Conductometric tyrosinase biosensor for the detection of diuron, atrazine and its main metabolites

Herbicide detection: A review of enzyme- and cell-based biosensors

Herbicides are the most widely used class of pesticides in the world. Their intensive use raises the question of their harmfulness to the environment and human health. These pollutants need to be detected at low concentrations, especially in water samples. Commonly accepted analytical techniques (HPLC-MS, GC-MS, ELISA tests) are available, but these highly sensitive and time-consuming techniques suffer from high cost and from the need for bulky equipment, user training and sample pre-treatment. Biosensors can be used as complementary early-warning systems that are less sensitive and less selective. On the other hand, they are rapid, inexpensive, easy-to-handle and allow direct detection of the sample, on-site, without any further step other than dilution. This review focuses on enzyme- and cell- (or subcellular elements) based biosensors. Different enzymes (such as tyrosinase or peroxidase) whose activity is inhibited by herbicides are presented. Photosynthetic cells such as algae or cyanobacteria are also reported, as well as subcellular elements (thylakoids, chloroplasts). Atrazine, diuron, 2,4-D and glyphosate appear as the most frequently detected herbicides, using amperometry or optical transduction (mainly based on chlorophyll fluorescence). The recent new WSSA/HRAC classification of herbicides is also included in the review.

Electrochemical Biosensors Based on Enzyme Inhibition Effect

Several electrochemical biosensors based on various enzyme inhibition effects have been designed; their laboratory prototypes have been manufactured and thoroughly investigated. It should be noted that such biosensors are adapted to large-scale production technologies. A number of advantages and disadvantages of developed biosensors based on enzyme inhibition has been discussed. It is important that all developed biosensors are not opposite to traditional analytical methods, but complement them. This is an additional system of quick and early warning about the presence of toxic substances in the environment. Such systems can save time and money in emergencies due to the possibility of quick decision-making on local environmental problems. If necessary, more accurate, but time-consuming and expensive traditional methods could be used for further validation and additional research of samples previously tested by biosensors.

Aptamer and bifunctional enzyme co-functionalized MOF-derived porous carbon for low-background electrochemical aptasensing

To improve the efficiency of aptasensors, a signal amplification strategy by coupling tyrosinase (Tyr)-triggered redox cycling with nanoscale porous carbon (NCZIF) has been proposed. The NCZIF was obtained by calcining ZIF-8 crystals in an inert atmosphere. It had high surface areas, great biocompatibility, and ease of functionalization, which was beneficial for immobilizing sufficient Tyr and aptamer covalently. When the target prostate-specific antigen (PSA) was present, the NCZIF functionalized with Tyr and an aptamer bound to the aptamer-modified Au electrode specifically through the sandwich structure. Then, Tyr acted to oxidize the electroinactive phenol, which led to low-background signal, in the substrate to electroactive catechol, and triggered the redox cycling under the action of NADH. The low detection limit of the proposed electrochemical aptasensor for PSA was 0.01 ng mL^-1, and the wide detection range was from 0.01 to 50 ng mL^-1. The use of ZIF-8 derived porous carbon and Tyr-triggered redox cycling system provided a promising solution for the development of simple, rapid, reliable, and low-background aptasensing methods, which had great potential in the field of disease diagnosis and biomedicine.

Engineered tyrosinases with broadened bio-catalysis scope: immobilization using nanocarriers and applications

Enzyme immobilization is a widely used technology for creating more stable, active, and reusable biocatalysts. The immobilization process also improves the enzyme's operating efficiency in industrial applications. Various support matrices have been designed and developed to enhance the biocatalytic efficiency of immobilized enzymes. Given their unique physicochemical attributes, including substantial surface area, rigidity, semi-conductivity, high enzyme loading, hyper catalytic activity, and size-assisted optical properties, nanomaterials have emerged as fascinating matrices for enzyme immobilization. Tyrosinase is a copper-containing monooxygenase that catalyzes the o-hydroxylation of monophenols to catechols and o-quinones. This enzyme possesses a wide range of uses in the medical, biotechnological, and food sectors. This article summarizes an array of nanostructured materials as carrier matrices for tyrosinase immobilization. Following a detailed background overview, various nanomaterials, as immobilization support matrices, including carbon nanotubes (CNTs), carbon dots (CDs), carbon black (CB), nanofibers, Graphene nanocomposite, platinum nanoparticles, nano-sized magnetic particles, lignin nanoparticles, layered double hydroxide (LDH) nanomaterials, gold nanoparticles (AuNPs), and zinc oxide nanoparticles have been discussed. Next, applied perspectives have been spotlights with particular reference to environmental pollutant sensing, phenolic compounds detection, pharmaceutical, and food industry (e.g., cereal processing, dairy processing, and meat processing), along with other miscellaneous applications.

