Rapid, sensitive, and reusable detection of glucose by a robust radiofrequency integrated passive device biosensor chip

Laser-Induced Graphene-Based Sensors in Health Monitoring: Progress, Sensing Mechanisms, and Applications

The rising global population and improved living standards have led to an alarming increase in non-communicable diseases, notably cardiovascular and chronic respiratory diseases, posing a severe threat to human health. Wearable sensing devices, utilizing micro-sensing technology for real-time monitoring, have emerged as promising tools for disease prevention. Among various sensing platforms, graphene-based sensors have shown exceptional performance in the field of micro-sensing. Laser-induced graphene (LIG) technology, a cost-effective and facile method for graphene preparation, has gained particular attention. By converting polymer films directly into patterned graphene materials at ambient temperature and pressure, LIG offers a convenient and environmentally friendly alternative to traditional methods, opening up innovative possibilities for electronic device fabrication. Integrating LIG-based sensors into health monitoring systems holds the potential to revolutionize health management. To commemorate the tenth anniversary of the discovery of LIG, this work provides a comprehensive overview of LIG's evolution and the progress of LIG-based sensors. Delving into the diverse sensing mechanisms of LIG-based sensors, recent research advances in the domain of health monitoring are explored. Furthermore, the opportunities and challenges associated with LIG-based sensors in health monitoring are briefly discussed.

Recent Advances in Real-Time Label-Free Detection of Small Molecules

The detection and analysis of small molecules, typically defined as molecules under 1000 Da, is of growing interest ranging from the development of small-molecule drugs and inhibitors to the sensing of toxins and biomarkers. However, due to challenges such as their small size and low mass, many biosensing technologies struggle to have the sensitivity and selectivity for the detection of small molecules. Notably, their small size limits the usage of labeled techniques that can change the properties of small-molecule analytes. Furthermore, the capability of real-time detection is highly desired for small-molecule biosensors' application in diagnostics or screening. This review highlights recent advances in label-free real-time biosensing technologies utilizing different types of transducers to meet the growing demand for small-molecule detection.

Integrated Passive Sensing Chip for Highly Sensitive and Reusable Detection of Differential-Charged Nanoplastics Concentration

In this work, a new type, highly sensitive, and reusable nanoplastics (NPs) microwave detection method is proposed, which can be used to rapidly analyze NPs with different surface charges and sizes. The effective dielectric constant of NPs varies according to the different concentrations, particle sizes, and surface charges of NPs in aqueous solution. The feasibility of the microwave method for differential-charged NPs detection is verified using a complementary split ring resonator sensor manufactured on a cost-effective printed circuit board, which shows a high sensitivity only for positively charged NPs (PS-NH2) detection. To achieve microwave detection of both positively and negatively charged NPs (PS-SO3H), a microscale spiral-coupled resonator sensing chip is manufactured through integrated passive technology, which demonstrates extremely low detection limits and high sensitivity for both PS-NH2 and PS-SO3H, with different concentrations, particle sizes, and charges. In addition, for NPs solution doped with methyl orange, the device can still perform stable measurements, overcoming the inability of traditional NPs molecular element determination and optical detection methods to detect NPs aqueous solution with organic matter doping and color presence. The proposed microwave detection method could also be extended to sensing detection for detecting other hazardous environmental substances.

VEGF Detection via Impedance Spectroscopy on Surface Functionalized Interdigitated Biosensor

Vascular endothelial growth factor (VEGF), a clinically important biomarker, often plays a key role in angiogenesis, would healing, tumor growth, lung development, and in retinal diseases. Hence, detecting and quantifying VEGF is deemed medically important in clinical diagnosis for many diseases. In this report, a simple yet highly cost-effective platform was proposed for VEGF protein detection using commercially available interdigitated sensors that are surface modified to present DNA optimally for VEGF capture. The dielectric characteristics between the fingers of the sensor were modulated by the negatively charged aptamer-VEGF capture, and the impedance was estimated using an impedance analyzer. Impedance-spectra tests were compared among pristine unmodified surfaces, functionalized monolayer surfaces, and aptamer-grafted surfaces in order to evaluate the efficacy of VEGF detection. From our results, the sensitivity experiments as conducted showed the ability of the interdigitated sensor to detect VEGF at a low concentration of 5 pM (200 pg/mL). The specificity of the functionalized sensor in detecting VEGF was further examined by comparing the impedance to platelet-derived growth factor, and the results confirm the specificity of the sensor. Finally, the Nyquist plot of impedance spectra was also presented to help data visualization and the overall performance of the device was found to be a highly suitable template for a smart biosensor for the detection of VEGF.

Ultrahigh-sensitivity multi-parameter tacrolimus solution detection based on an anchor planar millifluidic microwave biosensor

To detect drug concentration in tacrolimus solution, an anchor planar millifluidic microwave (APMM) biosensor is proposed. The millifluidic system integrated with the sensor enables accurate and efficient detection while eliminating interference caused by the fluidity of the tacrolimus sample. Different concentrations (10-500 ng mL^-1) of the tacrolimus analyte were introduced into the millifluidic channel, where it completely interacts with the radio frequency patch electromagnetic field, thereby effectively and sensitively modifying the resonant frequency and amplitude of the transmission coefficient. Experimental results indicate that the sensor has an extremely low limit of detection (LoD) of 0.12 pg mL^-1 and a frequency detection resolution (FDR) of 1.59 (MHz (ng mL^-1)). The greater the FDR and the lower the LoD, the more the feasibility of a label-free biosensing method. Regression analysis revealed a strong linear correlation (R² = 0.992) between the concentration of tacrolimus and the frequency difference of the two resonant peaks of APMM. In addition, the difference in the reflection coefficient between the two formants was measured and calculated, and a strong linear correlation (R² = 0.998) was found between the difference and tacrolimus concentration. Five measurements were performed on each individual sample of tacrolimus to validate the biosensor's high repeatability. Consequently, the proposed biosensor is a potential candidate for the early detection of tacrolimus drug concentration levels in organ transplant recipients. This study presents a simple method for constructing microwave biosensors with high sensitivity and rapid response.

