Electrochemical detection of extracellular hydrogen peroxide in Arabidopsis thaliana: a real-time marker of oxidative stress

Time-resolved chemical monitoring of whole plant roots with printed electrochemical sensors and machine learning

Traditional single-point measurements fail to capture dynamic chemical responses of plants, which are complex, nonequilibrium biological systems. We report TETRIS (time-resolved electrochemical technology for plant root environment in situ chemical sensing), a real-time chemical phenotyping system for continuously monitoring chemical signals in the often-neglected plant root environment. TETRIS consisted of low-cost, highly scalable screen-printed electrochemical sensors for monitoring concentrations of salt, pH, and H2O2 in the root environment of whole plants, where multiplexing allowed for parallel sensing operation. TETRIS was used to measure ion uptake in tomato, kale, and rice and detected differences between nutrient and heavy metal ion uptake. Modulation of ion uptake with ion channel blocker LaCl3 was monitored by TETRIS and machine learning used to predict ion uptake. TETRIS has the potential to overcome the urgent "bottleneck" in high-throughput screening in producing high-yielding plant varieties with improved resistance against stress.

The distribution of submerged macrophytes in response to intense solar radiation and salinity reveals hydrogen peroxide as an abiotic stress indicator

The feasible condition for submerged macrophyte growth is hard to understand as many environmental factors contribute to establishing macrophyte distribution with different intensities generating excess reactive oxygen species (ROS). Among various kinds of ROS, hydrogen peroxide (H₂O₂) is relatively stable and can be measured accurately. Thus, for the quantification of submerged macrophyte species, H₂O₂ can be used to evaluate their distribution in a lake. Submerged macrophytes, such as Potamogeton anguillanus, were abundant in Lake Shinji. The largest biomass distribution was around 1.35 m deep, under low solar radiation intensity, and nearly no biomass was found less than 0.3 m deep, where solar radiation was high. Tissue H₂O₂ concentrations varied in response to the diurnal photosynthetically active radiation (PAR) intensity, which was followed by antioxidant activities, though slightly delayed. Laboratory experiments were conducted with different PAR intensities or salinity concentrations. A stable level of H₂O₂ was maintained up to about 200 μmol m^-2 s^-1 of PAR for 30 days, followed by a gradual increase as PAR increased. The H₂O₂ concentration increased with higher salinity. A change in Chlorophyll a (Chl-a) concentration is associated with an altering H₂O₂ concentration, following a unique negative relationship with H₂O₂ concentration. If H₂O₂ exceeded 45 μmol/gFW, the homeostasis collapsed, and H₂O₂ and Chl-a significantly declined afterward. The above findings indicate that H₂O₂ has a negative effect on the physiological condition of the plant. The increase in H₂O₂ concentration was prevented by antioxidant activities, which elevated with increasing H₂O₂ concentration.

Heterostructure of Metal Oxides Integrated on a GCE for Estimation of H2O2 Capacity in Milk and Fruit Juice Samples

High levels of H2O2 in food can lead to oxidative stress. Which has been linked to a number of neurological diseases. Hence, its detection in beverages is essential. However, a complicated structure of the reaction medium of H2O2 makes the detection procedure very difficult. For this reason, sensitive strategic methods are required. In this study, quantification of H2O2 in milk and apple juice has been obtained via the electrochemical sensing platform based on GCE/SiO-CeONPs. Scanning Electron Microscopy (SEM), Cyclic voltammetry(CV), and electron impedance spectroscopy(EIS) were employed to characterize the composite. The kinetics investigation of the sensor with H2O2 revealed an a quasi-reversible one -electron adsorption process. Under optimized conditions, the Differential Pulse Voltammetry (DPV) in 0.1 M Phosphate buffer (PB) pH 5.5 of the H2O2 displayed a peak at 0.13 V vs. Ag/AgCl with the detection limits of 0.0004 µM, linearity range of 0.01–0.08 µM. The observed LOD values of this method for real samples were calculated to be 0.006 µM and 0.007 µM with LOQ of 0.02 µM for milk and apple juice, respectively. The recovery of the analyte was from 92 to 99%. Furthermore, due to good selectivity and stability, the benefit of this sensor is its applicability in multiple fields.