Catechol Dyes-Tyrosinase System for Colorimetric Determination and Discrimination of Dithiocarbamate Pesticides

A convenient and straightforward method, which is based on catechol dyes and tyrosinase, for colorimetric determination and discrimination of dithiocarbamate pesticides (DTCs) has been fabricated. Three catechol dyes, including pyrocatechol violet (PV), pyrogallol red (PR), and bromopyrogallol red (BPR), were chosen as both substrates and indicators in this method. Tyrosinase can facilitate oxidation of the catechol dyes, altering color and absorbance spectra of the dyes. DTCs can alter the absorbance spectra of the catechol dyes-tyrosinase system due to their inhibitory effects on tyrosinase. As a result, the detection limit of the PV-tyrosinase system on ziram was determined to be 4.5 μg L^-1. By implementing PV-tyrosinase, PR-tyrosinase, and BPR-tyrosinase, the colorimetric array successfully distinguished six DTCs (thiram, ziram, diram, ferbam, metiram, and mancozeb) at 5.0 μM using principal component analysis (PCA). The system can also determine ziram and distinguish DTCs in real samples. Furthermore, a smartphone can be used as a detector in this system to improve its real-world applications.

Enzymatic assays for the assessment of toxic effects of halogenated organic contaminants in water and food. A review

Halogenated organic compounds are a particular group of contaminants consisting of a large number of substances, and of great concern due to their persistence in the environment, potential for bioaccumulation and toxicity. Some of these compounds have been classified as persistent organic pollutants (POPs) under The Stockholm Convention and many toxicity assessments have been conducted on them previously. In this work we provide an overview of enzymatic assays used in these studies to establish toxic effects and dose-response relationships. Studies in vivo and in vitro have been considered with a particular emphasis on the impact of halogenated compounds on the activity of relevant enzymes to the humans and the environment. Most information available in the literature focuses on chlorinated compounds, but brominated and fluorinated molecules are also the target of increasing numbers of studies. The enzymes identified can be classified as enzymes: i) the activities of which are affected by the presence of halogenated organic compounds, and ii) those involved in their metabolisation/detoxification resulting in increased activities. In both cases the halogen substituent seems to have an important role in the effects observed. Finally, the use of these enzymes in biosensing tools for monitoring of halogenated compounds is described.

Impact of Silanization Parameters and Antibody Immobilization Strategy on Binding Capacity of Photonic Ring Resonators

Ring resonator-based biosensors have found widespread application as the transducing principle in “lab-on-a-chip” platforms due to their sensitivity, small size and support for multiplexed sensing. Their sensitivity is, however, not inherently selective towards biomarkers, and surface functionalization of the sensors is key in transforming the sensitivity to be specific for a particular biomarker. There is currently no consensus on process parameters for optimized functionalization of these sensors. Moreover, the procedures are typically optimized on flat silicon oxide substrates as test systems prior to applying the procedure to the actual sensor. Here we present what is, to our knowledge, the first comparison of optimization of silanization on flat silicon oxide substrates to results of protein capture on sensors where all parameters of two conjugation protocols are tested on both platforms. The conjugation protocols differed in the chosen silanization solvents and protein immobilization strategy. The data show that selection of acetic acid as the solvent in the silanization step generally yields a higher protein binding capacity for C-reactive protein (CRP) onto anti-CRP functionalized ring resonator sensors than using ethanol as the solvent. Furthermore, using the BS3 linker resulted in more consistent protein binding capacity across the silanization parameters tested. Overall, the data indicate that selection of parameters in the silanization and immobilization protocols harbor potential for improved biosensor binding capacity and should therefore be included as an essential part of the biosensor development process.

