Portable Sensor System Research Articles

Portable surface acoustic wave device platform coupled with a paper-based capillary fluidics for real-time biosensing applications

Surface acoustic wave (SAW) sensors have emerged as prominent real-time, label-free biosensors with diverse applications in immunoassays and nucleic acid detection. However, widespread adoption in diagnostics has been impeded by challenges such as miniaturization of instrumentation, microfluidics fabrication and high attenuation in liquid environments. In this study we address these limitations by presenting a portable platform capable of real-time monitoring of a SAW microarray chip comprising up to four sensing channels, combined with a novel paper-based capillary flow channel. For the fabrication of a portable, automated and versatile sensor platform, we integrated a microcontroller, RF components, and a micropump for flow control. Calibration procedures ensured accurate measurements for both amplitude and phase, with a low drift rate (0.72 mdB/h and 1.00 mdeg./h, respectively) and high resolution (2.10 mdB and 6.10 mdeg.), indicating stable operation with minimal interface electronics. The capillary flow channel, implemented by confining the fluid on the sensing surface using a nitrocellulose strip, facilitated laminar and continuous sample flow with minimum damping of the acoustic signal. The sensor system was evaluated with two SAW devices at 100 and 200 MHz using glycerol dilutions within the range of 1 % and 70 %, demonstrating real-time monitoring capabilities and linear correlations between amplitude and phase changes. To prove the biosensing and clinical validity of the SAW newly developed system, DNA adsorption on a poly(L-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG) functionalized SAW-surface was demonstrated with a detection limit of 0.001 μg/mL. Our study demonstrates the feasibility of a portable SAW sensor system coupled with a low-cost and replaceable capillary flow channel for real-time monitoring and biomolecular detection.

CuS-Cu hybrid nanostructures and their applications in electrochemical sensing of homocysteine

In this study, copper sulfide nanostructures (CuS) and CuS-Cu hybrid structures were synthesized and tested for their potential in electrochemical sensing of homocysteine (HcySH). The determination of HcySH assumes high clinical relevance, as it is a biomarker of cardiovascular diseases, and an indicator of vitamin B12 deficiency. We introduce a portable and versatile sensor system by preparing an FTO-based electrode, thus enhancing the practical utility of the CuS-based sensor in diverse applications. The electrochemical sensing activity is tested in GC/CuS-Cu and FTO/CuS-Cu electrodes. The fabricated FTO/CuS-Cu stand-alone electrode system exhibited superior performances in the quantitative estimation of HcySH. The cyclic voltammetric response showed linearity of current against the concentration of HcySH in the range from 0 to 50 μM.The amperometric response of the FTO/CuS-Cu electrode against different concentrations of HcySH varies linearly in the range of 16 to 83 μM. The limit of detection (LOD) of the system for HcySH is 1.63 µM. CuS and Cu NPs form an electrically conductive layer at the surface of the electrode, and they enable active sites and provide direct electron transfer. The synergetic combination of “binding Cu NPs with HcySH” and the “catalytic activity of CuS in the redox reaction of HcySH” might facilitate electrochemical communication. The platform is also studied in Fetal Bovine Serum (FBS), and it can be employed as a low-cost point-of-care diagnostic tool.

Effects of Temperature and Humidity on the Absorption Spectrum and Concentration of N2O Using an Open-Path Sensor System

This paper examines the effects of temperature and humidity on the absorption spectrum and concentration of nitrous oxide (N2O) using a compact, portable open optical-path gas detection sensor system. We obtained the absorption coefficient and widened the linear function of the N2O absorption spectrum related to temperature by theoretical analysis and the high-resolution transmission molecular absorption database (HITRAN). Afterward, we conducted real-time monitoring of N2O in both campus and laboratory environments using lasers for a duration of 32 h and 6 h, respectively, and the results were compared and analyzed with the theoretical derivation. The results show that the concentration of N2O increased with increasing environmental temperature but decreased with increasing humidity. Furthermore, the variations in temperature and humidity significantly affected the peak values of the second-harmonic (2f) and first-harmonic (1f) signals. Finally, the temperature N2O concentration and humidity N2O curves were calibrated separately, and temperature changes were positively correlated with the N2O concentration, while humidity changes were negatively correlated with the N2O concentration. The experimental results indicate that the concentration of N2O and its absorption spectra are influenced by humidity and temperature, which has a significant reference value in the absorption and measurement of N2O in practical applications.

