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

Hollow-Core Fiber-Based Biosensor: A Platform for Lab-in-Fiber Optical Biosensors for DNA Detection

In this paper, a novel platform for lab-in-fiber-based biosensors is studied. Hollow-core tube lattice fibers (HC-TLFs) are proposed as a label-free biosensor for the detection of DNA molecules. The particular light-guiding mechanism makes them a highly sensitive tool. Their transmission spectrum is featured by alternations of high and low transmittance at wavelength regions whose values depend on the thickness of the microstructured web composing the cladding around the hollow core. In order to achieve DNA detection by using these fibers, an internal chemical functionalization process of the fiber has been performed in five steps in order to link specific peptide nucleic acid (PNA) probes, then the functionalized fiber was used for a three-step assay. When a solution containing a particular DNA sequence is made to flow through the HC of the TLF in an 'optofluidic' format, a bio-layer is formed on the cladding surfaces causing a red-shift of the fiber transmission spectrum. By comparing the fiber transmission spectra before and after the flowing it is possible to identify the eventual formation of the layer and, therefore, the presence or not of a particular DNA sequence in the solution.

Monoclonal Antibody-Based Immunosensor for the Electrochemical Detection of Chlortoluron Herbicide in Groundwaters

Chlortoluron (3-(3-chloro-p-tolyl)-1,1-dimethyl urea) is an herbicide widely used in substitution to isoproturon to control grass weed in wheat and barley crops. Chlortoluron has been detected in groundwaters for more than 20 years; and dramatic increases in concentrations are observed after intense rain outbreaks. In this context; we developed an immunosensor for the determination of chlortoluron based on competitive binding of specific monoclonal antibodies on chlortoluron and immobilized biotinylated chlortoluron; followed by electrochemical detection on screen-printed carbon electrodes. The optimized immunosensor exhibited a logarithmic response in the range 0.01-10 µg·L-1; with a calculated detection limit (LOD) of 22.4 ng·L-1; which is below the maximum levels allowed by the legislation (0.1 µg·L-1). The immunosensor was used for the determination of chlortoluron in natural groundwaters, showing the absence of matrix effects.

Binding Properties of Photosynthetic Herbicides with the QB Site of the D1 Protein in Plant Photosystem II: A Combined Functional and Molecular Docking Study

Photosystem II (PSII) is a multi-subunit enzymatic complex embedded in the thylakoid membranes responsible for the primary photosynthetic reactions vital for plants. Many herbicides used for weed control inhibit PSII by interfering with the photosynthetic electron transport at the level of the D1 protein, through competition with the native plastoquinone for the Q_B site. Molecular details of the interaction of these herbicides in the D1 Q_B site remain to be elucidated in plants. Here, we investigated the inhibitory effect on plant PSII of the PSII-inhibiting herbicides diuron, metobromuron, bentazon, terbuthylazine and metribuzin. We combined analysis of OJIP chlorophyll fluorescence kinetics and PSII activity assays performed on thylakoid membranes isolated from pea plants with molecular docking using the high-resolution PSII structure recently solved from the same plant. Both approaches showed for terbuthylazine, metribuzin and diuron the highest affinity for the D1 Q_B site, with the latter two molecules forming hydrogen bonds with His215. Conversely, they revealed for bentazon the lowest PSII inhibitory effect accompanied by a general lack of specificity for the Q_B site and for metobromuron an intermediate behavior. These results represent valuable information for future design of more selective herbicides with enhanced Q_B binding affinities to be effective in reduced amounts.

A dual electro-optical biosensor based on Chlamydomonas reinhardtii immobilised on paper-based nanomodified screen-printed electrodes for herbicide monitoring

The indiscriminate use of herbicides in agriculture contributes to soil and water pollution, with important endangering consequences on the ecosystems. Among the available analytical systems, algal biosensors have demonstrated to be valid tools thanks to their high sensitivity, cost-effectiveness, and eco-design. Herein, we report the development of a dual electro-optical biosensor for herbicide monitoring, based on Chlamydomonas reinhardtii whole cells immobilised on paper-based screen-printed electrodes modified with carbon black nanomaterials. To this aim, a systematic study was performed for the selection and characterisation of a collection among 28 different genetic variants of the alga with difference response behaviour towards diverse herbicide classes. Thus, CC125 strain was exploited as case study for the study of the analytical parameters. The biosensor was tested in standard solutions and real samples, providing high sensitivity (detection limit in the pico/nanomolar), high repeatability (RSD of 5% with n = 100), long lasting working (10 h) and storage stability (3 weeks), any interference in the presence of heavy metals and insecticides, and low matrix effect in drinking water and moderate effect in surface one.

