Direct Readout Research Articles

Integration of multiple flexible electrodes for real-time detection of barrier formation with spatial resolution in a gut-on-chip system

In healthy individuals, the intestinal epithelium forms a tight barrier to prevent gut bacteria from reaching blood circulation. To study the effect of probiotics, dietary compounds and drugs on gut barrier formation and disruption, human gut epithelial and bacterial cells can be cocultured in an in vitro model called the human microbial crosstalk (HuMiX) gut-on-a-chip system. Here, we present the design, fabrication and integration of thin-film electrodes into the HuMiX platform to measure transepithelial electrical resistance (TEER) as a direct readout on barrier tightness in real-time. As various aspects of the HuMiX platform have already been set in their design, such as multiple compressible layers, uneven surfaces and nontransparent materials, a novel fabrication method was developed whereby thin-film metal electrodes were first deposited on flexible substrates and sequentially integrated with the HuMiX system via a transfer-tape approach. Moreover, to measure localized TEER along the cell culture chamber, we integrated multiple electrodes that were connected to an impedance analyzer via a multiplexer. We further developed a dynamic normalization method because the active measurement area depends on the measured TEER levels. The fabrication process and system setup can be applicable to other barrier-on-chip systems. As a proof-of-concept, we measured the barrier formation of a cancerous Caco-2 cell line in real-time, which was mapped at four spatially separated positions along the HuMiX culture area.

A Wide-Band Magnetoelectric Sensor Based on a Negative-Feedback Compensated Readout Circuit.

Magnetoelectric (ME) sensors cannot effectively detect broadband magnetic field signals due to their narrow bandwidth, and existing readout circuits are unable to vary the bandwidth of the sensors. To expand the bandwidth, this paper introduces a negative-feedback readout circuit, fabricated by introducing a negative-feedback compensation circuit based on the direct readout circuit of the ME sensor. The negative-feedback compensation circuit contains a current amplifier, a feedback resistor, and a feedback coil. For this purpose, a Metglas/PVDF/Metglas ME sensor was prepared. Experimental measurements show that there is a six-fold difference between the maximum and minimum values of the ME voltage coefficients in the 6-39 kHz frequency band for the ME sensor without the negative-feedback compensation circuit when the sensor operates at the optimal bias magnetic field. However, the ME voltage coefficient in this band remains stable, at 900 V/T, after the charge amplification of the direct-reading circuit and the negative-feedback circuit. In addition, experimental results show that this negative-feedback readout circuit does not increase the equivalent magnetic noise of the sensor, with a noise level of 240 pT/√Hz in the frequency band lower than 25 kHz, 63 pT/√Hz around the resonance frequency of 30 kHz, and 620 pT/√Hz at 39 kHz. This paper proposes a negative-feedback readout circuit based on the direct readout circuit, which greatly increases the bandwidth of ME sensors and promotes the widespread application of ME sensors in the fields of broadband weak magnetic signal detection and DBS electrode positioning.

Digital microfluidics with distance-based detection - a new approach for nucleic acid diagnostics.

There is great enthusiasm for using loop-mediated isothermal amplification (LAMP) in point-of-care nucleic acid amplification tests (POC NAATs), as an alternative to PCR. While isothermal amplification techniques like LAMP eliminate the need for rapid temperature cycling in a portable format, these systems are still plagued by requirements for dedicated optical detection apparatus for analysis and manual off-chip sample processing. Here, we developed a new microfluidic system for LAMP-based POC NAATs to address these limitations. The new system combines digital microfluidics (DMF) with distance-based detection (DBD) for direct signal readout. This is the first report of the use of (i) LAMP or (ii) DMF with DBD - thus, we describe a number of characterization steps taken to determine optimal combinations of reagents, materials, and processes for reliable operation. For example, DBD was found to be quite sensitive to background signals from low molecular weight LAMP products; thus, a Capto™ adhere bead-based clean-up procedure was developed to isolate the desirable high-molecular-weight products for analysis. The new method was validated by application to detection of SARS-CoV-2 in saliva. The method was able to distinguish between saliva containing no virus, saliva containing a low viral load (104 genome copies per mL), and saliva containing a high viral load (108 copies per mL), all in an automated system that does not require detection apparatus for analysis. We propose that the combination of DMF with distance-based detection may be a powerful one for implementing a variety of POC NAATs or for other applications in the future.

Visually distinguishing between tumor tissue and healthy tissue within ten minutes using proteolytic probes

Fluorescence-emitting probes designed to detect furin, a biomarker protease that is upregulated in tumor tissue, simplifying complex diagnostic workflows and enabling tissue-conserving surgery through direct visual readout.