A "Two-Part" Resonance Circuit Based Detachable Sweat Patch for Noninvasive Biochemical and Biophysical Sensing

Wearable electronics play important roles in noninvasive, continuous, and personalized monitoring of multiple biosignals generated by the body. To unleash their full potential for next-generation human centered bio-integrated electronics, the wireless sensing capability is a desirable feature. However, state-of-the-art wireless sensing technologies exploit rigid and bulky electronic modules for power supply, signal generation, and data transmission. This study reports a battery-free device technology based on a "two-part" resonance circuit model with modularized, physically separated, and detachable functional units for magnetic coupling and biosensing. The resulting platform combines advantages of electronics and microfluidics with low cost, minimized form factors, and improved performance stability. Demonstration of a detachable sweat patch capable of simultaneous recording of cortisol concentration, pH value, and temperature highlights the potential of the "two-part" circuit for advanced, transformative biosensing. The resulting wireless sensors provide a new engineering solution to monitoring biosignals through intimate and seamless integration with skin surfaces.

A Concise and Systematic Review on Non-Invasive Glucose Monitoring for Potential Diabetes Management

The current standard of diabetes management depends upon the invasive blood pricking techniques. In recent times, the availability of minimally invasive continuous glucose monitoring devices have made some improvements in the life of diabetic patients however it has its own limitations which include painful insertion, excessive cost, discomfort and an active risk due to the presence of a foreign body under the skin. Due to all these factors, the non-invasive glucose monitoring has remain a subject of research for the last two decades and multiple techniques of non-invasive glucose monitoring have been proposed. These proposed techniques have the potential to be evolved into a wearable device for non-invasive diabetes management. This paper reviews research advances and major challenges of such techniques or methods in recent years and broadly classifies them into four types based on their detection principles. These four methods are: optical spectroscopy, photoacoustic spectroscopy, electromagnetic sensing and nanomaterial based sensing. The paper primarily focuses on the evolution of non-invasive technology from bench-top equipment to smart wearable devices for personalized non-invasive continuous glucose monitoring in these four methods. With the rapid evolve of wearable technology, all these four methods of non-invasive blood glucose monitoring independently or in combination of two or more have the potential to become a reality in the near future for efficient, affordable, accurate and pain-free diabetes management.

Design of EM Sensor for Non-Contact Detection of Defective Wire Harness in Conveyor System

For a non-contact detection of defective wire harness in conveyor system, a new method using the electromagnetic (EM) sensor is proposed in this paper. A dual-feed and multi array microstrip patch antenna operating at 5.8 GHz is utilized to design the EM sensor. When the wire harness is located above patch antenna, the equivalent circuit of each patch antenna and wire harness can be modeled as shunt resistor, capacitor, and inductor. Moreover, a capacitive coupling between the patch antenna and the wire harness is generated. Next, the shunt resistor of wire harness increases due to the defect of the wire so that the reflection coefficient of the patch antenna is lower than that of the wire without defect; thus, the defect of wire harness can be detected by magnitude of reflection coefficient at resonant frequency. The performances of the designed EM sensor are verified and compared by the equivalent circuit modeling, full-wave simulation, and measurement.

Microfluidic microwave biosensor based on biomimetic materials for the quantitative detection of glucose

This paper presents a microwave microfluidic biosensor for monitoring blood glucose levels. The glucose sensor is a triple ring microstrip patch antenna integrated with a biomimetic microfluidic device capable of measuring a fixed volume of glucose solution. The sensor was utilized to detect 50–500 mg/dL glucose solutions. The interaction of the glucose solution with the electromagnetic field on the patch's surface influences both the resonance frequency and the magnitude of reflection coefficient. The results indicate that the microfluidic device can reduce experimental error and enhance the correlation between glucose concentration, resonant frequency, and reflection coefficient. Finally, the microfluidic sensor had a sensitivity of 0.25 MHz/(mg/dL), a detection limit as low as 7.7 mg/dL, and correlation coefficients of resonance frequency and reflection coefficient with a glucose concentration of 0.996 and 0.984, respectively. The experiment on the sensor's stability verifies the sensor's excellent stability and rapid response (~ 150 ms). Consequently, the device can be used to differentiate the concentration of glucose solutions, as well as to detect blood glucose levels at an early stage.

Battery-free, tuning circuit-inspired wireless sensor systems for detection of multiple biomarkers in bodily fluids

Tracking the concentration of biomarkers in biofluids can provide crucial information about health status. However, the complexity and nonideal form factors of conventional digital wireless schemes impose challenges in realizing biointegrated, lightweight, and miniaturized sensors. Inspired by the working principle of tuning circuits in radio frequency electronics, this study reports a class of battery-free wireless biochemical sensors: In a resonance circuit, the coupling between a sensing interface and an inductor-capacitor oscillator through a pair of varactor diodes converts a change in electric potential into a modulation in capacitance, resulting in a quantifiable shift of the resonance circuit. Proper design of sensing interfaces with biorecognition elements enables the detection of various biomarkers, including ions, neurotransmitters, and metabolites. Demonstrations of "smart accessories" and miniaturized probes suggest the broad utility of this circuit model. The design concepts and sensing strategies provide a realistic pathway to building biointegrated electronics for wireless biochemical sensing.

Design and Micro-Nano Fabrication of a GaAs-Based On-Chip Miniaturized Bandpass Filter with Intertwined Inductors and Circinate Capacitor Using Integrated Passive Device Technology

In this study, we propose a miniaturized bandpass filter (BPF) developed by combining an approximate circular (36-gon) winding inductor, a circinate capacitor, and five air-bridge structures fabricated on a gallium arsenide (GaAs) substrate using an integrated passive device (IPD) technology. We introduced air-bridge structures into the outer metal wire to improve the capacitance per unit volume while utilizing a miniaturized chip with dimensions 1538 μm × 800 μm (0.029 λ₀ × 0.015 λ₀) for the BPF. The pattern was designed and optimized by simulating different dimensional parameters, and the group delay and current density are presented. The equivalent circuit was modeled to analysis various parasitic effect. Additionally, we described the GaAs-based micro-nano scale fabrication process to elucidate the proposed IPD technology and the physical structure of the BPF. Measurements were conducted with a center frequency of 1.53 GHz (insertion loss of 0.53 dB) and a 3-dB fractional bandwidth (FBW) of 70.59%. The transmission zero was located at 4.16 GHz with restraint of 35.86 dB. Owing to the benefits from its miniaturized chip size and high performance, the proposed GaAs-based IPD BPF was verified as an excellent device for various S-band applications, such as satellite communication, keyless vehicle locks, wireless headphones, and radar.