Mathematical Modelling of Biosensing Platforms Applied for Environmental Monitoring

In recent years, mathematical modelling has known an overwhelming integration in different scientific fields. In general, modelling is used to obtain new insights and achieve more quantitative and qualitative information about systems by programming language, manipulating matrices, creating algorithms and tracing functions and data. Researchers have been inspired by these techniques to explore several methods to solve many problems with high precision. In this direction, simulation and modelling have been employed for the development of sensitive and selective detection tools in different fields including environmental control. Emerging pollutants such as pesticides, heavy metals and pharmaceuticals are contaminating water resources, thus threatening wildlife. As a consequence, various biosensors using modelling have been reported in the literature for efficient environmental monitoring. In this review paper, the recent biosensors inspired by modelling and applied for environmental monitoring will be overviewed. Moreover, the level of success and the analytical performances of each modelling-biosensor will be discussed. Finally, current challenges in this field will be highlighted.

Quantum dots functionalised artificial peptides bioinspired to the D1 protein from the Photosystem II of Chlamydomonas reinhardtii for endocrine disruptor optosensing

Herein we describe the design and synthesis of novel artificial peptides mimicking the plastoquinone binding niche of the D1 protein from the green photosynthetic alga Chlamydomonas reinhardtii, also able to bind herbicides. In particular, molecular dynamics (MD) simulations were performed to model in silico the behaviour of three peptides, D1Pep70-H, D1Pep70-S264K and D1Pep70-S268C, as genetic variants with different affinity towards the photosynthetic herbicide atrazine. Then the photosynthetic peptides were functionalised with quantum dots for the development of a hybrid optosensor for the detection of atrazine, one of the most employed herbicides for weed control in agriculture as well as considered as a putative endocrine disruptor case study. The excellent agreement between computational and experimental results self consistently shows resistance or super-sensitivity toward the atrazine target, with detection limits in the μg/L concentration range, meeting the requirements of E.U. legislation.

Ultra-high-sensitivity refractive index sensor based on dual-microfiber coupler structure with the Vernier effect

We demonstrate a novel, to the best of our knowledge, refractive index (RI) sensor based on the Vernier effect in dual-microfiber coupler (MFC) structures. The sensor sensitivity was studied both theoretically and experimentally. The numerical results show that by tracing the wavelength shifts of the envelope formed by the Vernier effect, the sensitivity can be improved by several times compared to that obtained for normal coupler-based sensors. In this Letter, two MFCs with a width and free spectral range (FSR) of $\sim{3.5}\;{\unicode{x00B5} \rm m}$∼3.5µm and 6 nm, respectively, were fabricated. Based on the sensitivity of 5820 nm/RIU for a single coupler, we experimentally achieved an ultra-high sensitivity of 126,540 nm/RIU using dual MFCs by the Vernier effect in the RI range of 1.3350 to 1.3455, which shows good agreement with numerical simulations. The proposed all-fiber RI sensor has the advantages of high sensitivity and low cost and can find applications in chemical and biological detection as well as electronic/magnetic field measurement.

Biotechnological Advances in the Design of Algae-Based Biosensors

In addition to their use in biomass production and bioremediation, algae have been extensively exploited in biosensing applications. Algae-based biosensors have demonstrated potential for sensitive, sustainable, and multiplexed detection of analytes of agroenvironmental and security interest. Their advantages include the availability of different algal bioreceptors including whole cells and their photosynthetic subcomponents, their potential to be integrated into dual transduction miniaturized devices, and the opportunity for continuous environmental monitoring. Despite obstacles including limited stability and selectivity, algae-based biosensing is a realistic prospect that has some recent effective applications. Strategic exploitation of cutting-edge technologies including materials science, nanotechnology, microfluidics, and genome editing will help to achieve the full potential of algae-based sensors.

