Miniature Sensor Research Articles

A microsystem for in vivo wireless monitoring of plastic biliary stents using magnetoelastic sensors.

With an interest in monitoring the patency of stents that are used to treat strictures in the bile duct, this paper reports the investigation of a wireless sensing system to interrogate a microsensor integrated into the stent. The microsensor is comprised of a 28-μm-thick magnetoelastic foil with 8.25-mm length and 1-mm width. Magnetic biasing is provided by permanent magnets attached to the foil. These elements are incorporated into a customized 3D polymeric package. The system electromagnetically excites the magnetoelastic resonant sensor and measures the resulting signal. Through shifts in resonant frequency and quality factor, the sensor is intended to provide an early indication of sludge accumulation in the stent. This work focuses on challenges associated with sensor miniaturization and placement, wireless range, drive signal feedthrough, and clinical use. A swine specimen in vivo experiment is described. Following endoscopic implantation of the sensor enabled plastic stent into the bile duct, at a range of approximately 17 cm, the signal-to-noise ratio of ~106 was observed with an interrogation time of 336 s. These are the first reported signals from a passive wireless magnetoelastic sensor implanted in a live animal.

Two-photon 3D printed fiber-optic Fabry–Perot probe for triaxial contact force detection of guidewire tips

The demand for real-time feedback and miniaturization of sensing elements is a crucial issue in the treating vascular diseases with minimally invasive interventions. Here, Fabry–Perot microcavities fabricated via direct laser writing using a two-photon polymerization technique on fiber tips are proposed, designed, simulated, and experimentally demonstrated as a miniature triaxial force sensor for monitoring real-time interactions between the tip of a guidewire and human blood vessels and tissues during minimally invasive surgeries. The sensor contains four fiber tip-based Fabry–Perot cavities, which can be seamlessly integrated into medical guidewires and achieves three-axis force decoupling through symmetrically arranged flexible structures. The results showed that the proposed sensor achieved a cross-sectional diameter of 890 μm and a high sensitivity of about 85.16 nm/N within a range of 0 to 0.5 N with a resolution of hundreds of micro-Newtons. The proposed triaxial force sensor exhibits high resolution, good biocompatibility, and electromagnetic compatibility, which can be utilized as an efficient monitoring tool integrated into minimally invasive surgical intervention devices for biomedical applications.

A ring resonators optical sensor for multiple biomarkers detection

In the recent years, the number of Point-Of-Care-Tests (POCTs) available for clinical diagnostic has steadily increased. POCTs provide a near-patient testing with the potential to generate a result quickly so that appropriate treatment can be implemented, leading to improved clinical outcomes compared to traditional laboratory testing. Technological advances, such as miniaturization of sensors and improved instrumentation, have revolutionized POCTs, enabling the development of smaller and more accurate devices. In this context, it has also gained increasing importance the screening of various analytes simultaneously to increase specificity and improve the characterization of the disease. This study is aimed at developing and characterizing a photonic integrated circuit for multiple markers detection, which represents the functional core towards a full developed POCT device for clinical pathology applications. The photonic sensor, based on microring resonators (MRRs), is functionalized by immobilizing specific antibodies on a copolymer layer deposited on the MRR’s surfaces. Surface chemical techniques were employed to analyse the surface chemical characteristics while fluorescence microscopy was involved to analyse the resulting bioreceptor surface density. The photonic sensor is characterized for the parallel detection of two biomarkers, the C-Reactive Protein (CRP) and the Creatine-Kinase-MB (CK-MB). The analyte-antibody binding curves were obtained both in buffer and in filtered un-diluted artificial saliva showing promising results both in terms of sensitivity, with limit of detection (LOD) of 103 pM for CRP and 140 pM for CK-MB, and in terms of specificity. These encouraging results let the assembly of a highly sensitive POC device for molecular diagnostics.

