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18 pages, 6821 KiB

Open AccessArticle

Strain Plethysmography Using a Hermetically Sealed MEMS Strain Sensor

by Xinyu Jiang, Brian Sang, Haoran Wen, Gregory Junek, Jin-Woo Park and Farrokh Ayazi

Biosensors 2025, 15(5), 325; https://doi.org/10.3390/bios15050325 - 20 May 2025

We present a hermetically sealed capacitive microelectromechanical system (MEMS) strain sensor designed for arterial pulse waveform extraction using the strain plethysmography (SPG) modality. The MEMS strain sensor features a small form factor of 3.3 mm × 3.3 mm × 1 mm, leverages a [...] Read more.

We present a hermetically sealed capacitive microelectromechanical system (MEMS) strain sensor designed for arterial pulse waveform extraction using the strain plethysmography (SPG) modality. The MEMS strain sensor features a small form factor of 3.3 mm × 3.3 mm × 1 mm, leverages a nano-gap fabrication process to improve the sensitivity, and uses a differential sensing mechanism to improve the linearity and remove the common mode drift. The MEMS strain sensor is interfaced with an application-specific integrated circuit (ASIC) to form a compact strain sensing system. This system exhibits a high strain sensitivity of 316 aF/µε, a gauge factor (GF) of 35, and a strain sensing resolution of 1.26 µε, while maintaining a linear range exceeding 700 µε. SPG signals have been reliably captured at both the fingertip and wrist using the MEMS strain sensor with high signal quality, preserving various photoplethysmography (PPG) features. Experimental results demonstrate that heart rate (HR) and heart rate variability (HRV) can be estimated from the SPG signal collected at the fingertip and wrist using the sensor with an accuracy of over 99%. Pulse arrival time (PAT) and pulse transit time (PTT) have been successfully extracted using the sensor together with a MEMS seismometer, showcasing its potential for ambulatory BP monitoring (ABPM) application. Full article

(This article belongs to the Special Issue Biosensors for Monitoring and Diagnostics)

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12 pages, 3121 KiB

Open AccessArticle

Analysis and Tracking of Intra-Needle Ultrasound Pleural Signals for Improved Anesthetic Procedures in the Thoracic Region

by Fu-Wei Su, Chia-Wei Yang, Ching-Fang Yang, Yi-En Tsai, Wei-Nung Teng and Huihua Kenny Chiang

Biosensors 2025, 15(4), 201; https://doi.org/10.3390/bios15040201 - 21 Mar 2025

Viewed by 331

Abstract

Background: Ultrasonography is commonly employed during thoracic regional anesthesia; however, its accuracy can be affected by factors such as obesity and poor penetration through the rib window. Needle-sized ultrasound transducers, known as intra-needle ultrasound (INUS) transducers, have been developed to detect the pleura [...] Read more.

Background: Ultrasonography is commonly employed during thoracic regional anesthesia; however, its accuracy can be affected by factors such as obesity and poor penetration through the rib window. Needle-sized ultrasound transducers, known as intra-needle ultrasound (INUS) transducers, have been developed to detect the pleura and fascia using a one-dimensional radio frequency mode ultrasound signal. In this study, we aimed to use time-frequency analysis to characterize the pleural signal and develop an automated tool to identify the pleura during medical procedures. Methods: We developed an INUS system and investigated the pleural signal it measured by establishing a phantom study, and an in vivo animal study. Signals from the pleura, endothoracic fascia, and intercostal muscles were analyzed. Additionally, we conducted time- and frequency-domain analyses of the pleural and alveolar signals. Results: We identified the unique characteristics of the pleura, including a flickering phenomenon, speckle-like patterns, and highly variable multi-band spectra in the ultrasound signal during the breathing cycle. These characteristics are likely due to the multiple reflections from the sliding visceral pleura and alveoli. This automated identification of the pleura can enhance the safety for thoracic regional anesthesia, particularly in difficult cases. Conclusions: The unique flickering pleural signal based on INUS can be processed by time-frequency domain analysis and further tracked by an auto-identification algorithm. This technique has potential applications in thoracic regional anesthesia and other interventions. However, further studies are required to validate this hypothesis. Key Points Summary: Question: How can the ultrasound pleural signal be distinguished from other tissues during breathing? Findings: The frequency domain analysis of the pleural ultrasound signal showed fast variant and multi-band characteristics. We suggest this is due to ultrasound distortion caused by the interface of multiple moving alveoli. The multiple ultrasonic reflections from the sliding pleura and alveoli returned in variable and multi-banded frequency. Meaning: The distinguished pleural signal can be used for the auto-identification of the pleura for further clinical respiration monitoring and safety during regional anesthesia. Glossary of Terms: intra-needle ultrasound (INUS); radio frequency (RF); short-time Fourier transform (STFT); intercostal nerve block (ICNB); paravertebral block (PVB); pulse repetition frequency (PRF). Full article