Red inalámbrica de biosensores enzimáticos para la detección de contaminantes en aguas

En este artículo se presenta el desarrollo de una red inalámbrica de biosensores amperimétricos, que podrá ser distribuida en las fuentes de agua potable, con el fin de alertar sobre la presencia de contaminantes tóxicos. Este sistema no reemplazará los métodos tradicionales para la detección de contaminantes, pero tiene la ventaja de ser un sistema de bajo costo, ideal para aplicaciones en campo y donde sea necesario el procesamiento de una gran cantidad de muestras. Se presentan resultados del desarrollo de los circuitos electrónicos necesarios para la transducción amperométrica, los circuitos para el procesamiento de datos y la comunicación inalámbrica.

Dynamics Properties of Photosynthetic Microorganisms Probed by Incoherent Neutron Scattering

Studies on the dynamical properties of photosynthetic membranes of land plants and purple bacteria have been previously performed by neutron spectroscopy, revealing a tight coupling between specific photochemical reactions and macromolecular dynamics. Here, we probed the intrinsic dynamics of biotechnologically useful mutants of the green alga Chlamydomonas reinhardtii by incoherent neutron scattering coupled with prompt chlorophyll fluorescence experiments. We brought to light that single amino acid replacements in the plastoquinone (PQ)-binding niche of the photosystem II D1 protein impair electron transport (ET) efficiency between quinones and confer increased flexibility to the host membranes, expanding to the entire cells. Hence, a more flexible environment in the PQ-binding niche has been associated to a less efficient ET. A similar function/dynamics relationship was also demonstrated in Rhodobacter sphaeroides reaction centers having inhibited ET, indicating that flexibility at the quinones region plays a crucial role in evolutionarily distant organisms. Instead, a different functional/dynamical correlation was observed in algal mutants hosting a single amino acid replacement residing in a D1 domain far from the PQ-binding niche. Noteworthy, this mutant displayed the highest degree of flexibility, and besides having a nativelike ET efficiency in physiological conditions, it acquired novel, to our knowledge, phenotypic traits enabling it to preserve a high maximal quantum yield of photosystem II photochemistry in extreme habitats. Overall, in the nanosecond timescale, the degree of the observed flexibility is related to the mutation site; in the picosecond timescale, we highlighted the presence of a more pronounced dynamic heterogeneity in all mutants compared to the native cells, which could be related to a marked chemically heterogeneous environment.

Fast pesticide pre-screening in marine environment using a green microalgae-based optical bioassay

The present study evaluates an optical bioassay based on green photosynthetic microalgae as a promising alternative for monitoring of relevant seawater pollutants. Photosystem II fluorescence parameters from several microalgae species were examined in the presence of three common marine pesticides that act as photosynthesis inhibitors. The three pollutants were detected within 10 min in concentrations between ng/L-μg/L. The different algae species showed slightly diverse pesticide sensitivities, being Chlorella mirabilis the most sensitive one. Potential interferences due to oil-spill pollutants were discarded. The lipid content was characterized to identify microorganisms with suitable mechanisms that could facilitate stress acclimatization. C. mirabilis presented elevated content of unsaturated lipids, showing a promising potential for biosensing in saline stress conditions. The optimized microalgae-based bioassay was preliminarily incorporated into a marine buoy for autonomous pre-screening of pesticides in coastal areas, demonstrating its suitability for real-time monitoring of marine water and quantitative evaluation of total biotoxicity.

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.

Sensing photosynthetic herbicides in an electrochemical flow cell

Specific inhibitory reactions of herbicides with photosynthetic reaction centers bound to working electrodes were monitored in a conventional electrochemical cell and a newly designed microfluidic electrochemical flow cell. In both cases, the bacterial reaction centers were bound to a transparent conductive metal oxide, indium-tin-oxide, electrode through carbon nanotubes. In the conventional cell, photocurrent densities of up to a few μA/cm² could be measured routinely. The photocurrent could be blocked by the photosynthetic inhibitor terbutryn (I ₅₀ = 0.38 ± 0.14 μM) and o-phenanthroline (I ₅₀ = 63.9 ± 12.2 μM). The microfluidic flow cell device enabled us to reduce the sample volume and to simplify the electrode arrangement. The useful area of the electrodes remained the same (ca. 2 cm²), similar to the classical electrochemical cell; however, the size of the cell was reduced considerably. The microfluidic flow control enabled us monitoring in real time the binding/unbinding of the inhibitor and cofactor molecules at the secondary quinone site.