An integrated electronic tag-based vertical flow assay (e-VFA) with micro-sieve and AlGaN/GaN HEMT sensors for multi-target detection in actual saliva.

Vertical flow assay (VFA) is an effective point-of-care (POC) diagnostic tool for widespread application. Nevertheless, the lack of multi-target detection and multi-signal readout capability still remains a challenge. Herein, a brand new VFA scheme for multi-target saliva detection based on electronic tags was proposed, where AlGaN/GaN HEMT sensors modified with different bio-receptors as electronic tags endowed the VFA with multi-target detection capability. In addition, the use of electronic tags instead of optical tags allowed the VFA to simultaneously carry out direct multi-target readouts, which ensure effective POC diagnostics for saliva analysis. Moreover, by integrating a hydrophilically optimized micro-sieve, impurities like sticky filaments, epidermal cells and other large-scale charged particles in saliva were effectively screened, which enabled the direct detection of saliva using AlGaN/GaN HEMT sensors. Glucose, urea, and cortisol were selected to verify the feasibility of the multi-target e-VFA scheme, and the results showed that the limit of detection (LOD) was as low as 100 aM. The linear response was demonstrated in the dynamic range of 100 aM to 100 μM, and the specificity, long-term stability and validity of the actual saliva test were also verified. These results demonstrated that the as-proposed e-VFA has potential for application in saliva detection for simultaneous multi-target detection, and it is expected to achieve the real-time detection of more biological targets in saliva.

Lambda CI Binding to Related Phage Operator Sequences Validates Alignment Algorithm and Highlights the Importance of Overlooked Bonds.

Bacteriophage λ's CI repressor protein controls a genetic switch between the virus's lysogenic and lytic lifecycles, in part, by selectively binding to six different DNA sequences within the phage genome-collectively referred to as operator sites. However, the minimal level of information needed for CI to recognize and specifically bind these six unique-but-related sequences is unclear. In a previous study, we introduced an algorithm that extracts the minimal direct readout information needed for λ-CI to recognize and bind its six binding sites. We further revealed direct readout information shared among three evolutionarily related lambdoid phages: λ-phage, Enterobacteria phage VT2-Sakai, and Stx2 converting phage I, suggesting that the λ-CI protein could bind to the operator sites of these other phages. In this study, we show that λ-CI can indeed bind the other two phages' cognate binding sites as predicted using our algorithm, validating the hypotheses from that paper. We go on to demonstrate the importance of specific hydrogen bond donors and acceptors that are maintained despite changes to the nucleobase itself, and another that has an important role in recognition and binding. This in vitro validation of our algorithm supports its use as a tool to predict alternative binding sites for DNA-binding proteins.

The "StemDif Sensor Test": A Straightforward, Non-Invasive Assay to Characterize the Secreted Stemness and/or Differentiation Activities of Tumor-Derived Cancer Cell Lines.

Cancer stem cells are a subpopulation of tumor cells characterized by their ability to self-renew, induce tumors upon engraftment in animals and exhibit strong resistance to chemotherapy and radiotherapy. These cells exhibit numerous characteristics in common with embryonic stem cells, expressing some of their markers, typically absent in non-pathological adult differentiated cells. The aim of this study was to investigate the potential of conditioned media from cancer stem cells to modulate the fate of Leukemia Inhibitory Factor (LIF)-dependent murine embryonic stem cells (mESCs) as a way to obtain a direct readout of the secretome of cancer cells. A functional assay, "the StemDif sensor test", was developed with two types of cancer stem cells derived from grade IV glioblastoma (adult and pediatric) or from gastric adenocarcinoma. We show that conditioned media from the selection of adult but not pediatric Glioma-Inducing Cells (GICs) maintain mESCs' pluripotency in correlation with LIF secretion and activation of STAT3 protein. In contrast, conditioned media from gastric adenocarcinoma cells display LIF-independent stemness and differentiation activities on mESC. Our test stands out for its user-friendly procedures, affordability and straightforward output, positioning it as a pioneering tool for in-depth exploration of cancer stem cell secretome characteristics.

Bypassing the brain barriers: upregulation of serum miR-495 and miR-543-3p reflects thyroid-mediated developmental neurotoxicity in the rat.

