Acetylecholinesterase-based biosensor electrodes for organophosphate pesticide detection. II. Immobilization and stabilization of acetylecholinesterase

The Effect of Amino-Phosphate Interactions on the Biosensing Performance of Enzymatic Graphene Field-Effect Transistors

The interaction between polyamines and phosphate species is found in a wide range of biological and abiotic systems, yielding crucial consequences that range from the formation of supramolecular colloids to structure determination. In this work, the occurrence of phosphate-amino interactions is evidenced from changes in the electronic response of graphene field effect transistors (gFETs). First, the surface of the transistors is modified with poly(allylamine), and the effect of phosphate binding on the transfer characteristics is interpreted in terms of its impact on the surface charge density. The electronic response of the polyamine-functionalized gFETs is shown to be sensitive to the presence of different phosphate anions, such as orthophosphate, adenosine triphosphate, and tripolyphosphate, and a simple binding model is developed to explain the dependence of the shift of the Dirac point potential on the phosphate species concentration. Afterward, the impact of phosphate-amino interactions on the immobilization of enzymes to polyamine-modified graphene surfaces is investigated, and a decrease in the amount of anchored enzyme as the phosphate concentration increases is found. Finally, multilayer polyamine-urease biosensors are fabricated while increasing the phosphate concentration in the enzyme solution, and the sensing properties of the gFETs toward urea are evaluated. It is found that the presence of simple phosphate anions alters the nanoarchitecture of the polyelectrolyte-urease assemblies, with direct implications on urea sensing.

Development of enzymatic electrochemical biosensors for organophosphorus pesticide detection

The enzymatic electrochemical biosensor has the advantages of simple operation, speed, and integration in the detection of organophosphorus pesticide (OPs) residues. It has the potential to become the best alternative to the traditional OP detection technology. This article introduces the OP identification principle of different enzymes, the OP detection mechanism of several common sensors, and the enzyme assembly method. In addition, the article discusses application of nanomaterials in sensor preparation and sensor performance parameters in the past decade. The related content of early sensors is outside the scope of this article.

Enzyme Immobilization on Nanomaterials for Biosensor and Biocatalyst in Food and Biomedical Industry

Enzymes exhibit a great catalytic activity for several physiological processes. Utilization of immobilized enzymes has a great potential in several food industries due to their excellent functional properties, simple processing and cost effectiveness during the past decades. Though they have several applications, they still exhibit some challenges. To overcome the challenges, nanoparticles with their unique physicochemical properties act as very attractive carriers for enzyme immobilization. The enzyme immobilization method is not only widely used in the food industry but is also a component methodology in the pharmaceutical industry. Compared to the free enzymes, immobilized forms are more robust and resistant to environmental changes. In this method, the mobility of enzymes is artificially restricted to changing their structure and properties. Due to their sensitive nature, the classical immobilization methods are still limited as a result of the reduction of enzyme activity. In order to improve the enzyme activity and their properties, nanomaterials are used as a carrier for enzyme immobilization. Recently, much attention has been directed towards the research on the potentiality of the immobilized enzymes in the food industry. Hence, the present review emphasizes the different types of immobilization methods that is presently used in the food industry and other applications. Various types of nanomaterials such as nanofibers, nanoflowers and magnetic nanoparticles are significantly used as a support material in the immobilization methods. However, several numbers of immobilized enzymes are used in the food industries to improve the processing methods which not only reduce the production cost but also the effluents from the industry.

Acetylcholine biosensor based on the electrochemical functionalization of graphene field-effect transistors

We present a new strategy of Acetylcholinesterease (AchE) immobilization on graphene field-effect transistors (gFETs) for building up Acetylcholine sensors. This method is based on the electrosynthesis of an amino moiety-bearing polymer layer on the graphene channel. The film of the copolymer poly(3-amino-benzylamine-co-aniline) (PABA) does not only provide the suitable electrostatic charge and non-denaturing environment for enzyme immobilization, but it also improves the pH sensitivity of the gFETs (from 40.8 to 56.3 μA/pH unit), probably due to its wider effective pKa distribution. The local pH changes caused by the enzyme-catalyzed hydrolysis produce a shift in the Dirac point of the gFETs to more negative values, which are evidenced as differences in the gFET conductivity and thereby constituted the signal transduction mechanism of the modified transistors. In this way, the constructed biosensors showed a LOD of 2.3 μM and were able to monitor Ach in the range from 5 to 1000 μM in a flow configuration. Moreover, they showed a sensitivity of -26.6 ± 0.7 μA/Ach decade and also exhibited a very low RSD of 2.6%, revealing good device-to-device reproducibility. The biosensors revealed an excellent selectivity to interferences known to be present in the extracellular milieu, and the response to Ach was recovered by 97.5% after the whole set of interferences injected. Finally, the biosensors showed a fast response time, with an average value of 130 s and a good long-term response.