The plastoquinol-plastoquinone exchange mechanism in photosystem II: insight from molecular dynamics simulations

In the photosystem II (PSII) of oxygenic photosynthetic organisms, the reaction center (RC) core mediates the light-induced electron transfer leading to water splitting and production of reduced plastoquinone molecules. The reduction of plastoquinone to plastoquinol lowers PSII affinity for the latter and leads to its release. However, little is known about the role of protein dynamics in this process. Here, molecular dynamics simulations of the complete PSII complex embedded in a lipid bilayer have been used to investigate the plastoquinol release mechanism. A distinct dynamic behavior of PSII in the presence of plastoquinol is observed which, coupled to changes in charge distribution and electrostatic interactions, causes disruption of the interactions seen in the PSII-plastoquinone complex and leads to the "squeezing out" of plastoquinol from the binding pocket. Displacement of plastoquinol closes the second water channel, recently described in a 2.9 Å resolution PSII structure (Guskov et al. in Nat Struct Mol Biol 16:334-342, 2009), allowing to rule out the proposed "alternating" mechanism of plastoquinol-plastoquinone exchange, while giving support to the "single-channel" one. The performed simulations indicated a pivotal role of D₁-Ser264 in modulating the dynamics of the plastoquinone binding pocket and plastoquinol-plastoquinone exchange via its interaction with D₁-His252 residue. The effects of the disruption of this hydrogen bond network on the PSII redox reactions were experimentally assessed in the D₁ site-directed mutant Ser264Lys.

A novel potentiometric sensor based on urease/ bovine serum albumin-poly(3,4-ethylenedioxythiophene)/Pt for urea detection

We have presented a potentiometric urea sensor using an urease/bovine serum albumin (BSA)-poly(3,4-ethylenedioxythiophene)(PEDOT)/Pt electrode. A urea detection sensitivity of 15.2 mV/decade (order of magnitude) has been achieved. BSA trapped in the PEDOT matrix was employed to bond urease molecules on the surface of a BSA-PEDOT/Pt electrode via amide bonds formed between the carboxyl functional groups on the enzyme and the amines on the BSA. The effects of PEDOT thickness, pH value of the urea solution, urease concentration, and temperature on the urea detection sensitivity were also studied. The lifetime of the sensor was studied for a period of 10 weeks, and the average sensing degradation rate was about 9 % per week. This sensor displayed a high selectivity to urea over glucose, KCl, and NaCl.

Structure/function/dynamics of photosystem II plastoquinone binding sites

Photosystem II (PSII) continuously attracts the attention of researchers aiming to unravel the riddle of its functioning and efficiency fundamental for all life on Earth. Besides, an increasing number of biotechnological applications have been envisaged exploiting and mimicking the unique properties of this macromolecular pigment-protein complex. The PSII organization and working principles have inspired the design of electrochemical water splitting schemes and charge separating triads in energy storage systems as well as biochips and sensors for environmental, agricultural and industrial screening of toxic compounds. An intriguing opportunity is the development of sensor devices, exploiting native or manipulated PSII complexes or ad hoc synthesized polypeptides mimicking the PSII reaction centre proteins as bio-sensing elements. This review offers a concise overview of the recent improvements in the understanding of structure and function of PSII donor side, with focus on the interactions of the plastoquinone cofactors with the surrounding environment and operational features. Furthermore, studies focused on photosynthetic proteins structure/function/dynamics and computational analyses aimed at rational design of high-quality bio-recognition elements in biosensor devices are discussed.

Photosynthetic machineries in nano-systems

Photosynthetic reaction centres are membrane-spanning proteins, found in several classes of autotroph organisms, where a photoinduced charge separation and stabilization takes place with a quantum efficiency close to unity. The protein remains stable and fully functional also when extracted and purified in detergents thereby biotechnological applications are possible, for example, assembling it in nano-structures or in optoelectronic systems. Several types of bionanocomposite materials have been assembled by using reaction centres and different carrier matrices for different purposes in the field of light energy conversion (e.g., photovoltaics) or biosensing (e.g., for specific detection of pesticides). In this review we will summarize the current status of knowledge, the kinds of applications available and the difficulties to be overcome in the different applications. We will also show possible research directions for the close future in this specific field.

