A multi-biosensor based on immobilized Photosystem II on screen-printed electrodes for the detection of herbicides in river water

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.

A green and easy-to-assemble electrochemical biosensor based on thylakoid membranes for photosynthetic herbicides detection

In this study, we report on an easy-to-assemble amperometric electrochemical biosensor incorporating thylakoid membranes for the detection of photosynthetic herbicides. These molecules interfere with the light-induced photosynthetic electron transport occurring at the level of the photosystems within the thylakoid membranes, thus reducing the current of the associated bioelectrode. Thylakoid membranes isolated from pea plants were adsorbed directly on a bare carbon paper working electrode and placed in the measurement cell in the absence of any electrochemical mediator, obtaining a fully environmental-friendly biodevice capable of photocurrent densities up to 14 μA/cm². Three photosynthetic herbicides inhibiting Photosystem II and belonging to different chemical classes, namely diuron, terbuthylazine and metribuzin, were detected by measuring the electrode photocurrent, which decreased reproducibly in a concentration-dependent manner in a range between 10^-7 - 5 × 10^-5 M of each herbicide. The limit of detection for the three herbicides was between 4-6 × 10^-7 M. Storage stability tests revealed for the biosensor a half-life longer than 15 days at 4 °C and full stability up to 4 months at -80 °C. This study provides a simple, environmental-friendly and cost-effective procedure for the fabrication of a mediatorless carbon paper-based electrochemical biosensor characterized by high photocurrents, long storage stability, reproducible detections and good sensitivity.

Reassessing the rationale behind herbicide biosensors: The case of a photosystem II/redox polymer-based bioelectrode

Interfacing photosynthetic protein complexes with electrodes is frequently used for the identification of electron transfer mechanisms and the fabrication of biosensors. Binding of herbicide compounds to the terminal plastoquinone Q_B at photosystem II (PSII) causes disruption of electron flow that is associated with a diminished performance of the associated biodevice. Thus, the principle of electron transport inhibition at PSII can be used for herbicide detection and has inspired the fabrication of several biosensors for this purpose. However, the biosensor performance may reveal a more complex behavior than generally expected. As we present here for a photobioelectrode constituted by PSII embedded in a redox polymer matrix, the effect caused by inhibitors does not only impact the electron transfer from PSII but also the properties of the polymer film used for immobilization and electrical wiring of the protein complexes. Incorporation of phenolic inhibitors into the polymer film surprisingly translates into enhanced photocurrents and, in particular cases, in a higher stability of the overall electrode architecture. The achieved results stress the importance to evaluate first the possible influence of analytes of interest on the biosensor architecture as a whole and provide important insights for consideration in future design of bioelectrochemical devices.

Electrochemical (Bio)Sensors for Pesticides Detection Using Screen-Printed Electrodes

Pesticides are among the most important contaminants in food, leading to important global health problems. While conventional techniques such as high-performance liquid chromatography (HPLC) and mass spectrometry (MS) have traditionally been utilized for the detection of such food contaminants, they are relatively expensive, time-consuming and labor intensive, limiting their use for point-of-care (POC) applications. Electrochemical (bio)sensors are emerging devices meeting such expectations, since they represent reliable, simple, cheap, portable, selective and easy to use analytical tools that can be used outside the laboratories by non-specialized personnel. Screen-printed electrodes (SPEs) stand out from the variety of transducers used in electrochemical (bio)sensing because of their small size, high integration, low cost and ability to measure in few microliters of sample. In this context, in this review article, we summarize and discuss about the use of SPEs as analytical tools in the development of (bio)sensors for pesticides of interest for food control. Finally, aspects related to the analytical performance of the developed (bio)sensors together with prospects for future improvements are discussed.

