and colorimetric patterns into one system for “on-demand” detecting pesticide. The two groups of results can mutually authenticate, which can effectively avoid false positive and negative detection. (3) This portable lab-on-paper device dispenses with complex sample pretreatment or sophisticated instruments, which makes it suitable for on-site monitoring. We anticipated that the meticulous design of ACC-HNFs provided a versatile approach for constructing artificial enzyme as a recognizer and amplifier to fill the gap in constructing robust artificial enzyme systems, making it practically functional for on-site applications in the contamination monitoring and biological diagnosis, just through changing the building blocks.

Acetylcholine and acetylcholinesterase inhibitors detection using gold nanoparticles coupled with dynamic light scattering

A novel sensitive method for the detection of acetylcholinesterase inhibitors is presented by using unmodified gold nanoparticle coupled with dynamic light scattering (DLS). The hydrolysis of acetylcholine (ACh) mediated by acetylcholinesterase (ACHE) yields the choline, which influences the gold nanoparticles (AuNPs) aggregation, and triggered the increase of their average diameter. The inhibition of the enzyme by pesticides (paraoxon) produces lower yields of choline, leading to less or no AuNP aggregate formation. This study is the first to describe a homogeneous AuNPs-based DLS nanosensor for ultrasensitive detection of paraoxon by measuring ACHE activity. The average diameter and count rate of unmodified AuNPs decreased with the increasing concentration of paraoxon, with a detection limit of 75.5 pmol.L−1. These results suggest that this DLS assay based on unmodified AuNPs could be used in the future for measuring ACHE activity and for non-selective detection of trace amounts of all ACHE inhibitors.

Determination of Picomolar Concentrations of Paraoxon in Human Urine by Fluorescence-Based Enzymatic Assay.

Organophosphate (OP) pesticides are widely used in the agricultural field and in the prevention of pest infestation in private and public areas of cities. Despite their unquestionable utility, several of these compounds demonstrate toxic effects to the environment and human health. In particular, the occurrence of some organophosphate pesticides is correlated to the incidence of nervous system disorders, especially in children. The detection of pesticide residues in the human body represents an important task to preserve human health. In our work we propose the use of esterase-based biosensors as a viable alternative to the expensive and time-consuming systems currently used for their detection in human fluids. Using the esterase-2 activity, coupled with a fluorescence inhibition assay, we are able to detect very low concentration levels of diethyl (4-nitrophenyl) phosphate (paraoxon) in the range of the femtomole (fmol). Method robustness tests indicate the stability of esterase-2 in a diluted solution of 4% human urine, and we are able to accurately determine concentration levels of paraoxon in the range from 0.1 to 2 picomoles (pmol). The system sensitivity for OP detection is calculated at 524 ± 14.15 fmol of paraoxon recognized at 10% of inhibition, with an estimated limit of quantification of 262 ± 8.12 pmol mL−1. These values are comparable with the most recent analysis methods based on mass spectrometry carried out on human samples for pesticide detection. This research represents a starting point to develop cheap and fast testing methods for a rapid screening of toxic substances in human samples.

Self-reduction bimetallic nanoparticles on ultrathin MXene nanosheets as functional platform for pesticide sensing

Two-dimensional (2D) transition metal carbides and nitrides, named MXene, appear promising application prospects in sensor filed. Metal nanoparticles, especially bimetallic nanoparticles, are the superior nanocatalyst, which process excellent features due to the high specific surface area and synergistic catalytic capacity. Using ultrathin MXene nanosheets as the natural reducing agent and support, we prepare the shape-controlled Au-Pd bimetallic nanoparticles via a self-reduction process at room temperature in a short time, which can well enhance the catalytic performance and are benefit for the acetylcholinesterase immobilization. Based on their desired properties, we propose a disposable electrochemical biosensor for the detection of organophosphorus pesticide using the multi-dimensional nanocomposites (MXene/Au-Pd) as the functional platform. Under the optimized conditions, our fabricated biosensor exhibits a favorable linear relationship with the concentration of paraoxon from 0.1 to 1000 μg L−1, with a low detection limit of 1.75 ng L−1. Furthermore, the biosensor can be applied for paraoxon detection in pear and cucumber samples, providing an effective and useful avenue for the applicability of novel 2D nanomaterials in biosensing field.