Methodologies for "Wiring" Redox Proteins/Enzymes to Electrode Surfaces

The immobilization of redox proteins or enzymes onto conductive surfaces has application in the analysis of biological processes, the fabrication of biosensors, and in the development of green technologies and biochemical synthetic approaches. This review evaluates the methods through which redox proteins can be attached to electrode surfaces in a "wired" configuration, that is, one that facilitates direct electron transfer. The feasibility of simple electroactive adsorption onto a range of electrode surfaces is illustrated, with a highlight on the recent advances that have been achieved in biotechnological device construction using carbon materials and metal oxides. The covalent crosslinking strategies commonly used for the modification and biofunctionalization of electrode surfaces are also evaluated. Recent innovations in harnessing chemical biology methods for electrically wiring redox biology to surfaces are emphasized.

Progress in enzyme inhibition based detection of pesticides

The previous few decades have seen the development of biosensors and their use in monitoring of pesticides in food and environmental samples. Although inhibition-based biosensors have been subject of several recent research works, their performance characteristics greatly depend on the type of immobilization and the presence of interfering compounds in the samples. Moreover, sensitivity, detection limits, and rapidity of the response are few of the other major features that need to be investigated further if they are to become operationally user-friendly. This review will highlight research carried out in the past on biosensors that are based on enzyme inhibition for determination of organophosphorus compounds and carbamate pesticides.

Bioconjugation and stabilisation of biomolecules in biosensors

Suitable bioconjugation strategies and stabilisation of biomolecules on electrodes is essential for the development of novel and commercially viable biosensors. In the present review, the functional groups that comprise the selectable targets for practical bioconjugation methods are discussed. We focus on describing the most common immobilisation techniques used in biosensor construction, which are classified into irreversible and reversible methods. Concerning the stability of proteins, the two main types of stability may be defined as (i) storage or shelf stability, and (ii) operational stability. Both types of stability are explained, as well as the introduction of an electrophoretic technique for predicting protein–polymer interactions. In addition, solution and dry stabilisation as well as stabilisation using the covalent immobilisation of proteins are discussed including possible factors that influence stability. Finally, the integration of nanomaterials, such as magnetic particles, with protein immobilisation is discussed in relation to protein stability studies.

Developing acetylcholinesterase-based inhibition assay by modulated synthesis of silver nanoparticles: applications for sensing of organophosphorus pesticides

A novel and highly sensitive probe for the detection of organophosphorus compounds (OPs) using acetylcholinesterase (AChE) and acetylthiocholine (ATCh) during the modulated synthesis of silver nanoparticles.

Acetylcholinesterase capillary enzyme reactor for screening and characterization of selective inhibitors

The aim of the present work is to report on the optimized preparation of capillary enzyme reactors (ICERs) based on acetylcholinesterase (AChE, EC 3.1.1.7), for the screening of selective inhibitors. The AChE-ICERs were prepared by using the homobifunctional linker glutaraldehyde through Schiff base linkage. The enzyme was anchored onto a modified fused silica capillary and employed as an LC biochromatography column for online studies, with UV-vis detection. Not only did the tailored AChE-ICER result in maintenance of the activity of the immobilized enzyme, but it also significantly improved the stability of the enzyme in the presence of organic solvents. In addition, the kinetic studies demonstrated that the enzyme retained its activity with high stability, preserving its initial activity over 10months. The absence of non-specific matrix interactions, immediate recovery of the enzymatic activity, and short analysis time were the main advantages of this AChE-ICER. The use of AChE-ICER in the ligands recognition assay was validated by evaluation of four known reversible inhibitors (galanthamine, tacrine, propidium, and rivastigmine), and the same order of inhibitory potencies described in the literature was found. The immobilized enzyme was utilized in the screening of 21 coumarin derivatives. In this library, two new potent inhibitors were identified: coumarins 20 (IC(50) 17.14±3.50μM) and 21 (IC(50) 6.35±1.20μM), which were compared to the standard galanthamine (IC(50) 12.68±2.40μM). Considering the high inhibitory activities of these compounds, with respect to the AChE-ICER, the mechanism of action was investigated. Both coumarins 20 and 21 exhibited a competitive mechanism of action, furnishing K(i) values of 8.04±0.18 and 2.67±0.18μM, respectively. The results revealed that the AChE-ICER developed herein represents a useful tool for the biological screening of inhibitor candidates and evaluation of action mechanism.

