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A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Biomedical Sensors".

Deadline for manuscript submissions: closed (31 March 2022) | Viewed by 43276

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Special Issue Editor

Dr. Jungsuk Kim

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Guest Editor

Department of Biomedical Engineering, Gachon University, Incheon 21936, Korea
Interests: implantable prosthetic system; neural–electronic interfaces; nanopore sensors; point-of-care devices for nanopore sequencing; integrated circuit; VLSI; deep learning technologies for biomedical applications
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Sensor technologies (including electrodes) have been widely utilized in many applications, especially industries such as smart factories, automations, clinic, laboratories and so on. Today, advances in microelectromechanical system (MEMS) and complementary metal oxide semiconductor (CMOS) technologies enable one to miniaturize sensors, and as a result, we can increase the number of sensor in a limited area. Accordingly, it is important to implement low-power, low-noise, multi-channel circuits and systems that can interface with the high-density sensors in order to diagnose diseases, restore neuron/muscle disorders, analyze DNA molecules, and so on. This Special Issue on “Circuit and System for Biomedical Applications” focuses on recent advances in wearable, implantable, flexible, optical, high-precision, wireless sensors, circuits and systems for biomedical applications.

This Special Issue is devoted but not limited to the following topics:

Flexible/wearable/implantable sensors, circuits and systems;
Integrated circuits and systems for biomedical applications;
High-precision circuits and systems for DNA/RNA molecule analysis;
Biomedical sensors for disease diagnosis;
Electrodes and stimulators for biomedical applications;
Low-power, low-noise, multi-channel circuits for neural interfaces;
Wireless telemetry circuits and systems for biomedical applications.

Prof. Jungsuk Kim
Guest Editor

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Keywords

Smart sensor system
Flexible sensor
Wearable sensor
Implantable sensor
High-precision sensor
Readout system

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Published Papers (11 papers)

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Editorial

Jump to: Research

3 pages, 170 KiB

Open AccessEditorial

Sensors, Circuits, and Systems for Biomedical Applications

by Jungsuk Kim

Sensors 2023, 23(6), 3295; https://doi.org/10.3390/s23063295 - 21 Mar 2023

Viewed by 2489

Abstract

Sensor technologies (including electrodes) have been widely utilized in many applications, especially in fields such as smart factories, automation, clinics, laboratories, and more [...] Full article

(This article belongs to the Special Issue Sensors, Circuit and System for Biomedical Applications)

Research

Jump to: Editorial

15 pages, 2520 KiB

Open AccessArticle

Comparative Study of Measurement Methods for Embedded Bioimpedance Spectroscopy Systems

by Bilel Ben Atitallah, Ahmed Yahia Kallel, Dhouha Bouchaala, Nabil Derbel and Olfa Kanoun

Sensors 2022, 22(15), 5801; https://doi.org/10.3390/s22155801 - 3 Aug 2022

Cited by 13 | Viewed by 4293

Abstract

Bioimpedance spectroscopy (BIS) is an advanced measurement method for providing information on impedance changes at several frequencies by injecting a low current into a device under test and analyzing the response voltage. Several methods have been elaborated for BIS measurement, calculating impedance with a gain phase detector (GPD), IQ demodulation, and fast Fourier transform (FFT). Although the measurement method has a big influence on the measurement system performance, a systematical comparative study has not been performed yet. In this paper, we compare them based on simulations and experimental studies. To maintain similar conditions in the implementation of all methods, we use the same signal generator followed by a voltage-controlled current source (VCCS) as a signal generator. For performance analysis, three DUTs have been designed to imitate the typical behavior of biological tissues. A laboratory impedance analyzer is used as a reference. The comparison addresses magnitude measurement accuracy, phase measurement accuracy, signal processing, hardware complexity, and power consumption. The result shows that the FFT-based system excels with high accuracy for amplitude and phase measurement while providing the lowest hardware complexity, and power consumption, but it needs a much higher software complexity. Full article

(This article belongs to the Special Issue Sensors, Circuit and System for Biomedical Applications)