Evaluating the neurodevelopmental effects of thyroid-disrupting chemicals is challenging. Although some standardized developmental and reproductive toxicity studies recommend serum thyroxine (T4) measures in developing rats, extrapolating between a serum T4 reduction and neurodevelopmental outcomes is not straightforward. Previously, we showed that the blood-brain and blood-cerebrospinal fluid barriers may be affected by developmental hypothyroidism in newborn rats. Here, we hypothesized that if the brain barriers were functionally disturbed by abnormal thyroid action, then small molecules may escape from the brain tissue and into general circulation. These small molecules could then be identified in blood samples, serving as a direct readout of thyroid-mediated developmental neurotoxicity. To address these hypotheses, pregnant rats were exposed to propylthiouracil (PTU, 0 or 3 ppm) to induce thyroid hormone insufficiency, and dams were permitted to give birth. PTU significantly reduced serum T4 in postnatal offspring. Consistent with our hypothesis, we show that tight junctions of the brain barriers were abnormal in PTU-exposed pups, and the blood-brain barrier exhibited increased permeability. Next, we performed serum microRNA Sequencing (miRNA-Seq) to identify noncoding RNAs that may reflect these neurodevelopmental disturbances. Of the differentially expressed miRNAs identified, 7 were upregulated in PTU-exposed pups. Validation by qRT-PCR shows that miR-495 and miR-543-3p were similarly upregulated in males and females. Interestingly, these miRNAs have been linked to cell junction dysfunction in other models, paralleling the identified abnormalities in the rat brain. Taken together, these data show that miR-495 and miR-543-3p may be novel in vivo biomarkers of thyroid-mediated developmental neurotoxicity.

Revealing emergent magnetic charge in an antiferromagnet with diamond quantum magnetometry.

Whirling topological textures play a key role in exotic phases of magnetic materials and are promising for logic and memory applications. In antiferromagnets, these textures exhibit enhanced stability and faster dynamics with respect to their ferromagnetic counterparts, but they are also difficult to study due to their vanishing net magnetic moment. One technique that meets the demand of highly sensitive vectorial magnetic field sensing with negligible backaction is diamond quantum magnetometry. Here we show that an archetypal antiferromagnet-haematite-hosts a rich tapestry of monopolar, dipolar and quadrupolar emergent magnetic charge distributions. The direct read-out of the previously inaccessible vorticity of an antiferromagnetic spin texture provides the crucial connection to its magnetic charge through a duality relation. Our work defines a paradigmatic class of magnetic systems to explore two-dimensional monopolar physics, and highlights the transformative role that diamond quantum magnetometry could play in exploring emergent phenomena in quantum materials.

A biotin targeting chimera (BioTAC) system to map small molecule interactomes in situ

Understanding how small molecules bind to specific protein complexes in living cells is critical to understanding their mechanism-of-action. Unbiased chemical biology strategies for direct readout of protein interactome remodelling by small molecules would provide advantages over target-focused approaches, including the ability to detect previously unknown ligand targets and complexes. However, there are few current methods for unbiased profiling of small molecule interactomes. To address this, we envisioned a technology that would combine the sensitivity and live-cell compatibility of proximity labelling coupled to mass spectrometry, with the specificity and unbiased nature of chemoproteomics. In this manuscript, we describe the BioTAC system, a small-molecule guided proximity labelling platform that can rapidly identify both direct and complexed small molecule binding proteins. We benchmark the system against µMap, photoaffinity labelling, affinity purification coupled to mass spectrometry and proximity labelling coupled to mass spectrometry datasets. We also apply the BioTAC system to provide interactome maps of Trametinib and analogues. The BioTAC system overcomes a limitation of current approaches and supports identification of both inhibitor bound and molecular glue bound complexes.

Dissection of integrated readout reveals the structural thermodynamics of DNA selection by transcription factors

Nucleobases such as inosine have been extensively utilized to map direct contacts by proteins in the DNA groove. Their deployment as targeted probes of dynamics and hydration, which are dominant thermodynamic drivers of affinity and specificity, has been limited by a paucity of suitable experimental models. We report a joint crystallographic, thermodynamic, and computational study of the bidentate complex of the arginine side chain with a Watson-Crick guanine (Arg×GC), a highly specific configuration adopted by major transcription factors throughout the eukaryotic branches in the Tree of Life. Using the ETS-family factor PU.1 as a high-resolution structural framework, inosine substitution for guanine resulted in a sharp dissection of conformational dynamics and hydration and elucidated their role in the DNA specificity of PU.1. Our work suggests an under-exploited utility of modified nucleobases in untangling the structural thermodynamics of interactions, such as the Arg×GC motif, where direct and indirect readout are tightly integrated.

