Sensors For Biomedical Applications Research Articles

Performance analysis of surrounding cylindrical gate all around nanowire transistor for biomedical application

This paper proposes a highly sensitive, more accurate, and faster device using silicon on insulator based cylindrical surrounding gate all around nanowire (SCGAA-NW) transistor for biomedical sensor applications and different chemicals present in the blood or environment by setting and analysing proper physical parameters of the device. Different physical parameters, channel material (i.e. SiN, CdS, GaN, ZnO, GaP, Si, GaAs, Ge), oxide material (i.e. SiO2, Si3N4, Al2O3, Er2O3, Y2O3, HfO2, Ta2O5, La2O3), channel radius (1-10 nm), oxide thickness (1-10 nm), the concentration of different material have been employed on the sensor acting as a gate to source voltage, drain to source voltage (−0.5 V to 0.5 V), channel doping (107 to 1014) respectively for the best suitable biomedical application in different environments. Analytical modelling of SCGAA-NW transistor was performed by solving 1-D Poisson's equation, using Gauss law and parabolic approximation method using Matlab simulator.

Performance analysis of surrounding cylindrical gate all around nanowire transistor for biomedical application

This paper proposes a highly sensitive, more accurate, and faster device using silicon on insulator based cylindrical surrounding gate all around nanowire (SCGAA-NW) transistor for biomedical sensor applications and different chemicals present in the blood or environment by setting and analysing proper physical parameters of the device. Different physical parameters, channel material (i.e. SiN, CdS, GaN, ZnO, GaP, Si, GaAs, Ge), oxide material (i.e. SiO2, Si3N4, Al2O3, Er2O3, Y2O3, HfO2, Ta2O5, La2O3), channel radius (1-10 nm), oxide thickness (1-10 nm), the concentration of different material have been employed on the sensor acting as a gate to source voltage, drain to source voltage (−0.5 V to 0.5 V), channel doping (107 to 1014) respectively for the best suitable biomedical application in different environments. Analytical modelling of SCGAA-NW transistor was performed by solving 1-D Poisson's equation, using Gauss law and parabolic approximation method using Matlab simulator.

Pyranine-Modified Amphiphilic Polymer Conetworks as Fluorescent Ratiometric pH Sensors.

The fluorescent dye 8-hydroxypyrene-1,3,6-trisulfonate (pyranine) combines high photostability with ratiometric pH detection in the physiological range, making it a prime candidate for optical sensors in biomedical applications, such as pH-based chronic wound monitoring. However, pyranine's high water solubility and the difficulty of covalent attachment pose severe limitations in terms of leaching from sensor matrices. Herein, pyranine-modified nanophase-separated amphiphilic polymer conetworks (APCNs) are reported as fluorescent ratiometric pH sensors. The thin, freestanding APCN membranes composed of one hydrophilic and one hydrophobic polymer provide an optically transparent, flexible, and stable ideal matrix that enables contact between dye and aqueous environment. An active ester-based conjugation approach results in a highly homogeneous and stable pyranine modification of the APCN's hydrophilic phase. This concept effectively solves the leaching challenge for pyranine without compromising its functionality, which is demonstrated by ratiometric pH detection in the range of pH 5-9.

A Simulation Platform to Study the Human Body Communication Channel.

Human Body Communication (HBC) is an attractive low complexity technology with promising applications in wearable biomedical sensors. In this paper, a simple parametric model based on the finite-element method (FEM) using a full human body model is developed to virtually emulate and examine the HBC channel. FEM allows better modeling and quantification of the underlying physical phenomena including the impact of the human body for the desired applications. By adjusting the parameters of the model, a good match with the limited measurement results in the literature is observed. Having a flexible and customizable simulation platform could be very helpful to better understand the communication medium for capacitively coupled electrodes in HBC. This knowledge, in turn, leads to better transceiver design for given applications. The platform presented here can also be extended to study communication channel characteristics when the HBC mechanism is used by an implant device.