Immobilized Enzymes in Biosensor Applications

Enzyme-based biosensing devices have been extensively developed over the last few decades, and have proven to be innovative techniques in the qualitative and quantitative analysis of a variety of target substrates over a wide range of applications. Distinct advantages that enzyme-based biosensors provide, such as high sensitivity and specificity, portability, cost-effectiveness, and the possibilities for miniaturization and point-of-care diagnostic testing make them more and more attractive for research focused on clinical analysis, food safety control, or disease monitoring purposes. Therefore, this review article investigates the operating principle of enzymatic biosensors utilizing electrochemical, optical, thermistor, and piezoelectric measurement techniques and their applications in the literature, as well as approaches in improving the use of enzymes for biosensors.

Kinetic, spectroscopic and computational docking study of the inhibitory effect of the pesticides 2,4,5-T, 2,4-D and glyphosate on the diphenolase activity of mushroom tyrosinase

The inhibitory effect of 2,4,5-T, 2,4-D, glyphosate and paraquat on the diphenolase activity of mushroom tyrosinase for oxidation of L-DOPA has been investigated by kinetic measurements, fluorescence spectroscopy and computational docking analysis. 2,4,5-T and 2,4-D inhibit the diphenolase activity of the enzyme following a competitive mechanism, while glyphosate is a mixed inhibitor according to Lineweaver-Burk kinetic analysis. The inhibitory activity follows the order glyphosate >2,4,5-T > 2,4-D with IC50 values of 65, 90 and 106 μM, respectively. Intrinsic tyrosinase fluorescence quenching and computational docking analysis suggest that 2,4,5-T and 2,4-D interact with the active site of the enzyme through hydrophobic interactions, while glyphosate also interacts with external residues of the active site of the enzyme by hydrogen bonding and hydrophilic interactions inducing conformational changes in the protein structure.

Cantilever nanobiosensor using tyrosinase to detect atrazine in liquid medium

The aim of this study was to develop a cantilever nanobiosensor for atrazine detection in liquid medium by immobilising the biological recognition element (tyrosinase vegetal extract) on its surface with self-assembled monolayers using gold, 16-mercaptohexadecanoic acid, 1-ethyl-3-[3-dimethylaminopropyl] carbodiimide hydrochloride/n-hydroxysuccinimide. Cantilever nanobiosensors presented a surface compression tension increase when atrazine concentrations were increased, with a limit of detection and limit of quantification of 7.754 ppb (parts per billion) and 22.792 ppb, respectively. From the voltage results obtained, the evaluation of atrazine contamination in river and drinking water were very close to those of the reference sample and ultrapure water, demonstrating the ability of the cantilever nanobiosensor to distinguish different water samples and different concentrations of atrazine. Cantilever nanosensor surface functionalization was characterised by combining polarisation modulation infrared reflection-absorption spectroscopy and atomic force microscopy and indicating film thickness in nanometric scale (80.2 ± 0.4 nm). Thus, the cantilever nanobiosensor developed for this study using low cost tyrosinase vegetal extract was adequate for atrazine detection, a potential tool in the environmental field.

Optimized design of a nanostructured SPCE-based multipurpose biosensing platform formed by ferrocene-tethered electrochemically-deposited cauliflower-shaped gold nanoparticles

The demand for on-site nanodevices is constantly increasing. The technology development for the design of such devices is highly regarded. In this work, we report the design of a disposable platform that is structured with cauliflower-shaped gold nanoparticles (cfAuNPs) and we show its applications in immunosensing and enzyme-based detection. The electrochemical reduction of Au(III) allows for the electrodeposition of highly dispersed cauliflower-shaped gold nanoparticles on the surface of screen-printed carbon electrodes (SPCEs). The nanostructures were functionalized using ferrocenylmethyl lipoic acid ester which allowed for the tethering of the ferrocene group to gold, which serves as an electrochemical transducer/mediator. The bioconjugation of the surface with anti-human IgG antibody (α-hIgG) or horseradish peroxidase (HRP) enzyme yields biosensors, which have been applied for the selective electrochemical detection of human IgG (hIgG) or H2O2 as model analytes, respectively. Parameters such as the number of sweeps, amount of charge generated from the oxidation of the electrodeposited gold, time of incubation and concentration of the ferrocene derivatives have been studied using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). Selectivity and specificity tests have been also performed in the presence of potentially interfering substances to either hIgG or H2O2. Results showed that the devised immunosensor is endowed with good selectivity and specificity in the presence of several folds of competitive analytes. The enzyme-based platform showed a good catalytic activity towards H2O2 oxidation which predestined it to potential applications pertaining to enzymatic kinetics studies. The levels of hIgG in human serum and H2O2 in honey were successfully determined and served as assessment tools of the applicability of the platforms for real samples analysis.