Continuous monitoring of chemical signals in plants under stress

Time is an often-neglected variable in biological research. Plants respond to biotic and abiotic stressors with a range of chemical signals, but as plants are non-equilibrium systems, single-point measurements often cannot provide sufficient temporal resolution to capture these time-dependent signals. In this article, we critically review the advances in continuous monitoring of chemical signals in living plants under stress. We discuss methods for sustained measurement of the most important chemical species, including ions, organic molecules, inorganic molecules and radicals. We examine analytical and modelling approaches currently used to identify and predict stress in plants. We also explore how the methods discussed can be used for applications beyond a research laboratory, in agricultural settings. Finally, we present the current challenges and future perspectives for the continuous monitoring of chemical signals in plants.

Paper-Based Analytical Devices for the Rapid and Direct Electrochemical Detection of Hydrogen Peroxide in Tomato Leaves Inoculated with Botrytis cinerea

Hydrogen peroxide (H₂O₂) is an important signaling molecule and plays key roles in multiple plant physiological processes. The rapid and direct monitoring of H₂O₂ could improve our understanding of its regulatory mechanisms in plants. In this study, we developed a paper-based analytical device consisting of a disposable nano-gold modified indium tin oxide working electrode to provide a platform for the rapid and direct detection of H₂O₂. The total analytical time was dramatically shortened to be approximate 3 min due to the avoidance of the time-consuming and complex treatment of plant samples. In addition, the amount of plant samples required was less than 3 mg in our approach. We used this system to monitor the concentrations of H₂O₂ in tomato leaves infected by Botrytiscinerea within 24 h. Our results showed that the concentration of H₂O₂ in tomato leaves was increased in the initial phase, peaked at 1.5 μmol gFW⁻¹ at 6 h, and then decreased. The production trend of H₂O₂ in tomato leaves inoculated with Botrytiscinerea detected with our approach is similar to the 3,3-diaminobenzidine staining method. Taken together, our study offers a rapid and direct approach for the detection of H₂O₂, which will not only pave the way for the further investigation of the regulation mechanisms of H₂O₂ in plants, but also promote the development of precision agriculture technology.

Modulating physicochemical properties in Gd3+@Yb2O3 nanospheres for efficient electrochemical monitoring of H2O2

Herein, a uniform spherical shaped Gd(III) doped Yb₂O₃ (Gd@Yb₂O₃) nanoparticles (NPs) was successfully synthesized via hydrothermal method for electrochemical detection of H₂O₂. The calcination effect and porosity of the materials well elaborated in the present work. The optical properties, size, morphological, thermal, sensing, surface and crystalline properties of synthesized materials were examined by several techniques. The enhanced electrocatalytic performance of Gd@Yb₂O₃ make the present sensor excellent towards the determination of H₂O₂.The anodic and cathodic peak current increased regularly with addition of H₂O₂ solution. The electrode coating surface was stable even after a number of electrochemical cycles and have high limit of detection (51 nM). Moreover, the present sensor was successfully employed for detection of H₂O₂ in real samples.

New Reusable Solid Biosensor with Covalent Immobilization of the Horseradish Peroxidase Enzyme: In Situ Liberation Studies of Hydrogen Peroxide by Portable Chemiluminescent Determination

Herein, we reported a chemiluminescent biosensor based on the covalent immobilization of the horseradish peroxidase (HRP) enzyme on a polydimethylsiloxane (PDMS) support to quantify in situ hydrogen peroxide (H₂O₂). The chemiluminescent reaction based on the use of luminol as an oxidizable substrate, with HRP as the catalyst, has been used in order to quantify H₂O₂ as the oxidizing agent. The performance of the proposed biosensor has been demonstrated to determine H₂O₂ liberated by cells in a culture medium and for evaluating the delivery of H₂O₂ from denture cleaner tablets, as examples of application. For both analyses, the results indicated that the biosensor is cost-effective, sensitive, and selective with a detection limit of 0.02 μM and good linearity over the range 0.06-10 μM. Precision was also satisfactory (relative standard deviation, % RSD < 6). The strength of this biosensing system is the simplicity, portability, and reusability of the devices; it can be applied up to 60 times with 90% of its activity maintained.

