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

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.

Biosensors: Electrochemical Devices-General Concepts and Performance

This review provides a general overview of different biosensors, mostly concentrating on electrochemical analytical devices, while briefly explaining general approaches to various kinds of biosensors, their construction and performance. A discussion on how all required components of biosensors are brought together to perform analytical work is offered. Different signal-transducing mechanisms are discussed, particularly addressing the immobilization of biomolecular components in the vicinity of a transducer interface and their functional integration with electronic devices. The review is mostly addressing general concepts of the biosensing processes rather than specific modern achievements in the area.

Photosystem II in bio-photovoltaic devices

Hybrid photoelectrodes containing biological pigment-protein complexes can be used for environmentally friendly solar energy conversion, herbicide detection, and other applications. The total number of scientific publications on hybrid bio-based devices has grown rapidly over the past decades. Particular attention is paid to the integration of the complexes of PSII into photoelectrochemical devices. A notable feature of these complexes from a practical point of view is their ability to obtain electrons from abundant water. The utilization or imitation of the PSII functionality seems promising for all of the following: generating photoelectricity, photo-producing hydrogen, and detecting herbicides. This review summarizes recent advances in the development of hybrid devices based on PSII. In a brief historical review, we also highlighted the use of quinone-type bacterial reaction centers in hybrid devices. These proteins are the first from which the photoelectricity signal was detected. The photocurrent in these first systems, developed in the 70s-80s, was about 1 nA cm-2. In the latest work, by Güzel et al. (2020), a stable current of about 888 μA cm-2 as achieved in a PSII-based solar cell. The present review is inspired by this impressive progress. The advantages, disadvantages, and future endeavors of PSII-inspired bio-photovoltaic devices are also presented.

Photosynthetic Nanomaterial Hybrids for Bioelectricity and Renewable Energy Systems

Harvesting solar energy in the form of electricity from the photosynthesis of plants, algal cells, and bacteria has been researched as the most environment-friendly renewable energy technology in the last decade. The primary challenge has been the engineering of electrochemical interfacing with photosynthetic apparatuses, organelles, or whole cells. However, with the aid of low-dimensional nanomaterials, there have been many advances, including enhanced photon absorption, increased generation of photosynthetic electrons (PEs), and more efficient transfer of PEs to electrodes. These advances have demonstrated the possibility for the technology to advance to a new level. In this article, the fundamentals of photosynthesis are introduced. How PE harvesting systems have improved concerning solar energy absorption, PE production, and PE collection by electrodes is discussed. The review focuses on how different kinds of nanomaterials are applied and function in interfacing with photosynthetic materials for enhanced PE harvesting. Finally, the review analyzes how the performance of PE harvesting and stand-alone systems have evolved so far and its future prospects.

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.

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.

Trends and Perspectives in Immunosensors for Determination of Currently-Used Pesticides: The Case of Glyphosate, Organophosphates, and Neonicotinoids

Pesticides, due to their intensive use and their peculiar chemical features, can persist in the environment and enter the trophic chain, thus representing an environmental risk for the ecosystems and human health. Although there are several robust and reliable standard analytical techniques for their monitoring, the high frequency of contamination caused by pesticides requires methods for massive monitoring campaigns that are capable of rapidly detecting these compounds in many samples of different origin. Immunosensors represent a potential tool for simple, rapid, and sensitive monitoring of pesticides. Antibodies coupled to electrochemical or optical transducers have resulted in effective detection devices. In this review, the new trends in immunosensor development and the application of immunosensors for the detection of pesticides of environmental concern-such as glyphosate, organophosphates, and neonicotinoids-are described.

Electrochemical characterization of LHCII on graphite electrodes - Potential-dependent photoactivation and arrangement of complexes

Light-dependent electrochemical properties of the light harvesting complexes of Photosystem II (LHCII) and the corresponding interactions with screen-printed graphite electrodes (GEs) are determined. No exogenous soluble redox mediators are used. LHCII isolated from spinach leaves are immobilized on GE by physical adsorption and through interactions with glutaraldehyde. Importantly, the insertion of LHCII into the pores of a GE is achieved by subjecting the electrode to specific potentials. Both trimeric and aggregated forms of LHCII located within the graphite layer retain their native structures. Voltammetric current peaks centred at ca. -230 and + 50 mV vs. Ag/AgCl (+94 and + 374 mV vs. NHE) limit the investigation of the reduction and oxidation processes of immobilized LHCII. An anodic photocurrent is generated in the LHCII-GE proportional to light intensity and can reach a value of 150 nA/cm². Light-dependent charge separation in LHCII followed by electron transfer to the GE occurs only at potentials of above -200 mV vs. Ag/AgCl (+124 mV vs. NHE). Our results illustrate the importance of the structural proximity of LHCII and GE for photocurrent generation.

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.

Protein film voltammetry and co-factor electron transfer dynamics in spinach photosystem II core complex

Direct protein film voltammetry (PFV) was used to investigate the redox properties of the photosystem II (PSII) core complex from spinach. The complex was isolated using an improved protocol not used previously for PFV. The PSII core complex had high oxygen-evolving capacity and was incorporated into thin lipid and polyion films. Three well-defined reversible pairs of reduction and oxidation voltammetry peaks were observed at 4 °C in the dark. Results were similar in both types of films, indicating that the environment of the PSII-bound cofactors was not influenced by film type. Based on comparison with various control samples including Mn-depleted PSII, peaks were assigned to chlorophyll a (Chl a) (Em = -0.47 V, all vs. NHE, at pH 6), quinones (-0.12 V), and the manganese (Mn) cluster (Em = 0.18 V). PFV of purified iron heme protein cytochrome b-559 (Cyt b-559), a component of PSII, gave a partly reversible peak pair at 0.004 V that did not have a potential similar to any peaks observed from the intact PSII core complex. The closest peak in PSII to 0.004 V is the 0.18 V peak that was found to be associated with a two-electron process, and thus is inconsistent with iron heme protein voltammetry. The -0.47 V peak had a peak potential and peak potential-pH dependence similar to that found for purified Chl a incorporated into DMPC films. The midpoint potentials reported here may differ to various extents from previously reported redox titration data due to the influence of electrode double-layer effects. Heterogeneous electron transfer (hET) rate constants were estimated by theoretical fitting and digital simulations for the -0.47 and 0.18 V peaks. Data for the Chl a peaks were best fit to a one-electron model, while the peak assigned to the Mn cluster was best fit by a two-electron/one-proton model.

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.

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.