A high-throughput enzyme assay for organophosphate residues in milk

A rapid, high-sensitivity, chemiluminescence (CL) enzyme assay for the determination of organophosphate (OP) residues in milk is presented. The assay for quantification of OP residues in milk is based on the inhibition of enzyme butyrylcholinesterase (BuChE). BuChE was stabilized and preloaded in 384 well plates at 30 °C. The assay permits rapid determination of OPs in milk within 12 min including an incubation step. The enzyme assay was tested for individual and mixtures of OPs such as methyl paraoxon (MPOx), methyl parathion (MP) and malathion (MT) in milk to evaluate their synergistic effect on BuChE inhibition. Good linearity was obtained in the range 0.005–50 μg·L⁻¹ for MPOx and 0.5–1,000 μg·L⁻¹ for MP as well as MT in milk. Mean recovery of 93.2%–98.6% was obtained for MPOx spiked milk samples with 0.99%–1.67% reproducibility (RSD). The proposed method facilitated rapid screening of milk samples in 384 well plate formats with further miniaturization presented in 1,536 well plates.

Variation of cholinesterase-based biosensor sensitivity to inhibition by organophosphate due to ionizing radiation

A cholinesterase based biosensor was constructed in order to assess the effects of ionizing radiation on exposed AChE. Although the primary objective of the experiment was to investigate the effect of ionizing radiation on the activity of the biosensor, no changes in cholinesterase activity were observed. Current provided by oxidation of thiocholine previously created from acetylthiocholine by enzyme catalyzed reaction was in a range 395-455 nA. No significant influence of radiation on AChE activity was found, despite the current variation. However, a surprising phenomenon was observed when a model organophosphate paraoxon was assayed. Irradiated biosensors seem to be more susceptible to the inhibitory effects of paraoxon. Control biosensors provided a 94 ± 5 nA current after exposure to 1 ppm paraoxon. The biosensors irradiated by a 5 kGy radiation dose and exposed to paraoxon provided a current of 49 ± 6 nA. Irradiation by doses ranging from 5 mGy to 100 kGy were investigated and the mentioned effect was confirmed at doses above 50 Gy. After the first promising experiments, biosensors irradiated by 5 kGy were used for calibration on paraoxon and compared with the control biosensors. Limits of detection 2.5 and 3.8 ppb were achieved for irradiated and non-irradiated biosensors respectively. The overall impact of this effect is discussed.

Molecular Recognition and Specific Interactions for Biosensing Applications

Molecular recognition and specific interactions are reliable and versatile routes for site-specific and well-oriented immobilization of functional biomolecules on surfaces. The control of surface properties via the molecular recognition and specific interactions at the nanoscale is a key element for the nanofabrication of biosensors with high sensitivity and specificity. This review intends to provide a comprehensive understanding of the molecular recognition- and specific interaction-mediated biosensor fabrication routes that leads to biosensors with well-ordered and controlled structures on both nanopatterned surfaces and nanomaterials. Herein self-assembly of the biomolecules via the molecular recognition and specific interactions on nanoscaled surfaces as well as nanofabrication techniques of the biomolecules for biosensor architecture are discussed. We also describe the detection of molecular recognition- and specific interaction-mediated molecular binding as well as advantages of nanoscale detection.

A new method for immobilization of acetylcholinesterase

A new method for immobilization of acetylcholinesterase (AChE) to alginate gel beads by activating the carbonyl groups of alginate using carbodiimide coupling agent has been successfully developed. Maximum reaction rate (V (max)) and Michaelis-Menten constant (K (m)) were determined for the free and binary immobilized enzyme. The effects of pH, temperature, storage stability, reuse number and thermal stability on the free and immobilized AChE were also investigated. For the free and binary immobilized enzyme on the Ca-alginate gel beads, optimum pH values were found to be 7 and 8, respectively. Optimum temperatures for the free and immobilized enzyme were observed to be 30 and 35 degrees C, respectively. Upon 60 days of storage the preserved activity of free and immobilized enzyme were found as 4 and 68%, respectively. In addition, reuse number, and thermal stability of the free AChE were increased by as a result of binary immobilization.