Microchip capillary electrophoresis based electroanalysis of triazine herbicides

The number of pesticides used in agriculture is increasing steadily, leading to contamination of soil and drinking water. Herein, we present a microfluidic platform to detect the extent of contamination in soil samples. A microchip capillary electrophoresis system with in-channel electrodes was fabricated for label-free electroanalytical detection of triazine herbicides. The sample mixture contained three representative triazines: simazine, atrazine and ametryn. The electropherogram for each individual injection of simazine, atrazine and ametryn showed peaks at 58, 66 and 72 s whereas a mixture of them showed distinct peaks at 59, 67 and 71 s respectively. The technique as such may prove to be a useful qualitative and quantitative tool for the similar environmental pollutants.

Enhanced response of a proteinase K-based conductometric biosensor using nanoparticles

Proteinases are involved in a multitude of important physiological processes, such as protein metabolism. For this reason, a conductometric enzyme biosensor based on proteinase K was developed using two types of nanoparticles (gold and magnetic). The enzyme was directly adsorbed on negatively charged nanoparticles and then deposited and cross-linked on a planar interdigitated electrode (IDE). The biosensor was characterized with bovine serum albumin (BSA) as a standard protein. Higher sensitivity was obtained using gold nanoparticles. The linear range for BSA determination was then from 0.5 to 10 mg/L with a maximum response of 154 μs. These results are greater than that found without any nanoparticles (maximum response of 10 μs). The limit of detection (LOD) was 0.3 mg/L. An inter-sensor reproducibility of 3.5% was obtained.

A lower limit of detection for atrazine was obtained using bioluminescent reporter bacteria via a lower incubation temperature

The present article reports on the influence of various atrazine concentrations to the response of genetically modified Escherichia coli TV1061 bacterial cells while modulating the experimental conditions. Interesting increases of bioluminescence signals are recorded for E. coli TV1061 bacteria in the presence of 10 μg/mL atrazine concentration named "high-toxicity bacteria alert" when compared with 1 μg/mL -10 fg/mL atrazine termed "low-toxicity bacteria alert". Detecting the effect of atrazine via its effect on bioluminescence of bacteria has been carried out by two consecutive measurements (fresh and overnight modes) at different concentrations of analyte. We have shown that a more precise discrimination at lower-toxicity concentrations can be obtained through overnight incubation of bacteria with the analyte at 4 °C. In addition, centrifugation of bacterial cells and analyte dilutions has been performed in order to ensure a better interaction between the insoluble atrazine pesticide and the bacterial cells.

Review on the use of enzymes for the detection of organochlorine, organophosphate and carbamate pesticides in the environment

Pesticides are released intentionally into the environment and, through various processes, contaminate the environment. Three of the main classes of pesticides that pose a serious problem are organochlorines, organophosphates and carbamates. While pesticides are associated with many health effects, there is a lack of monitoring data on these contaminants. Traditional chromatographic methods are effective for the analysis of pesticides in the environment, but have limitations and prevent adequate monitoring. Enzymatic methods have been promoted for many years as an alternative method of detection of these pesticides. The main enzymes that have been utilised in this regard have been acetylcholinesterase, butyrylcholinesterase, alkaline phosphatase, organophosphorus hydrolase and tyrosinase. The enzymatic methods are based on the activation or inhibition of the enzyme by a pesticide which is proportional to the concentration of the pesticide. Research on enzymatic methods of detection, as well as some of the problems and challenges associated with these methods, is extensively discussed in this review. These methods can serve as a tool for screening large samples which can be followed up with the more traditional chromatographic methods of analysis.