A Storable Mediatorless Electrochemical Biosensor for Herbicide Detection

A novel mediatorless photo-bioelectrochemical sensor operated with a biofilm of the cyanobacterium Synechocystis PCC6803 wt. for herbicide detection with long term stability (>20 days) was successfully developed and tested. Photoanodic current generation was obtained in the absence of artificial mediators. The inhibitory effect on photocurrent of three commonly used herbicides (i.e., atrazine, diuron, and paraquat) was used as a means of measuring their concentrations in aqueous solution. The injection of atrazine and diuron into the algal medium caused an immediate photocurrent drop due to the inhibition of photosynthetic electron transport. The detected concentrations were suitable for environmental analysis, as revealed by a comparison with the freshwater quality benchmarks set by the Environmental Protection Agency of the United States (US EPA). In contrast, paraquat caused an initial increase (~2 h) of the photocurrent effect of about 200%, as this compound can act as a redox mediator between the cells and the anode. A relatively long-term stability of the biosensor was demonstrated, by keeping anodes colonized with cyanobacterial biofilm in the dark at 4 °C. After 22 days of storage, the performance in terms of the photocurrent was comparable with the freshly prepared biosensor. This result was confirmed by the measurement of chlorophyll content, which demonstrated preservation of the cyanobacterial biofilm. The capacity of this biosensor to recover after a cold season or other prolonged environmental stresses could be a key advantage in field applications, such as in water bodies and agriculture. This study is a step forward in the biotechnological development and implementation of storable mediatorless electrochemical biosensors for herbicide detection.

Effect of sucrose-bound polynuclear iron oxyhydroxide nanoparticles on the efficiency of electron transport in the photosystem II membranes

Effect of water-soluble and stable sucrose-bound iron oxyhydroxide nanoparticles [Fe[III] sucrose complex (FSC)] on the efficiency of electron transport in the photosystem II membranes was studied. FSC significantly increases (by a factor 1.5) the rate of light-induced oxygen evolution in the presence of alternative electron acceptor 2,6-dichloro-p-benzoquinone (DCBQ). Without DCBQ, FSC only slightly (5%) provides the oxygen evolution. Electron transport supported by pair DCBQ + FSC is inhibited by diuron. Maximum of stimulating effect was recorded at Fe(III) concentration 5 µM. In the case of another benzoquinone electron acceptor (2-phenyl-p-benzoquinone and 2,3-dimethyl-p-benzoquinone) and 2,6-dichlorophenolindophenol, stimulating effect of FSC was not observed. Incubation of PSII membranes at different concentrations with FSC is accompanied by binding of Fe(III) by membrane components but only about 50% of iron can be extracted by membranes from Fe(III) solution at pH 6.5. This result implies the heterogeneity of FSC solution in a buffer. The heterogeneity depends on pH and decreases with its rising. At pH around 9.0 Fe(III), sucrose solution is homogeneous. The study of pH effect has shown that stimulation of electron transport is induced only by iron cations which can be bound by membranes. Not extractable iron pool cannot activate electron transfer from oxygen-evolving complex to DCBQ.

An eco-designed paper-based algal biosensor for nanoformulated herbicide optical detection

In this study we reported the development of a paper-based algal biosensor for the optical detection of nanoencapsulated-atrazine, a forefront nanoformulated herbicide with a high effective post-emergence herbicidal activity. In particular, the unicellular green photosynthetic algae Chlamydomonas reinhardtii was immobilised on a paper substrate soaked with an agar thin film and placed in a glass optical measurement cell, obtaining a totally environmental-friendly device. Nanoencapsulated-atrazine was detected by following the variable fluorescence (1-V_J) parameter, which decreased inversely proportional to the herbicide concentrations, in a range between 0.5 and 200 nM, indicating a linear relationship in the measured dose-response curves and a detection limit of 4 pM. Interference studies resulted in a very slight interference in presence of 2 ppm copper and 10 ppb arsenic at safety limits, as well as a slight matrix effect and a satisfactory recovery value of 96 ± 5% for 75 nM nanoencapsulated-atrazine in tap water. Stability studies were also performed obtaining a good storage stability up to 3 weeks. Results demonstrated the suitability of the proposed paper-based optical biosensor as a valid support in smart agriculture for on site, environmental friendly, cost effective and sensitive nanoencapsulated-atrazine analysis.