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13 pages, 4178 KiB

Open AccessArticle

Two-Way Communication Digital Power Controllers for Wireless Retinal Prosthesis Systems

by Ruhaifi Bin Abdullah Zawawi and Jungsuk Kim

Sensors 2022, 22(8), 2970; https://doi.org/10.3390/s22082970 - 13 Apr 2022

Cited by 3 | Viewed by 2355

Abstract

Power-efficient digital controllers are proposed for wireless retinal prosthetic systems. Power management plays an important role in reducing the power consumption and avoiding malfunctions in implantable medical devices. In the case of implantable devices with only one-way communication, the received power level is uncertain because there is no feedback on the power status. Accordingly, system breakdown due to inefficient power management should be avoided to prevent harm to patients. In this study, digital power controllers were developed for achieving two-way communication. Three controllers—a forward and back telemetry control unit, a power control unit, and a preamble control unit—operated simultaneously to control the class-E amplifier input power, provided command data to stimulators, monitored the power levels of the implanted devices, and generated back telemetry data. For performance verification, we implemented a digital power control system using a field-programmable gate array and then demonstrated it by employing a wireless telemetry system. Full article

(This article belongs to the Special Issue Sensors, Circuit and System for Biomedical Applications)

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12 pages, 4569 KiB

Open AccessArticle

Hexagonal Stimulation Digital Controller Design and Verification for Wireless Subretinal Implant Device

by Wajahat Abbasi, Hojong Choi and Jungsuk Kim

Sensors 2022, 22(8), 2899; https://doi.org/10.3390/s22082899 - 10 Apr 2022

Cited by 4 | Viewed by 2312

Abstract

Significant progress has been made in the field of micro/nano-retinal implant technologies. However, the high pixel range, power leakage, reliability, and lifespan of retinal implants are still questionable. Active implantable devices are safe, cost-effective, and reliable. Although a device that can meet basic safety requirements set by the Food and Drug Administration and the European Union is reliable for long-term use and provides control on current and voltage parameters, it will be expensive and cannot be commercially successful. This study proposes an economical, fully controllable, and configurable wireless communication system based on field-programmable gated arrays (FPGAs) that were designed with the ability to cope with the issues that arise in retinal implantation. This system incorporates hexagonal biphasic stimulation pulses generated by a digital controller that can be fully controlled using an external transmitter. The integration of two separate domain analog systems and a digital controller based on FPGAs is proposed in this study. The system was also implemented on a microchip and verified using in vitro results. Full article

(This article belongs to the Special Issue Sensors, Circuit and System for Biomedical Applications)

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14 pages, 4783 KiB

Open AccessArticle

Sensitive Electrochemical Non-Enzymatic Detection of Glucose Based on Wireless Data Transmission

by Young-Joon Kim, Somasekhar R. Chinnadayyala, Hien T. Ngoc Le and Sungbo Cho

Sensors 2022, 22(7), 2787; https://doi.org/10.3390/s22072787 - 5 Apr 2022

Cited by 16 | Viewed by 5333

Abstract

Miniaturization and wireless continuous glucose monitoring are key factors for the successful management of diabetes. Electrochemical sensors are very versatile and can be easily miniaturized for wireless glucose monitoring. The authors report a microneedle-based enzyme-free electrochemical wireless sensor for painless and continuous glucose monitoring. The microneedles (MNs) fabricated consist of a 3 × 5 sharp and stainless-steel electrode array configuration. Each MN in the 3 × 5 array has 575 µm × 150 µm in height and width, respectively. A glucose-catalyzing layer, porous platinum black, was electrochemically deposited on the tips of the MNs by applying a fixed cathodic current of 2.5 mA cm⁻² for a period of 200 s. For the non-interference glucose sensing, the platinum (Pt)-black-coated MN was carefully packaged into a biocompatible ionomer, nafion. The surface morphologies of the bare and modified MNs were studied using field-emission scanning electron microscopy (FESEM) and energy-dispersive X-ray analysis (EDX). The wireless glucose sensor displayed a broad linear range of glucose (1→30 mM), a good sensitivity and higher detection limit of 145.33 μA mM⁻¹ cm⁻² and 480 μM, respectively, with bare AuMN as a counter electrode. However, the wireless device showed an improved sensitivity and enhanced detection limit of 445.75, 165.83 μA mM⁻¹ cm⁻² and 268 μM, respectively, with the Pt-black-modified MN as a counter electrode. The sensor also exhibited a very good response time (2 s) and a limited interference effect on the detection of glucose in the presence of other electroactive oxidizing species, indicating a very fast and interference-free chronoamperometric response. Full article