Directed Printing and Reconfiguration of Thermoresponsive Silica-pNIPAM Nanocomposites.

Printing of polymeric composites into desired patterns and shapes has revolutionized small-scale manufacturing processes. However, high-resolution printing of adaptive materials that change shape in response to external stimuli remains a significant technical challenge. The article presents a new approach of printing thermoresponsive poly(N-isopropylacrylamide) into macroscopic structures that dynamically reconfigure in response to heating and cooling cycles. The printing process is performed using an external laser source, which enables thermal cross-linking of the polymer ink consisting of monomer, cross-linker, initiator, and inorganic nanoparticles. It is shown that the addition of silica nanoparticles enhances the mechanical properties of poly(N-isopropylacrylamide) while maintaining its thermoresponsiveness at micrometer-scale resolution, which otherwise is not feasible by extrusion-based three-dimensional printing techniques. It is demonstrated that spatial reconfiguration of the printed monolayers upon increasing temperature is governed by the local geometry, which enables mimicking the reconfiguration of plant leaves in a natural environment. The study lays a foundation for developing a new fabrication platform to print thermoresponsive structures that may find applications in biomedical implants, sensors, and other multi-responsive materials.

Medical gesture recognition using dynamic arc length warping

Hand gesture recognition is a promising research area often used in applications of human–computer interactions in the medical field. In this paper, we present a novel approach to differentiate gestures based on an arc-length parametrization and a curvature analysis of 3D trajectories. This new method called dynamic arc length warping (DALW) can outperform classic multi dimensional-dynamic time warping (MD-DTW) algorithm as it is invariant to sensor location and more tolerant to temporal distortions. Experimental validation of the algorithm is presented using different gestures and sensors in biomedical applications: an exoskeleton apparatus, surgical gestures captured by an instrumented laparoscopic device and finally, a birth simulator with an instrumented forceps. A basic perceptron multilayer neural network was implemented in order to perform the classification. Results involve an average increase of 7.14% in the classification rates by using DALW distance, compared to the classical MD-DTW.

Highly Uniform, Flexible Microelectrodes Based on the Clean Single-Walled Carbon Nanotube Thin Film with High Electrochemical Activity

Electrochemical sensors based on carbon nanotubes (CNTs) have great potential for use in wearable or implantable biomedical sensor applications because of their excellent mechanical flexibility and biocompatibility. However, the main challenge associated with CNT-based sensors is their uniform and reproducible fabrication on the flexible plastic film. Here, we introduce and demonstrate a highly reliable technique to fabricate flexible CNT microelectrodes on a plastic film. The technique involves a process whereby the CNT film is formed by the dry transfer process based on the floating-catalyst chemical vapor deposition. An oxide protection layer, which is used to cover the CNT thin film during the fabrication process, minimizes contamination of the surface. The fabricated flexible CNT microelectrodes show almost ideal electrochemical characteristics for microelectrodes with the average value of the quartile potentials, Δ E = | E3/4 - E1/4|, being 60.4 ± 2.9 mV for the 28 electrodes, while the ideal value of Δ E = 56.4 mV. The CNT microelectrodes also showed enhanced resistance to surface fouling during dopamine oxidation in comparison to carbon fiber and gold microelectrodes; the degradation of the oxidation current after 10 consecutive cycles were 1.8, 8.3, and 13.9% for CNT, carbon fiber, and gold microelectrodes, respectively. The high-sensitivity detection of dopamine is also demonstrated with differential-pulse voltammetry, with a resulting limit of detection of ∼50 nM. The reliability, uniformity, and sensitivity of the present CNT microelectrodes provide a platform for flexible electrochemical sensors.