Advances in Enzyme-Based Biosensors for Pesticide Detection

The intensive use of toxic and remanent pesticides in agriculture has prompted research into novel performant, yet cost-effective and fast analytical tools to control the pesticide residue levels in the environment and food. In this context, biosensors based on enzyme inhibition have been proposed as adequate analytical devices with the added advantage of using the toxicity of pesticides for detection purposes, being more "biologically relevant" than standard chromatographic methods. This review proposes an overview of recent advances in the development of biosensors exploiting the inhibition of cholinesterases, photosynthetic system II, alkaline phosphatase, cytochrome P450A1, peroxidase, tyrosinase, laccase, urease, and aldehyde dehydrogenase. While various strategies have been employed to detect pesticides from different classes (organophosphates, carbamates, dithiocarbamates, triazines, phenylureas, diazines, or phenols), the number of practical applications and the variety of environmental and food samples tested remains limited. Recent advances focus on enhancing the sensitivity and selectivity by using nanomaterials in the sensor assembly and novel mutant enzymes in array-type sensor formats in combination with chemometric methods for data analysis. The progress in the development of solar cells enriched the possibilities for efficient wiring of photosynthetic enzymes on different surfaces, opening new avenues for development of biosensors for photosynthesis-inhibiting herbicides.

Methods for evaluating the pollution impact of urban wet weather discharges on biocenosis: A review

Rainwater becomes loaded with a large number of pollutants when in contact with the atmosphere and urban surfaces. These pollutants (such as metals, pesticides, PAHs, PCBs) reduce the quality of water bodies. As it is now acknowledged that physico-chemical analyses alone are insufficient for identifying an ecological impact, these analyses are frequently completed or replaced by impact studies communities living in freshwater ecosystems (requiring biological indices), ecotoxicological studies, etc. Thus, different monitoring strategies have been developed over recent decades aimed at evaluating the impact of the pollution brought by urban wet weather discharges on the biocenosis of receiving aquatic ecosystems. The purpose of this review is to establish a synthetic and critical view of these different methods used, to define their advantages and disadvantages, and to provide recommendations for futures researches. Although studies on aquatic communities are used efficiently, notably on benthic macroinvertebrates, they are difficult to interpret. In addition, despite the fact that certain bioassays lack representativeness, the literature at present appears meagre regarding ecotoxicological studies conducted in situ. However, new tools for studying urban wet weather discharges have emerged, namely biosensors. The advantages of biosensors are that they allow monitoring the impact of discharges in situ and continuously. However, only one study on this subject has been identified so far, making it necessary to perform further research in this direction.

Evaluation of a biohybrid photoelectrochemical cell employing the purple bacterial reaction centre as a biosensor for herbicides

The Rhodobacter sphaeroides reaction centre is a relatively robust and tractable membrane protein that has potential for exploitation in technological applications, including biohybrid devices for photovoltaics and biosensing. This report assessed the usefulness of the photocurrent generated by this reaction centre adhered to a small working electrode as the basis for a biosensor for classes of herbicides used extensively for the control of weeds in major agricultural crops. Photocurrent generation was inhibited in a concentration-dependent manner by the triazides atrazine and terbutryn, but not by nitrile or phenylurea herbicides. Measurements of the effects of these herbicides on the kinetics of charge recombination in photo-oxidised reaction centres in solution showed the same selectivity of response. Titrations of reaction centre photocurrents yielded half maximal inhibitory concentrations of 208 nM and 2.1 µM for terbutryn and atrazine, respectively, with limits of detection estimated at around 8 nM and 50 nM, respectively. Photocurrent attenuation provided a direct measure of herbicide concentration, with no need for model-dependent kinetic analysis of the signal used for detection or the use of prohibitively complex instrumentation, and prospects for the use of protein engineering to develop the sensitivity and selectivity of herbicide binding by the Rba. sphaeroides reaction centre are discussed.

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The Rhodobacter sphaeroides reaction centre was used as a biosensor for herbicides.

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Herbicide concentration was assessed through the attenuation of a photocurrent.

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The biosensor showed selectivity for triazine herbicides.

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The limit of detection of the biosensor was in the low nanomolar range.

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Photocurrent attenuation is a simple and direct basis for a herbicide biosensor.