(This article belongs to the Special Issue Sensors, Circuit and System for Biomedical Applications)

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10 pages, 2788 KiB

Open AccessArticle

Low-Area Four-Channel Controlled Dielectric Breakdown System Design for Point-of-Care Applications

by Jonggi Hong, Yeonji Oh, Hojong Choi and Jungsuk Kim

Sensors 2022, 22(5), 1895; https://doi.org/10.3390/s22051895 - 28 Feb 2022

Cited by 2 | Viewed by 2904

Abstract

In this study, we propose a low-area multi-channel controlled dielectric breakdown (CDB) system that simultaneously produces several nanopore sensors. Conventionally, solid-state nanopores are prepared by etching or drilling openings in a silicon nitride (SiNx) substrate, which is expensive and requires a long processing time. To address these challenges, a CDB technique was introduced and used to fabricate nanopore channels in SiNx membranes. However, the nanopore sensors produced by the CDB result in a severe pore-to-pore diameter variation as a result of different fabrication conditions and processing times. Accordingly, it is indispensable to simultaneously fabricate nanopore sensors in the same environment to reduce the deleterious effects of pore-to-pore variation. In this study, we propose a four-channel CDB system that comprises an amplifier that boosts the command voltage, a 1-to-4 multiplexer, a level shifter, a low-noise transimpedance amplifier and a data acquisition device. To prove our design concept, we used the CDB system to fabricate four nanopore sensors with diameters of <10 nm, and its in vitro performance was verified using λ-DNA samples. Full article

(This article belongs to the Special Issue Sensors, Circuit and System for Biomedical Applications)

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12 pages, 3268 KiB

Open AccessArticle

A Fully Implantable Miniaturized Liquid Crystal Polymer (LCP)-Based Spinal Cord Stimulator for Pain Control

by Seunghyeon Yun, Chin Su Koh, Jungmin Seo, Shinyong Shim, Minkyung Park, Hyun Ho Jung, Kyungsik Eom, Jin Woo Chang and Sung June Kim

Sensors 2022, 22(2), 501; https://doi.org/10.3390/s22020501 - 10 Jan 2022

Cited by 11 | Viewed by 3730

Abstract

Spinal cord stimulation is a therapy to treat the severe neuropathic pain by suppressing the pain signal via electrical stimulation of the spinal cord. The conventional metal packaged and battery-operated implantable pulse generator (IPG) produces electrical pulses to stimulate the spinal cord. Despite its stable operation after implantation, the implantation site is limited due to its bulky size and heavy weight. Wireless communications including wireless power charging is also restricted, which is mainly attributed to the electromagnetic shielding of the metal package. To overcome these limitations, here, we developed a fully implantable miniaturized spinal cord stimulator based on a biocompatible liquid crystal polymer (LCP). The fabrication of electrode arrays in the LCP substrate and monolithically encapsulating the circuitries using LCP packaging reduces the weight (0.4 g) and the size (the width, length, and thickness are 25.3, 9.3, and 1.9 mm, respectively). An inductive link was utilized to wirelessly transfer the power and the data to implanted circuitries to generate the stimulus pulse. Prior to implantation of the device, operation of the pulse generator was evaluated, and characteristics of stimulation electrode such as an electrochemical impedance spectroscopy (EIS) were measured. The LCP-based spinal cord stimulator was implanted into the spared nerve injury rat model. The degree of pain suppression upon spinal cord stimulation was assessed via the Von Frey test where the mechanical stimulation threshold was evaluated by monitoring the paw withdrawal responses. With no spinal cord stimulation, the mechanical stimulation threshold was observed as 1.47 ± 0.623 g, whereas the stimulation threshold was increased to 12.7 ± 4.00 g after spinal cord stimulation, confirming the efficacy of pain suppression via electrical stimulation of the spinal cord. This LCP-based spinal cord stimulator opens new avenues for the development of a miniaturized but still effective spinal cord stimulator. Full article

