Developed Sensor Probe Research Articles

Cardiac Troponin I Detection Using Gold/Cerium-Oxide Nanoparticles Assisted Hetro-Core Fiber Structure.

The article describes the development of a hetro-core optical fiber sensor structure based on localized surface plasmon resonance (LSPR) for the detection of cardiac troponin I (cTnI) solution. This was accomplished by fabricating a single-mode fiber - multimode fiber - single-mode fiber (SMS) structure. Then, fiber structure is immobilized with gold nanoparticles (AuNPs) and cerium oxide nanoparticles (CeO2-NPs) to improve its sensing capabilities. An UV-Vis spectrophotometer and a high-resolution transmission electron microscope (HR-TEM) are used to determine the morphology of synthesized nanoparticles. Scanning electron microscopy (SEM) is used to examine the state of immobilized NPs on the surface of sensing region. The developed sensor probe has a linear range of 0 to 1000 ng/mL cTnI, a sensitivity of 3 pm/(ng/mL), and a limit of detection (LoD) of 108.15 ng/mL. In real time, the proposed sensor will be used in a practice to detect acute myocardial infarction (AMI).

Crack Detection for Welded Joint With Surface Coating Using Unsaturated AC Magnetic Flux Leakage

Fatigue cracks occurred in the welds of steel structure are easily propagated. Therefore, it is important to detect the fatigue cracks at an early stage. However, most of the steel structures are protected by surface coating, which requires removing and restoring the coating for the inspection. This makes the inspection time-consuming. Magnetic methods such as eddy current testing (ECT) and magnetic flux leakage (MFL) can be used without removal of surface coating. However, these magnetic methods are difficult to apply to the shape of the welds and affected by nonuniform magnetic permeability. In this study, we developed a sensor probe adapted to the shape of the welded joint using the unsaturated ac MFL (USAC-MFL), which is less affected by the nonuniform magnetic permeability. To evaluate the performance of the developed sensor probe, the welded joint samples with the surface coating and shallow cracks of which depth ranges from 1 to 5 mm were measured. The measurement results showed a strong correlation between the intensity of the MFL and the crack depth. The detection performance was evaluated using the confusion matrix and the receiver-operating characteristic (ROC) curve. The area under curves (AUCs) of the ROC curves were around 0.9. In order to maximize the true positive rate (TPR) and minimize the false negative rate, the threshold of the intensity to identify a crack was obtained using the ROC curve. As the results of evaluating the detection performance using the obtained threshold, the four metrics (accuracy, precision, recall, and specification) were all above 0.8.

Fabrication of multi-functional CuO@PDA-MoS2 mediated dual-functional fluorescence Aptamer for the detection of Hg2+ ions and chloramphenicol through desulfurization cleavage reaction and exonuclease I activity

We progress a new sensor probe for the simultaneous detection of Hg2+ ions and chloramphenicol (CAP) by integrating FAM and TAMRA fluorophore labelled phosphorothioate RNA modified *ssDNA (*-PS probe) and CuO@PDA-MoS2 nanosphere. This work also stated a simplistic method to prepare CuO@PDA-MoS2 nanosphere via in-situ growth of MoS2 on the CuO@PDA nanosphere. The multi-functional CuO@PDA-MoS2 having rich binding sites with nanoscale architecture display great potential as an adsorbents for FAM-*ssDNA-TAMRA owing to the several interaction between them. This is lead to robustly quenching the fluorophores emission and minimizing the signal to noise ratio because of the FRET mechanism. In the developed sensor probe consisted of two interaction sections: Hg2+-induced cleavage of the PS-probe can efficiently liberates the FAM fluorophore, leads to remarkable enhancement of FAM emission. Second, the CAP can preferentially bind with remaining ssDNA-TAMRA and the formed CAP-ssDNA-TAMRA complex can be released from CuO@PDA-MoS2 surface, resulting in the regaining of TAMRA emission. Sequentially, the introduction of Exo I is to prompt and digest the CAP-ssDNA-TAMRA complex, caused in the significant regaining of TAMRA emission. Concurrently, the released CAP mediates a new digestion cycle, tends to result in ultra-trace detection of CAP. Under optimal circumstances, the suggested detecting scheme remarkably achieved for the extremely sensitive and selective detection of Hg2+ and CAP with in a wide linear range (0–10 nM Hg2+ and 0–5 nM CAP) and limit of detection 86 and 45 pM, respectively. Our current method is simpler and less expensive than existing methods of detecting Hg2+ and CAP in real water samples. More importantly, the presented approach can be detect the targets simultaneously and/or sequentially without loss of detection accuracy.