Skeletonema marinoi (Bacillariophyceae) sensitivity to herbicides and effects of temperature increase on cellular responses to terbuthylazine exposure

The North East area of Italy is an intensively farmed area, where the use of herbicides has increased dramatically during the last years. Some of the most detected herbicides are triazine compounds, such as: simazine (SIM), terbuthylazine (TBA), its degradation product desethyl-terbuthylazine (D-TBA) and other herbicides, such as metolachlor (MET). In this paper, the sensitivity of the diatom Skeletonema marinoi to the most detected herbicides (TBA, D-TBA, SIM and MET) was preliminarily studied. All the pollutants tested significantly inhibited the diatom growth and photosynthetic efficiency (from the concentration of 15 μg L(-1)) with the exception of TBA which had the strongest effects on S. marinoi starting from the concentration of 5 μg L(-1). Consequently, cellular physiological responses to TBA exposure (1, 5, 10, 20 and 30 μg L(-1)) were further studied at increasing temperature conditions (15, 20 and 25°C). Inhibition of growth rate and photosynthetic efficiency was observed earlier and determined by lower TBA levels than those affecting cell growth. These responses were significantly enhanced at increasing temperature conditions when growth rates were higher than those measured at 15°C. Carbon cell content increased in the cultures exposed to high concentrations of TBA (from 20 μg L(-1)) compared to the controls, especially at high temperatures. Cell chlorophyll significantly increased from the added concentration of 10 μg L(-1) of TBA at all the temperatures and, as a consequence, also the Chl:C ratio significantly increased. The C:N ratio followed the pattern of nitrate uptake and was characterized, at all the temperatures, by low values during the lag phase in cultures with 20 and 30 μg L(-1) of TBA; in these conditions, in fact, the nutrient in the medium was exhausted later then in the controls. Only cultures exposed to 30 μg L(-1) of TBA at 25°C, which stopped to take up nutrients earlier and could not increase chlorophyll levels, did not display any growth capacity. This study shows that S. marinoi is affected by TBA concentrations lower than those affecting some harmful flagellate species frequently observed in the Adriatic Sea. Thus, it raises the question of the combined effects of herbicides pollution and high temperature pressures on phytoplankton composition.

Combined effects of the herbicide terbuthylazine and temperature on different flagellates from the Northern Adriatic Sea

The triazinic herbicide terbuthylazine (TBA) is becoming an emergent contaminant in Italian rivers and in coastal and groundwater. A preliminary analysis of the sensitivity of marine flagellates to TBA was performed by monitoring the photosynthetic efficiency of nine species (belonging to the Dinophyceae or Raphidophyceae class) isolated from the Adriatic Sea. Different sensitivity levels for each flagellate were observed and the most sensitive microalgae, based on PSII inhibition, were: Gonyaulax spinifera>Fibrocapsa japonica>Lingulodinium polyedrum while the most resistant were two species belonging to the Prorocentrum genus. Then the response of two microalgae to drivers, such as temperature and terbuthylazine, applied in combination was also investigated. Two potentially toxic flagellates, Prorocentrum minimum and G. spinifera, were exposed, under different temperature conditions (15, 20 and 25°C), to TBA concentrations that did not completely affect PSII. For both flagellates, effects of TBA on algal growth, measured through cell density and carbon analysis, as well as on the photosynthetic activity are reported. All parameters analyzed showed a negative effect of TBA from the exponential phase. TBA effect on algal growth was significantly enhanced at the optimal temperature conditions (20 and 25°C), while no difference between control and herbicide treatments were detected for G. spinifera grown at 15°C, which represented a stress condition for this species. The maximum inhibition of photosynthetic efficiency was found at 20°C for both organisms. Both flagellates increased cell carbon and nitrogen content in herbicide treatments compared to the control, except G. spinifera grown at 15°C. Chlorophyll-a production was increased only in G. spinifera exposed to 5 μg L(-1) of TBA and the effect was enhanced with the increase of temperature. Herbicide-induced variations in cellular components determined changes in cellular carbon:nitrogen (C:N) and chlorophyll:carbon (Chl:C) ratios. The C:N ratio decreased in both species, while only G. spinifera showed an increase in the Chl:C ratio at all temperature conditions. In response to TBA exposure G. spinifera increased extracellular polysaccharides release at 20 and 25°C, while no difference was reported for P. minimum. Changes in nutrient uptake rates were also observed for P. minimum. Nitrate and phosphate uptake significantly increased in the presence of TBA and this response was enhanced at 25°C, while nitrate uptake increased in G. spinifera only when grown at 25°C. As for growth rates, the observed changes in intracellular component contents increased at optimal temperature conditions. In this work it is shown that temperature conditions can have an important role on the effect of terbuthylazine on algal growth and on the physiological responses of different species. Furthermore, the algal resistance and recovery can be dependent on nutrient availability.