RFID-Based Microwave Biosensor for Non-Contact Detection of Glucose Solution

Due to the increasing number of diabetic patients, early monitoring of glucose levels is particularly important; therefore, glucose biosensors have attracted enormous attention from researchers. In this paper, we propose a glucose microwave biosensor based on RFID and achieve a non-contact measurement of the concentration of glucose solutions. The Reader is a complementary split-ring resonator (CSRR), and the Tag is comprised of a squared spiral capacitor (SSC). A polydimethylsiloxane microfluidic quantitative cavity with a volume of 1.56 μL is integrated on the Tag to ensure that the glucose solution can be accurately set to the sensitive area and fully contacted with the electromagnetic flux. Because the SSC exhibits different capacitances when it contacts glucose solutions of different concentrations, changing the resonant frequency of the CSRR, we can use the relationship to characterize the biosensing response. Measurement results show that bare CSRR and RFID-based biosensors have achieved sensitivities of 0.31 MHz/mg·dL⁻¹ and 10.27 kHz/mg·dL⁻¹, and detection limits of 13.79 mg/dL and 1.19 mg/dL, respectively, and both realize a response time of less than 1 s. Linear regression analysis of the abovementioned biosensors showed an excellent linear relationship. The proposed design provides a feasible solution for microwave biosensors aiming for the non-contact measurement of glucose concentration.

Ultrasensitive and Reusable Graphene Oxide-Modified Double-Interdigitated Capacitive (DIDC) Sensing Chip for Detecting SARS-CoV-2

This research reveals the promising functionalization of graphene oxide (GrO)-glazed double-interdigitated capacitive (DIDC) biosensing platform to detect severe acute respiratory syndrome coronavirus (SARS-CoV-2) spike (S1) proteins with enhanced selectivity and rapid response. The DIDC bioactive surface consisting of Pt/Ti featured SiO₂ substrate was fabricated using GrO/EDC-NHS/anti-SARS-CoV-2 antibodies (Abs) which is having layer-by-layer interface self-assembly chemistry method. This electroactive immune-sensing platform exhibits reproducibility and sensitivity with reference to the S1 protein of SARS-CoV-2. The outcomes of analytical studies confirm that GrO provided a desired engineered surface for Abs immobilization and amplified capacitance to achieve a wide detection range (1.0 mg/mL to 1.0 fg/mL), low limit of detection (1 fg/mL) within 3 s of response time, good linearity (18.56 nF/g), and a high sensitivity of 1.0 fg/mL. Importantly, the unique biochip was selective against blood-borne antigens and standby for 10 days at 5 °C. Our developed DIDC-based SARS-CoV-2 biosensor is suitable for point-of-care (POC) diagnostic applications due to portability and scaling-up ability. In addition, this sensing platform can be modified for the early diagnosis of severe viral infections using real samples.

Rapid and real-time monitoring of bacterial growth against antibiotics in solid growth medium using a contactless planar microwave resonator sensor

Infection diagnosis and antibiotic susceptibility testing (AST) are pertinent clinical microbiology practices that are in dire need of improvement, due to the inadequacy of current standards in early detection of bacterial response to antibiotics and affordability of contemporarily used methods. This paper presents a novel way to conduct AST which hybridizes disk diffusion AST with microwave resonators for rapid, contactless, and non-invasive sensing and monitoring. In this research, the effect of antibiotic (erythromycin) concentrations on test bacterium, Escherichia coli (E. coli) cultured on solid agar medium (MH agar) are monitored through employing a microwave split-ring resonator. A one-port microwave resonator operating at a 1.76 GHz resonant frequency, featuring a 5 mm² sensitive sensing region, was designed and optimized to perform this. Upon introducing uninhibited growth of the bacteria, the sensor measured 0.005 dB/hr, with a maximum change of 0.07 dB over the course of 15 hours. The amplitude change decreased to negligible values to signify inhibited growth of the bacteria at higher concentrations of antibiotics, such as a change of 0.005 dB in resonant amplitude variation while using 45 µg of antibiotic. Moreover, this sensor demonstrated decisive results of antibiotic susceptibility in under 6 hours and shows great promise to expand automation to the intricate AST workflow in clinical settings, while providing rapid, sensitive, and non-invasive detection capabilities.

Biosensors and biomarkers for determining gestational diabetes mellitus and jaundice in children

Gestational diabetes and jaundice are the correlated diseases predominantly found in mother and newborn child. Jaundice is a neonatal complication with an increased risk when mother has gestational diabetes. Mothers with diabetes at an early stage of gestational age are at higher risk for hyperbilirubinemia (jaundice) and hypoglycemia. So, it is mandatory to monitor the condition of diabetes and jaundice during the pregnancy period for a healthy child and safest delivery. On the other hand, nanotechnology has displayed a rapid advancement that can be implemented to overcome these issues. The development of high-performance diagnosis using appropriate biomarkers provides their efficacy in the detection gestational diabetes and jaundice. This review covers the aspects from a fast-developing field to generate nanosensors in the nanosized dimensions for the applications to overcome these complications by coupling diagnostics with biomarkers. Further, the serum-based biomarkers have been discussed for these inborn complications and also the diagnosis with the current trend.

Zinc ferrite nanoparticles: simple synthesis via lyophilisation and electrochemical application as glucose biosensor

With increasing diabetes patients in the near future, development of non-enzymatic glucose biosensor is highly demanded due to their greater sensitivity and resistance to external stimuli compared to enzymatic biosensors. Zinc ferrite (ZnFe2O4, ZFO) nanoparticles (NPs) were fabricated using a simple solution combustion method together with freeze drying. The NPs have high crystallinity, large aspect ratios and narrow size distributions. Plenty of defects have been induced during lyophilisation and greatly improves the glucose biosensing performance during electrochemistry test. The freeze-dried ZFO NPs are highly crystalline and agglomeration-free, these assures the sample with high sensitivity, superior selectivity, low detection limit and outstanding stability for electrochemical glucose biosensing.

Radio-Frequency Biosensors for Real-Time and Continuous Glucose Detection

This review paper focuses on radio-frequency (RF) biosensors for real-time and continuous glucose sensing reported in the literature, including our recent research. Diverse versions of glucose biosensors based on RF devices and circuits are briefly introduced, and their performances are compared. In addition, the limitations of the developed RF glucose biosensors are discussed. Finally, we present perspectives on state-of-art RF biosensing chips for point-of-care diagnosis and describe their future challenges.