Design and biophysical characterization of atrazine-sensing peptides mimicking the Chlamydomonas reinhardtii plastoquinone binding niche

The plastoquinone (Q(B)) binding niche of the Photosystem II (PSII) D1 protein is the subject of intense research due to its capability to bind also anthropogenic pollutants. In this work, the Chlamydomonas reinhardtii D1 primary structure was used as a template to computationally design novel peptides enabling the binding of the herbicide atrazine. Three biomimetic molecules, containing the Q(B)-binding site in a loop shaped by two α-helices, were reconstituted by automated protein synthesis, and their structural and functional features deeply analysed by biophysical techniques. Standing out among the others, the biomimetic mutant peptide, D1pepMut, showed high ability to mimic the D1 protein in binding both Q(B) and atrazine. Circular dichroism spectra suggested a typical properly-folded α-helical structure, while isothermal titration calorimetry (ITC) provided a complete thermodynamic characterization of the molecular interaction. Atrazine binds to the D1pepMut with a high affinity (Kd = 2.84 μM), and a favourable enthalpic contribution (ΔH = -11.9 kcal mol(-1)) driving the interaction. Fluorescence spectroscopy assays, in parallel to ITC data, provided hyperbolic titration curves indicating the occurrence of a single atrazine binding site. The binding resulted in structural stabilisation of the D1pepMut molecule, as suggested by atrazine-induced cooperative profiles for the fold-unfold transition. The interaction dynamics and the structural stability of the peptides in response to the ligand were particularly considered as mandatory parameters for biosensor/biochip development. These studies paved the way to the set-up of an array of synthetic mutant peptides with a wide range of affinity towards different classes of target analytes, for the development of optical nanosensing platforms for herbicide detection.

A powerful molecular engineering tool provided efficient Chlamydomonas mutants as bio-sensing elements for herbicides detection

This study was prompted by increasing concerns about ecological damage and human health threats derived by persistent contamination of water and soil with herbicides, and emerging of bio-sensing technology as powerful, fast and efficient tool for the identification of such hazards. This work is aimed at overcoming principal limitations negatively affecting the whole-cell-based biosensors performance due to inadequate stability and sensitivity of the bio-recognition element. The novel bio-sensing elements for the detection of herbicides were generated exploiting the power of molecular engineering in order to improve the performance of photosynthetic complexes. The new phenotypes were produced by an in vitro directed evolution strategy targeted at the photosystem II (PSII) D1 protein of Chlamydomonas reinhardtii, using exposures to radical-generating ionizing radiation as selection pressure. These tools proved successful to identify D1 mutations conferring enhanced stability, tolerance to free-radical-associated stress and competence for herbicide perception. Long-term stability tests of PSII performance revealed the mutants capability to deal with oxidative stress-related conditions. Furthermore, dose-response experiments indicated the strains having increased sensitivity or resistance to triazine and urea type herbicides with I(50) values ranging from 6 × 10(-8) M to 2 × 10(-6) M. Besides stressing the relevance of several amino acids for PSII photochemistry and herbicide sensing, the possibility to improve the specificity of whole-cell-based biosensors, via coupling herbicide-sensitive with herbicide-resistant strains, was verified.

Increasing the open-circuit voltage of photoprotein-based photoelectrochemical cells by manipulation of the vacuum potential of the electrolytes

The innately highly efficient light-powered separation of charge that underpins natural photosynthesis can be exploited for applications in photoelectrochemistry by coupling nanoscale protein photoreaction centers to man-made electrodes. Planar photoelectrochemical cells employing purple bacterial reaction centers have been constructed that produce a direct current under continuous illumination and an alternating current in response to discontinuous illumination. The present work explored the basis of the open-circuit voltage (V(OC)) produced by such cells with reaction center/antenna (RC-LH1) proteins as the photovoltaic component. It was established that an up to ~30-fold increase in V(OC) could be achieved by simple manipulation of the electrolyte connecting the protein to the counter electrode, with an approximately linear relationship being observed between the vacuum potential of the electrolyte and the resulting V(OC). We conclude that the V(OC) of such a cell is dependent on the potential difference between the electrolyte and the photo-oxidized bacteriochlorophylls in the reaction center. The steady-state short-circuit current (J(SC)) obtained under continuous illumination also varied with different electrolytes by a factor of ~6-fold. The findings demonstrate a simple way to boost the voltage output of such protein-based cells into the hundreds of millivolts range typical of dye-sensitized and polymer-blend solar cells, while maintaining or improving the J(SC). Possible strategies for further increasing the V(OC) of such protein-based photoelectrochemical cells through protein engineering are discussed.