(This article belongs to the Special Issue Biosensors for Monitoring and Diagnostics)

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16 pages, 3822 KiB

Open AccessArticle

Detecting Hypoxia Through the Non-Invasive and Simultaneous Monitoring of Sweat Lactate and Tissue Oxygenation

by Cindy Cheng, Sayan Ganguly, Pei Li and Xiaowu Tang

Biosensors 2024, 14(12), 584; https://doi.org/10.3390/bios14120584 - 30 Nov 2024

Viewed by 1560

Abstract

Hypoxia, characterized by inadequate tissue oxygenation, may result in tissue damage and organ failure if not addressed. Current detection approaches frequently prove insufficient, depending on symptoms and rudimentary metrics such as tissue oxygenation, which fail to comprehensively identify the onset of hypoxia. The [...] Read more.

Hypoxia, characterized by inadequate tissue oxygenation, may result in tissue damage and organ failure if not addressed. Current detection approaches frequently prove insufficient, depending on symptoms and rudimentary metrics such as tissue oxygenation, which fail to comprehensively identify the onset of hypoxia. The European Pressure Ulcer Advisory Panel (EPUAP) has recognized sweat lactate as a possible marker for the early identification of decubitus ulcers, nevertheless, neither sweat lactate nor oxygenation independently provides an appropriate diagnosis of hypoxia. We have fabricated a wearable device that non-invasively and concurrently monitors sweat lactate and tissue oxygenation to fill this gap. The apparatus comprises three essential components: (i) a hydrogel-based colorimetric lactate biosensor, (ii) a near-infrared (NIR) sensor for assessing tissue oxygenation, and (iii) an integrated form factor for enhanced wearability. The lactate sensor alters its hue upon interaction with lactate in sweat, whereas the NIR sensor monitors tissue oxygenation levels in real-time. The device underwent testing on phantom exhibiting tissue-mimicking characteristics and on human sweat post aerobic and anaerobic activities. Moreover, the device was demonstrated to be capable of real-time “on-body” simultaneous monitoring of sweat lactate spikes and tissue oxygenation (StO₂) drops, which showed strong correlation during a hypoxia protocol. This innovative technology has a wide range of potential applications, such as post-operative care, sepsis detection, and athletic performance monitoring, and may provide economical healthcare solutions in resource-limited regions. Full article

(This article belongs to the Special Issue Biosensors for Monitoring and Diagnostics)

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15 pages, 2123 KiB

Open AccessArticle

Optimization of Paper-Based Alveolar-Mimicking SERS Sensor for High-Sensitivity Detection of Antifungal Agent

by Hyunjun Park, Kyunghwan Chai, Eugene Park, Woochang Kim, Gayoung Kim, Joohyung Park, Wonseok Lee and Jinsung Park

Biosensors 2024, 14(12), 566; https://doi.org/10.3390/bios14120566 - 22 Nov 2024

Cited by 1 | Viewed by 1270

Abstract

Crystal violet (CV) is a disinfectant and antifungal agent used in aquaculture that plays a vital role in treating aquatic diseases and sterilizing water. However, its potential for strong toxicity, including carcinogenicity and mutagenicity, upon accumulation in the body raises concerns regarding its [...] Read more.