The non-linear electrical properties of human skin make it a generic memristor

An electrical measurement is non-linear when the applied stimulus itself affects the electrical properties of the underlying tissue. Corresponding voltage-current plots may exhibit pinched hysteresis loops which is the fingerprint of a memristor (memory resistor). Even though non-linear electrical properties have been demonstrated for different biological tissues like apples, plants and human skin, non-linear measurements as such have not been defined, yet. We are studying the non-linear properties of human skin systematically and initiate non-linear measurements on biological tissues as a field of research in general by introducing applicable recording techniques and parameterization. We found under which voltage stimulus conditions a measurement on human skin is non-linear and show that very low voltage amplitudes are already sufficient. The non-linear properties of human skin originate from the sweat ducts, as well as, from the surrounding tissue, the stratum corneum and we were able to classify the overall skin memristor as a generic memristor. Pinched hysteresis loops vary largely among subjects; an indication for the potential use in biomedical sensor applications.

Palladium Nanoneedles on Carbon Fiber: Highly Sensitive Peroxide Detection for Biomedical and Wearable Sensor Applications

The development of a single carbon fiber electrode has been investigated as a potential non-enzymatic sensor capable of quantifying peroxide. Electrodeposition of palladium is shown to create nanostructured deposits with a nanoneedle and nano-rod like morphology. The electrode modification is shown to be facile, and the resulting sensors exhibit a high sensitivity toward the oxidation ( $388~\mu \text{A} \cdot {\mathrm {mM}}^{-1} \cdot {\mathrm {cm}}^{-2}$ ) and the reduction of peroxide. Interference from uric acid has been investigated, and the use of Nafion shown to greatly reduce its influence without unduly compromising the sensitivity of the sensors toward peroxide.

Kinetics of Aggregation and Magnetic Separation of Multicore Iron Oxide Nanoparticles: Effect of the Grafted Layer Thickness.

In this work, we have studied field-induced aggregation and magnetic separation—realized in a microfluidic channel equipped with a single magnetizable micropillar—of multicore iron oxide nanoparticles (IONPs) also called “nanoflowers” of an average size of 27 ± 4 nm and covered by either a citrate or polyethylene (PEG) monolayer having a thickness of 0.2–1 nm and 3.4–7.8 nm, respectively. The thickness of the adsorbed molecular layer is shown to strongly affect the magnetic dipolar coupling parameter because thicker molecular layers result in larger separation distances between nanoparticle metal oxide multicores thus decreasing dipolar magnetic forces between them. This simple geometrical constraint effect leads to the following important features related to the aggregation and magnetic separation processes: (a) Thinner citrate layer on the IONP surface promotes faster and stronger field-induced aggregation resulting in longer and thicker bulk needle-like aggregates as compared to those obtained with a thicker PEG layer; (b) A stronger aggregation of citrated IONPs leads to an enhanced retention capacity of these IONPs by a magnetized micropillar during magnetic separation. However, the capture efficiency Λ at the beginning of the magnetic separation seems to be almost independent of the adsorbed layer thickness. This is explained by the fact that only a small portion of nanoparticles composes bulk aggregates, while the main part of nanoparticles forms chains whose capture efficiency is independent of the adsorbed layer thickness but depends solely on the Mason number Ma. More precisely, the capture efficiency shows a power law trend , with n ≈ 1.4–1.7 at 300 < Ma < 104, in agreement with a new theoretical model. Besides these fundamental issues, the current work shows that the multicore IONPs with a size of about 30 nm have a good potential for use in biomedical sensor applications where an efficient low-field magnetic separation is required. In these applications, the nanoparticle surface design should be carried out in a close feedback with the magnetic separation study in order to find a compromise between biological functionalities of the adsorbed molecular layer and magnetic separation efficiency.

An Ultra-Low-Power RFID/NFC Frontend IC Using 0.18 μm CMOS Technology for Passive Tag Applications.