Design and Characterization of Effective Ag, Pt and AgPt Nanoparticles to H₂O₂ Electrosensing from Scrapped Printed Electrodes

The use of disposable screen-printed electrodes (SPEs) has extraordinarily grown in the last years. In this paper, conductive inks from scrapped SPEs were removed by acid leaching, providing high value feedstocks suitable for the electrochemical deposition of Ag, Pt and Ag core-Pt shell-like bimetallic (AgPt) nanoparticles, onto screen-printed carbon electrodes (M_L@SPCEs, M = Ag, Pt or AgPt, L = metal nanoparticles from leaching solutions). M_L@SPCEs were characterized by scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. The results were compared to those obtained when metal nanoparticles were synthesised using standard solutions of metal salts (M_S@SPCEs). Both M_L@SPCEs and M_S@SPCEs exhibited similar cyclic voltammetric patterns referred to the electrochemical stripping of silver or the adsorption/desorption of hydrogen/anions in the case of platinum, proving leaching solutions extremely effective for the electrodeposition of metallic nanoparticles. The use of both M_L@SPCEs and M_S@SPCEs proved effective in enhancing the sensitivity for the detection of H₂O₂ in phosphate buffer solutions (pH = 7). The AgPt_L@SPCE was used as proof of concept for the validation of an amperometric sensor for the determination of H₂O₂ within laundry boosters and antiseptic samples. The electrochemical sensor gave good agreement with the results obtained by a spectrophotometric method with H₂O₂ recoveries between 100.6% and 106.4%.

Chromogenic, Fluorescent, and Redox Sensors for Multichannel Imaging and Detection of Hydrogen Peroxide in Living Cell Systems

Hydrogen peroxide (H₂O₂) is an important reactive oxygen species (ROS). Maintaining the H₂O₂ concentration at a normal level is critical to achieve the normal physiological activities of cells, which otherwise might trigger various diseases. Therefore, it is necessary to develop new and practical multisignaling sensors for both visualization of intracellular H₂O₂ and accurate detection of extracellular H₂O₂. In this paper, a novel multichannel signaling fluorescence-electrochemistry combined probe 1 (FE-H₂O₂) is presented for imaging and detection of H₂O₂ in living cell systems. In our design, the probe FE-H₂O₂ consists of a H₂O₂ reaction site and 4-ferrocenyl(vinyl)pyridine unit which affords chromogenic, fluorescent, and electrochemical signals. These structural motifs yield a combined chromogenic, fluorescent, and redox sensor in a single molecule. Probe FE-H₂O₂ showed a "Turn-On" fluorescence response to H₂O₂, which can be used for monitoring intracellular H₂O₂ in vivo. Furthermore, the electrochemical response of probe FE-H₂O₂ was decreased after the addition of H₂O₂, which can be applied for accurate detection of H₂O₂ released from living cells. When the fluorescence imaging method is combined with electrochemical analysis technology, it is hopeful that the well-designed multimodule probe can serve as a practical tool for understanding the metabolism and homeostasis of H₂O₂ in a complex biological system.