Crystal violet (CV) is a disinfectant and antifungal agent used in aquaculture that plays a vital role in treating aquatic diseases and sterilizing water. However, its potential for strong toxicity, including carcinogenicity and mutagenicity, upon accumulation in the body raises concerns regarding its safe use. Therefore, there is a growing need for the quantitative detection of CV in its early application stages to ensure human safety. Recently, Raman spectroscopy-based surface-enhanced Raman scattering (SERS) detection research has been actively conducted; consequently, an alveolar-mimicking SERS paper (AMSP) inspired by the structure of the human lungs was developed. The AMSP was optimized through various factors, including paper type, reducing agent, reducing agent concentration, and reaction time. This optimization enhanced the surface area of interaction with the target substances and promoted hotspot formation, resulting in enhanced SERS performance. The substrate exhibited exceptional uniformity, reproducibility, and reliability. CV was successfully detected at a concentration of 1 nM in laboratory settings. Furthermore, the AMSP detected CV at 1 nM in real-world environmental samples, including fish farm water and human serum, confirming its potential as a practical detection and monitoring platform for CV in real-world samples. Full article

(This article belongs to the Special Issue Biosensors for Monitoring and Diagnostics)

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14 pages, 3413 KiB

Open AccessArticle

Novel Multiparametric Bioelectronic Measurement System for Monitoring Virus-Induced Alterations in Functional Neuronal Networks

by Heinz-Georg Jahnke, Verena te Kamp, Christoph Prönnecke, Sabine Schmidt, Ronny Azendorf, Barbara Klupp, Andrea A. Robitzki and Stefan Finke

Biosensors 2024, 14(6), 295; https://doi.org/10.3390/bios14060295 - 5 Jun 2024

Viewed by 1466

Abstract

Development and optimisation of bioelectronic monitoring techniques like microelectrode array-based field potential measurement and impedance spectroscopy for the functional, label-free and non-invasive monitoring of in vitro neuronal networks is widely investigated in the field of biosensors. Thus, these techniques were individually used to [...] Read more.

Development and optimisation of bioelectronic monitoring techniques like microelectrode array-based field potential measurement and impedance spectroscopy for the functional, label-free and non-invasive monitoring of in vitro neuronal networks is widely investigated in the field of biosensors. Thus, these techniques were individually used to demonstrate the capabilities of, e.g., detecting compound-induced toxicity in neuronal culture models. In contrast, extended application for investigating the effects of central nervous system infecting viruses are rarely described. In this context, we wanted to analyse the effect of herpesviruses on functional neuronal networks. Therefore, we developed a unique hybrid bioelectronic monitoring platform that allows for performing field potential monitoring and impedance spectroscopy on the same microelectrode. In the first step, a neuronal culture model based on primary hippocampal cells from neonatal rats was established with reproducible and stable synchronised electrophysiological network activity after 21 days of cultivation on microelectrode arrays. For a proof of concept, the pseudorabies model virus PrV Kaplan-ΔgG-GFP was applied and the effect on the neuronal networks was monitored by impedance spectroscopy and field potential measurement for 72 h in a multiparametric mode. Analysis of several bioelectronic parameters revealed a virus concentration-dependent degeneration of the neuronal network within 24–48 h, with a significant early change in electrophysiological activity, subsequently leading to a loss of activity and network synchronicity. In conclusion, we successfully developed a microelectrode array-based hybrid bioelectronic measurement platform for quantitative monitoring of pathologic effects of a herpesvirus on electrophysiological active neuronal networks. Full article

(This article belongs to the Special Issue Biosensors for Monitoring and Diagnostics)

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Review

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18 pages, 2586 KiB

Open AccessReview

Quantum Dot Applications Using Kinetic Data: A Promising Approach for Enhanced Analytical Determinations

by Rafael C. Castro, Ricardo N. M. J. Páscoa, David S. M. Ribeiro and João L. M. Santos

Biosensors 2025, 15(3), 167; https://doi.org/10.3390/bios15030167 - 5 Mar 2025

Viewed by 687

Abstract

The acquisition of kinetic data in QD-based PL sensing methodologies has been revealed to be an auspicious alternative in applying these nanomaterials in analytical chemistry, enabling enhanced discrimination and quantification of analytes, even in complex sample matrices. The accessibility of kinetic measurements, which [...] Read more.