A Survey on Data-Driven Approaches for Reliability, Robustness, and Energy Efficiency in Wireless Body Area Networks

Wireless Body Area Networks (WBANs) are pivotal in health care and wearable technologies, enabling seamless communication between miniature sensors and devices on or within the human body. These biosensors capture critical physiological parameters, ranging from body temperature and blood oxygen levels to real-time electrocardiogram readings. However, WBANs face significant challenges during and after deployment, including energy conservation, security, reliability, and failure vulnerability. Sensor nodes, which are often battery-operated, expend considerable energy during sensing and transmission due to inherent spatiotemporal patterns in biomedical data streams. This paper provides a comprehensive survey of data-driven approaches that address these challenges, focusing on device placement and routing, sampling rate calibration, and the application of machine learning (ML) and statistical learning techniques to enhance network performance. Additionally, we validate three existing models (statistical, ML, and coding-based models) using two real datasets, namely the MIMIC clinical database and biomarkers collected from six subjects with a prototype biosensing device developed by our team. Our findings offer insights into strategies for optimizing energy efficiency while ensuring security and reliability in WBANs. We conclude by outlining future directions to leverage approaches to meet the evolving demands of healthcare applications.

Multilayer patch functionalized microfibrillated cellulosic paper sensor for sweat glucose monitoring.

Electrochemical analysis of glucose monitoring without painful blood collection provides a new noninvasive route for monitoring glucose levels. Thus, in this study, biobased cellulosic papers (methylated and phosphorylated one) based glucose monitoring sensor is developed. To achieve high hydrophilicity, microfibrillated cellulose (MFC) were functionalized using hexokinase mediated phosphorylation (-OH to -[Formula: see text]). The instinctive increased surface charge density from 36.2 ± 3.4 to 118.4 ± 1.2 µmol/g and decrease contact angle (45°-22°) confirms the increased hydrophilicity of paper. Furthermore, functionalized phos-MFC paper increase the capillary flow of sweat, required low quantity (1µl) of sweat for accurate analysis of glucose level. Additionally, chemically induced methyl groups (-CH3) make the sensor more barrier to other chemicals. In addition, a multilayer patch design combined with sensor miniaturization was used to lead to an increase in the efficiency of the sweat collection and sensing processes. Besides, this paper sensor integrated with artificial transdermal drug delivery unit (agarose gel as skin) for monitoring glucose levels in sweat. The patch monitoring system increase the accuracy of sensing with fluctuation in sweat vol. (1-4µl), temperature (20-70 °C), and pH (4.0-7.0). In addition, temperature dependency artificial transdermal delivery (within agarose gel) of drug metformin agrees the measurement accuracy of sensor, called "switch system" without any error. As a result, the reported MFC paper based multi-patch disposable sensing system provides a novel closed-loop solution for the noninvasive sweat-based management of diabetes mellitus.

Real-time, specific, and label-free transistor-based sensing of organophosphates in liquid

Organophosphates (OP), commonly used in agriculture and as chemical warfare agents, pose significant environmental risks, necessitating real-time, low-cost OP detection methods. In particular, liquid-phase OP sensing with minimal sample volumes is crucial. While several methods allow rapid detection of low concentrations of OP vapors, they are effective only in the short term, while vapors are still being produced. Many OP compounds are semi-volatile, leading to the contamination of water, soil, and surfaces, posing a risk of secondary, long-term exposure. Detecting this contamination requires methods that can be directly applied to droplets of the affected medium. Currently, no method provides the desired combination of ultra-sensitivity, quantitative detection, rapid response, and low-cost for detecting OPs in liquid samples. This study aims to demonstrate quantitative, low-cost, real-time, specific, and label-free OP sensing in ultra-small samples using a transistor-based approach. The current work employs the 2-(4-Aminophenyl)-1,1,1,3,3,3-hexafluoro-2-propanol (aminophenyl-HFIP) functionalized meta-nano-channel field-effect chemical sensor (MNChem sensor) to monitor the organophosphate, diethyl cyanophosphonate (DCNP), in liquid samples. The silicon component of the MNChem is fabricated using a complementary metal-oxide semiconductor (CMOS) process, and the amine-based chemical functionalization of the sensing area is performed post-fabrication. The MNChem sensor provides electrostatic control over the source-drain current (IDS), allowing an optimized channel configuration that efficiently transduces localized OP recognition events into significant IDS variations. Sensing is performed using 0.5 μL buffer solution to simulate a miniature field-deployable sensor for on-site liquid analysis. We report the sensing of DCNP with a limit-of-detection of 100 fg/mL, a dynamic range of 9 orders of magnitude, and excellent linearity (≥0.97) and sensitivity. Control measurements confirm the specificity and reliability of the sensor's response, validating its applicability. This study introduces a novel method for OP detection in contaminated droplets using a low-cost disposable transistor technology.