Abstract C002: Identification of biomarkers predictive of sensitivity to the CHK1/2 inhibitor ACR-368 using high-resolution phosphoproteomics and development of an ACR-368-tailored patient responder identification 3-marker test, ACR-368 OncoSignature

Abstract Introduction ACR-368 (prexasertib) is a potent and selective CHK1/2 inhibitor with demonstrated durable, single-agent activity in patients with advanced solid tumors. Genomic biomarkers have been unsuccessful in predicting response to ACR-368 due in part to the complex genetic changes in cancer that translate into dysregulated protein signaling pathways. To address this challenge, we sought to identify protein-based, predictive biomarkers that measure the ACR-368-sensitive dysregulated signaling driving tumorigenesis using our proprietary approach, AP3 (Acrivon Predictive Precision Proteomics). Methods ACR-368 anticancer activity was measured in a panel of ovarian cancer cell lines using CellTiter-Glo. Quantitative phosphoproteomics was performed on ACR-368 sensitive and resistant ovarian cancer cell lines using data-independent acquisition mass spectrometry (DIA-MS). Kinase activity inference analysis and signaling pathway analyses were conducted to uncover ACR-368-regulated pathways associated with tumorigenesis. A quantitative, multiplexed immunofluorescent (IF) assay was developed based on three biomarkers, termed ACR-368 OncoSignature. Ovarian PDX studies were conducted in female athymic nude or CB-17 Scid mice. Results ACR-368 demonstrated diverse anti-proliferative activity in ovarian cancer cell lines. Phosphoproteome-profiling analysis from ACR-368 sensitive and resistant cells exposed to ACR-368 yielded >17,000 confidently localized phospho-sites (localization probability > 0.75), with 8272 being significantly regulated by ACR-368 (FC > 1.5, Q-value < 0.05, Limma t-test). Unsupervised hierarchical clustering analysis revealed overrepresentation of ATM/ATR and CDK1/2-associated substrate sites in the upregulated group, while the downregulated group showed overrepresentation of CHK1-associated sites. Pathway enrichment analysis highlighted the differential regulation of the homology-directed repair (HDR) pathway between sensitive and non-sensitive ovarian cancer cells. Through analysis of HDR-related signaling networks, three functionally orthogonal predictive biomarkers were assembled into a quantitative multiplex in situ assay for FFPE tissue that provides a direct readout of a tumor’s dependency on the signaling axis inhibited by ACR-368. Quantitation of these biomarkers in cancer cell lines using the IF-based OncoSignature demonstrated efficient classification based on ACR-368 sensitivity. The assay accurately predicted sensitivity to ACR-368 across ovarian cancer PDX models with an AUC of 0.9 (95% confidence interval: 0.71 to 1; p-value = 0.025). Conclusions Employing our AP3 platform, which combines MS-based phosphoproteomics and quantitative multiplexed-IF staining of drug-tailored biomarkers, we developed a response-predictive test for ACR-368 that enables identification of responders to ACR-368 treatment. A clinical trial (NCT05548296) evaluating the efficacy of ACR-368 based on the OncoSignature test status is currently recruiting in patients with platinum-resistant ovarian, endometrial, and urothelial cancer. Citation Format: Caroline Wigerup, Michail Shipitsin, Ayesha Murshid, Lei Shi, Magnus E. Jakobsson, Dorte Bekker-Jensen, Sibgat Choudry, James Dunyak, David Proia, Jesper V. Olsen, Kristina Masson, Peter Blume-Jensen. Identification of biomarkers predictive of sensitivity to the CHK1/2 inhibitor ACR-368 using high-resolution phosphoproteomics and development of an ACR-368-tailored patient responder identification 3-marker test, ACR-368 OncoSignature [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr C002.

FeNi foam with specifically boosted peroxidase-like activity for smartphone-based rapid visual detection