Magnesium and nitrogen co-doped carbon dots as fluorescent probes for quenchometric determination of paraoxon using pralidoxime as a linker

Carbon dots codoped with magnesium and nitrogen (Mg,N-CDs) were synthesized via a one-step microwave-assisted method. They display blue fluorescence (with excitation/emission peaks at 380/460nm and a 33% quantum yield) and possess high dispersity in aqueous solution. The fluorescence of theMg,N-CDs is highly sensitive to paraoxon in the presence of pralidoxime (PAM) acting as the linking agent. Electron transfer from Mg,N-CDs to paraoxon in the presence of PAM leads to the fluorescence quenching of Mg,N-CDs. The concentration of paraoxon is determined by measuring the quenching efficiency of the Mg,N-CD-PAM assay system. Fluorescence drops with increasing concentrations of paraoxon in the 0.005-3.0μM range, and the limit of detection is 0.87nM. The method is highly selective for paraoxon even in the presence of possible interferences. Real sample study of tap and river water showed the assay to have good repeatability and accuracy. Graphical abstract Schematic diagram of magnesium and nitrogen co-doped carbon dots (Mg,N-CDs) as a fluorescent probe for paraoxon detection by using pralidoxime as a linker.

Blood-Brain Barrier Cellular Responses Toward Organophosphates: Natural Compensatory Processes and Exogenous Interventions to Rescue Barrier Properties.

Organophosphorus compounds (OPs) are highly toxic chemicals widely used as pesticides (e.g., paraoxon (PX)- the active metabolite of the insecticide parathion) and as chemical warfare nerve agents. Blood-brain barrier (BBB) leakage has been shown in rodents exposed to PX, which is an organophosphate oxon. In this study, we investigated the cellular mechanisms involved in BBB reaction after acute exposure to PX in an established in vitro BBB system made of stem-cell derived, human brain-like endothelial cells (BLECs) together with brain pericytes that closely mimic the in vivo BBB. Our results show that PX directly affects the BBB in vitro both at toxic and non-toxic concentrations by attenuating tight junctional (TJ) protein expression and that only above a certain threshold the paracellular barrier integrity is compromised. Below this threshold, BLECs exhibit a morphological coping mechanism in which they enlarge their cell area thus preventing the formation of meaningful intercellular gaps and maintaining barrier integrity. Importantly, we demonstrate that reversal of the apoptotic cell death induced by PX, by a pan-caspase-inhibitor ZVAD-FMK (ZVAD) can reduce PX-induced cell death and elevate cell area but do not prevent the induced BBB permeability, implying that TJ complex functionality is hindered. This is corroborated by formation of ROS at all toxic concentrations of PX and which are even higher with ZVAD. We suggest that while lower levels of ROS can induce compensating mechanisms, higher PX-induced oxidative stress levels interfere with barrier integrity.

Functional cell surface displaying of acetylcholinesterase for spectrophotometric sensing organophosphate pesticide

The inhibition of acetylcholinesterase (AChE) activity based methods have been widely used for rapid detection of organophosphate (OP) pesticide residues. However, the sensitivity of the enzyme toward pesticides is not desirable and complex purification steps increase production cost. In this study, we optimized and synthesized the cDNA of carp AChE based on the preferred codon using Saccharomyces cerevisiae, which was ligated into expression vector pYD1.The AChE was successfully presented on yeast surface through a-agglutinin mediated display system. In shake-flask after induction with galactose in YPD medium for 24 h, this strain expressed AChE activity at a high level of 0.15 U/OD600/ml. The correct location of AChE was confirmed by immunofluorescence analysis. The whole cell catalyst was applied to visible spectrophotometry detection for OP pesticides based on inhibition rate. The inhibition rate was linear with paraoxon concentration in the range of 0.5 ng/ml–10 μg/ml and parathion concentration in the range of 5 ng/ml–10 μg/ml. The low detection limit was 0.136 ng/ml paraoxon and 3.72 ng/ml parathion (S/N = 3). The proposed method is applicable to analyzing OP pesticides in real samples. Therefore, the recombinant strain developed could be an efficient and affordable biomaterial for rapid and accurate detection of OP pesticide residues.