Portable self-powered electrochemical aptasensor for ultrasensitive and real-time detection of microcystin-RR based on hydrovoltaic-photothermal coupling effect

Coupling different energy harvesting technologies to obtain an excellent output signal is essential for the development of high-performance self-powered electrochemical sensors. Herein, a novel hydrovoltaic-photothermal coupling self-powered electrochemical aptasensing platform was designed for sensitive detection of microcystin (MC-RR) with a digital multimeter as a direct visual readout strategy. The straightforward ultrasonic method was employed to synthesize polyaniline (PANI) and bismuth oxybromide (BiOBr) nanosheets, which were then integrated as active components in a hydrovoltaic device. The unique layer structure of two-dimensional (2D) nanomaterials BiOBr can create flexible interlayer spaces to accommodate various ions and water molecules, which was beneficial to construct evaporation-driven channels. Meanwhile, the exceptional photothermal characteristics of polyaniline could accelerate the water evaporation rate, consequently boosting the migration speed of charge carriers and increasing output signal. Moreover, a digital multimeter was connected to the constructed sensor for real-time displaying the output signal. With the assistance of aptamer, a novel self-powered electrochemical aptasensing platform was constructed for sensitive detection of MC-RR. Under optimum conditions, the output signal of the hydrovoltaic-photothermal coupling cell was linearly related to the logarithm of MC-RR concentration in the range of 1 fM to 1 nM with a detection limit of 0.31 fM (S/N = 3). Furthermore, this sensor also exhibited many advantages such as high selectivity, good repeatability and portability. Such novel strategy not only offers a completely new general approach to construct high-performance self-powered devices for the detection of MC-RR, but also provides a new strategy for advancing the miniaturization and field application of self-powered electrochemical sensors.

Miniature optical fiber photoacoustic spectroscopy gas sensor based on a 3D micro-printed planar-spiral spring optomechanical resonator

Photoacoustic spectroscopy (PAS) gas sensors based on optomechanical resonators (OMRs) have garnered significant attention for ultrasensitive trace-gas detection. However, a major challenge lies in balancing small size with high performance when developing ultrasensitive miniaturized optomechanical resonant PAS (OMR-PAS) gas sensors for space-constrained applications. Here, we present a miniature optical fiber PAS gas sensor based on a planar-spiral spring OMR (PSS-OMR) that is in situ 3D micro-printed on the end-face of a fiber-optic ferrule. Experimental results demonstrate that mechanical vibrational resonance can enhance the sensor's acoustic sensitivity by over two orders of magnitude. Together with a 1.4 μL non-resonant photoacoustic cell, it can detect C2H2 gas concentration at the 45-ppb level, and its response is very fast approximating 0.2seconds. This optical fiber OMR-PAS gas sensor holds great promise for the detection or monitoring of rapidly varying trace gas in many applications ranging from production process control to industrial environmental surveillance.

12-Lead Holter Integrated with Sleep Monitoring Module

ECG signals and sleep monitoring parameters complement each other and can be used for qualitative diagnosis of sleep apnea syndrome and cardio-related diseases. However, due to the limitations of the instrument volume and the detection environment, it is often challenging to integrate these two functions in practical applications. In this paper, a 12-lead dynamic electrocardiograph integrated with sleep monitoring is designed. The system's volume is reduced by combining the integrated ECG simulation front end with a miniature sensor. The system achieves the extraction, conditioning, and calculation of 12-lead ECG signals and sleep-related parameters and writes the data to a memory card in real time, which offers convenience for users and doctors in the diagnostic process.

Elastomeric Sensor-Triboelectric Nanogenerator Coupled System for Multimodal Strain Sensing and Organic Vapor Detection.