Pesticide detection with a liposome-based nano-biosensor

Monitoring of the organophosphorus pesticides dichlorvos and paraoxon at very low levels has been achieved with liposome-based nano-biosensors. The enzyme acetylcholinesterase was effectively stabilized within the internal nano-environment of the liposomes. Within the liposomes, the pH sensitive fluorescent indicator pyranine was also immobilized for the optical transduction of the enzymatic activity. Increasing amounts of pesticides lead to the decrease of the enzymatic activity for the hydrolysis of the acetylcholine and thus to a decrease in the fluorescent signal of the pH indicator. The decrease of the liposome biosensors signal is relative to the concentration of dichlorvos and paraoxon down to 10(-10)M levels. This biosensor system has been applied successfully to the detection of total toxicity in drinking water samples. Also a colorimetric screening device for pesticide analysis has been evaluated.

Chapter 29 Rapid detection of organophosphates, Ochratoxin A, and Fusarium sp. in durum wheat via screen printed based electrochemical sensors

Most of the inhibition bioassays or biosensors for organophosphate and carbamate pesticides are based on the amperometric detection of the enzymatic product of the reaction. Applications of amperometric biosensing strategies for pesticide detection in real or spiked food samples have been recently reported. Most of the applications have been developed for vegetable matrices. Different formats of biosensors have been used: disposable screenprinted choline oxidase biosensors using acetylcholinesterase (AChE) in solution were utilized to detect pesticides. Screen-printed sensor developed using photolithographic conducting copper track, graphite–epoxy composite, and either AChE or butirrylcholinesterase was also used in the analysis of spiked (paraoxon and carbofuran) samples of tap water and fruit juices at sub-nanomolar concentration. Additionally, the developed device, which consists of the hand-held potentiostat, the multiplexer for eight-channel control and a dedicated software, can be used to detect organophosphates pesticides, such as dichlorvos and pirimiphos methyl at contamination level below the maximum residue limit settled by the European Union and also amplified DNA of F. culmorum.

Recent advances in biosensor techniques for environmental monitoring

Biosensors for environmental applications continue to show advances and improvements in areas such as sensitivity, selectivity and simplicity. In addition to detecting and measuring specific compounds or compound classes such as pesticides, hazardous industrial chemicals, toxic metals, and pathogenic bacteria, biosensors and bioanalytical assays have been designed to measure biological effects such as cytotoxicity, genotoxicity, biological oxygen demand, pathogenic bacteria, and endocrine disruption effects. This article is intended to discuss recent advances in the area of biosensors for environmental applications.

A novel matrix for the immobilization of acetylcholinesterase

In this study, a new matrix for immobilization of acetylcholinesterase was investigated by using alginate and kappa-carrageenan. The effects of pH, temperature, storage and thermal stability on the free and immobilized acetylcholinesterase activity were examined. Maximum reaction rate (V(max)) and Michaelis-Menten constant (K(m)) was also investigated for free and immobilized enzymes. For free and immobilized enzymes into Ca-alginate and alginate/kappa-carrageenan polymer blends, optimum pH and temperature was found to be 7 and 30 degrees C, respectively. For free enzyme, maximum reaction rate (V(max)) and Michaelis-Menten constant (K(m)) values were found to be 6.35 mM and 50 mM min(-1), respectively, the same values for immobilized enzymes were determined as 8.68, 12.7 mM and 39.7, 52.9 mM min(-1), respectively. Storage and thermal stability of acetylcholinesterase was increased by as a result of immobilization.

Sonochemically fabricated acetylcholinesterase micro-electrode arrays within a flow injection analyser for the determination of organophosphate pesticides

This report describes the development of novel sonochemically fabricated, bioengineered acetylcholinesterase and polyaniline carbon/cobalt phthalocyanine biosensors for the ultra-sensitive determination of a number of different pesticides. Arrays of this type typically have population micro-electrode densities of up to approximately 2 x 10(5) cm(-2); these represent the highest micro-electrode population densities reported to date by any fabrication means. The enzymatic response of the sensors is inhibited upon incubation with the pesticide, and we have shown that Dichlorvos, Parathion and Azinphos may be determined down to concentrations of approximately 1 x 10(-17) M, approximately 1 x 10(-16) M and approximately 1 x 10(-16) M, respectively. These lower limits of detection are lower than otherwise achievable by any other analytical approach. Measurements were performed within a custom built flow injection system that operates at a constant flow of 1 ml min(-1). Sensor stability studies were also performed whereby a stabilizer mixture of sucrose and polygalacturonic acid was added to the immobilised enzyme matrix at the working electrode and left to dry. Sixty-five percent of the initial enzyme activity was found to remain after a period of 92 days to allow storage of these electrodes and facilitating transportation if required.