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Sensitivity, selectivity, reliability, and measurement range of a sensor are vital parameters for its wide applications. Fast growing number of various detection systems seems to justify worldwide efforts to enhance one or some of the parameters. Therefore, as one of the possible solutions, multi-domain sensing schemes have been proposed. This means that the sensor is interrogated simultaneously in, e.g., optical and electrochemical domains. An opportunity to combine the domains within a single sensor is given by optically transparent and electrochemically active transparent conductive oxides (TCOs), such as indium tin oxide (ITO). This work aims to bring understanding of electro-optically modulated lossy-mode resonance (LMR) effect observed for ITO-coated optical fiber sensors. Experimental research supported by numerical modeling allowed for identification of the film properties responsible for performance in both domains, as well as interactions between them. It has been found that charge carrier density in the semiconducting ITO determines the efficiency of the electrochemical processes and the LMR properties. The carrier density boosts electrochemical activity but reduces capability of electro-optical modulation of the LMR. It has also been shown that the carrier density can be tuned by pressure during magnetron sputtering of ITO target. Thus, the pressure can be chosen as a parameter for optimization of electro-optical modulation of the LMR, as well as optical and electrochemical responses of the device, especially when it comes to label-free sensing and biosensing.

Spectroelectrochemical (SEC) measurements are widely applied in analytical chemistry. Transparent or semitransparent electrodes are typically used for optical analysis of the electrochemical (EC) processes, where mainly EC readout indicates the state of the electrode while changes in transmitted optical spectrum help to identify products of the EC reactions. In this work, we propose SEC measurements enhanced by additional optical monitoring of the electrode. In this setup, an optical fiber sensor or rather a section of the polymer-clad silica multimode fiber core coated with a thin conductive oxide, i.e., indium tin oxide (ITO), acts also as the electrode. The properties of the film were appropriately tailored to give rise to the lossy-mode resonance (LMR) phenomenon and therefore, except for the SEC readouts, optical monitoring of the electrode was simultaneously possible. The LMR response depends on the properties of the ITO and the optical properties of the surrounding medium. Thus, in the proposed setup, three interrogation readouts may be received, i.e., EC, optical spectrum corresponding to the volume of the analyte as for standard SEC, and the LMR spectrum dependent on the state of the sensor/electrode surface. It must be noted that the optical measurements are performed in two, separate, perpendicularly arranged, spectrophotometric paths with the EC activation (S2EC). In this work, the three readouts have been correlated and compared to the application of other working electrodes applied in standard SEC, such as platinum mesh and ITO-coated glass slide. First, every interrogation path was investigated individually during the cyclic voltammetry (CV) with two metal ion oxidation-reduction reaction (redox) probes, such as potassium ferricyanide and methylene blue. Then simultaneous measurements during chronoamperometry (CA) were conducted with the sensor and cross-correlation between the readouts had been discussed. By combining the sensing techniques an enhancement in the amount of gathered information about the analyte has been achieved.

A sensing system with indium tin oxide-based lossy-mode resonance optical fiber sensors as a working electrode inducing spectroelectrochemical interactions and additionally capable for optical monitoring of electrochemical processes is reported.

Triacylglycerol is a key lipid compound involved in maintaining homeostasis of both membrane lipids and free fatty acids (FFA) in plant cells under adverse environmental conditions. However, its role in the process of lipid remodeling has not been fully recognized, especially in monocots, including grass species. For our study, two closely related introgression forms of Lolium multiflorum (Italian ryegrass) and Festuca arundinacea (tall fescue), distinct in their level of drought tolerance, were selected as plant models to study rearrangements in plant lipidome under water deficit and further re-watering. The low drought tolerant (LDT) form revealed an elevated level of cellular membrane damage accompanied by an increased content of polyunsaturated FFA and triacylglycerol under water deficit, compared with the high drought tolerant (HDT) form. However, the LDT introgression form demonstrated also the ability to regenerate its membranes after stress cessation. The obtained results clearly indicated that accumulation of triacylglycerol under advanced drought in the LDT form could serve as a cellular protective mechanism against overaccumulation of toxic polyunsaturated FFA and other lipid intermediates. Furthermore, accumulation of triacylglycerol under drought conditions could serve also as storage of substrates required for further regeneration of membranes after stress cessation. The rearrangements in triacylglycerol metabolism were supported by the upregulation of several genes, involved in a biosynthesis of triacylglycerol. With respect to this process, diacylglycerol O-acyltransferase DGAT2 seems to play the most important role in the analyzed grasses.