Stretchable, flexible sensors are one of the most critical components of smart wearable electronics and Internet of Things (IoT), thereby attracting multipronged research interest in the last decades. Following miniaturization and multicomponent development of several sensors in one could further propel the demand for wireless, multimodal platforms. Greener substitutes to conventional sensors that can operate in a self-powered configuration are highly desirable in terms of all-in-one sensor utilities. However, fabrication of composite-based ultrastretchable, self-powered sensors with multifunctionality, robustness, and conformability is still only partially achieved and, therefore, demands further investigation. In this work, we report a triboelectric nanogenerator (TENG)-based multifunctional strain and organic vapor sensor using cross-linked ethylene propylene diene monomer (EPDM) elastomer and conducting carbon black as active fillers in the presence of an ionic liquid. The resulting piezoresistive sensor demonstrates ultrahigh gauge factor (GF > 220k) and wide range strain sensitivity and is, therefore, suitable for subtle-to-high frequency motion detection devices. Supported by excellent triboelectric outputs (force sensitivity 0.5 V/N in the range of 50-300 N, maximum output voltage VOC ∼ 178 V, short circuit current ISC ∼ 18 μA, maximum power density 0.11 mW/cm2), the hybrid sensors offer remarkable mechanical toughness and seamless voltage generation under contact-separation, even after several thousand cycles of operations. Furthermore, the sensor substrates exhibited reproducible organic vapor-sensing behavior, with high responsivity of 1.92 and 1 for ethanol and acetone, respectively, under flowing vapor conditions. This work lays a strong foundation for developing a truly multimodal, TENG-based, self-powered organic vapor and strain sensors.

Microfabricated vapor cells with chemical polishing and two-step low-temperature anodic bonding for single-beam magnetometer

With the miniaturization of quantum sensors, the fabrication of alkali metal vapor cells based on micro-electromechanical systems (MEMS) has become increasingly important. However, the fabrication of MEMS vapor cells remains a challenge. In this study, a microfabricated millimeter-level vapor cell was fabricated and tested. The silicon cavity was fabricated by dry etching and chemical polishing. After injection of alkali metal and buffer gas, a two-step low-temperature anodic bonding was employed. The first step was non-isothermal to keep the alkali metal in the low-temperature pole plate and the second step was isothermal to improve the bonding strength, enhancing the hermeticity. Then, the vapor cell was tested for sidewall roughness, bonding strength, and leakage rate. Subsequently, Rb D1 line absorption spectroscopy, stability, and the single-beam magnetometer signal were tested. The results show the fabricated vapor cell had high stability, providing a basis for the miniaturization of quantum devices.

Vector magnetometry employing a rotating RF field in a single-beam optically pumped magnetometer

Magnetic field vector information is crucial for many advanced applications, such as navigation and biomedical imaging. However, existing methods often lack high sensitivity or require complex setups. This study addresses these challenges by proposing a novel vector magnetometry method using a single-beam optically pumped magnetometer. A rotating radio-frequency field is innovatively utilized to excite atomic spin precession, enabling accurate measurement of the magnetic field direction based on scalar measurement. The method is tested through physical experiments with different magnetic field configurations to validate its performance. The experimental results demonstrate high accuracy, and achieve a magnetic field amplitude sensitivity of 800 fT/Hz1/2, an azimuth sensitivity of 100 μrad/Hz1/2, and a polar angle sensitivity of 13 μrad/Hz1/2. The proposed method facilitates sensor miniaturization and is suitable for applications in high magnetic field environments, such as geomagnetic field.

Highly efficient SnO2-Carbon nanosphere heterojunctions decorated with Ag for detecting isopropanol at low operating temperatures

The design of a sensing material for detecting isopropanol gas with low operating temperature is extremely important for miniaturization and wearability of gas sensors. Herein, a novel gas sensor based on SnO2-Carbon nanosphere heterojunctions decorated with Ag nanoparticles (SCA) was fabricated and its gas sensing performance was evaluated and compared systematically. The measurement results indicated that the sensing performance was influenced by the ratio of Sn/C and the length of Ag plating, and the SCA sensor provided the best response. For 100 ppm isopropanol at 100 °C, the SCA sensor exhibited a response value of 50.51, a response time of 7 s and a recovery time of 60 s. The enhanced sensing performance and reduced operating temperature of the SCA could be attributed to the synergistic effect of the SnO2-Carbon nanosphere heterojunctions and the significant catalytic performance of the decorated Ag nanoparticles. In addition, the density functional theory calculation method based on the first-principles theory was used to study the adsorption performance and electronic behavior, as well asthe influence of Ag decoration on SnO2 for isopropanol detection. The calculated results were consistent with the experimental results.