Visualization of microwave near-field distribution in sodium chloride and glucose aqueous solutions by a thermo-elastic optical indicator microscope

In this study, a new optical method is presented to determine the concentrations of NaCl and glucose aqueous solutions by using a thermo-elastic optical indicator microscope. By measuring the microwave near-field distribution intensity, concentration changes of NaCl and glucose aqueous solutions were detected in the 0-100 mg/ml range, when exposed to microwave irradiation at 12 GHz frequency. Microwave near-field distribution intensity decreased as the NaCl or glucose concentration increased due to the changes of the absorption properties of aqueous solution. This method provides a novel approach for monitoring NaCl and glucose in biological liquids by using a CCD sensor capable of visualizing NaCl and glucose concentrations without scanning.

Ultrafast Detection and Discrimination of Methanol Gas Using a Polyindole-Embedded Substrate Integrated Waveguide Microwave Sensor

The fast and sensitive detection of methanol gas using cost-effective sensors in the industry is a significant issue to be addressed. Herein, a polyindole (PIn)-deposited substrate integrated waveguide (SIW) has been introduced to perform quantitative and qualitative methanol gas sensing with quick response and recovery time at room temperature. First, PIn is synthesized and deposited in the microwell etched at the intensified electric field region of the microwave-based cavity resonator, which gives a sensing response through variation of PIn's high-frequency conductivity and dielectric property caused by the adsorption and desorption of methanol gas. Second, an enhanced filling factor and high Q factor have been attained using the proposed microwell etched SIW structure, which exhibits high sensitivity in terms of frequency shift (3.33 kHz/ppm), amplitude shift (0.005 dB/ppm), bandwidth broadening (3.66 kHz/ppm), and loaded Q factor (10.60 Q value/ppm). Third, the gas measurement results reveal excellent long-term stability with a relative standard deviation (RSD) of 0.02% for 7 days, excellent repeatability with an RSD of 0.004%, and desired response and recovery time of 95 and 120 s, respectively. The results indicate that the proposed microwave sensor has great potential to achieve high sensitivity and fast response toward methanol gas molecules at room temperature.

Hypersensitized Metamaterials Based on a Corona-Shaped Resonator for Efficient Detection of Glucose

In this work, a new design for a real-time noninvasive metamaterial sensor, based on a corona-shaped resonator, is proposed. The sensor was designed numerically and fabricated experimentally in order to be utilized for efficient detection of glucose in aqueous solutions such as water and blood. The sensor was inspired by a corona in-plane-shaped design with the presumption that its circular structure might produce a broader interaction of the electromagnetic waves with the glucose samples. A clear shift in the resonance frequency was observed for various glucose samples, which implies that the proposed sensor has a good sensitivity and can be easily utilized to distinguish any glucose concentration, even though their dielectric coefficients are close. Results showed a superior performance in terms of resonance frequency shift (1.51 GHz) and quality factor (246) compared to those reported in the literature. The transmission variation level ∆|S21| was investigated for glucose concentration in both water and blood. The sensing mechanism was elaborated through the surface current, electric field and magnetic field distributions on the corona resonator. The proposed metamaterials sensor is considered to be a promising candidate for biosensor and medicine applications in human glycaemia monitoring.

Design of an ELC resonator-based reusable RF microfluidic sensor for blood glucose estimation

Design of a reusable microfluidic sensor for blood glucose estimation at microwave frequencies is presented. The sensing unit primarily comprises a complementary electric LC (CELC) resonator, which is made reusable by filling the test sample in a glass capillary before mounting it inside a groove cut in the central arm of the resonator. The use of glass capillary in the present situation to contain the blood sample actually eliminates the possibility of any direct contact of the sensor with the test sample, and hence wards off any coincidental contamination of the sensor. Usage of the capillary provides additional benefits as only microliters of the sample are required, besides offering sterile measuring environment since these capillaries are disposable. The capillary made of borosilicate glass is highly biocompatible and exhibits exceptionally high chemical resistance in corrosive environments. Apart from reusability, the novelty of the proposed sensor also lies in its enhanced sensitivity which is quite an essential factor when it comes to the measurement of glucose concentration in the human physiological range. The applicability of the proposed scheme for glucose sensing is demonstrated by performing RF measurements of aqueous glucose solutions and goat blood samples using the fabricated sensor.

Highly Stable Passive Wireless Sensor for Protease Activity Based on Fatty Acid-Coupled Gelatin Composite Films

Proteases are often used as biomarkers of many pathologies as well as of microbial contamination and infection. Therefore, extensive efforts are devoted to the development of protease sensors. Some applications would benefit from wireless monitoring of proteolytic activity at minimal cost, e.g., sensors embedded in care products like wound dressings and diapers to track wound and urinary infections. Passive (batteryless) and chipless transponders stand out among wireless sensing technologies when low cost is a requirement. Here, we developed and extensively characterized a composite material that is biodegradable but still highly stable in aqueous media, whose proteolytic degradation could be used in these wireless transponders as a transduction mechanism of proteolytic activity. This composite material consisted of a cross-linked gelatin network with incorporated caprylic acid. The digestion of the composite when exposed to proteases results in a change of its resistivity, a quantity that can be wirelessly monitored by coupling the composite to an inductor-capacitor resonator, i.e., an antenna. We experimentally proved this wireless sensor concept by monitoring the presence of a variety of proteases in aqueous media. Moreover, we also showed that detection time follows a relationship with protease concentration, which enables quantification possibilities for practical applications.

Fly Ash-Based Zeolite-Complexed Polyethylene-Glycol on an Interdigitated Electrode Surface for High-Performance Determination of Diabetes Mellitus

BACKGROUND

Diabetes is a complex metabolic disorder known to induce a high blood glucose level that fluctuates outside the normal range. Diabetes affects and damages the organs in the body and causes heart issues, blindness and kidney failure. Continuous monitoring is mandatory to keep the blood glucose level within a healthy range.

MATERIALS AND METHODS

This research was focused on diagnosing diabetes mellitus on zeolite nanoparticle-polyethylene glycol complex-immobilized interdigitated electrode sensor (IDE) surfaces. Zeolite nanoparticles were extracted from the fly ash of a thermal power plant by alkaline extraction. The surface morphology of the synthesized nanoparticles was observed by field-emission scanning electron microscopy and transmission electron microscopy, and the presence of certain elements and the particle size were determined by energy-dispersive X-ray spectroscopy and particle size analysis, respectively.