(This article belongs to the Special Issue Sensors, Circuit and System for Biomedical Applications)

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17 pages, 2485 KiB

Open AccessArticle

Flexible Ultra-Thin Nanocomposite Based Piezoresistive Pressure Sensors for Foot Pressure Distribution Measurement

by Dhivakar Rajendran, Rajarajan Ramalingame, Saravanan Palaniyappan, Guntram Wagner and Olfa Kanoun

Sensors 2021, 21(18), 6082; https://doi.org/10.3390/s21186082 - 10 Sep 2021

Cited by 25 | Viewed by 6742

Abstract

Foot pressure measurement plays an essential role in healthcare applications, clinical rehabilitation, sports training and pedestrian navigation. Among various foot pressure measurement techniques, in-shoe sensors are flexible and can measure the pressure distribution accurately. In this paper, we describe the design and characterization of flexible and low-cost multi-walled carbon nanotubes (MWCNT)/Polydimethylsiloxane (PDMS) based pressure sensors for foot pressure monitoring. The sensors have excellent electrical and mechanical properties an show a stable response at constant pressure loadings for over 5000 cycles. They have a high sensitivity of 4.4 k

Ω

/kPa and the hysteresis effect corresponds to an energy loss of less than 1.7%. The measurement deviation is of maximally 0.13% relative to the maximal relative resistance. The sensors have a measurement range of up to 330 kPa. The experimental investigations show that the sensors have repeatable responses at different pressure loading rates (5 N/s to 50 N/s). In this paper, we focus on the demonstration of the functionality of an in-sole based on MWCNT/PDMS nanocomposite pressure sensors, weighing approx. 9.46 g, by investigating the foot pressure distribution while walking and standing. The foot pressure distribution was investigated by measuring the resistance changes of the pressure sensors for a person while walking and standing. The results show that pressure distribution is higher in the forefoot and the heel while standing in a normal position. The foot pressure distribution is transferred from the heel to the entire foot and further transferred to the forefoot during the first instance of the gait cycle. Full article

(This article belongs to the Special Issue Sensors, Circuit and System for Biomedical Applications)

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13 pages, 5338 KiB

Open AccessArticle

Ambient Light Rejection Integrated Circuit for Autonomous Adaptation on a Sub-Retinal Prosthetic System

by Hosung Kang, Hojong Choi and Jungsuk Kim

Sensors 2021, 21(16), 5638; https://doi.org/10.3390/s21165638 - 21 Aug 2021

Cited by 5 | Viewed by 2982

Abstract

This paper introduces an ambient light rejection (ALR) circuit for the autonomous adaptation of a subretinal implant system. The sub-retinal implants, located beneath a bipolar cell layer, are known to have a significant advantage in spatial resolution by integrating more than a thousand pixels, compared to epi-retinal implants. However, challenges remain regarding current dispersion in high-density retinal implants, and ambient light induces pixel saturation. Thus, the technical issues of ambient light associated with a conventional image processing technique, which lead to high power consumption and area occupation, are still unresolved. Thus, it is necessary to develop a novel image-processing unit to handle ambient light, considering constraints related to power and area. In this paper, we present an ALR circuit as an image-processing unit for sub-retinal implants. We first introduced an ALR algorithm to reduce the ambient light in conventional retinal implants; next, we implemented the ALR algorithm as an application-specific integrated chip (ASIC). The ALR circuit was fabricated using a standard 0.35-μm CMOS process along with an image-sensor-based stimulator, a sensor pixel, and digital blocks. As experimental results, the ALR circuit occupies an area of 190 µm², consumes a power of 3.2 mW and shows a maximum response time of 1.6 s at a light intensity of 20,000 lux. The proposed ALR circuit also has a pixel loss rate of 0.3%. The experimental results show that the ALR circuit leads to a sensor pixel (SP) being autonomously adjusted, depending on the light intensity. Full article