Development of Corrosion Diagnosis Method Using Sensor Probe Involving Copper Reference Electrode

A sensor probe involving a copper reference electrode was developed for copper corrosion diagnosis（CCD）in fresh water. Electrochemical measurements are often employed for CCD in three-electrode system. In such cases, commercial glass reference electrodes are used for electrochemical measurements. Because the repeated use of commercial glass reference electrodes in fresh water with different compositions degrades the reference electrode, a maintenance-free reference electrode is necessary for fieldwork involving CCD. In this study, a copper tube was selected as the reference electrode for electrochemical measurements. Our newly developed sensor probe for CCD comprises three copper tubes as the working electrode, counter electrode, and reference electrode. Each 1.6-mm-diameter copper tube was covered with a polyvinyl chloride insulator and was arranged as parallel with the others, with 1.6 mm spacing. Because these copper tubes can be cut off easily after electrochemical measurements, the maintenance-free reference electrode can be used for each electrochemical measurement. Potentiostatic polarization and galvanostatic polarization were conducted using the sensor probe. Then the obtained values（current and potential）and pH of the test solution were applied to the three-dimensional diagram, designated as corrosion map 3D, for CCD. Results confirmed that the corrosion diagnosis in corrosion map 3D can be categorized as having no corrosion, pitting corrosion, or general dissolution. Moreover, results obtained using the sensor probe showed good agreement with results obtained using the three-electrode system involving the commercial glass reference electrode.

Convex fiber-tapered seven core fiber-convex fiber (CTC) structure-based biosensor for creatinine detection in aquaculture.

The purpose of this article is to propose an optical fiber sensor probe based on the localized surface plasma resonance (LSPR) technique for the detection of creatinine in aquaculture. The sensing probe is functionalized through the use of gold nanoparticles (AuNPs), niobium carbide (Nb2CTx) MXene, and creatinase (CA) enzyme. The intrinsic total internal reflection (TIR) mechanism is modified to increase the evanescent field intensity using a heterogeneous core mismatch and tapering probe structure (i.e., convex fiber-tapered seven core fiber-convex fiber (CTC) structure). Strong evanescent fields can stimulate AuNPs and induce the LSPR effect, thereby increasing probe sensitivity. The specific recognition is enhanced by Nb2CTx MXene adsorbing more active CA enzymes. The developed sensor probe has a sensitivity and limit of detection of 3.1 pm/µM and 86.12 µM, respectively, in the linear range of 0-2000µM. Additionally, the sensor probe's reusability, reproducibility, stability, and selectivity were evaluated, with satisfactory results obtained with impact for areas like food protein, marine life and healthcare.

Localized Plasmon-Based Multicore Fiber Biosensor for Acetylcholine Detection

In this work, tapered/etched multicore fiber (MCF) probes are spliced with multimode fiber (MMF) to fabricate the sensor structure. To improve sensitivity, gold nanoparticles (AuNPs) and molybdenum disulfide nanoparticles (MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -NPs) are used to immobilize both probes. Synthesized AuNPs and molybdenum disulfide (MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> )-nanoparticles (NPs) have peak absorption wavelengths of 519 and 330 nm, respectively. High-resolution transmission electron microscopy is used to examine the morphology of the NPs. The scanning electron microscope (SEM) is used to characterize the NP-immobilized optical fiber sensor structures, and SEM-EDX is used to verify the NP-coating over fiber structure. The functionalization of the acetylcholinesterase enzyme over the NP-immobilized probe increases the specificity of the sensor later on. Finally, the developed sensor probes are tested by detecting various acetylcholine concentrations. In addition, performance analyses, such as reusability, reproducibility, and selectivity (in the presence of ascorbic acid, glucose, dopamine, and uric acid), are carried out, and proposed biosensors are experimentally evaluated. The developed tapered fiber sensor with a sensitivity of 0.062 nm/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{M}$ </tex-math></inline-formula> can detect even very low concentrations, such as 14.28 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{M}$ </tex-math></inline-formula> , over a wide detection range of 0–1000 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{M}$ </tex-math></inline-formula> .