Battery-less passive sensor tags based on RFID or NFC technology have achieved much popularity in recent times. Passive tags are widely used for various applications like inventory control or in biotelemetry. In this paper, we present a new RFID/NFC frontend IC (integrated circuit) for 13.56 MHz passive tag applications. The design of the frontend IC is compatible with the standard ISO 15693/NFC 5. The paper discusses the analog design part in details with a brief overview of the digital interface and some of the critical measured parameters. A novel approach is adopted for the demodulator design, to demodulate the 10% ASK (amplitude shift keying) signal. The demodulator circuit consists of a comparator designed with a preset offset voltage. The comparator circuit design is discussed in detail. The power consumption of the bandgap reference circuit is used as the load for the envelope detection of the ASK modulated signal. The sub-threshold operation and low-supply-voltage are used extensively in the analog design—to keep the power consumption low. The IC was fabricated using 0.18 m CMOS technology in a die area of 1.5 mm × 1.5 mm and an effective area of 0.7 . The minimum supply voltage desired is 1.2 V, for which the total power consumption is 107 W. The analog part of the design consumes only 36 W, which is low in comparison to other contemporary passive tags ICs. Eventually, a passive tag is developed using the frontend IC, a microcontroller, a temperature and a pressure sensor. A smart NFC device is used to readout the sensor data from the tag employing an Android-based application software. The measurement results demonstrate the full passive operational capability. The IC is suitable for low-power and low-cost industrial or biomedical battery-less sensor applications. A figure-of-merit (FOM) is proposed in this paper which is taken as a reference for comparison with other related state-of-the-art researches.

Development and characterization of thermal responsivehydrogel films for biomedical sensor application

Two flexible stimuli-responsive hydrogel films were elaborated as biomedical sensor application. The hydrogel systems were contained in glass moulds and synthesized using gamma radiation at a dose rate of 10.1 kGy h−1, and absorbed dose of 50 kGy. The poly(NIPAAm) with a low critical solution temperature (LCST) close to the human body temperature, was employed as the principal component for the responsive materials. The addition of dimethyl acrylamide (DMAAm) for hydrophilic effect, methyl methacrylate (MMA) for mechanical property, and ethoxyethyl methacrylate (EEM) for mechanical property, modified the thermo dynamic transition point, obtaining viable responsive films with LCST of 36 °C and 39 °C. The samples were characterized by DSC to analyse the LCST, FT-IR to characterize the functional groups of the resulting films, AFM to examine the surface morphology, and swelling measurement to support the flexibility. Responsive ‘intelligent’ films with thermo sensitivity, biocompatibility, resistance, and conformableness are important to the development of flexible polymers for the application of biological sensor, smart membranes, or flexible electronics.

Fiber optic sensors for sub-centimeter spatially resolved measurements: Review and biomedical applications

Abstract One of the current frontier of optical fiber sensors, and a unique asset of this sensing technology is the possibility to use a whole optical fiber, or optical fiber device, as a sensor. This solution allows shifting the whole sensing paradigm, from the measurement of a single physical parameter (such as temperature, strain, vibrations, pressure) to the measurement of a spatial distribution, or profiling, of a physical parameter along the fiber length. In the recent years, several technologies are achieving this task with unprecedentedly narrow spatial resolution, ranging from the sub-millimeter to the centimeter-level. In this work, we review the main fiber optic sensing technologies that achieve a narrow spatial resolution: Fiber Bragg Grating (FBG) dense arrays, chirped FBG (CFBG) sensors, optical frequency domain reflectometry (OFDR) based on either Rayleigh scattering or reflective elements, and microwave photonics (MWP). In the second part of the work, we present the impact of spatially dense fiber optic sensors in biomedical applications, where they find the main impact, presenting the key results obtained in thermo-therapies monitoring, high-resolution diagnostic, catheters monitoring, smart textiles, and other emerging applicative fields.