RESULTS

The crystalline PEG-zeolite nanoparticles were synthesized with a size of 40±10 nm according to high-resolution microscopy. A particle size analyzer revealed the sizes of the fly ash and PEG-zeolite particles as 60±10 µm and 50±10 nm, respectively. The IDE surface was evaluated for its ability to display antifouling properties and sense glucose levels on the abovementioned nanoparticle-modified surface. Glucose oxidase was probed on the PEG-zeolite-modified IDE surface, and glucose was detected. PEG zeolite performed well with excellent antifouling properties on the IDE sensor surface and improved the glucose detection limit to 0.03 mg/mL from 0.08 mg/mL, as determined by linear regressions [y = 5.365x - 6.803; R2 = 0.9035 (zeolite surface) and y = 5.498x + 5.914R2 = 0.9061 (PEG-zeolite surface)]. This enhancement was ~3-fold, and sensitivities were found to be 0.03 and 0.06 mg/mL glucose for the PEG-zeolite- and zeolite-modified surfaces, respectively, showing a 2-fold difference.

CONCLUSION

The excellent biocompatible surface modified by PEG zeolite exhibited high performance and is useful for medical diagnosis.

Evanescent Wave Optical Trapping and Sensing on Polymer Optical Fibers for Ultra-Trace Detection of Glucose

Graphene sensitization of glucose-imprinted polymer (G-IP)-coated optical fiber has been introduced as a new biosensor for evanescent wave trapping on the polymer optical fiber to detect low-level glucose. The developed sensor operates based on the evanescent wave modulation principle. Full characterization via atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, high-resolution transmission electron microscopy (HRTEM), and N₂ adsorption/desorption of as-prepared G-IP-coated optical fibers was experimentally tested. Accordingly, related operational parameters such as roughness and diameter were optimized. Incorporating graphene into the G-IP not only steadily promotes the electron transport between the fiber surface and as-proposed G-IP but also significantly enhances the sensitivity by acting as a carrier for immobilizing G-IP with specific imprinted cavities. The sensor demonstrates a fast response time (5 s) and high sensitivity, selectivity, and stability, which cause a wide linear range (10-100 nM) and a low limit of detection (LOD = 2.54 nM). Experimental results indicate that the developed sensor facilitates online monitoring and remote sensing of glucose in biological liquids and food samples.

Gold-on-glass microwave split-ring resonators with PDMS microchannels for differential measurement in microfluidic sensing

This paper describes a microwave resonator incorporating microfluidic lab-on-chip sensor system capable of performing simultaneous differential measurement based sensing of liquid samples. The resonators are split-ring resonator shapes made of gold on glass substrates. Directly bonded on glass substrates are polydimethylsiloxane microchannels. Sensor system design incorporates a pair of identical resonators, one of which performs reference reading from the background. Tracking the difference of the responses of both resonators simultaneously, rather than a single one, is used to obtain a more linear and noise-free reading. The sensor system was produced with conventional fabrication techniques. It is compatible with low-cost, simple, easy to handle sensing applications. Results indicate that reliable differential measurement was possible owing to a well-matched pair of sensors with a response error as low as 0.1%. It was also demonstrated that differential measurement capability enables sensing with improved linearity. Measurements were performed with glucose solutions in the range of 3.2-16.1 mM, achieving a sensitivity of 0.16 MHz/mM.

Non-invasive continuous-time glucose monitoring system using a chipless printable sensor based on split ring microwave resonators

This paper reports a highly sensitive, non-invasive sensor for real-time glucose monitoring from interstitial fluid. The structure is comprised of a chip-less tag sensor which may be taped over the patient’s skin and a reader, that can be embedded in a smartwatch. The tag sensor is energized through the established electromagnetic coupling between the tag and the reader and its frequency response is reflected on the spectrum of the reader in the same manner. The tag sensor consumes zero power as there is no requirement for any active readout or communication circuitry on the tag side. When measuring changes in glucose concentrations within saline replicating interstitial fluid, the sensor was able to detect glucose with an accuracy of ~ 1 mM/l over a physiological range of glucose concentrations with 38 kHz of the resonance frequency shift. This high sensitivity is attained as a result of the proposed new design and extended field concentration on the tag. The impact of some of the possible interferences on the response of the sensor’s performance was also investigated. Variations in electrolyte concentrations within the test samples have a negligible effect on the response of the sensor unless these variations are supra-physiologically large.

An In-Vitro Study of Wireless Passive Inductor Integrated Cavity for Future long-term Implantable resonator-based Glucose Monitoring

In this paper, a label-free biosensor is developed for monitoring the glucose level in the solution. A wireless passive inductor integrated cavity (IIC)-based biosensor is studied. The proposed IIC consists of a passive spiral inductor integrated cavity resonator for continuous monitoring of capillary blood glucose. The proposed method is based on the cavity perturbation theory, where the solution with different glucose levels perturbs and interacts with the passive IIC-based biosensor. The variation in the effective permittivity ε_eff and permeability μ_eff of the cavity resonator due to different glucose levels changes the equivalent capacitance and inductance of the proposed IIC. In turn, the corresponding resonance frequency changes. The in-vitro measurements are performed on deionized water glucose solutions of various glucose concentrations within the range of 75 mg/dL to 250 mg/dL. The results demonstrate that the sensor's resonant frequency increases with the increase in glucose level in the solution with a sensitivity of 32 kHz/mgdL^-1.

Detection of Cardiovascular CRP Protein Biomarker Using a Novel Nanofibrous Substrate

It is known that different diseases have characteristic biomarkers that are secreted very early on, even before the symptoms have developed. Before any kind of therapeutic approach can be used, it is necessary that such biomarkers be detected at a minimum concentration in the bodily fluids. Here, we report the fabrication of an interdigitated sensing device integrated with polyvinyl alcohol (PVA) nanofibers and carbon nanotubes (CNT) for the detection of an inflammatory biomarker, C-reactive protein (CRP). The limit of detection (LOD) was achieved in a range of 100 ng mL-1 and 1 fg mL-1 in both phosphate buffered saline (PBS) and human serum (hs). Furthermore, a significant change in the electrochemical impedance from 45% to 70% (hs) and 38% to 60% (PBS) over the loading range of CRP was achieved. The finite element analysis indicates that a non-redox charge transduction at the solid/liquid interface on the electrode surface is responsible for the enhanced sensitivity. Furthermore, the fabricated biosensor consists of a large electro-active surface area, along with better charge transfer characteristics that enabled improved specific binding with CRP. This was determined both experimentally and from the simulated electrochemical impedance of the PVA nanofiber patterned gold electrode.