Metallic Transition Metal Dichalcogenide Nanosheets as an Effective and Biocompatible Transducer for Electrochemical Detection of Pesticide.

Owing to their large specific surface, favorable electrical conductivity, and excellent electrocatalytic capabilities, two-dimensional transition metal dichalcogenides have received considerable attention in the field of biosensors. On the basis of these properties, we developed a portable and disposable enzyme-based biosensor for paraoxon detection using a metallic MoS2 nanosheets modified screen-printed electrode (SPE). The exfoliated ultrathin metallic MoS2 nanosheets can accelerate the electron transfer on electrode surface and contribute to the immobilization of acetylcholinesterase (AChE) via the cross-linking of glutaraldehyde. Electrodeposited gold nanoparticles (AuNPs) on SPE were used to immobilize MoS2 nanosheets through the interaction between Au atoms on AuNPs and S atoms on MoS2. Using acetylcholine as the substrate, AChE can catalyze the formation of electroactive thiocholine and further generate the redox current. In the presence of paraoxon, the activity of AChE can be inhibited, making the related electrochemical signals weaken. Under the optimized conditions, this electrochemical biosensor exhibited a favorable linear relationship with the concentration of paraoxon from 1.0 to 1000 μg L-1, with the detection limit of 0.013 μg L-1. Furthermore, this developed biosensor was successfully applied to detect paraoxon in pretreated apple and pakchoi samples, which can provide a reliable method for the rapid analysis of organophosphorus pesticides in agricultural products.

Quantitative assessment of paraoxon adsorption to amphiphilic β-sheet peptides presenting the catalytic triad of esterases

Organophosphate compounds that are used as pesticides affect the nervous system by binding irreversibly to the active site of the enzyme acetylcholine esterase (AChE) and disrupting neuro-signaling nerve cells. In this study we characterized adsorption of paraoxon to a set of designed peptides that present different arrangements of the three amino acids of the AChE catalytic site: histidine, glutamic-acid and serine. The peptides set included two β-strands with no net charge and three β-hairpins that differ in their net charge. Circular dichroism, Thioflavin T assays and TEM images provided only qualitative insights on paraoxon binding to the different peptides. Paraoxon binding to the different peptides was measured with dialysis membrane tubes filled with the peptide solutions and suspended in a reservoir of paraoxon solution. Among all the tested peptides, the single strand peptide, denoted ssESH exhibited at 100 μM in random conformation prefibrillar state, the maximum paraoxon adsorption, with a binding mol ratio of one paraoxon per two peptides and an estimated equilibrium binding constant 5 ∗ 104 M−1. The three β-hairpin peptides demonstrated that a net negative charge is unfavorable for paraoxon adsorption. Surface enhanced Raman spectroscopy measurements with ssESH enabled the detection of nanomolar adsorbed concentrations of paraoxon.

A case-control study: The association of serum paraoxonase 1 activity and concentration with the development of type 2 diabetes mellitus.