Algal fluorescence sensor integrated into a microfluidic chip for water pollutant detection

We report the first miniaturized fluorescent sensor based on algae, with an organic light emitting diode (OLED) and an organic photodetector (OPD) integrated into a microfluidic chip. The blue emission OLED was used as the excitation source, while a blend of PTB3/PC(61)BM was used for the fabrication of the organic photodetector. Excitation and emission color filters based on acid/base dyes and a metal complex were developed and assembled with the organic optoelectronic components in order to complete the fluorescent detection system. The detection system was then integrated in a microfluidic chip made from (poly)dimethylsiloxane (PDMS). The complete sensor is designed to detect algal fluorescence in the microfluidic chamber. Algal chlorophyll fluorescence enables evaluation of the toxicity of pollutants like herbicides and metals-ions from agricultural run-offs. The entirely organic bioassay here presented allowed detection of the toxic effects of the herbicide Diuron on Chlamydomonas reinhardtii green algae that gave 50% inhibition of the algae photochemistry (EC(50)) with a concentration as low as 11 nM.

Enhanced photocurrent generation by photosynthetic bacterial reaction centers through molecular relays, light-harvesting complexes, and direct protein-gold interactions

The utilization of proteins as nanodevices for solar cells, bioelectronics, and sensors generally necessitates the transfer of electrons to or from a conducting material. Here we report on efforts to maximize photocurrent generation by bacterial photosynthetic reaction center pigment-protein complexes (RCs) interfaced with a metal electrode. The possibility of adhering RCs to a bare gold electrode was investigated with a view to minimizing the distance for electron tunneling between the protein-embedded electron-transfer cofactors and the metal surface. Substantial photocurrents were achieved despite the absence of coating layers on the electrode or engineered linkers to achieve the oriented deposition of RCs on the surface. Comparison with SAM-covered gold electrodes indicating enhanced photocurrent densities was achieved because of the absence of an insulating layer between the photoactive pigments and the metal. Utilizing RCs surrounded by light-harvesting 1 complex resulted in higher photocurrents, surprisingly not due to enhanced photoabsorption but likely due to better surface coverage of uniformly oriented RC-LH1 complexes and the presence of a tetraheme cytochrome that could act as a connecting wire. The introduction of cytochrome-c (cyt-c) as a molecular relay also produced increases in current, probably by intercalating between the adhered RCs or RC-LH1 complexes and the electrode to mediate electron transfer. Varying the order in which components were introduced to the electrode indicated that dynamic rearrangements of RCs and cyt-c occurred at the bare metal surface. An upper limit for current generation could not be detected within the range of the illumination power available, with the maximum current density achieved by RC-LH1 complexes being on the order of 25 μA/cm(2). High currents could be generated consecutively for several hours or days under ambient conditions.

Biomaterials based on photosynthetic membranes as potential sensors for herbicides

In this study, ultrathin film multilayers of Photosystem II-enriched photosynthetic membranes (BBY) were prepared and immobilized on quartz substrates by means of a Layer by Layer procedure exploiting electrostatic interactions with poly(ethylenimine) as polyelectrolyte. The biomaterials thus obtained were characterized by means of optical techniques and Atomic Force Microscopy, highlighting the fact that the Layer by Layer approach allowed the BBYs to be immobilized with satisfactory results. The activity of these hybrid materials was evaluated by means of optical assays based on the Hill Reaction, indicating that the biosamples, which preserved about 65% of their original activity even ten weeks after preparation, were both stable and active. Furthermore, an investigation of the biochips' sensitivity to the herbicide terbutryn, as a model analyte, gave interesting results: inhibition of photosynthetic activity was observed at terbutryn concentrations higher than 10(-7)M, thus evidencing the potential of such biomaterials in the environmental biosensor field.

Structural and mechanistic investigations of photosystem II through computational methods

The advent of oxygenic photosynthesis through water oxidation by photosystem II (PSII) transformed the planet, ultimately allowing the evolution of aerobic respiration and an explosion of ecological diversity. The importance of this enzyme to life on Earth has ironically been paralleled by the elusiveness of a detailed understanding of its precise catalytic mechanism. Computational investigations have in recent years provided more and more insights into the structural and mechanistic details that underlie the workings of PSII. This review will present an overview of some of these studies, focusing on those that have aimed at elucidating the mechanism of water oxidation at the CaMn₄ cluster in PSII, and those exploring the features of the structure and dynamics of this enzyme that enable it to catalyse this energetically demanding reaction. This article is part of a Special Issue entitled: Photosystem II.