Directly-digitized pulsed eddy current based quantification of aluminum sheet thickness

Direct interfacing technique (DIT) eradicates additional circuit requirements for sensor-embedded system interface and digitization of analog signals. This technique provides advantages in designing an efficient, portable, and low-cost sensor system. Pulsed eddy current testing (PECT) systems are used for thickness and defect measurements of conductive materials. Circuitous sensor-interfacing methods and tedious data interpretation processes make PECT systems inapt for miniaturization and portable applications. In this work, DIT is used in conjunction with PECT for thickness estimation of conductive material. Change in the de-energizing time of a single coil probe with sample thickness, with respect to air, is used as a signal. The curve fitting method yields a maximum relative error of ≈2% in the thickness estimation. Effects of temperature and liftoff on system accuracy are also investigated. A liftoff compensation method using a 3-signal data group is proposed. It is shown that for thicknesses in the range of 0.508 mm–3.175 mm and liftoffs up to 3.000 mm (step size: 0.500 mm), the proposed scheme produces a maximum relative error of 5.2%. The DIT and PECT combination can be applied for different structural eddy current testing in the future.

Engineering of polarity-responsive fluorescent probe for real-time measurement and visualization of total polar materials in edible oils

The content of total polar materials (TPM) in edible oils is generally accepted as a reliable indicator of the quality of edible oils. A high TPM value may signify that the flavor has been compromised and its consumption may lead to adverse effects on human health. However, the lack of convenient and user-friendly detection methods for the detection of TPM remains a challenge. To address this, a sensitive polarity-responsive fluorescent probe has been designed. A good linear relationship was observed for the ratio of the intensity of green to red fluorescence signal (I504 nm/I625 nm) and the TPM content over the range 1.1–29.3% for soybean oil and 0.1–27.5% for salad oil, respectively. A portable fluorescence sensor system was constructed, which provided a stable platform for the convenient detection of TPM via naked eye observation. These results indicate that the probe has great potential for TPM detection of edible oils in the food safety industry.

Field-Deployable Determinations of Peroxide Index and Total Phenolic Content in Olive Oil Using a Promising Portable Sensor System.

Useful information about the oxidative stability of a virgin olive oil in terms of oxidation products and antioxidant compounds can be obtained by analyzing the peroxide index (PI) and total phenolic content (TPC), respectively. These quality parameters are usually determined in a chemical laboratory using expensive equipment, toxic solvents, and well-trained personnel. This paper presents a novel portable sensor system for in the field and rapid determination of PI and TPC that is particularly suited in the case of small production environments that cannot afford an internal laboratory for quality control analysis. The system is small, can be powered by both USB ports and batteries, is easy to operate, and integrates a Bluetooth module for wireless data transmission. It estimates the PI and TPC in olive oil from the measurement of the optical attenuation of an emulsion between a reagent and the sample under test. The system has been tested on a set of 12 olive oil samples (eight for calibration and four for validation), and the results have shown how the considered parameters can be estimated with good accuracy. The maximum deviation from the results obtained with the reference analytical techniques is 4.7 meq O2/kg in the case of PI and 45.3 ppm in the case of TPC for the calibration set, while it is 14.8 meq O2/kg in the case of PI and 55 ppm in the case of TPC for the validation set.

Integration of on-chip lysis and paper-based sensor for rapid detection of viral and exosomal RNAs

In recent years, paper-based nucleic acid sensors have been demonstrated for the ability to detect DNA and RNA molecules extracted from viruses and bacteria. In clinical samples, these nucleic acids are mostly encapsulated in lipid membranes and need to be released before being analyzed using paper-based sensors. For the nucleic acid amplification tests (NAATs), it is also desirable to remove the interfering molecules that can inhibit the nucleic acid amplification. To achieve a field deployable NAAT, we report a portable sensor system that combines the thermolysis and paper-based NAATs to detect target RNA molecules carried by viral and exosomal nanoparticles. The sensor cartridge includes a lysis chamber with a pressure-controlled diaphragm valve, paper flow channels, and three paper-based NAAT reaction chambers to extract, transport, and detect nucleic acids respectively. A compact instrument was prototyped to automate the assay, collect fluorescence images of the nucleic acid amplification, and generate amplification curves for NAATs. The pump-free and paper-based sensor achieved quantitative analysis of influenza A virus (IAV) RNA and exosome microRNA within 1 h, with the lowest detect concentration of 104 TCID50/mL and 106 EV/mL for IAV and exosome, respectively. Owing to the advantages of easy storage, simple operation, and low cost, such as system has great potential to be used as a point-of-care test for in-field diagnosis of viral and bacterial infections.