Depth-resolved imaging and detection of micro-retroreflectors within biological tissue using Optical Coherence Tomography

A new approach to in vivo biosensor design is introduced, based on the use of an implantable micron-sized retroreflector-based platform and non-invasive imaging of its surface reflectivity by Optical Coherence Tomography (OCT). The possibility of using OCT for the depth-resolved imaging and detection of micro-retroreflectors in highly turbid media, including tissue, is demonstrated. The maximum imaging depth for the detection of the micro-retroreflector-based platform within the surrounding media was found to be 0.91 mm for porcine tissue and 1.65 mm for whole milk. With further development, it may be possible to utilize OCT and micro-retroreflectors as a tool for continuous monitoring of analytes in the subcutaneous tissue.

Electrochemical biosensors

Electrochemical biosensors combine the sensitivity of electroanalytical methods with the inherent bioselectivity of the biological component. The biological component in the sensor recognizes its analyte resulting in a catalytic or binding event that ultimately produces an electrical signal monitored by a transducer that is proportional to analyte concentration. Some of these sensor devices have reached the commercial stage and are routinely used in clinical, environmental, industrial, and agricultural applications. The two classes of electrochemical biosensors, biocatalytic devices and affinity sensors, will be discussed in this critical review to provide an accessible introduction to electrochemical biosensors for any scientist (110 references).

Validation of a conductometric bienzyme biosensor for the detection of proteins as marker of organic matter in river samples

This article describes a conductometric bi-layer based bienzyme biosensor for the detection of proteins as a marker of organic matter in rivers. Proteins were chosen to be used as indicators of urban pollution. The working mechanism of the bienzyme biosensor is based on the enzymatic hydrolysis of proteins into several fractions (peptides and amino acids), which results in a local conductivity change depending of the concentration of proteins. In this work, we began with the optimization of biosensor response using bovine serum albumin (BSA) as standard protein. For this objective seven enzymatic biosensors were prepared: four enzymatic sensors with only one layer of enzyme (proteinase K, trypsin, pronase or protease X) and three other enzymatic sensors with two layers (first layer: membrane containing proteinase K; second layer: one of the three other enzymes: trypsin, pronase or protease X). The biosensors were obtained through the deposition of enzymatic layers and the cross-linking process between enzymes and BSA in saturated glutaraldehyde vapour. The response of the various biosensors, described previously, were compared with the values of total organic carbon (TOC), and those of organic nitrogen (Norg), as determined by the laboratory accredits (CEMAGREF of Lyon) using the traditional method of analysis (NF EN 1484, infrared spectroscopy) and (NF EN 25663, mineralization/colorimetry assay) respectively for each water sample obtained from different sites in Lyon (France). The linear correlations obtained with the response of the seven biosensors showed the most important indices of correlations for the biosensor with two enzymatic layers: proteinase K + pronase (pkp). The optimum conditions for the preparation of the pkp biosensor increased the sensitivity and gave a limit of quantification of 0.583 microg/L for TOC and 0.218 microg/L for Norg in water samples. This sensor shows good reproducibility (2.28%), a capacity to be used at temperatures range 10-30 degrees C (depending on the season) and moreover a long lifetime (5 weeks).

Conductometric Microbiosensors for Environmental Monitoring

This review presents the principles of conductometric measurements in ionic media and the equivalent electrical circuits of different designs for conductometric measurements. These types of measurements were first applied for monitoring biocatalytic reactions. The use of conductometric microtransducers is then presented and detailed in the case of pollutant detection for environmental monitoring. Conductometric biosensors have advantages over other types of transducers: they can be produced through inexpensive thinfilm standard technology, no reference electrode is needed and differential mode measurements allow cancellation of a lot of interferences. The specifications obtained for the detection of different pesticides, herbicides and heavy metal ions, based on enzyme inhibition, are presented as well as those obtained for the detection of formaldehyde, 4- chlorophenol, nitrate and proteins as markers of dissolved organic carbon based on enzymatic microbiosensors.