Soft and transient magnesium plasmonics for environmental and biomedical sensing

Due to its controlled reaction with water and biofluids, Mg as a dissolvable conductor has enabled the development of many transient electronic devices. In addition, Mg is a novel plasmonic material with high extinction efficiency, but its transientoptical properties have not been explored thoroughly. In this study, for the first time, we exploit the transient and tunable plasmonic properties of Mg in environmental and biomedical sensor applications. We used soft nanoimprint lithography to fabricate flexible and large-area Mg plasmonic structures that can be applied on the human skin. Their resonance (or color) can be tuned in the visible range by gradual Mg dissolution in a water fluid or vapor-rich environment; these structures can be easily implemented as passive optical sensors without the need for complex electronic circuits or a power supply. We demonstrate the applications of our optical sensors in the accurate monitoring of environmental humidity and physiological detection of sweat loss on the human skin during exercise. Our devices could be used as decomposable/resorbable optical sensors and can help minimize long-term health effects and environmental risks associated with consumer device waste, which will lead to many new possibilities in transient photonic device applications.

Strain induced graphite/PDMS sensors for biomedical applications

This paper presents the design, fabrication and implementation of novel graphite/PDMS sensors for biomedical applications. The fabrication involves 3-D printed molds which were developed using acrylonitrile thermoplastic polymer as the filament. Graphite and PDMS were used to develop the electrodes and substrate of the sensor patches respectively. The electrodes were patterned in an interdigitated manner with the casting of graphite powder on the 3-D printed molds. The operating principle of the sensor patches is described along with the COMSOL simulation result which depicts the electric field density distribution between the two groups of electrode fingers of opposite polarity under an applied stress. The characterization and experimentation of sensor patches were done by analyzing the changes in their complex conductivities at different operating conditions. The highest bending radius of curvature achieved by the developed sensor patches is 6 mm. The sensor patches were then employed for strain-sensing purposes by attaching them on different parts of the body like finger, elbow, neck and knee. Strain sensing was successfully done based on the bending of the different joints on which the sensor patches were attached. The promising results shown by the sensor patches increase the chances of utilizing them in future in the biomedical world.

Nanoscale electromechanical properties of template-assisted hierarchical self-assembled cellulose nanofibers.

Cellulose, a major constituent of our natural environment and a structured biodegradable biopolymer, has been shown to exhibit shear piezoelectricity with potential applications in energy harvesters, biomedical sensors, electro-active displays and actuators. In this regard, a high-aspect ratio nanofiber geometry is particularly attractive as flexing or bending will likely produce a larger piezoelectric response as compared to axial deformation in this material. Here we report self-assembled cellulose nanofibers (SA-CNFs) fabricated using a template-wetting process, whereby parent cellulose nanocrystals (CNCs) introduced into a nanoporous template assemble to form rod-like cellulose clusters, which then assemble into SA-CNFs. Annealed SA-CNFs were found to exhibit an anisotropic shear piezoelectric response as directly measured using non-destructive piezo-response force microscopy (ND-PFM). We interpret these results in light of the distinct hierarchical structure in our template-grown SA-CNFs as revealed by scanning electron microscopy (SEM) and high resolution transmission electron microscopy (TEM).

CTAB-assisted hydrothermal synthesis of Cu2Se films composed of nanowire networks

A simple hydrothermal method has been developed to synthesize Cu2Se film on copper foil with the assistance of cetyltrimethylammonium bromide (CTAB) as a surfactant. The Cu2Se film was constructed by novel nanowire networks with length up to 50µm. The obtained product was characterized by XRD, SEM, HRTEM, Raman, and XPS techniques, revealing that Cu2Se nanowire possessed single-crystal structures. The shape of Cu2Se film changed from nanowire networks to perfect microflowers as the amount of CTAB increased. Such Cu2Se film may have great potential applications in biomedical engineering, sensors, and catalysis.