Lossy-mode resonance optical fiber sensors with indium tin oxide (ITO) thin overlay for combined optical and electrochemical label-free biosensing are discussed. Properties of ITO were tuned by the film deposition conditions towards reducing the cross- domain interference.

This work discuses an optical fiber lossy-mode resonance-based sensor used for label- free biosensing of protein in optical and electrochemical domains. Thanks to application of electrochemical domain biological receptor was electropolymerized on the sensor’s surface.

Lolium multiflorum/Festuca arundinacea introgression forms have been proved several times to be good models to identify key components of grass metabolism involved in the mechanisms of tolerance to water deficit. Here, for the first time, a relationship between photosynthetic and antioxidant capacities with respect to drought tolerance of these forms was analyzed in detail. Two closely related L. multiflorum/F. arundinacea introgression forms distinct in their ability to re-grow after cessation of prolonged water deficit in the field were selected and subjected to short-term drought in pots to dissect precisely mechanisms of drought tolerance in this group of plants. The studies revealed that the form with higher drought tolerance was characterized by earlier and higher accumulation of abscisic acid, more stable cellular membranes, and more balanced reactive oxygen species metabolism associated with a higher capacity of the antioxidant system under drought conditions. On the other hand, both introgression forms revealed the same levels of stomatal conductance, CO2 assimilation, and consequently, intrinsic water use efficiency under drought and recovery conditions. However, simultaneous higher adjustment of the Calvin cycle to water deficit and reduced CO2 availability, with respect to the accumulation and activity of plastid fructose-1,6-bisphosphate aldolase, were clearly visible in the form with higher drought tolerance.

In this work, we present a direct electrochemical biofunctionalization of an indium-tin-oxide-coated lossy-mode resonance optical fiber sensor. The functionalization using a biotin derivative was performed by cyclic voltammetry in a 10 mM biotin hydrazide solution. All stages of the experiment were simultaneously verified with optical and electrochemical techniques. Performed measurements indicate the presence of a poly-biotin layer on the sensor’s surface. Furthermore, dual-domain detection of 0.01 and 0.1 mg/mL of avidin confirms the sensor’s viability for label-free detection.

Impact of photosynthetic and antioxidant capacities on drought tolerance of two closely related forage grasses, Festuca arundinacea and Festuca glaucescens, was deciphered. Within each species, two genotypes distinct in drought tolerance were subjected to a short-term drought, followed by a subsequent re-watering. The studies were focused on: (i) analysis of plant physiological performance, including: water uptake, abscisic acid (ABA) content, membrane integrity, gas exchange, and relative water content in leaf tissue, (ii) analysis of plant photosynthetic capacity (chlorophyll fluorescence, gene expression, protein accumulation, and activity of selected enzymes of the Calvin cycle), and (iii) analysis of plant antioxidant capacity (reactive oxygen species (ROS) generation, gene expression, protein accumulation and activity of selected enzymes). Though, F. arundinacea and F. glaucescens revealed different strategies in water uptake, and partially also in ABA signaling, their physiological reactions to drought and further re-watering, were similar. On the other hand, performance of the Calvin cycle and antioxidant system differed between the analyzed species under drought and re-watering periods. A stable efficiency of the Calvin cycle in F. arundinacea was crucial to maintain a balanced network of ROS/redox signaling, and consequently drought tolerance. The antioxidant capacity influenced mostly tolerance to stress in F. glaucescens.