Fabrication of QFN-Packaged Miniaturized GaAs-Based Bandpass Filter with Intertwined Inductors and Dendritic Capacitor

This article presents a compact quad flat no-lead (QFN)-packaged second-order bandpass filter (BPF) with intertwined inductors, a dendritic capacitor, and four air-bridge structures, which was fabricated on a gallium arsenide (GaAs) substrate by integrated passive device (IPD) technology. Air-bridge structures were introduced into an approximate octagonal outer metal track to provide a miniaturized chip size of 0.021 × 0.021 λ₀ (0.8 × 0.8 mm²) for the BPF. The QFN-packaged GaAs-based bandpass filter was used to protect the device from moisture and achieve good thermal and electrical performances. An equivalent circuit was modeled to analyze the BPF. A description of the manufacturing process is presented to elucidate the physical structure of the IPD-based BPF. Measurements were performed on the proposed single band BPF using a center frequency of 2.21 GHz (return loss of 26.45 dB) and a 3-dB fractional bandwidth (FBW) of 71.94% (insertion loss of 0.38 dB). The transmission zero is located at the 6.38 GHz with a restraint of 30.55 dB. The manufactured IPD-based BPF can play an excellent role in various S-band applications, such as a repeater, satellite communication, and radar, owing to its miniaturized chip size and high performance.

Highly Sensitive Closed Loop Enclosed Split Ring Biosensor With High Field Confinement for Aqueous and Blood-Glucose Measurements

This paper presents a highly sensitive closed loop enclosed split ring biosensor operating in microwave frequencies for measuring blood glucose levels in the human body. The proposed microwave glucose biosensor, working on the principle of high field confinement and concentrated energy, has been tested using both in-vitro and in-vivo methods. This principle allows the sensor to concentrate energy at the surface which results in improved accuracy of measurements. For in-vitro measurements, the biosensor has been tested using de-ionized water glucose solutions of different concentrations. The miniaturized micrometer scale biosensor is fabricated over a thin Si-substrate using photolithographic technique. The biosensor has been designed in a way to operate at desired microwave frequencies. Highly confined fields and concentrated energy inside the closed loop line containing the split ring resonators are responsible for the sensitivity enhancement. This new biosensor has obtained a high sensitivity of 82 MHz/mgmL^-1 within the clinical diabetic range during in-vivo testing over the human body. In addition, the subjects (undergoing experiments) steady state has been continuously monitored throughout the experiment which helps in improving the accuracy of the results. The proposed biosensor has further obtained a low detection limit of <0.05 wt.% and can be useful for continuous non-invasive blood glucose monitoring.

Electrochemical Impedance Characterization of Blood Cell Suspensions. Part 1: Basic Theory and Application to Two-Phase Systems

Electrochemical impedance spectra of composite materials contain information on the topological arrangement, volume fraction, and shape of particles, as well as the dielectric properties of the matrix and particles. The objective of this study is to investigate how these parameters affect the dielectric spectrum and what reliable information can be extracted from experimental data. The main attention was focused on systems with dielectric behavior similar to that of human blood. Mostly plasma and erythrocytes determine the dielectric properties of whole blood. Erythrocytes suspended in plasma can be considered as three-phase systems with single-shelled particles. A theoretical approach based on the effective medium theory is developed for calculating the effective permittivity and conductivity of three-phase composites at a wide frequency range (from 0 to 1 GHz). A finite-difference method is applied to model three-dimensional periodic structures. A special case of two-phase materials is used to demonstrate the influence of the shape and arrangement of particles on dielectric properties. Theoretical and numerical approaches are applied to two-phase composites with spherical, spheroidal and biconcave particles and are compared with each other and with published data. It is shown that two-phase composites exhibit only β-dispersion. In contrast to the quasi-static limit, the wide-bandwidth impedance spectroscopy makes it possible to distinguish between disordered and regular arrangements of spheroidal and biconcave particles. The results can be used to analyze the dielectric properties of blood, which is very promising for various medical applications. This study of two-phase composites can be further extended to three-phase composites.

A Flexible Wireless Dielectric Sensor for Noninvasive Fluid Monitoring

A flexible wireless dielectric sensor is presented here for noninvasively monitoring the permittivity and conductivity of fluids, based on resistor–inductor–capacitor (RLC) resonant circuit and capacitively coupled contactless conductivity detection (C⁴D) technique. The RLC sensor consists of one single-turn inductor and one interdigital capacitor. The resonant frequency of the device is sensitive to the surrounding environment, thanks to the electric field leaked out between the interdigital capacitor electrodes. Through the high-frequency structure simulator (HFSS) simulation, and experiments on ethanol/water solutions and NaCl solutions, it was confirmed that a fluid’s permittivity and conductivity could be detected by the return loss curve (S₁₁). With great repeatability and stability, the proposed sensor has potential for broad applications, especially in wearable low-cost smart devices.

Real-Time Noninvasive Measurement of Glucose Concentration Using a Modified Hilbert Shaped Microwave Sensor

We developed a microwave glucose sensor based on the modified first-order Hilbert curve design and measured glucose concentration in aqueous solutions by using a real-time microwave near-field electromagnetic interaction technique. We observed S₂₁ transmission parameters of the sensor at resonant frequencies depend on the glucose concentration. We could determine the glucose concentration in the 0-250 mg/dL concentration range at an operating frequency of near 6 GHz. The measured minimum detectable signal was 0.0156 dB/(mg/dL) and the measured minimum detectable concentration was 1.92 mg/dL. The simulation result for the minimum detectable signal and the minimum detectable concentration was 0.0182 dB/(mg/dL) and 1.65 mg/dL, respectively. The temperature instability of the sensor for human glycemia in situ measurement range (27-34 °C for fingers and 36-40 °C for body temperature ranges) can be improved by the integration of the temperature sensor in the microwave stripline platform and the obtained data can be corrected during signal processing. The microwave signal-temperature dependence is almost linear with the same slope for a glucose concentration range of 50-150 mg/dL. The temperature correlation coefficient is 0.05 dB/°C and 0.15 dB/°C in 27-34 °C and 36-40 °C temperature range, respectively. The presented system has a cheap, easy fabrication process and has great potential for non-invasive glucose monitoring.

Glucose oxidase complexed gold-graphene nanocomposite on a dielectric surface for glucose detection: a strategy for gestational diabetes mellitus

BACKGROUND

Gestational diabetes mellitus is a commonly occurring metabolic disorder during pregnancy, affecting >4% of pregnant women. It is generally defined as the intolerance of glucose with the onset or initial diagnosis during pregnancy. This illness affects the placenta and poses a threat to the baby as it affects the supply of proper oxygen and nutrients.