A photosynthetic biosensor with enhanced electron transfer generation realized by laser printing technology

One of the limits of current electrochemical biosensors is a lack of methods providing stable and highly efficient junctions between biomaterial and solid-state devices. This paper shows how laser-induced forward transfer (LIFT) can enable efficient electron transfer from photosynthetic biomaterial immobilized on screen-printed electrodes (SPE). The ideal pattern, in terms of photocurrent signal of thylakoid droplets giving a stable response signal with a current intensity of approximately 335 ± 13 nA for a thylakoid mass of 28 ± 4 ng, was selected. It is shown that the efficiency of energy production of a photosynthetic system can be strongly enhanced by the LIFT process, as demonstrated by use of the technique to construct an efficient and sensitive photosynthesis-based biosensor for detecting herbicides at nanomolar concentrations.

Self-assembly and sensor response of photosynthetic reaction centers on screen-printed electrodes

Photosynthetic reaction centers were immobilized onto gold screen-printed electrodes (Au-SPEs) using a self-assembled monolayer (SAM) of mercaptopropionic acid (MPA) which was deliberately defective in order to achieve effective mediator transfer to the electrodes. The pure Photosystem II (PS II) cores from spinach immobilize onto the electrodes very efficiently but fair badly in terms of photocurrent response (measured using duroquinone as the redox mediator). The cruder preparation of PS II known as BBY particles performs significantly better under the same experimental conditions and shows a photocurrent response of 20-35 nA (depending on preparation) per screen-printed electrode surface (12.5mm(2)). The data was corroborated using AFM, showing that in the case of BBY particles a defective biolayer is indeed formed, with grooves spanning the whole thickness of the layer enhancing the possibility of mass transfer to the electrodes and enabling biosensing. In comparison, the PS II core layer showed ultra-dense organization, with additional formation of aggregates on top of the single protein layer, thus blocking mediator access to the electrodes and/or binding sites. The defective monolayer biosensor with BBY particles was successfully applied for the detection of photosynthesis inhibitors, demonstrating that the inhibitor binding site remained accessible to both the inhibitor and the external redox mediator. Biosensing was demonstrated using picric acid and atrazine. The detection limits were 1.15 nM for atrazine and 157 nM for picric acid.

High sensitivity biosensor measurement based on synchronous detection

The principle of synchronous detection (SD) has been applied to biosensor measurement. SD principle achieves significant increases in the signal to noise ratio, limit of detection and overall measurement robustness. Application of SD in biosensor measurement improves the analysis of the response and avoids the influence of interference/noise produced by stirring, electromagnetic effects and influence of parasitic currents. SD also enables the decomposition of signal to stimulation response and phenomena with long time of response. Second-order phenomena are identifiable in the signal. Linear statistical model was used to develop software for identification of the stimulation signal in the output current. SD was applied to the response signal of a Photosystem II complex (PSII) biosensor. PSII response to light stimulation follows first order kinetics. The inhibition kinetics of PSII has been studied. Kinetic constants of herbicide binding to PSII depend linearly on herbicide concentration and enable measurement of its concentration at low concentrations (linear range for diuron is 10⁻⁶ to 10⁻⁴ mM).

A whole-cell amperometric herbicide biosensor based on magnetically functionalised microalgae and screen-printed electrodes

We report the fabrication of an amperometric whole-cell herbicide biosensor based on magnetic retention of living cells functionalised with magnetic nanoparticles (MNPs) on the surface of a screen-printed electrode. We demonstrate that Chlorella pyrenoidosa microalgae cells coated with biocompatible MNPs and retained on the electrode with a permanent magnet act as a sensing element for the fast detection of herbicides. The magnetic functionalisation does not affect the viability and photosynthesis activity-mediated triazine herbicide recognition in microalgae. The current of ferricyanide ion was recorded during alternating illumination periods and biosensor fabricated was used to detect atrazine (from 0.9 to 74 µM) and propazine (from 0.6 to 120 µM) (the limits of detection 0.7 and 0.4 µM, respectively). We believe that the methodology presented here can be widely used in fabrication of a number of whole cell biosensors since it allows for efficient and reversible cells immobilisation and does not affect the cellular metabolism.