Rapid and sensitive detection of selective 1,2-diaminobenzene based on facile hydrothermally prepared doped Co3O4/Yb2O3 nanoparticles.

In this approach, the performance of a newly developed sensor probe coated with low-dimensional Co3O4/Yb2O3 nanoparticles (NPs) in rapidly detecting 1,2-diaminobenzene was evaluated by an electrochemical technique. The sensor probe was fabricated by depositing a very thin layer consisting of synthesized Co3O4/Yb2O3 NPs using a 5% Nafion conducting binder onto a glassy carbon electrode (GCE). The facile hydrothermally prepared Co3O4/Yb2O3 NPs were totally characterized by conventional methods such as FTIR, UV-vis, TEM, XPS, EDS, and XRD analyses. The fabricated chemical sensor probe was found to exhibit long-term activity, stability in electrochemical response, good sensitivity (5.6962 μAμM-1cm-2), lowest detection limit (0.02±0.001 pM), and broad linear dynamic range (0.1 pM to 0.01 mM). The observed performances suggest that the newly introduced sensor could play an efficient role in detecting 1,2-diaminobenzene especially in healthcare and environmental applications on a broad scale.

Tapered Optical Fiber-Based LSPR Biosensor for Ascorbic Acid Detection

The ascorbic acid (AA) is a biomarker that can be used to detect the symptoms of severe disorders such as scurvy, Parkinson’s, Alzheimer’s, and cardiovascular diseases. In this work, a simple and effective sensor model is developed to diagnose the presence of AA samples. To develop the sensor, a tapered single-mode optical fiber has been used with the well-known phenomenon of localized surface plasmon resonance (LSPR). For LSPR, the tapered region is immobilized with synthesized gold nanoparticles (AuNPs) and zinc oxide nanoparticles (ZnO-NPs) whose absorbance peak wavelengths appear at 519nm and 370nm, respectively. On the basis of nanoparticles (NPs) configurations, two different biosensor probes are developed. In the first one, the sensing region is immobilized with AuNPs and named Probe I. In the second probe, the immobilized layer of AuNPs is further coated with a layer of ZnO-NPs, and a resultant probe is termed as Probe II. The characterizations of synthesized AuNPs and developed fiber probes are done by the ultraviolet-visible (UV-vis) spectrophotometer, high-resolution transmission electron microscope (HR-TEM), atomic force microscopy (AFM), and scanning electron microscope (SEM). To enhance the selectivity, a sensing region of probes is functionalized with ascorbate oxidase enzyme that oxidizes the AA in the presence of oxygen. The response of developed sensor probes is authenticated by sensing the samples of AA in the range from 500 nM to 1 mM, which covers the range of AA found in human bodies, i.e., 40µM–120µM. The performance analysis of the developed sensor probes has been done in terms of their stability, reproducibility, reusability, and selectivity. To observe the stability of AA, a pH-test has also been done that results in a better solubility of AA molecules in phosphate-buffered saline (PBS) solution.