Amperometric biosensing of carbamate and organophosphate pesticides utilizing screen-printed tyrosinase-modified electrodes

A tyrosinase (Tyr) screen-printed biosensor based on the electroreduction of enzymatically generated quinoid products was electrochemically characterized and optimized for determination of carbamates and organophosphorus pesticides. A composite electrode prepared by screen-printing a cobalt (II) phthalocyanine (CoPc) modified cellulose-graphite composite on a polycarbonate support was employed as electrochemical transducer. The Tyr biosensor was prepared by immobilization of enzyme on the composite electrode surface by cross-linking with glutaraldehyde and bovine serum albumin. Parameters affecting the biosensor response such as response time, enzyme loading, concentration and pH of the buffer solution were optimized utilizing catechol as substrate. The maximum response for o-quinone enzymatically generated was obtained after 2 min of reaction. A good reproducibility and high operational stability were found for Tyr biosensor (60 units) at 50 mM phosphate buffer, pH 6.50. Under these conditions, the useful lifetime of biosensor was 10 days. After 15 days, the biosensor could be used with 20% of the initial value. Inhibition studies on the o-quinone steady-state current (at -0.20 V versus Ag/AgCl) were performed to investigate the inhibition kinetics of the pesticides in the enzymatic activity of mushroom tyrosinase. The results shown that the methyl parathion and carbofuran can lead to competitive inhibition process of the enzyme, while diazinon and carbaryl act as mixed inhibitors. Linear relationships were found for methyl parathion (6-100 ppb), diazinon (19-50 ppb), carbofuran (5-90 ppb) and carbaryl (10-50 ppb). Analysis of natural river water samples spiked with 30 ppb of each pesticide showed recoveries between 92.50% and 98.50% and relative standard deviations of 2%.

Determination of triazine herbicides: development of an electroanalytical method utilizing a solid amalgam electrode that minimizes toxic waste residues, and a comparative study between voltammetric and chromatographic techniques

The use of a copper solid amalgam electrode (CuSAE) for the analytical determination of triazine herbicides (atrazine and ametryne) instead of the conventional hanging mercury drop electrode (HMDE) is reported. The results obtained using electroanalytical methods utilizing each of these electrodes were also compared with those provided by the HPLC technique. The results indicated that the CuSAE electrode can be used to detect the herbicides studied, since the detection limits reached using the electrode (3.06 microg L-1 and 3.78 microg L-1 for atrazine and ametryne, respectively) are lower than the maximum values permitted by CONAMA (Brazilian National Council for the Environment) for wastewaters (50 microg L-1) and by the US EPA (Environmental Protection Agency of the United States) in natural water samples (10.00 microg L-1). An electroanalytical methodology employing CuSAE and square wave voltammetry (SWV) was successfully applied to the determination of atrazine and ametryne in natural water samples, yielding good recoveries (70.30%-79.40%). This indicates that the CuSAE provides a convenient substitute for the HMDE, particularly since the CuSAE minimizes the toxic waste residues produced by the use of mercury in HDME-based analyses.

Amperometric biosensor based on tyrosinase immobilized on a boron-doped diamond electrode

A novel method has been developed to immobilize tyrosinase onto the surface of boron-doped diamond (BDD) electrode. The hydrogen-terminated BDD (HBDD) surface was first functionalized by photochemically linking vinyl groups of allylamine, producing covalently linked amine-terminated active BDD (ABDD) surface. Then the tyrosinase was immobilized onto the ABDD surface by carbodiimide coupling reaction. The amperometric response was measured as a function of concentration of phenolic compounds in 0.1M phosphate buffer solution (pH 6.5). The tyrosinase-modified ABDD electrode gave a linear response range of 1-175, 1-200 and 1-200 microM and sensitivity of 80.0, 181.4 and 110.0 mA M(-1)cm(-2) for phenol, p-cresol, 4-chlorophenol, respectively. Moreover, selective detection of dopamine (DA) in the presence of ascorbic acid (AA) has been demonstrated with the tyrosinase-modified ABDD electrode. Linearity was observed within the range of 5-120 microM. The above enzyme electrode could maintain 90% of its original activity after intermittent use for 1 month when storing in a dry state at 4 degrees C.