A Comparative Study of Poly(Azure A) Film-Modified Disposable Electrodes for Electrocatalytic Oxidation of H₂O₂: Effect of Doping Anion

In the present paper, poly(azure A) (PAA) films were electrosynthetized in the presence of different doping anions on disposable screen-printed carbon electrodes (SPCEs). The anions used included inorganic monoatomic (chloride and fluoride), inorganic polyatomic (nitrate and sulfate) and organic polyatomic (dodecyl sulfate, DS) species. The coated electrodes thus obtained were characterized by electrochemical techniques and SEM. They showed improved electrocatalytic activities towards hydrogen peroxide oxidation compared to that of a bare SPCE. In particular, the insertion of DS anions inside PAA films provided a special sensitivity to the electrocatalysis of H₂O₂, which endowed these electrodes with promising analytical features for H₂O₂ quantification. We obtained a wide linear response for H₂O₂ within a range of 5 µM to 3 mM and a limit of detection of 1.43 ± 0.10 µM (signal-to-noise ratio of 3). Furthermore, sensitivity was 72.4 ± 0.49 nA·µM⁻¹∙cm⁻² at a relatively low electrocatalytic oxidation overpotential of 0.5 V vs. Ag. The applicability of this boosted system was tested by the analysis of H₂O₂ in commercial samples of a hair lightener and an antiseptic and was corroborated by spectrophotometric methods.

In-vivo electrochemical monitoring of H2O2 production induced by root-inoculated endophytic bacteria in Agave tequilana leaves

A dual-function platinum disc microelectrode sensor was used for in-situ monitoring of H₂O₂ produced in A. tequilana leaves after inoculation of their endophytic bacteria (Enterobacter cloacae). Voltammetric experiments were carried out from 0.0 to -1.0V, a potential range where H₂O₂ is electrochemically reduced. A needle was used to create a small cavity in the upper epidermis of A. tequilana leaves, where the fabricated electrochemical sensor was inserted by using a manual three-dimensional micropositioner. Control experiments were performed with untreated plants and the obtained electrochemical results clearly proved the formation of H₂O₂ in the leaves of plants 3h after the E. cloacae inoculation, according to a mechanism involving endogenous signaling pathways. In order to compare the sensitivity of the microelectrode sensor, the presence of H₂O₂ was detected in the root hairs by 3,3-diaminobenzidine (DAB) stain 72h after bacterial inoculation. In-situ pH measurements were also carried out with a gold disc microelectrode modified with a film of iridium oxide and lower pH values were found in A. tequilana leaves treated with bacteria, which may indicate the plant produces acidic substances by biosynthesis of secondary metabolites. This microsensor could be an advantageous tool for further studies on the understanding of the mechanism of H₂O₂ production during the plant-endophyte interaction.

Non-invasive continuous monitoring of pro-oxidant effects of engineered nanoparticles on aquatic microorganisms

Engineered nanomaterials (ENMs) are key drivers for the development of highly sophisticated new technologies. As all new attainments, the rapidly increasing used of ENMs raise concerns about their safety for the environment and humans. There is growing evidence showing that if engineered nanomaterials are released into the environment, there is a possibility that they could cause harm to aquatic microorganisms. Among the divers effects triggering their toxicity the ability of ENMs to generate reactive oxygen species (ROS) capable of oxidizing biomolecules is currently considered a central mechanism of toxicity. Therefore, development of sensitive tools for quantification of the ROS generation and oxidative stress are highly sought. After briefly introducing ENMs-induced ROS generation and oxidative stress in the aquatic microorganisms (AMOs), this overview paper focuses on a new optical biosensor allowing sensitive and dynamic measurements of H₂O₂ in real-time using multiscattering enhanced absorption spectroscopy. Its principle is based on sensitive absorption measurements of the heme protein cytochrome c whose absorption spectrum alters with the oxidation state of constituent ferrous Fe^II and ferric Fe^III. For biological applications cytochrome c was embedded in porous random media resulting in an extended optical path length through multiple scattering of light, which lowers the limit of detection to a few nM of H₂O₂. The sensor was also integrated in a microfluidic system containing micro-valves and sieves enabling more complex experimental conditions. To demonstrate its performance, abiotic absorption measurements of low concentrations of dye molecules and 10 nm gold particles were carried out achieving limits of detection in the low nM range. Other biologically relevant reactive oxygen species can be measured at sub-μM concentrations, which was shown for glucose and lactate through enzymatic reactions producing H₂O₂. In ecotoxicological investigations H₂O₂ excreted by aquatic microorganisms exposed to various stressors were measured. Pro-oxidant effects of nano-TiO₂ and nano-CuO towards green alga Chlamydomonas reinhardtii were explored in various exposure media and under different light illuminations. Dynamics of Cd²⁺ induced effects on photosynthetic activity, sensitisation and recovery of cells of C. reinhardtii was also studied.