Cathodic stripping voltammetry of clothianidin: Application to environmental studies

A new, rapid and very sensitive electrochemical method for the determination of a new pesticide clothianidin in tap and river water was developed. The electrochemical reduction and determination of clothianidin have been carried out at a hanging mercury drop electrode (HMDE) in various aqueous solutions in the pH range of 2–10 by cyclic voltammetry (CV) and cathodic stripping square wave voltammetry (SW CSV). The best results were obtained for the clothianidin determination by SW CSV method in 0.04 mol l–1 Britton Robinson buffer at pH 8.1. Various conditions of the procedure were checked. Elaborated electroanalytical procedure enable clothianidin determination in the concentration range of 2.0 × 10–8–9.9 × 10–7 mol l–1. The limit of detection (LOD) and limit of quantification (LOQ) were obtained as 2.00 × 10–9 and 2.36 × 10–8 mol l–1, respectively. Precision and accuracy of the developed method were checked by recovery studies in spiked tap and river water. The voltammetric determination has been validated using HPLC with UV detection.

Physical and chemical immobilization methods of photosynthetic materials

Isolated photosynthetic materials have a relatively short active life time that limits their effective use. To circumvent this limitation, various immobilization techniques have been designed to improve their stability both under storage and working conditions. The immobilization methods are identified either as chemical or physical procedures depending on whether covalent bonds are established or not. In this chapter, two immobilization methods frequently used are described: a physical one based on the entrapment of photosynthetic materials in photo-crosslinkable poly(vinylalcohol) polymer bearing styrylpyridinium groups (PVA-SbQ) and a chemical one where the photosynthetic materials are immobilized by coreticulation in an albumin-glutaraldehyde cross-linked matrix (BSA-Glu). Different immobilization procedures in relation with various photosynthetic materials are mentioned.

Detection of photosynthetic herbicides: algal growth inhibition test vs. electrochemical photosystem II biosensor

We compared a novel PSII-biosensor assay with a standard algal growth inhibition test for detection of photosynthetic herbicides--diuron, atrazine and isoproturon in liquid samples. To evaluate the convenience and sensitivity, values of the parameters EC50 and LOD and the duration of assays were compared. The biosensor assay was made with an electrochemical biosensor toxicity analyser with immobilised Photosystem II (PSII) complex. Using the PSII-biosensor assay, higher sensitivity (LOD) to herbicides (10(-8)-10(-9)M) was achieved as compared to standard algal growth inhibition tests (about 10(-7)M). The results of both assays showed a good correlation as concerns their EC50 values while the interval of detectable concentrations is about twice wider for PSII-biosensor. A proposed measurement protocol includes the reference standard of phytotoxicity (RSP). The main advantage of the PSII-biosensor assay is that it can be completed in about 1h and is by 1-2 orders more sensitive than standard algal growth inhibition test, which takes 72 h.

Fabrication of a novel atrazine biosensor and its subpart-per-trillion levels sensitive performance

The present study describes an atrazine biosensor with the detection limit of 0.1 part-per-trillion (ppt). The atrazine biosensor is fabricated on tyrosinase-immobilized vertical growth TiO(2) nanotubes (Tyr/TiO(2)-NTs), based on the inhibition of tyrosinase by atrazine. The designed Tyr/TiO(2)-NTs present excellent applicability in atrazine determination, with high sensitivity and stability, and rapid response. The outstanding sensing characteristics for atrazine is attributed to the appropriate bioelectrochemical interface of Tyr/TiO(2)-NTs, resulting from the preponderant tubular structure, excellent biocompatibility, and hydrophilicity of TiO(2)-NTs. The atrazine biosensor possesses a wide detection range from 0.2 ppt to 2 part-per-billion (ppb). The practical application of the biosensor is realized for the determination of atrazine and the analysis of its transport in soil samples. A new method for determination of atrazine in soil samples is thus established, which greatly simplifies the preparation procedure of sample and is helpful to evaluate the pollution risk of atrazine to soil, groundwater, and surface water.