PURPOSE

Due to the high percentage of affected pregnant women, it should be mandatory to evaluate glucose levels during pregnancy and there is a need for a continuous monitoring system.

METHODS

Herein, the investigators modified the interdigitated (di)electrodes (IDE) sensing surface to detect the glucose on covalently immobilized glucose oxidase (GOx) with the graphene. The characterization of graphene and gold nanoparticle (GNP) was performed by high-resolution microscopy.

RESULTS

Sensitivity was found to be 0.06 mg/mL and to enhance the detection, GOx was complexed with GNP. GNP-GOx was improved the sensitive detection twofold from 0.06 to 0.03 mg/mL, and it also displayed higher levels of current changes at all the concentrations of glucose that were tested. High-performance of the above IDE sensing system was attested by the specificity, reproducibility and higher sensitivity detections. Further, the linear regression analysis indicated the limit of detection to be between 0.02 and 0.03 mg/mL.

CONCLUSION

This study demonstrated the potential strategy with nanocomposite for diagnosing gestational diabetes mellitus.

EM-Wave Biosensors: A Review of RF, Microwave, mm-Wave and Optical Sensing

This article presents a broad review on optical, radio-frequency (RF), microwave (MW), millimeter wave (mmW) and terahertz (THz) biosensors. Biomatter-wave interaction modalities are considered over a wide range of frequencies and applications such as detection of cancer biomarkers, biotin, neurotransmitters and heart rate are presented in detail. By treating biological tissue as a dielectric substance, having a unique dielectric signature, it can be characterized by frequency dependent parameters such as permittivity and conductivity. By observing the unique permittivity spectrum, cancerous cells can be distinguished from healthy ones or by measuring the changes in permittivity, concentration of medically relevant biomolecules such as glucose, neurotransmitters, vitamins and proteins, ailments and abnormalities can be detected. In case of optical biosensors, any change in permittivity is transduced to a change in optical properties such as photoluminescence, interference pattern, reflection intensity and reflection angle through techniques like quantum dots, interferometry, surface enhanced raman scattering or surface plasmon resonance. Conversely, in case of RF, MW, mmW and THz biosensors, capacitive sensing is most commonly employed where changes in permittivity are reflected as changes in capacitance, through components like interdigitated electrodes, resonators and microstrip structures. In this paper, interactions of EM waves with biomatter are considered, with an emphasis on a clear demarcation of various modalities, their underlying principles and applications.

Radio-Frequency and Microwave Techniques for Non-Invasive Measurement of Blood Glucose Levels

This paper reviews non-invasive blood glucose measurements via dielectric spectroscopy at microwave frequencies presented in the literature. The intent is to clarify the key challenges that must be overcome if this approach is to work, to suggest some possible ways towards addressing these challenges and to contribute towards prevention of unnecessary ‘reinvention of the wheel’.

Left-Handed Metamaterial-Inspired Unit Cell for S-Band Glucose Sensing Application

This paper presents an oval-shaped sensor design for the measurement of glucose concentration in aqueous solution. This unit cell sensing device is inspired by metamaterial properties and is analytically described for better parametric study. The mechanism of the sensor is a sensing layer with varying permittivity placed between two nozzle-shaped microstrip lines. Glucose aqueous solutions were characterized considering the water dielectric constant, from 55 to 87, and were identified with a transmission coefficient at 3.914 GHz optimal frequency with double negative (DNG) metamaterial properties. Consequently, the sensitivity of the sensor was estimated at 0.037 GHz/(30 mg/dL) glucose solution. The design and analysis of this sensor was performed using the finite integration technique (FIT)-based Computer Simulation Technology (CST) microwave studio simulation software. Additionally, parametric analysis of the sensing characteristics was conducted using experimental verification for the justification. The performance of the proposed sensor demonstrates the potential application scope for glucose level identification in aqueous solutions regarding qualitative analysis.

Alleviating concentration polarization: a micro three-electrode interdigitated glucose sensor based on nanoporous gold from a mild process

Precisely detecting the concentration of glucose in the human body is an attractive way to prevent or diagnose diabetes. Compared with the traditional enzyme-based electrochemical glucose sensors, the non-enzymatic ones have gradually come to people's attention recently. By integrating three electrodes into one device, glucose sensors can achieve superior performance and are convenient to carry. Herein, a non-enzymatic three-electrode interdigitated glucose sensor (TEIDGS) based on nanoporous gold is designed and fabricated. To our best knowledge, it is the first time that interdigitated electrodes are combined in a single non-enzymatic glucose sensor device. Due to the advantage of the interdigitated structure and the smart design of the three-electrode circuit board, the TEIDGS can effectively reduce concentration polarization and achieve a high detective sensitivity for glucose of 1217 μA mM⁻¹ cm⁻² and 343 μA mM⁻¹ cm⁻² in the ranges of 0.001–0.590 mM and 0.59–7.00 mM, respectively. Moreover, a low detection limit of 390 nM can be reached. In addition, this TEIDGS possesses excellent selectivity for glucose among other interferents. Strikingly, after three weeks of operation, it can still retain a high detection performance. This work will certainly provide an efficient structure and proper catalytic material choice for future non-enzymatic glucose sensors.

An interdigitated three-electrode non-enzymatic glucose sensor based on nanoporous gold is achieved and presents excellent sensing performance including great sensitivity, high stability and low detective limit.

Microfabricated intracortical extracellular matrix-microelectrodes for improving neural interfaces

Intracortical neural microelectrodes, which can directly interface with local neural microcircuits with high spatial and temporal resolution, are critical for neuroscience research, emerging clinical applications, and brain computer interfaces (BCI). However, clinical applications of these devices remain limited mostly by their inability to mitigate inflammatory reactions and support dense neuronal survival at their interfaces. Herein we report the development of microelectrodes primarily composed of extracellular matrix (ECM) proteins, which act as a bio-compatible and an electrochemical interface between the microelectrodes and physiological solution. These ECM-microelectrodes are batch fabricated using a novel combination of micro-transfer-molding and excimer laser micromachining to exhibit final dimensions comparable to those of commercial silicon-based microelectrodes. These are further integrated with a removable insertion stent which aids in intracortical implantation. Results from electrochemical models and in vivo recordings from the rat's cortex indicate that ECM encapsulations have no significant effect on the electrochemical impedance characteristics of ECM-microelectrodes at neurologically relevant frequencies. ECM-microelectrodes are found to support a dense layer of neuronal somata and neurites on the electrode surface with high neuronal viability and exhibited markedly diminished neuroinflammation and glial scarring in early chronic experiments in rats.