Development of Collagen-IV Sensor Using Optical Fiber-Based Mach-Zehnder Interferometer Structure

This study presents a label-free and efficient method for the diagnosis of collagen-IV by using an optical fiber-based Mach-Zehnder interferometer (MZI) structure. The structure of MZI is fabricated by splicing a 2.3 cm long segment of single-mode fiber (SMF) between two ~ 45 cm strands of multi-mode fibers (MMF). Owing to the mismatch of core diameters, cladding of SMF guides the light. SMF's cladding is partially etched by using 40% hydrofluoric (HF) acid so that a part of propagating energy is released that can interplay with the surroundings. The etched region is immobilized with ~ 10 nm size of gold nanoparticles (AuNPs) and ~ 50 nm size of copper oxide nanoparticles (CuO-NPs) to initiate the influence of localized surface plasmon resonance (LSPR) phenomenon. For a comparative study, two different probes are developed and analyzed. In one probe, CuO NPs are immobilized over the etched part of SMF and named as CuO-NPs probe. In other probe, a monolayer of AuNPs is sandwiched between fiber surface and CuO-NPs and termed as AuNPs/CuO-NPs probe. The characterization of NPs and developed sensor probe are performed using UV-Vis spectroscopy, high-resolution transmission electron microscopy (HR-TEM), scanning electron microscopy (SEM), and energy distribution spectroscopy (EDS). The sensor probes are made very specific towards collagen-IV by functionalizing them with collagenase enzyme obtained from Clostridium histolyticum. A wide range of Collagen-IV solutions of concentrations from 2 μm/ml to 40 μm/ml are sensed through the collagenase functionalized probe. The specificity of the probes are analyzed by sensing other biomolecules present in the human body.

Highly sensitive and selective sensor probe using glucose oxidase/gold nanoparticles/graphene oxide functionalized tapered optical fiber structure for detection of glucose

A tapered optical fiber structure based glucose sensor using graphene oxide (GO) and gold nanoparticles (AuNPs) is presented in this study. The waist diameter and length of the taper region are 25 μm and 6 mm, respectively. The taper region was created to expose the evanescent waves to the cladding boundaries and to get interact with the external medium. Further, the cladding of tapered region is covered with GO and AuNPs to increase the biocompatibility of sensor and to initiate the phenomenon of localized surface plasmon resonance (LSPR), respectively. The synthesized GO and AuNPs show the good absorbance properties at the peak absorbance wavelengths of 230 nm and 519 nm, respectively. The characterization of synthesized nanomaterials was done by using UV–vis spectrophotometer and TEM. The characterization of nanomaterial coated fiber probe was done by using SEM and SEM-EDS. The specificity of developed sensor probe is enhanced by immobilizing them with the glucose oxidase enzyme, that oxidized only in the presence of glucose solution. The attained results show that the developed sensor model is highly sensitive for the detection of glucose concentrations in human bodies with a sensitivity of 1.06 nm/mM in the linear range of 0 mM–11 mM with the autocorrelation accuracy of 0.9386.

Localized Surface Plasmon Resonance Based Hetero-Core Optical Fiber Sensor Structure for the Detection of L-Cysteine

In this article, a hetero-core optical fiber sensor structure is developed for the diagnosis of L-Cysteine content in human urine. The hetero-core structure is created by sequentially cascading the single mode-multimode-single mode fibers using thermal fusion splicing. The multimode section of fiber probe is etched out and coated with synthesized gold nanoparticles (AuNPs), polyvinyl alcohol stabilized silver nanoparticles (PVA-AgNPs) and graphene oxide (GO). The AuNPs and PVA-AgNPs are used to initiate the localized surface plasmon resonance (LSPR) phenomenon on the application of exponentially decaying evanescent waves. The layer of GO is used to provide the larger surface area and binding sites for the L-Cysteine (L-Cys) molecules. Based on the combination of NPs, two different configurations of sensor probes are developed. In first one, a layer of AuNPs is deposited over fiber surface and further followed by the coating of GO, and named Probe I. In the second one, a layer of PVA-AgNPs is sandwiched between the fiber surface and GO layer and termed as Probe II. The characterization of synthesized NPs and GO solutions, and developed sensor probes are done by using UV-Vis spectrophotometry, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM). To authenticate the biocompatibility of developed sensor probes, the artificial aqueous samples of L-Cys ranges from 0 μM to 1 mM are tested. To determine the stability of L-Cys, a pH level based study is also carried out to ensure the good stability of analyte in aqueous samples. From the results, it was ascertained that the response of Probe II is better in terms of attained limit of detection and sensitivity that is 126.6 μM and 0.0009 nm/μM, respectively.