Dual-Purpose Aptamer-Based Sensors for Real-Time, Multiplexable Monitoring of Metabolites in Cell Culture Media.

The availability of high-frequency, real-time measurements of the concentrations of specific metabolites in cell culture systems will enable a deeper understanding of cellular metabolism and facilitate the application of good laboratory practice standards in cell culture protocols. However, currently available approaches to this end either are constrained to single-time-point and single-parameter measurements or are limited in the range of detectable analytes. Electrochemical aptamer-based (EAB) biosensors have demonstrated utility in real-time monitoring of analytes in vivo in blood and tissues. Here, we characterize a pH-sensing capability of EAB sensors that is independent of the specific target analyte of the aptamer sequence. We applied this dual-purpose EAB to the continuous measurement of pH and phenylalanine in several in vitro cell culture settings. The miniature EAB sensor that we developed exhibits rapid response times, good stability, high repeatability, and biologically relevant sensitivity. We also developed and characterized a leak-free reference electrode that mitigates the potential cytotoxic effects of silver ions released from conventional reference electrodes. Using the resulting dual-purpose sensor, we performed hourly measurements of pH and phenylalanine concentrations in the medium superfusing cultured epithelial tumor cell lines (A549, MDA-MB-23) and a human fibroblast cell line (MRC-5) for periods of up to 72 h. Our scalable technology may be multiplexed for high-throughput monitoring of pH and multiple analytes in support of the broad metabolic qualification of microphysiological systems.

Sensing performance comparison for temperature and liquid level sensor based on uniform and step-Etched microfiber TFBG

By using the hydrofluoric acid uniform-etching and step-etching methods, a tilted fiber Bragg grating (TFBG) microfiber structure was fabricated, where the cladding diameter of the traditional TFBG was reduced to micrometer scale. The temperature sensing characteristics of the uniform-etched and step-etched microfiber TFBGs were experimentally studied and compared. The core mode of its transmission spectrum was used for sensing the temperature change; while the normalized area of cladding modes has been used for real-time monitoring the liquid level. The simultaneous measurement of temperature and liquid level has been experimentally demonstrated for the proposed microfiber TFBG. By combining the strong evanescent field of microfiber and the unique structural advantages of TFBG, the proposed microfiber TFBG has a great potential in developing the miniature optical fiber sensors.

Cosmic radiation monitoring in aeronautics and astronautics

The growth of the aerospace industry has made the detection of cosmic radiation essential. That led to a proposal for the development of an optoelectronic detector of cosmic radiation. This will allow continuous measurement of acceptable levels of radiation. The device is currently in its initial development phase, focusing on the detection of ionising radiation. Tests have been carried out with high-energy radiation simulators in the form of natural radioactive sources, confirming the performance of the overall system. The cosmic ray sensor of the study has numerous potential applications, particularly in the aerospace industry. Crew safety could be enhanced by a miniature sensor that measures the absorbed dose of cosmic radiation. Existing passive methods of dose measurement have been ineffective because they provide information about radiation with a delay of several weeks. Active monitoring of irradiation levels enables ongoing control of the dose taken, which is crucial for employee health.