(This article belongs to the Special Issue Sensors, Circuit and System for Biomedical Applications)

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17 pages, 41705 KiB

Open AccessArticle

Common-Mode Voltage Reduction in Capacitive Sensing of Biosignal Using Capacitive Grounding and DRL Electrode

by Tadeas Bednar, Branko Babusiak, Michal Labuda, Milan Smetana and Stefan Borik

Sensors 2021, 21(7), 2568; https://doi.org/10.3390/s21072568 - 6 Apr 2021

Cited by 5 | Viewed by 4052

Abstract

A capacitive measurement of the biosignals is a very comfortable and unobtrusive way suitable for long-term and wearable monitoring of health conditions. This type of sensing is very susceptible to noise from the surroundings. One of the main noise sources is power-line noise, which acts as a common-mode voltage at the input terminals of the acquisition unit. The origin and methods of noise reduction are described on electric models. Two methods of noise removal are modeled and experimentally verified in the paper. The first method uses a passive capacitive grounding electrode, and the second uses an active capacitive Driven Right Leg (DRL) electrode. The effect of grounding electrode size on noise suppression is experimentally investigated. The increasing electrode area reduces power-line noise: the power of power-line frequency within the measured signal is 70.96 dB, 59.13 dB, and 43.44 dB for a grounding electrode area of 1650 cm², 3300 cm², and 4950 cm², respectively. The capacitive DRL electrode shows better efficiency in common-mode noise rejection than the grounding electrode. When using an electrode area of 1650 cm², the DRL achieved 46.3 dB better attenuation than the grounding electrode at power-line frequency. In contrast to the grounding electrode, the DRL electrode reduces a capacitive measurement system’s financial costs due to the smaller electrode area made of the costly conductive textile. Full article

(This article belongs to the Special Issue Sensors, Circuit and System for Biomedical Applications)

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15 pages, 4901 KiB

Open AccessArticle

A Microfluidic System for Stable and Continuous EEG Monitoring from Multiple Larval Zebrafish

by Yuhyun Lee, Hee Won Seo, Kyeong Jae Lee, Jae-Won Jang and Sohee Kim

Sensors 2020, 20(20), 5903; https://doi.org/10.3390/s20205903 - 19 Oct 2020

Cited by 23 | Viewed by 4054

Abstract

Along with the increasing popularity of larval zebrafish as an experimental animal in the fields of drug screening, neuroscience, genetics, and developmental biology, the need for tools to deal with multiple larvae has emerged. Microfluidic channels have been employed to handle multiple larvae simultaneously, even for sensing electroencephalogram (EEG). In this study, we developed a microfluidic chip capable of uniform and continuous drug infusion across all microfluidic channels during EEG recording. Owing to the modular design of the microfluidic channels, the number of animals under investigation can be easily increased. Using the optimized design of the microfluidic chip, liquids could be exchanged uniformly across all channels without physically affecting the larvae contained in the channels, which assured a stable environment maintained all the time during EEG recording, by eliminating environmental artifacts and leaving only biological effects to be seen. To demonstrate the usefulness of the developed system in drug screening, we continuously measured EEG from four larvae without and with pentylenetetrazole application, up to 60 min. In addition, we recorded EEG from valproic acid (VPA)-treated zebrafish and demonstrated the suppression of seizure by VPA. The developed microfluidic system could contribute to the mass screening of EEG for drug development to treat neurological disorders such as epilepsy in a short time, owing to its handy size, cheap fabrication cost, and the guaranteed uniform drug infusion across all channels with no environmentally induced artifacts. Full article

(This article belongs to the Special Issue Sensors, Circuit and System for Biomedical Applications)

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