Gold Nanoparticles and Uricase Functionalized Tapered Fiber Sensor for Uric Acid Detection

In this paper, a tapered optical fiber-based sensor is developed for the detection of uric acid (UA) in human serum. The fiber probes were fabricated using single-mode fiber (SMF) with taper diameter of $40~\mu \text{m}$ . The diameter of taper section has culminated on the basis of excretion of evanescent waves and their handling capacity. To enhance the sensitivity, taper section (sensing region) was immobilized with synthesized gold nanoparticles (AuNPs). The AuNPs were used to initiate the excitation of surface plasmons (SP) at the fiber surface and ultimately leads to the localized surface plasmon resonance (LSPR) phenomenon. The comparative studies were also done to analyze the effect of size of AuNPs by immobilizing the sensor probes with ~10 nm and ~30 nm size of AuNPs. The UV-Vis spectrophotometry, high resolution-transmission electron microscopy (HR-TEM) and scanning electron microscopy (SEM) were used for the characterization of AuNPs solution and developed sensor probes. The sensing ability of sensors was authenticated by recording the transmitted intensity of LSPR spectrum for a wide range of UA from $10~\mu \text{M}$ to $800~\mu \text{M}$ . The detected range of UA completely covers its concentration available in human serum that is from $150~\mu \text{M}$ to $420~\mu \text{M}$ . Thereafter, the wavelength shift in LSPR spectrums was evaluated to determine the sensitivity and detection limit of sensors. The selectivity of the sensor probe was enhanced by functionalizing it with uricase enzyme (0.672 U/ml). The specificity of uricase functionalized sensor probes were also analyzed in the presence of other biomolecules found in human-serum.

Highly Sensitive, Selective and Portable Sensor Probe using Germanium-Doped Photosensitive Optical Fiber for Ascorbic Acid Detection

Ascorbic acid (AA) works as an antioxidant and plays a key role in the regulation of immune system and health maintenance. Low level of AA causes disease like scurvy whereas, its higher-level induces stomach throes in human body. So, for the detection of AA, a sensitive sensor probe is fabricated by splicing a short section of highly germanium (Ge)-doped photosensitive fiber (PSF) to a single-mode fiber. In the present study, PSF’s core is easily expanded by etching with hydrofluoric acid because PSF’s core is 5-times Ge-doped. It also helps in partial removal of cladding. Thereafter, gold nanoparticles (AuNPs) are immobilized over the sensing probe for localized surface plasmon resonance (LSPR) phenomena. Further, graphene oxide (GO) is decorated over the AuNPs-coated sensor probe. The AuNPs and GO helps to increase the sensitivity and biocompatibility of sensor probe. Ascorbate oxidase from Cucurbita species has been used to increase the specificity of the sensor. The developed sensor probe has been characterized by the UV-Visible spectrophotometer, high-resolution transmission electron microscope (HR-TEM), TEM - Energy dispersive spectroscopy (EDS), atomic force microscopy (AFM), field emission scanning electron microscope (FE-SEM), and SEM-EDS. The sensor exhibited a wide linear range of detection from $1~\mu \text{M}$ to 1 mM, with 3.5 %/mM of sensitivity. A detection limit of proposed sensor is found to be $15.12~\mu \text{M}$ , which is lower than the physiological AA level in serum of healthy human body (40 – $120~\mu \text{M}$ ). The selectivity of sensor probe has been verified by performing the experiments with various other biomolecules present in serum. The proposed LSPR sensor has many advantages such as low cost, less fragile probe, remote sensing, low electromagnetic interference, online monitoring, detection from micro-droplets, low detection limit, fast response, highly sensitive, and high specificity.

A supramolecule based fluorescence turn-on and ratiometric sensor for ATP in aqueous solution.