Optical biosensors for environmental monitoring based on computational and biotechnological tools for engineering the photosynthetic D1 protein of Chlamydomonas reinhardtii

Homology-based protein modelling and computational screening followed by virtual mutagenesis analyses were used to identify functional amino acids in the D1 protein of the photosynthetic electron transfer chain interacting with herbicides. A library of functional mutations in the unicellular green alga Chlamydomonas reinhardtii for preparing biomediators was built and their interactions with herbicides were calculated. D1 proteins giving the lowest and highest binding energy with herbicides were considered as suitable for preparing the environmental biosensors for detecting specific herbicide classes. Arising from the results of theoretical calculations, three mutants were prepared by site-directed mutagenesis and characterized by fluorescence analysis. Their adsorption and selective recognition ability were studied by an equilibrium-adsorption method. The S268C and S264K biomediators showed high sensitivity and resistance, respectively, to both triazine and urea classes of herbicides. When immobilized on a silicon septum, the biomediators were found to be highly stable, remaining so for at least 1-month at room temperature. The fluorescence properties were exploited and a reusable and portable multiarray optical biosensor for environmental monitoring was developed with limits of detection between 0.8 x 10(-11) and 3.0 x 10(-9), depending on the target analyte. In addition, biomediator regeneration without obvious deterioration in performance was demonstrated.

Chlamydomonas reinhardtii genetic variants as probes for fluorescence sensing system in detection of pollutants

The unicellular green alga Chlamydomonas reinhardtii is employed here for the setup of a biosensor demonstrator based on multibiomediators for the detection of herbicides. The detection is based on the activity of photosystem II, the multienzymatic chlorophyll-protein complex located in the thylakoid membrane that catalyzes the light-dependent photosynthetic primary charge separation and the electron transfer chain in cyanobacteria, algae, and higher plants. Several C. reinhardtii mutants modified on the D1 photosystem II protein are generated by site-directed mutagenesis and experimentally tested for the development of a biosensor revealing the modification of the fluorescence parameter (1 - V (J)) in the presence of herbicides. The A250R, A250L, A251C, and I163N mutants are highly sensitive to the urea and triazine herbicide classes; the newly generated F255N mutant is shown to be especially resistant to the class of urea. It follows that the response of the multibiomediators is associated to a particular herbicide subclass and can be useful to monitor several species of pollutants.

Energy from photobioreactors: Bioencapsulation of photosynthetically active molecules, organelles, and whole cells within biologically inert matrices

Photosynthesis is a highly efficient solar energy transformation process. Exploiting this natural phenomenon is one way to overcome the shortage in the Earth’s fuel resources. This review summarizes the work carried out in the field of photobioreactor design via the immobilization of photosynthetically active matter within biologically inert matrices and the potential biotechnological applications of the obtained hybrid materials within the domain of solar energy to chemical energy transformation. The first part deals with the design of artificial photosynthetic reaction centers (RCs) by the encapsulation of pigments, proteins, and complexes. The action of thylakoids, chloroplasts, and whole plant cells, immobilized in biocompatible supports, in the conversion of CO2 into chemical energy, is also addressed. Finally, the latest advances in the exploitation of the bioactivity of photosynthetically active micro-organisms are explored in terms of the production of secondary metabolites and hydrogen.

One-shot screen-printed thylakoid membrane-based biosensor for the detection of photosynthetic inhibitors in discrete samples