Enhanced magneto-optical Kerr effect and index sensitivity in Au/Fe_xCo_1-x magnetoplasmonic transducers

Magnetoplasmonic sensors are attractive candidates for ultrasensitive chemical and biomedical sensor applications. A variety of ferromagnetic metal thin films have been used for magnetoplasmonic device applications, yet the dependence of sensor performance on the optical and magneto-optical properties of ferromagnetic metal materials has been rarely studied. In this work, we report the study of enhanced magneto-optical Kerr effect (MOKE) and sensing performance in Au/FexCo1−x bilayer magneto-optical surface plasmon resonance (MOSPR) transducers. The optical constants of FexCo1−x (x=0, 0.29, 0.47, 0.65, and 1) in a sputter-deposited Au/FexCo1−x device are characterized by the attenuated total internal reflection (ATR) method. FexCo1−x thin films show different MOKEs as a function of the chemical concentration, with the highest transverse MOKE signal observed in Fe0.7Co0.3. Index sensing performance is closely related to the material’s optical and magneto-optical constants. By studying the sensing performance in the parameter space of the Au/FexCo1−x bilayer thicknesses, the highest sensitivity is found to be 0.385 (theoretical) and 0.306 RIU−1 (experimental) in the Au/Fe0.7Co0.3 MOSPR devices. Our research highlights the influence of the optical properties of ferromagnetic material to device sensitivity in MOSPR transducers. The high sensitivity in Au/FexCo1−x MOSPR devices make these structures attractive candidates for chemical and biomedical sensing applications.

An NFC on Two-Coil WPT Link for Implantable Biomedical Sensors under Ultra-Weak Coupling.

The inductive link is widely used in implantable biomedical sensor systems to achieve near-field communication (NFC) and wireless power transfer (WPT). However, it is tough to achieve reliable NFC on an inductive WPT link when the coupling coefficient is ultra-low (0.01 typically), since the NFC signal (especially for the uplink from the in-body part to the out-body part) could be too weak to be detected. Traditional load shift keying (LSK) requires strong coupling to pass the load modulation information to the power source. Instead of using LSK, we propose a dual-carrier NFC scheme for the weak-coupled inductive link; using binary phase shift keying (BPSK) modulation, its downlink data are modulated on the power carrier (2 MHz), while its uplink data are modulated on another carrier (125 kHz). The two carriers are transferred through the same coil pair. To overcome the strong interference of the power carrier, dedicated circuits are introduced. In addition, to minimize the power transfer efficiency decrease caused by adding NFC, we optimize the inductive link circuit parameters and approach the receiver sensitivity limit. In the prototype experiments, even though the coupling coefficient is as low as 0.008, the in-body transmitter costs only 0.61 mW power carrying 10 kbps of data, and achieves a 1 × 10 bit error rate under the strong interference of WPT. This dual-carrier NFC scheme could be useful for small-sized implantable biomedical sensor applications.

Nanocrystalline Magnetic Glass-Coated Microwires Using the Effect of Superparamagnetism Are Usable as Temperature Sensors in Biomedical Applications

For the control and study of the post-implantation biomechanical processes of TiAl6V4 implants, the ability of wireless in vivo measurement of various parameters (i.e., temperature in this case) at the tissue–implant interface is required. Compared with other types of sensors, which consist of sensing and transmitting elements, nanocrystalline magnetic glass-coated microwires combine both of these features into unit. Thanks to a Pyrex coating, the microwires are biocompatible, and due to their size, they do not intervene into the surface structures of implants. The studied as-cast microwire has a low Curie temperature due to the high amount of molybdenum, and is not magnetically bistable at room temperature. In order to create its bistability at room temperature and enhance its temperature sensitivity in the range from 37 °C up to 42 °C, the microwire is specially annealed under axial stress above crystallization temperature. Extreme temperature sensitivity in the required temperature range is achieved using the superparamagnetism effect; moreover, due to this effect, the switching field increased in an almost linear way. The temperature dependence of the switching field is employed to sense the temperature in two TiAl6V4 samples produced by additive manufacturing and representing implants with different types of fixations of the microwire onto the surface. Sensitivity up to 0.01 K is achieved.