A longitudinal study assessed serum paraoxonase 1 (PON1) activity and concentration as affected by age and as associated with the development of type 2 diabetes (T2D). PON1's recently established physiological function is the hydrolysis of lipolactones in oxidized LDL particles. Serum samples and clinical data collected and stored at different time points over a 20-year interval in the Air Force Health Study were analysed. PON1 activity and concentration and C-reactive protein concentration in samples from the same individuals 20years apart were compared using a paired t test (n=159). A case-control study design and multivariable logistic regression analysis assessed the association of PON1's activity and concentration with the subsequent development of T2D (n=222 and α=0.10). No difference with age was found in PON1 activity assessed using 3 substrates, paraoxon (P=0.897), phenyl acetate (P=0.994), and dihydrocoumarin (P=0.505), or PON1 serum concentration (P=0.357). C-reactive protein concentration increased 0.7mg/L (P=0.004) over the 20-year interval. Lower PON1 activity assayed with phenyl acetate (P=0.015, OR=1.25 per 1000U/L decrease) was associated with an increased risk of developing T2D as was a lower PON1 serum concentration (P=0.004, OR=1.72 per 2μmol/L decrease). PON1 activity assayed with paraoxon (P=0.681) or dihydrocoumarin (P=0.136) was not associated with the development of T2D. Lower PON1 activity and concentration were associated with an increased risk of developing T2D when adjusted for many of the common risk markers for T2D previously identified. Thus, PON1 may have merit as a biomarker for the development of T2D.

Selective detection of organophosphate through molecularly imprinted GERS‐active hybrid organic–inorganic materials

A selective sensing platform for the organophosphate paraoxon, a highly toxic organic pollutant, has been designed and tested on water samples. A porous hybrid organic–inorganic film, synthesised using tetraethoxysilane, 1,8‐bis(triethoxysilyl)octane and cetyltrimethylammonium bromide, has been molecularly imprinted with a structural analogue of paraoxon, the diethyl(4‐nitrobenzyl)phosphonate, to induce selective recognition. Exfoliated graphene has been incorporated into the porous matrix to provide enhancement of the Raman scattering signal. The Raman sensor has been tested on different concentrations of paraoxon in both ethanol and water/ethanol mixture. The molecular selectivity has been assessed by comparing the Raman signal enhancement of paraoxon with a similar organophosphate, the bis‐(4‐nitrophenyl) phosphate. The molecularly imprinted film has shown a fourfold increase of the paraoxon signal, when compared with the corresponding not‐imprinted. The evaluation of the density of molecular cavities into the molecularly imprinted samples (4.50 * 10−10 μmol μm−3) has allowed assuming that each molecular cavity is capable of providing a remarkable signal enhancement of 1.47 * 1012 count * μmol−1 only when recognising paraoxon. The material design has allowed coupling the sensitivity of the graphene‐mediated enhancement of Raman scattering with the selectivity of molecular imprinting into a single and potentially portable, analytical system. Copyright © 2017 John Wiley & Sons, Ltd.

Carbon quantum dots as fluorescence resonance energy transfer sensors for organophosphate pesticides determination

Carbon quantum dots (CQDs) obtained from natural organics attract significant attention due to the abundance of carbon sources, varieties of heteroatom doping (such as N, S, P) and good biocompatibility of precursor. In this study, tunable fluorescence emission CQDs originated from chlorophyll were synthesized and characterized. The fluorescence emission can be effectively quenched by gold nanoparticles (Au NPs) via fluorescence resonance energy transfer (FRET). Thiocholine, which was produced from acetylthiocholine (ATC) by the hydrolysis of butyrylcholinesterase (BChE), could cause the aggregation of Au NPs and the corresponding recovery of FRET-quenched fluorescence emission. The catalytic activity of BChE could be irreversibly inhibited by organophosphorus pesticides (OPs), thus, the recovery effect was reduced. By evaluating the fluorescence emission intensity of CQDs, a FRET-based sensing platform for OPs determination was established. Paraoxon was studied as an example of OPs. The sensing platform displayed a linear relationship with the logarithm of the paraoxon concentrations in the range of 0.05–50μgL−1 and the limit of detection (LOD) was 0.05μgL−1. Real sample study in tap and river water revealed that this sensing platform was repeatable and accurate. The results indicate that the OP sensor is promising for applications in food safety and environmental monitoring.