Screen-printing technology offers the possibility to produce a large number of sensors at low cost. Thus, due to their intrinsic characteristics and reproducibility, screen-printed electrodes can be used in the development of disposable electrochemical devices. In the present work, carbon-based screen-printed electrodes (SPCEs) have been used to develop a one-shot-measure biosensor for the detection of photosynthetic inhibitors in discrete samples. The measurement was based on the electrochemical evaluation of the activity of photosystem II (PSII), a protein complex present in photosynthetic organisms and involved in the photosynthesis. The biosensor was prepared by the modification of the working electrode of a SPCE, using thylakoid membranes extracted from spinach leaves. The modified sensors were then used as one-shot system to measure the presence of PSII activity inhibitors in discrete standard solutions. The coupling of the developed biosensor with a custom-made cell made it possible to perform tests using only 50 microL of total sample volume with a measurement time of 10 min. Inhibition curves were recorded for some photosynthetic inhibitors in a concentration range of 10(-6) to 10(-8) molL(-1). A reproducibility (relative standard deviation, R.S.D.%) of 10% was found and the calculated limit of detections (LODs) were in the nanomolar range. The effect of storage on sensitivity and reproducibility of a biosensor prepared by direct lyophilisation of thylakoid membranes on the electrode surface was also evaluated, confirming the possible use of the modified sensor up to one week after the preparation. Measurements on real samples were also reported, comparing the results with those obtained using a fluorescence-based commercial instrument for the analysis of photosynthetic inhibitors.

Determination of herbicides by solid phase extraction gas chromatography–mass spectrometry in drinking waters

A solid phase extraction (SPE) method has been optimized for the gas chromatography-mass spectrometry (GC-MS) simultaneous determination of herbicides belonging to the following different families: carbamate (molinate), atrazines (atrazine, propazine, simazine, ametryne, cyanazine, terbutylazine, deethylterbutylazine, deethylatrazine), dinitroaniline (trifluralin, pendimethalin), chloroacetamide (alachlor, metolachlor). Different solid substrates have been compared (C18, cyano, styrene-divinylbenzene, phenyl, graphitic carbon). The type of conditioning and elution solvent, its volume, and the sample flow rate have been considered as variables affecting the recovery yields of the herbicides. The optimized experimental conditions are C18 phase conditioned with 3 mL acetone, loaded with 1L water sample at 5 mL min(-1), and eluted with 3 mL acetone. Good recoveries (included between 79% and 99%) and R.S.D. (included between 2% and 12%) have been obtained for all analytes, except for deethylatrazine whose recovery was 46+/-7%. The recovery of deethylatrazine increases up to 94+/-17% if a non-porous graphitic carbon is coupled to the C18 phase, keeping the other parameters constant as optimized. The optimized method has been successfully checked for the identification and quantitation of the selected herbicides in raw and drinking water samples, with quantitation limits as low as 0.01 microg L(-1), fully in agreement with the current legislation. The method is easily routinable. After development, the method is currently routinely applied for the analysis of herbicides in waters and, up today, more than one thousand samples have been analysed at the "Laboratorio della Società Metropolitana Acque di Torino" (Laboratory of the Municipal Waterworks of Turin) in charge of the control of drinking water quality in Torino.

A disposable electrochemical immunosensor for flow injection immunoassay of carcinoembryonic antigen

A new simple immunoassay method for carcinoembryonic antigen (CEA) detection using a disposable immunosensor coupled with a flow injection system was developed. The immunosensor was prepared by coating CEA/colloid Au/chitosan membrane at a screen-printed carbon electrode (SPCE). Using a competitive immunoassay format, the immunosensor inserted in the flow system with an injection of sample and horseradish peroxidase (HRP)-labeled CEA antibody was used to trap the labeled antibody at room temperature for 35 min. The current response obtained from the labeled HRP to thionine-H(2)O(2) system decreased proportionally to the CEA concentration in the range of 0.50-25 ng/ml with a correlation coefficient of 0.9981 and a detection limit of 0.22 ng/ml (S/N=3). The immunoassay system could automatically control the incubation, washing and current measurement steps with good stability and acceptable accuracy. Thus, the proposed method proved its potential use in clinical immunoassay of CEA.

Photosynthetic proteins for technological applications

Photosynthetic proteins are a source of biological material well-suited to technological applications. They exhibit light-induced electron transfer across lipid membranes that can be exploited for the construction of photo-optical electrical devices. The structure and function of photosynthetic proteins differ across the photosynthetic evolutionary scale, allowing for their application in a range of technologies. Here we provide a general description of the basic and technical research in this sector and an overview of biochips and biosensors based on photochemical activity that have been developed for the bioassay of pollutants.