Smartphone-based analysis is an emerging technique that provides a wide range of biomedical applications in point-of-care testing (POCT). Here, we have developed a portable and rapid sensing platform. It integrates an activated FeNi foam with specifically boosted peroxidase (POD)-like activity as signal generator, a lower light photography device and an image digitization application (APP) that help to realize direct signal readout through a smartphone. Significantly, by introducing polydopamine nanoparticles (PDNPs) on activated FeNi foam, the POD-like activity can be enhanced over tenfold, in sharp contrast to the silent oxidase (OXD)-like activity. It is determined that the improved catalytic performance originates from the winkle structures on activated FeNi foam, synergistic effect between Fe and Ni and the cycles between Fe3+/Fe2+ and catechol/quinones for electron transfer and mass transport. Further, the use of PDNPs as an immobilization linker enables the construction of an integrated nanozyme by immobilizing natural enzymes like glucose oxidase. Combined with a multifunctional photography system, sensitive and rapid detection of H2O2 and glucose were achieved, the limit of detection (LOD) was 10.2 µM and 40.6 µM, respectively, and detection time was less than 6 min. This highlights the potential of the smartphone-based sensing platform for online monitoring biomarkers in a high-throughput and point-of-care format. Considering the significance of efficient catalysts and the growing demand for POCT, our study contributes to the development of peroxidase mimics based on metal foam and provides valuable insights for improving the performance of photography devices in visual detection.

Enhancing sensitivity and versatility of Tn5-based single cell omics

The analysis of chromatin features in single cells centers around Tn5 transposase and exploits its activity to simultaneously fragment target DNA and integrate adapter sequences of choice. This reaction provides a direct readout in the assay for transposase-accessible chromatin in single cells (scATAC-seq) to map open chromatin loci. However, a current limitation is the sparse coverage of these open sites in a given single cell by droplet-based methods. Thus, enhancing Tn5 activity to improve genomic coverage of scATAC-seq or facilitating multi-omics readouts of chromatin features via Tn5 together with the transcriptome is of great interest. Here, we address these issues by optimizing scATAC-seq for an increased number of integrations per cell. In addition, we provide a protocol that combines mapping of histone modification with scRNA-seq from the same cell by targeting Tn5 to antibody-bound chromatin epitopes. Our experimental workflows improve the results obtained from the downstream data analysis and serve to better resolve epigenetic heterogeneity and transcription regulation in single cells.

A single fiber view of the nucleosome organization in eukaryotic chromatin.

Eukaryotic cells are thought to arrange nucleosomes into extended arrays with evenly spaced nucleosomes phased at genomic landmarks. Here we tested to what extent this stereotypic organization describes the nucleosome organization in Saccharomyces cerevisiae using Fiber-Seq, a long-read sequencing technique that maps entire nucleosome arrays on individual chromatin fibers in a high throughput manner. With each fiber coming from a different cell, Fiber-Seq uncovers cell-to-cell heterogeneity. The long reads reveal the nucleosome architecture even over repetitive DNA such as the ribosomal DNA repeats. The absolute nucleosome occupancy, a parameter that is difficult to obtain with conventional sequencing approaches, is a direct readout of Fiber-Seq. We document substantial deviations from the stereotypical nucleosome organization with unexpectedly long linker DNAs between nucleosomes, gene bodies missing entire nucleosomes, cell-to-cell heterogeneity in nucleosome occupancy, heterogeneous phasing of arrays and irregular nucleosome spacing. Nucleosome array structures are indistinguishable throughout the gene body and with respect to the direction of transcription arguing against transcription promoting array formation. Acute nucleosome depletion destroyed most of the array organization indicating that nucleosome remodelers cannot efficiently pack nucleosomes under those conditions. Given that nucleosomes are cis-regulatory elements, the cell-to-cell heterogeneity uncovered by Fiber-Seq provides much needed information to understand chromatin structure and function.

Single molecule MATAC-seq reveals key determinants of DNA replication origin efficiency.

Stochastic origin activation gives rise to significant cell-to-cell variability in the pattern of genome replication. The molecular basis for heterogeneity in efficiency and timing of individual origins is a long-standing question. Here, we developed Methylation Accessibility of TArgeted Chromatin domain Sequencing (MATAC-Seq) to determine single-molecule chromatin accessibility of four specific genomic loci. MATAC-Seq relies on preferential modification of accessible DNA by methyltransferases combined with Nanopore-Sequencing for direct readout of methylated DNA-bases. Applying MATAC-Seq to selected early-efficient and late-inefficient yeast replication origins revealed large heterogeneity of chromatin states. Disruption of INO80 or ISW2 chromatin remodeling complexes leads to changes at individual nucleosomal positions that correlate with changes in their replication efficiency. We found a chromatin state with an accessible nucleosome-free region in combination with well-positioned+1 and+2 nucleosomes as a strong predictor for efficient origin activation. Thus, MATAC-Seq identifies the large spectrum of alternative chromatin states that co-exist on a given locus previously masked in population-based experiments and provides a mechanistic basis for origin activation heterogeneity during eukaryotic DNA replication. Consequently, our single-molecule chromatin accessibility assay will be ideal to define single-molecule heterogeneity across many fundamental biological processes such as transcription, replication, or DNA repair in vitro and ex vivo.