A Miniature PMUT Array for Medical Applications

Abstract Wearable continuous monitoring technology and internal and cerebrovascular imaging are the frontier hot area of current scientific research, which are of great significance to improving human life and health. Ultrasonic imaging can obtain information such as deep tissue structure by transmitting ultrasonic waves into the tissue and detecting echo signals, and ultrasonic imaging technology has the advantages of high imaging depth, high resolution, high safety, fast and convenient, etc. It is one of the important technologies in the medical field such as wearable continuous monitoring technology and internal cardiovascular and cerebrovascular imaging. But miniaturization and low power consumption are necessary conditions for the success of such medical applications. Therefore, the ultrasonic imaging technology using a miniature ultrasonic probe is one of the most promising imaging technologies for this type of medical application. Aiming at the common technical problems of traditional ultrasonic transducers such as large volume, narrow bandwidth, high power consumption, difficulty in preparing two-dimensional arrays, and difficulty in integrating with ICs. In this paper, the electromechanical-acoustic multi-field coupling mechanism and array structure design technology of MEMS high-performance PMUT ultrasonic transducer elements are first studied, and a CMOS-compatible miniature PMUT high-performance array ultrasonic device suitable for this type of medical application is developed. The simulation results of the transducer are given. The measurement of various physical parameters of the transducer sample and the results of its application in the ultrasonic imaging system show that the miniature PMUT linear array ultrasonic sensor we designed is a kind of high performance ultrasonic array sensors that can be widely used in wearable continuous monitoring technology and internal cardiovascular and cerebrovascular imaging.

A size-distinguishing miniature electromagnetic tomography sensor for small object detection

Electromagnetic tomography (EMT) is an emerging imaging technique that presents the property distribution of conductive or magnetic materials based on signals from the coil array on the EMT sensor. However, conventional EMT researches generally involve large-size EMT sensors, which are ineffective in detecting and discerning the size of small objects due to limited spatial resolution, sensitivity and relatively high noise level. As such, this paper presents a novel miniature EMT sensor, which incorporates 8 small coils around the circumference for imaging and 2 larger horizontal coils that generate a vertical field for target size distinction. Moreover, a novel equivalent theory is proposed to approximate the effect of the horizontal coils by the cumulative effect of the 8 small coils. An EMT testing system is established with the proposed sensor array and the multi-channel instrument developed in our lab. Experiments based on multiple sample distributions and different reconstruction algorithms validate the ability of the sensor to detect and distinguish the size of small objects of different materials. Furthermore, the equivalent theory was validated through the experiments.

Recent advances on application of continuum robots in minimally invasive surgery

Continuum robots have emerged as pivotal tools in advancing minimally invasive surgery (MIS), offering enhanced flexibility and precision compared to traditional rigid instruments. This review categorizes continuum robots based on structural designs and actuation strategies, highlighting their ability to navigate complex surgical environments with minimal invasiveness. The integration of advanced sensing technologies for shape and environmental perception is examined, underscoring their role in improving surgical accuracy and patient safety. Specific applications in bronchoscopy, gastrointestinal endoscopy, and orthopedic procedures demonstrate the diverse capabilities of continuum robots in clinical settings. Despite challenges in material stiffness and sensor miniaturization, continuum robots show promising potential to reshape the landscape of MIS through continued innovation and research advancements.

Electrochemical detection of the cardiac biomarker cardiac troponin I

AbstractAcute myocardial infarction (AMI) is a major cause of cardiovascular disease‐related death. It is essential for patients with cardiovascular disease to receive an early diagnosis of AMI. The most popular technique for the early detection of AMI is the use of biosensors to monitor the concentration of pertinent biomarkers, such as cardiac troponin I (cTnI), in the blood. The electrochemical detection methods hold great promise because of their simplicity, miniaturization, ease of integration, high sensitivity, and rapid response. The prime motive of this review is to present a comprehensive understanding of the pros and cons of methodologies employed for the electrochemical approaches toward the detection of cTnI. A detailed summary is provided for the immunosensors, aptamer sensors, molecular imprinting sensors, and peptide sensors based on various affinity elements. We enumerate the modified electrode materials for electrochemical sensors as well as popular detection techniques. Furthermore, this paper reviews some recent significant advances in point‐of‐care assays for rapid, accurate detection of cTnI as a smart integrated device for home monitoring. The accumulation of knowledge about these functions will lead to new insights into and concepts for the design of portable miniature sensors for cardiovascular patients at risk of AMI. It is anticipated that the interdisciplinary collaboration can bring more enlightenment to the progress of cardiac biomarkers sensor in the future.