Monitoring intra- and extracellular redox capacity of intact barley aleurone layers responding to phytohormones

Redox regulation is important for numerous processes in plant cells including abiotic stress, pathogen defence, tissue development, seed germination and programmed cell death. However, there are few methods allowing redox homeostasis to be addressed in whole plant cells, providing insight into the intact in vivo environment. An electrochemical redox assay that applies the menadione-ferricyanide double mediator is used to assess changes in the intracellular and extracellular redox environment in living aleurone layers of barley (Hordeum vulgare cv. Himalaya) grains, which respond to the phytohormones gibberellic acid and abscisic acid. Gibberellic acid is shown to elicit a mobilisation of electrons as detected by an increase in the reducing capacity of the aleurone layers. By taking advantage of the membrane-permeable menadione/menadiol redox pair to probe the membrane-impermeable ferricyanide/ferrocyanide redox pair, the mobilisation of electrons was dissected into an intracellular and an extracellular, plasma membrane-associated component. The intracellular and extracellular increases in reducing capacity were both suppressed when the aleurone layers were incubated with abscisic acid. By probing redox levels in intact plant tissue, the method provides a complementary approach to assays of reactive oxygen species and redox-related enzyme activities in tissue extracts.

Pro-oxidant effects of nano-TiO2on Chlamydomonas reinhardtii during short-term exposure

This is the first continuous quantification of abiotic and biotic nano-TiO₂– stimulated H₂O₂revealing that measured extracellular and intracellular pro-oxidant endpoints inC. reinhardtiican differ significantly.

Reactive oxygen species: Reactions and detection from photosynthetic tissues

Reactive oxygen species (ROS) have long been recognized as compounds with dual roles. They cause cellular damage by reacting with biomolecules but they also function as agents of cellular signaling. Several different oxygen-containing compounds are classified as ROS because they react, at least with certain partners, more rapidly than ground-state molecular oxygen or because they are known to have biological effects. The present review describes the typical reactions of the most important ROS. The reactions are the basis for both the detection methods and for prediction of reactions between ROS and biomolecules. Chemical and physical methods used for detection, visualization and quantification of ROS from plants, algae and cyanobacteria will be reviewed. The main focus will be on photosynthetic tissues, and limitations of the methods will be discussed.

Auxin and cytokinin metabolism and root morphological modifications in Arabidopsis thaliana seedlings infected with Cucumber mosaic virus (CMV) or exposed to cadmium

Arabidopsis thaliana L. is a model plant but little information is available about morphological root changes as part of a phytohormonal common response against both biotic and abiotic stressors. For this purpose, two-week-old Arabidopsis seedlings were treated with 10 μM CdSO₄ or infected with CMV. After 12 days the entire aerial parts and the root system were analyzed, and the presence of CMV or the accumulation of Cd were detected. Microscopic analysis revealed that both CMV and Cd influenced root morphology by a marked development in the length of root hairs and an intense root branching if compared to controls. Among the three treatments, Cd-treated seedlings showed a shorter root axis length and doubled their lateral root diameter, while the lateral roots of CMV-infected seedlings were the longest. The root growth patterns were accompanied by significant changes in the levels of indole-3-acetic acid, trans-zeatin riboside, dihydrozeatin riboside, as a probable consequence of the regulation of some genes involved in their biosynthesis/degradation. The opposite role on root development played by the phythormones studied is discussed in detail. The results obtained could provide insights into novel strategies for plant defense against pathogens and plant protection against pollutants.