Direct readout of mirror reflectivity for cavity-enhanced gas sensing using Pound-Drever-Hall signals.

The operation of cavity-enhanced techniques usually requires independent pre-calibration of the mirror reflectivity to precisely quantify the absorption. Here we show how to directly calibrate the effective mirror reflectivity without using any gas samples of known concentration or high-speed optical/electrical devices. Leveraging a phase modulator to generate sidebands, we are able to record Pound-Drever-Hall error signals shaped by cavity modes that can reveal the effective reflectivity after waveform analysis. As an example, we demonstrated the reflectivity calibration of a pair of near-infrared mirrors over 80 nm with a free spectral range-limited resolution, illustrating a reflectivity uncertainty of 2 × 10-5 in the center part of the refection wavelength range of the mirrors and larger at the edges. With an effective reflectivity of 0.9982 (finesse ∼1746) inferred at 1531.6 nm, a short ∼ 8-cm Fabry-Pérot cavity achieved a minimum detectable absorption coefficient of 9.1 × 10-9 cm-1 for trace C2H2 detection. This method, by providing convenient calibration in an almost real-time manner, would enable more practical cavity-enhanced gas measurement even with potential mirror reflectivity degradation.

Unlocking the Mysteries of Chromatin Biology through Functional Epigenomics.

In the ever-evolving field of functional genomics, CRISPR-based screening technologies have become pivotal tools for elucidating gene function across various cell types. A recent study by Gilan and colleagues advances this technological frontier by introducing CRISPR-ChIP, a platform designed to investigate the complex dynamics of epigenetic regulation of chromatin. In proof-of-concept experiments, the authors demonstrate the potential of this tool to identify key molecular regulators of two major histone modifications associated with active transcription, H3 lysine 4 trimethylation (H3K4me3) and H3 lysine 79 dimethylation (H3K79me2). They further unveiled a previously unknown functional partitioning of the H3K79-specific methyltransferase DOT1L into an oncogenic complex with MLL-AF9 and a native complex with MLLT10, which cooperatively regulate Mixed Lineage Leukemia fusion protein (MLL-FP) target gene expression. This novel epigenomic approach integrates high-throughput CRISPR screening with ChIP-based direct readout of chromatin modifications in situ, offering a powerful tool to investigate the epigenetic regulatory layers across a diverse spectrum of biological processes and disease states.

Enhanced pH sensing with Ce-doped YTixOy sensing membrane in high-performance electrolyte–insulator–semiconductor devices

Electrolyte-insulator-semiconductor (EIS)-based sensors are a novel class of electronic chips designed for biochemical sensing that offer a direct electronic readout, making them part of a new generation of sensing technologies. To enhance the pH sensitivity, in this research we fabricated the CeYTixOy-based EIS sensors with different Ce concentrations (1 %, 5 %, and 10%) by the solution-processing method. The crystal orientation, surface topography, and chemical composition of the sensing film were examined by X-ray diffraction, atomic force microscopy, and X-ray photoelectron spectroscopy, respectively. The CeYTixOy-based EIS sensor treated with an optimal 5% Ce concentration displays a Super-Nernstian pH response of 66.59 mV/pH with an excellent linearity of 0.99. In the context of reliability, the device exhibited a smaller hysteresis voltage of 7 mV and a lower drift rate of 0.75 mV/h. This result may be attributed to the optimal Ce content in the CeYTixOy leads to the formation of redox couple Ce4+/Ce3+ resulting in less than one electron transferred per proton in the redox reaction.

Direct wireless readout of fiber Bragg grating sensors using radio-over-fiber.

Wireless readout of optical fiber sensors is of interest for a variety of applications. In the state of the art, the sensor data are digitized before the wireless transmission. We propose a wireless evaluation scheme for fiber Bragg gratings where the sensor signal is transmitted directly without any processing in a simplified sensor node. The underlying concept is explained in detail and validated experimentally. It is based on radio-over-fiber technology and evaluates not only the magnitude of the received analog electrical sensor signal but also the phase. Additionally, signal correction and signal processing schemes are discussed. A series of experimental measurements indicates not only advantages of the phase evaluation method over the magnitude evaluation method but also approves the general feasibility of the direct interrogation approach for wireless sensing applications. Future subjects of interest involve absolute accuracy considerations and maximum achievable sampling rates.