Variation of UV-A/UV-B daily profiles depending on locations and altitude

Solar UV/visible monitoring has increased its importance in the recent years due to the global warming, unexpected atmospheric anomalies and storms, and the increasing needs for additional human protection. In mountain areas with high elevation the interest to UV irradiation measurements is expected to increase due to atmospheric transparency, however frequent events of lightning and risk of equipment failures has to be taken into account. The cost of the UV measurement systems can be greatly reduced by employing low-cost integrated inexpensive digital sensors with on-chip signal conditioning as detectors which are more convenient for field deployment and outdoor measurements. Thus, a compact portable UV/visible sensor equipment is in great demand for annual solar irradiation monitoring and seasonal all-day measurement campaigns. In this work, we report on the development of an in-house portable UV sensor system based on digital sensors with I2C communication, open-source hardware and software. The developed equipment is based on integrated digital sensors (VEML 6075, TSL 2591). It has been developed by employing Wi-Fi ESP 32 microcontroller, ODROID microcomputer and open-source software (InfluxDB and Grafana visualization tool). We investigate the system performance by measuring daily profiles of UV-B/UV-A irradiation in different locations and under different atmospheric conditions in order to evaluate its feasibility for prevention of humans from UV overexposure during outdoor operations. On-field tests are performed for 2 years in 7 different locations in Bulgaria. Interestingly, in downtown during particular days with high traffic an increased UV scattering and absorption due to urban pollution has been observed.

A portable sensor for the determination of tree canopy air quality

A low-cost portable sensor system has been developed and described to interrogate individual trees and quantify their impact on air quality (CO, NO2, PM2.5).

Batch Nanofabrication of Suspended Single 1D Nanoheaters for Ultralow-Power Metal Oxide Semiconductor-Based Gas Sensors.

The demand for power-efficient micro-and nanodevices is increasing rapidly. In this regard, electrothermal nanowire-based heaters are promising solutions for the ultralow-power devices required in IoT applications. Herein, a method is demonstrated for producing a 1D nanoheater by selectively coating a suspended pyrolyzed carbon nanowire backbone with a thin Au resistive heater layer and utilizing it in a portable gas sensor system. This sophisticated nanostructure is developed without complex nanofabrication and nanoscale alignment processes, owing to the suspended architecture and built-in shadow mask. The suspended carbon nanowires, which are batch-fabricated using carbon-microelectromechanical systems technology, maintain their structural and functional integrity in subsequent nanopatterning processes because of their excellent mechanical robustness. The developed nanoheater is used in gas sensors via user-designable localization of the metal oxide semiconductor nanomaterials onto the central region of the nanoheater at the desired temperature. This allows the sensing site to be uniformly heated, enabling reliable and sensitive gas detection. The 1D nanoheater embedded gas sensor can be heated immediately to 250°C at a remarkably low power of 1.6mW, surpassing the performance of state-of-the-art microheater-based gas sensors. The presented technology offers facile 1D nanoheater production and promising pathways for applications in various electrothermal devices.

Antilope A low-cost portable sensor system for air quality monitoring

Antilope A low-cost portable sensor system for air quality monitoring

Portable shifted excitation Raman difference spectroscopy for on‐site soil analysis

AbstractOn‐site soil analysis in the framework of precision agriculture is gaining significant importance to achieve improved crop productivity, increased soil health and reduced fertilizer application. In situ sensing techniques can provide the information required for decision support systems immediately on the field, for example, to control fertilization and liming. Shifted excitation Raman difference spectroscopy (SERDS) pilot investigations for on‐site soil analysis are presented using a portable SERDS sensor system specifically developed for in‐field studies. The SERDS sensor includes a dual‐wavelength diode laser at 785 nm integrated in an in‐house realized turnkey laser system and an optical power of 36 mW at the sample was chosen for our experiments. Outdoor pre‐investigations with the device and polystyrene as test sample show the capability of SERDS for qualitative and quantitative analysis under changing daylight conditions. On‐site soil analysis is carried out and SERDS extracts Raman signals from disturbing background interference with a 15‐fold improvement of the signal‐to‐background‐noise ratio. Beside others, closely neighboured Raman signals of calcite and dolomite are identified and even mixtures of both soil carbonates are discriminated using SERDS. The number of accumulations for generating an averaged SERDS spectrum of soil with a sufficient signal stability and signal‐to‐background‐noise ratio is evaluated to optimize the overall exposure time for such in situ experiments. The presented results demonstrate the large capability of the developed portable SERDS sensor system for on‐site soil investigations as promising tool for precision agriculture.