Considering the biological relevance of adenosine triphosphate (ATP) as an "energy currency" in all organisms and significance of its detection in various diseased conditions, enormous efforts have been made to develop selective and sensitive fluorescent sensors for the detection of ATP. However, these developed sensor probes frequently involve technically challenging and time-consuming synthetic protocols for the production of sensor molecules and often suffer from poor solubility in aqueous medium. Another major disadvantage of these developed sensor systems is their single wavelength based operation which makes their performance susceptible to minute changes in experimental conditions. Herein, we report a fluorescence turn-on ratiometric sensor for the detection of ATP which operates by the dissociation of Thioflavin-T-sulphated-β-cyclodextrin supramolecular assembly by Zn2+ followed by ATP induced reassociation of the same. This modulation of the monomer/aggregate equilibrium of the supramolecular assembly followed by subsequent interactions with Zn2+ and ATP acts as an optimal scheme for the ratiometric detection of ATP. Overall this supramolecular ensemble based sensing platform provides a simple, sensitive, selective and label free detection approach for ATP in aqueous solution. Importantly, our sensor platform responds to ATP in the biologically complex media of serum samples suggesting its potential for possible applications in real-life scenarios.

Novel Sensing Assembly Comprising Engineered Gold Dendrites and MWCNT‐AuNPs Nanohybrid for Acetaminophen Detection in Human Urine

AbstractA layered nanohybrid comprising of multi walled carbon nanotubes(MWCNT)‐gold nanoparticles (AuNPs) has been designed as a matrix for the development of Au dendritic nanostructures (AuDN) with enhanced catalytic activity. The developed sensor matrix was thoroughly characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), and energy dispersive X‐ray spectroscopy (EDX). The developed sensor probe MWCNT‐AuNPs/AuDN over glassy carbon electrode (GCE) was used for the label free detection of acetaminophen (AP), a commonly used drug associated with hepatotoxicity when overdosed, as a model molecule. The final sensor probe was characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), linear sweep voltammetry (LSV), and differential pulse voltammetry (DPV). The sensor shows excellent analytical performances with a linear dynamic range (LDR) of 100 to 7500 nM, and a low limit of detection (LOD) of 2.12 (±0.03) nM, which is better than recently reported AP sensors. The practical application / clinical possibilities of the final sensor were evaluated by real sample analysis in human urine by spike and recovery method, where the AP recoveries were found in between 92 % to 96 %. The sensor probe shows negligible response towards co‐existing interfering molecules like glucose, urea, uric acid and various amino acids, which are commonly found in real samples (p&lt;0.001, n=3). The shelf life of the sensor probe was evaluated and found to be stable for 8 weeks. The fabricated sensor probe using MWCNT‐AuNPs/AuDN is easy to fabricate, simple, robust, and able to detect AP in urine with high recoveries shows its possibilities to be used in clinical settings.

Optimization of Plasmonic U-Shaped Optical Fiber Sensor for Mercury Ions Detection Using Glucose Capped Silver Nanoparticles

Heavy metal contamination of water bodies has an adverse effect on human health and the environment even at very low concentrations. In this paper, we report U-shaped fiber optic probe coated with glucose capped silver nanoparticles (AgNPs) for label-free detection of mercury ions in aqueous solution. The reaction between glucose capped AgNPs and mercury ions resulted in a reduction in the plasmonic absorbance. The developed sensor probe was able to detect mercury ions concentration as low as 2 ppb, which is less than the World Health Organization acceptable limit for mercury ions in drinking water. The sensor probes displayed excellent selectivity towards mercury ions over other metal ions. Furthermore, the developed sensor probe was able to detect mercury ions down to 5 ppb in domestic tap water, i.e., selective detection of mercury even in real matrix having high concentration mixtures of various essential ions. The response of AgNPs coated sensor probe was found to be better than glucose capped gold nanoparticles and hollow gold-silver nanostructures coated fiber-optic probes.