Micro-Fabricated Resonator Based on Inscribing a Meandered-Line Coupling Capacitor in an Air-Bridged Circular Spiral Inductor

This letter presents a high-performance micro-fabricated resonator based on inscribing a meandered-line square coupling capacitor in an air-bridged circular spiral inductor on the GaAs-integrated passive device (IPD) technology. The main advantages of the proposed method, which inserts a highly effective coupling capacitor between the two halves of a circular spiral inductor, are the miniaturized size, enhanced coupling coefficient, and improved selectivity. Moreover, using an air-bridge structure utilizes the enhanced mutual inductance in which it maximizes the self-inductance by a stacking inductor layout to obtain a high coupling effect. The simulated and measured S-parameters of a prototype resonator with an effective overall circuit size of 1000 µm × 800 µm are in good agreement. The measured insertion and return losses of 0.41 and 24.21 dB, respectively, at a measured central frequency of 1.627 GHz, as well as an upper band transmission zero with a suppression level of 38.7 dB, indicate the excellent selectivity of the developed resonator.

Radio Frequency Detection and Characterization of Water-Ethanol Solution through Spiral-Coupled Passive Micro-Resonator Sensor

We present a microfabricated spiral-coupled passive resonator sensor realized through integrated passive device (IPD) technology for the sensitive detection and characterization of water-ethanol solutions. In order to validate the performance of the proposed device, we explicitly measured and analyzed the radio frequency (RF) characteristics of various water-ethanol solution compositions. The measured results showed a drift in the resonance frequency from 1.16 GHz for deionized (DI) water to 1.68 GHz for the solution containing 50% ethanol, whereas the rejection level given by the reflection coefficient decreased from −29.74 dB to −14.81 dB. The obtained limit of detection was 3.82% volume composition of ethanol in solution. The derived loaded capacitance was 21.76 pF for DI water, which gradually decreased to 8.70 pF for the 50% ethanol solution, and the corresponding relative permittivity of the solution decreased from 80.14 to 47.79. The dissipation factor increased with the concentration of ethanol in the solution. We demonstrated the reproducibility of the proposed sensor through iterative measures of the samples and the study of surface morphology. Successive measurement of different samples had no overlapping and had very minimum bias between RF characteristics for each measured sample. The surface profile for bare sensors was retained after the sample test, resulting a root mean square (RMS) value of 11.416 nm as compared to 10.902 nm for the bare test. The proposed sensor was shown to be a viable alternative to existing sensors for highly sensitive water-ethanol concentration detection.

Real-time Humidity Sensor Based on Microwave Resonator Coupled with PEDOT:PSS Conducting Polymer Film

A real-time humidity sensor based on a microwave resonator coupled with a poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) conducting polymer (CP) film is proposed in this paper. The resonator is patterned on a printed circuit board and is excited by electromagnetic field coupling. To enhance the sensitivity of the sensor, the CP film is located in the area with the strongest electric field in the resonator. To investigate the performance, the proposed sensor is placed alongside a reference sensor in a humidity chamber, and humidity is injected at room temperature. The experimental results indicate that the electrical properties of the resonator with the CP film, such as the transmission coefficient (S₂₁) and resonance frequency, change with the relative humidity (RH). Specifically, as the RH changes from 5% to 80%, S₂₁ and the resonance frequency change simultaneously. Moreover, the proposed sensor exhibits great repeatability in the middle of the sensing range, which is from 40% to 60% RH. Consequently, our resonator coupled with the CP film can be used as a real-time humidity-sensing device in the microwave range, where various radio-frequency devices are in use.

Microfabricated passive resonator biochip for sensitive radiofrequency detection and characterization of glucose

Passive sensors provide a new route for the characterization of concentration-dependent radiofrequency parameters with high reproducibility in real time. We propose a microfabricated resonator realized using integrated passive device technology for the sensitive detection and characterization of glucose. Experimental results verify the high performance of the proposed biosensor, because radiofrequency parameters such as resonance frequency (from 0.541 to 1.05 GHz) and reflection coefficient (from −34.04 to −24.11 dB) linearly vary in response to deionized water and subsequent iterative measurements of different glucose concentrations (from 50 to 250 mg dL⁻¹). The biosensor has a very low limit of detection of 8.46 mg dL⁻¹, a limit of quantitation of 25.63 mg dL⁻¹, a minimum frequency sensitivity of 29 MHz, and a minimum magnitude sensitivity of 0.22 dB. Moreover, the coupling coefficient consistently decreases with the increasing glucose concentration. We also used the measured radiofrequency parameters to determine the unknown permittivity of glucose samples through mathematical modeling. A decreasing trend in the loss tangent and an increasing trend in the characteristic wave impedance were observed with the increase of glucose concentration. The reproducibility of the sensor was verified through iterative measurements on the same sensor surface and subsequent study of surface morphology.

Passive sensors provide a new route for the characterization of concentration-dependent radiofrequency parameters with high reproducibility in real time.

Passive Wearable Skin Patch Sensor Measures Limb Hemodynamics Based on Electromagnetic Resonance

OBJECTIVE

The objectives of this study were to design and develop an open-circuit electromagnetic resonant skin patch sensor, characterize the fluid volume and resonant frequency relationship, and investigate the sensor's ability to measure limb hemodynamics and pulse volume waveform features.

METHODS

The skin patch was designed from an open-circuit electromagnetic resonant sensor comprised of a single baseline trace of copper configured into a square planar spiral which had a self-resonating response when excited by an external radio frequency sweep. Using a human arm phantom with a realistic vascular network, the sensor's performance to measure limb hemodynamics was evaluated.

RESULTS

The sensor was able to measure pulsatile blood flow which registered as shifts in the sensor's resonant frequencies. The time-varying waveform pattern of the resonant frequency displayed a systolic upstroke, a systolic peak, a dicrotic notch, and a diastolic down stroke. The resonant frequency waveform features and peak systolic time were validated against ultrasound pulse wave Doppler. A statistical correlation analysis revealed a strong correlation () between the resonant sensor peak systolic time and the pulse wave Doppler peak systolic time.

CONCLUSION

The sensor was able to detect pulsatile flow, identify hemodynamic waveform features, and measure heart rate with 98% accuracy.

SIGNIFICANCE

The open-circuit resonant sensor design leverages the architecture of a thin planar spiral which is passive (does not require batteries), robust and lightweight (does not have electrical components or electrical connections), and may be able to wirelessly monitor cardiovascular health and limb hemodynamics.