The acquisition of kinetic data in QD-based PL sensing methodologies has been revealed to be an auspicious alternative in applying these nanomaterials in analytical chemistry, enabling enhanced discrimination and quantification of analytes, even in complex sample matrices. The accessibility of kinetic measurements, which use routine laboratory instrumentation, is a significant advantage that increases the practicality of this methodology. The simple acquisition of these kinds of second-order data combined with chemometric analysis can ensure accurate results in environmental, biomedical, and food monitoring applications. These developments emphasize the vital importance of kinetic approaches in increasing sensitivity, improving analyte discrimination, and making the application of QDs in complex samples possible. Full article

(This article belongs to the Special Issue Biosensors for Monitoring and Diagnostics)

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28 pages, 3456 KiB

Open AccessReview

The Interpretation of Carbon Nanotubes’ Electrochemistry: Electrocatalysis and Mass Transport Regime in the Apparent Promotion of Electron Transfer

by Josipa Dugeč, Ivana Škugor Rončević, Nives Vladislavić, Josip Radić, Maša Buljac and Marijo Buzuk

Biosensors 2025, 15(2), 89; https://doi.org/10.3390/bios15020089 - 5 Feb 2025

Viewed by 981

Abstract

Carbon nanotubes (CNTs) are widely used in electrochemical sensors due to their significant impact on the electroanalytical signal. However, there remain significant doubts regarding the origin of the improved electroanalytical response observed in CNT-based sensors, particularly concerning the precise role of CNTs in [...] Read more.

Carbon nanotubes (CNTs) are widely used in electrochemical sensors due to their significant impact on the electroanalytical signal. However, there remain significant doubts regarding the origin of the improved electroanalytical response observed in CNT-based sensors, particularly concerning the precise role of CNTs in these systems. In particular, the origin of the electrochemical response is controversial, as it may be due to either electrocatalytic or non-electrocatalytic processes. The latter implies that the electroanalytical response is mainly governed by the mass transport phenomena within the porous CNT layer. This article briefly reviews the several comprehensive models based on the role of porosity (diffusion in a ‘thin-layer’) on the electrochemical behavior as well as on the electrocatalytic properties of CNTs to resolve conflicts arising from misinterpretations of the electroanalytical response of CNT-based sensors. However, even though there are some explanations and conclusions on this topic, they seem to be valuable for specific electroactive species, the type of CNTs and/or electrode architecture, the electrode surface, etc. Accordingly, general theories and conclusions are not yet defined, so different approaches to this topic are still needed, since the main phenomenological effects responsible for the nature of the electrochemical response of the electrodes modified with CNTs need to be determined in a rational way. Full article

(This article belongs to the Special Issue Biosensors for Monitoring and Diagnostics)

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14 pages, 4065 KiB

Open AccessReview

Recent Status on Lactate Monitoring in Sweat Using Biosensors: Can This Approach Be an Alternative to Blood Detection?

by Leonardo Messina and Maria Teresa Giardi

Biosensors 2025, 15(1), 3; https://doi.org/10.3390/bios15010003 - 24 Dec 2024

Viewed by 1572

Abstract

Recent studies have shown that lactate is a molecule that plays an indispensable role in various physiological cellular processes, such as energy metabolism and signal transductions related to immune and inflammatory processes. For these reasons, interest in its detection using biosensors for non-invasive [...] Read more.

Recent studies have shown that lactate is a molecule that plays an indispensable role in various physiological cellular processes, such as energy metabolism and signal transductions related to immune and inflammatory processes. For these reasons, interest in its detection using biosensors for non-invasive analyses of sweat during sports activity and in clinical reasons assessments has increased. In this minireview, an in-depth study was carried out on biosensors that exploited using electrochemical methods and innovative nanomaterials for lactate detection in sweat. This detection of lactate by biosensors in the sweat method seems to be feasible and highly desirable. From this commentary analysis, we can conclude that the correlation between lactate concentrations in sweat and blood is not yet clear, and studies are needed to clarify some key issues essential for the future application of this technology. Full article

(This article belongs to the Special Issue Biosensors for Monitoring and Diagnostics)

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