Depassivation of Steel Rebar in Concrete Investigated By Electrochemical Impedance

The degradation of concrete and the corrosion of steel-reinforcing bar are serious problem in infrastructures. The electrochemical measurements are useful to evaluate the stability of passive film formed on steel rebar in concrete, which are mainly measurements of corrosion potential [1] and polarization curve. Dawson et al. [2] applied an electrochemical impedance spectroscopy (EIS) to the investigation of rebar corrosion in concrete because the charge transfer resistance at rebar/concrete interface can be determined from the impedance spectrum. Recently, the authors developed an electrode in Fig. 1 as a sensor probe to monitor concrete degradation and rebar corrosion. A couple of electrodes, which were made of same material as steel rebar, can be embedded in concrete structure and complex impedance can be measured continuously on the basis of two-electrode method. The authors’ group has performed the following three types of impedance measurements in order to prove the of the developed sensor probe. (1) Impedance between two electrodes in aqueous solution that simulates the water quality of transition zone (laboratory test). (2) Impedance between two electrodes embedded in the concrete which was fabricated in the laboratory. (3) Field test at bridge pier of the highway in coastal marine environment. It is well known that the rebar corrosion in concrete is strongly influenced by the conditions of cover concrete. Thin water layer is formed at rebar/concrete interface due to water absorption in the concrete. The concrete is good health status and the passive film is formed on steel rebar when the pH of water layer on steel rebar is sufficiently high. The breakdown of passive film occurs by neutralization and enriched chloride ions in the water layer with the degradation of concrete. In this presentation, the authors investigate the critical values of pH and chloride concentration to maintain the passive film on steel rebar and discuss the depassivation mechanisms by the measurements of electrochemical impedance with the developed sensor probe.

Characterization of Encapsulating Materials for Fiber Bragg Grating-Based Temperature Sensors

An experimental study has been carried out for the characterization of encapsulating materials for fiber Bragg grating-based temperature sensors to prevent the formation of micro-cracks and devitrification on the fiber surface at elevated temperatures by making use of a rigid probe. The developed sensor probe was configured by encapsulating a type 1 fiber Bragg grating with an aluminum nitride tube and is used to measure temperatures from 20°C to 500°C. The adapted encapsulation technique validated the sensor to achieve linearity of 99.979%, sensitivity of 14.03 ± 0.02 pm/°C, and good repeatability; its practical use in harsh environments is predicted.

Theoretical modeling, simulation and experimental studies of fiber optic bundle displacement sensor

This paper reports unified mathematical model of fiber optic bundle displacement sensor (FOBDS) based on ray tracing technique. The sensor response for concentric, random and hemispherical fiber bundle configurations is simulated using the developed model. The sensor performance parameters viz. sensitivity and linear operating range are calculated by differentiating the sensor response curve. It is observed that for a fiber bundle having two crowns of fibers with central illuminating fiber, sensitivity varies as 0.22, 0.42, 0.47 and linear operating range varies as 40mm, 22mm and 45mm for concentric, random and hemispherical configurations respectively. These results are validated by performing experiments with the developed sensor probe. Experimental results are almost matching the simulated results. After comparing the results for three configurations, it is concluded that the hemispherical configuration is best suitable configuration for sensor showing concurrent improvement in both the sensor performance parameters.

Neural activation to upright and inverted faces in infants measured by near infrared spectroscopy

The present study examined infants' brain activity in response to upright and inverted faces using near infrared spectroscopy (NIRS), which can non-invasively record hemodynamic changes of the brain. NIRS is particularly useful for recording in infants, since recordings can be made, even while the infants are awake, without fixing their body and brain. For this objective, we used newly developed sensor probes of NIRS for recording in infants. We measured changes in cerebral oxygenation in 10 5–8-month-olds' left and right lateral areas while they were looking at upright and inverted faces. The results are summarized as follows: (1) the concentration of oxyhemoglobin (oxy-Hb) and total hemoglobin (total-Hb) increased significantly in the right lateral area during the upright face condition, (2) the concentration of total-Hb in the right lateral area differed significantly between the upright and inverted conditions, (3) hemodynamic changes were maximal in the temporal region, probably in the superior temporal sulcus (STS) in both hemispheres, and (4) the right hemisphere seems to be more important for recognizing upright faces. This is the first evidence showing that there is an inter-hemispheric difference on the effect of face inversion in the infant brain using a hemodynamic method.