Sensitive inkjet printing paper-based colormetric strips for acetylcholinesterase inhibitors with indoxyl acetate substrate

A new paper-based biosensing approach has been developed for sensitive and rapid detection of acetylcholinesterase (AChE) inhibitors. The biosensing zone of the paper strip is constructed with an inkjet printing method, and the biomolecule AChE is immobilized into two layers of biocompatible sol-gel-derived silica ink with a “sandwich” form. Indoxyl acetate (IDA) is used as a chromogenic substrate, which is colorless and can be catalytically hydrolyzed into blue-colored indigo dipolymer. When the enzymatic activity of AChE is inhibited after incubation with organophosphate pesticides (OPs), there is a decreased hydrolysis of IDA accompanying with a drop in color intensity. Paraoxon and trichlorfon are used as the representative OPs in the assay. Due to the low solubility and high molar absorption coefficient of the IDA dipolymer product, the paper-based strip can form a neat blue sensing zone and shows obviously improved sensitivity with a limit of detection (LOD) of 0.01ngmL−1 paraoxon and 0.04ngmL−1 trichlorfon (S/N=3) and the LODs for visual detection are 0.03ngmL−1 for paraoxon and 0.1ngmL−1 for trichlorfon comparing with the previously reported colorimetric methods. The concentrations of paraoxon in apple juice samples are also detected, and the results are in accord well with these results from high-performance liquid chromatography, showing great potential for on-site detection of OPs in practical application. The developed assay can be used to qualitatively and semiquantitatively estimate with naked eyes and quantitatively assess OPs through image analysis.

Protein capped Cu nanoclusters-SWCNT nanocomposite as a novel candidate of high performance platform for organophosphates enzymeless biosensor

A biocompatible nanocomposite including bovine serum albumin (BSA) template Cu nanoclusters (CuNCs@BSA) and single-walled carbon nanotubes (SWCNT) was synthesized to fabricate a highly sensitive electrochemical biosensor for paraoxon as a model of organophosphates. The UV–vis, fluorescence and Fourier transform infrared (FTIR) demonstrated that BSA entrapped in the nanocomposite film have been changed in its secondary structure so that it provided an enzyme like activity attributing to the high electrical conductivity of the entrapped copper nanoclusters. Also, the morphology and structure of prepared nanocomposites were investigated by transmission electronic microscopy (TEM) and scanning electron microscopy (SEM). In the prepared nanocomposite, the CuNCs@BSA found to play as a conductive holder as well as an accumulator of redox active centers on the surface of the electrode, and SWCNT improves the electrocatalytic activity along with conductivity of glassy carbon electrode (GCE) surface. The fabricated biosensor exhibited excellent sensitivity, acceptable stability, fast response, and high electrocatalytic activity toward the reduction of paraoxon. The reduction peak current vs paraoxon concentration was linear over the range 50nM to 0.5μM and 0.5–35μM, with a limit of detection of 12.8nM. Notable electrocatalytic properties of the developed electrode toward paraoxon indicated that the nanocomposite possesses a promising potential to fabricate the third generation enzyme-free electrochemical biosensors, bioelectronics and state-of-the-art biomedical devices in the future.

Sensitive fluorescence assay of organophosphorus pesticides based on the fluorescence resonance energy transfer between CdTe quantum dots and porphyrin.

A sensitive and selective quantum dot (QD)-based fluorescence resonance energy transfer (FRET) biosensor was successfully fabricated for the detection of organophosphorus pesticides (OPs). 5,10,15,20-Tetra(4-pyridyl)porphyrin (TPyP) with meso-pyridyl substituents was bound to the surface of CdTe QDs to produce self-assembled nanosensors, and the process of FRET between QDs and TPyP occurred. However, the process of FRET was switched off with the addition of OPs, due to the combination between TPyP and OPs. The fluorescence intensity of TPyP (donor) would decrease gradually with the increasing concentration of OPs. Under optimal conditions, a linear correlation was established between the fluorescence intensity ratio ITPyP/IQDs and the concentration of paraoxon in the range of 9.09 × 10(-12)-1.09 × 10(-6) mol L(-1) with a detection limit of 3.15 × 10(-12) mol L(-1). The attractive sensitivity was obtained due to the efficient FRET and the superior fluorescence properties of QDs. The proposed method was successfully applied to the determination of the OPs in real fruit samples with satisfactory results.