Impact of photosynthetic and antioxidant capacities on drought tolerance of two closely related forage grasses, Festuca arundinacea and Festuca glaucescens, was deciphered. Within each species, two genotypes distinct in drought tolerance were subjected to a short-term drought, followed by a subsequent re-watering. The studies were focused on: (i) analysis of plant physiological performance, including: water uptake, abscisic acid (ABA) content, membrane integrity, gas exchange, and relative water content in leaf tissue; (ii) analysis of plant photosynthetic capacity (chlorophyll fluorescence; gene expression, protein accumulation, and activity of selected enzymes of the Calvin cycle); and (iii) analysis of plant antioxidant capacity (reactive oxygen species (ROS) generation; gene expression, protein accumulation and activity of selected enzymes). Though, F. arundinacea and F. glaucescens revealed different strategies in water uptake, and partially also in ABA signaling, their physiological reactions to drought and further re-watering, were similar. On the other hand, performance of the Calvin cycle and antioxidant system differed between the analyzed species under drought and re-watering periods. A stable efficiency of the Calvin cycle in F. arundinacea was crucial to maintain a balanced network of ROS/redox signaling, and consequently drought tolerance. The antioxidant capacity influenced mostly tolerance to stress in F. glaucescens.

Background: Photosynthesis is among the primary processes affected by drought and its disturbances result with the reduction of growth, reactive oxygen species (ROS) overproduction, and alterations in antioxidant system activity. Our study was performed on two closely related forage grasses: Festuca arundinacea and F. glaucescens. Two genotypes within each species significantly differing with the potential of drought resistance: high drought resistant (HDR) and low drought resistant (LDR), were used. The research involved: (i) the analysis of gene expression at transcript and protein levels for the selected enzymes of Calvin cycle (fructose-1,6-bisphosphate aldolase (pFBA), phosphoglycerate kinase (PGK) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH)) and (ii) the activity of pFBA, as a protein marker of the Calvin cycle, (iii) the analysis of gene expression at protein level for the selected antioxidant enzymes (glutathione reductase (GR), glutathione peroxidase (GPX), L-ascorbate peroxidase (APX), catalase (CAT), and superoxide dismutase (SOD)), (iv) the measurements of physiological parameters describing a plant’s physiological status under control, drought and re-watering conditions (relative water content (RWC), electrolyte leakage (EL), lipid peroxidation, chlorophyll fluorescence, gas exchange, and ROS level).Results: Our analysis clearly showed that physiological reactions to water deficit were similar in both HDR and both LDR genotypes of Festuca arundinacea and F. glaucescens but the species revealed significant differences in the potential to tolerate tissue dehydration, what was correlated with distinct expression of the Calvin cycle enzymes under drought stress.Conclusions: The maintenance of stable efficiency of dark phase of photosynthesis seems to be crucial for drought tolerance and recovery in F. glaucescnes, whereas acquisition of drought tolerance in F. arundinacea and F. glaucescens does not involve marked changes at the protein level in the enzymatic antioxidant system.

This work is devoted to the identification properties of indium tin oxide (ITO) thin films responsible for their possible application in combined optical and electrochemical label-free sensing systems offering enhanced functionalities. Since any post-processing would make it difficult to identify direct relation between deposition parameters and properties of the ITO films, especially when deposition on temperature-sensitive substrates is considered, the films were deposited using reactive high power impulse magnetron sputtering (HiPIMS) at low temperature and with no post-deposition annealing. We focused mainly on the impact of reactive gases, such as oxygen or nitrogen introduced to the process chamber, on control over plasma parameters and subsequently properties of the films. The properties of the films were investigated using X-ray diffractometry, spectroscopic ellipsometry, four-point probe, and cyclic voltammetry. For presenting optical sensing capabilities, the tailored ITO films in addition to silicon and glass wafers were also deposited on the core of optical fibers to induce the lossy-mode resonance (LMR) phenomenon. The existence of specific deposition conditions resulting in ITO film properties offering both high-quality electrochemical and LMR responses has been experimentally proven. It has been found that the crystalline structure of ITO plays a key role in the determination of both the sensing capabilities. Finally, label-free sensing of antibody-antibody interactions in both optical and electrochemical domains for the sensor with tailored ITO film has been shown.