A Portable Battery-Operated Sensor System for Simple and Rapid Assessment of Virgin Olive Oil Quality Grade

Virgin olive oil quality is assessed by chemical as well as sensory analysis. Two of the most important parameters that define the quality of virgin olive oils are the free acidity and the peroxide index. These chemical parameters are usually determined by manual titration procedures that must be carried out in a laboratory by trained personnel. In this paper, a portable sensor system to support the quality grade assessment of virgin olive oil is presented. The system is battery operated and characterized by small dimensions, light weight and quick measurement response (about 30 s). The working principle is based on the measurement of the electrical conductance of an emulsion between a chemical reagent and the olive oil sample. Two different chemical reagents have been investigated: (1) a hydro-alcoholic solution (HAS), made of 60% ethanol and 40% distilled water; (2) 100% distilled water (DW). Tests have been carried out on a set of 40 olive oil samples. The results have shown how, for most of the fresh virgin olive oil samples (31 samples out of 40), the free acidity can be estimated with good accuracy from the electrical conductance of the emulsion using HAS as the reagent. In the case of the full set of samples, the emulsion electrical conductance, using HAS as the reagent, is a function of both the sample free acidity as well as the compounds produced by oil oxidation, and a compensation method based on the measured electrical conductance, using DW as the reagent, has been introduced to improve the accuracy in the estimated free acidity. Tests have also been carried out on the full set of samples, using a k-nearest neighbors algorithm, to demonstrate the feasibility of olive oil classification according to the quality grade. The results have shown how measurements carried out using only the HAS reagent provide better classification accuracy than measurements carried out using both the HAS and DW reagents. The proposed system can be a low-cost alternative to standard laboratory analyses to evaluate the quality grade of virgin olive oil.

Integrated near-infrared QEPAS sensor based on a 28 kHz quartz tuning fork for online monitoring of CO2 in the greenhouse

In this paper, a highly sensitive and integrated near-infrared CO2 sensor was developed based on quartz-enhanced photoacoustic spectroscopy (QEPAS). Unlike traditional QEPAS, a novel pilot line manufactured quartz tuning fork (QTF) with a resonance frequency f0 of 28 kHz was employed as an acoustic wave transducer. A near-infrared DFB laser diode emitting at 2004 nm was employed as the excitation light source for CO2 detection. An integrated near-infrared QEPAS module was designed and manufactured. The QTF, acoustic micro resonator (AmR), gas cell, and laser fiber are integrated, resulting in a super compact acoustic detection module (ADM). Compared to a traditional 32 kHz QTF, the QEPAS signal amplitude increased by > 2 times by the integrated QEPAS module based on a 28 kHz QTF. At atmospheric pressure, a 5.4 ppm detection limit at a CO2 absorption line of 4991.25 cm−1 was achieved with an integration time of 1 s. The long-term performance and stability of the CO2 sensor system were investigated using Allan variance analysis. Finally, the minimum detection limit (MDL) was improved to 0.7 ppm when the integration time was 125 s. A portable CO2 sensor system based on QEPAS was developed for 24 h continuous monitoring of CO2 in the greenhouse located in Guangzhou city. The CO2 concentration variations were clearly observed during day and night. Photosynthesis and respiration plants can be further researched by the portable CO2 sensor system.

A Portable Sensor System with Ultramicro Electrode Chip for the Detection of Heavy-Metal Ions in Water.

In this study, an ultramicro interdigital electrode array chip (UIEA) was designed and fabricated by using Micro-Electro-Mechanical systems (MEMS) technology, and a portable detection system, using the chip for determination of heavy-metal ions in water, was developed. The working electrode of the UIEA was modified with gold nanoparticles by electrodeposition. The detection sensitivity of the UIEA chip for copper ions was 0.0138 μA·L·μg−1, with the linear range of 0–400 μg/L and the detection limit of 18.89 μg/L (3σ), which was better than that of the compared columnar glassy carbon electrode. The results of the interference experiment verified that the UIEA chip has a certain anti-interference ability against common heavy-metal ions in water, such as Pb2+, Zn2+, and Mg2+ ions. The standard addition method was used to investigate the performance of the developed s ystem for copper ion determination in real water. The recovery range from 87.5% to 94.7% was achieved.

Fabrication of Skin-Mountable Flexible Sensor Patch for Monitoring of Swallowing Function.

Swallowing is a critical function that enables humans to sustain life. When swallowing is compromised, the consequences can be devastating and include malnutrition, dehydration, respiratory compromise, and even death. Swallowing disorders (i.e., dysphagia) are very common in many disorders and diseases, such as stroke, ALS, Parkinson disease, and more, and in fact millions of people across the world are diagnosed with oropharyngeal swallowing disorders every year. Current rehabilitative interventions for dysphagia can be effective, but require daily performance of swallowing exercises that primarily rely on expensive biofeedback devices (e.g., oral manometers, electromyographic (EMG) devices, and endoscopic devices). These types of devices are often only available in medical facilities. However, it is not feasible or economically viable for patients to make multiple visits per day or week to a clinic to receive intensive treatment, especially givenmobility limitations that many affectedpatients often experience. This can reduce treatment adherence and result in decreased rehabilitation potential, re-hospitalizations, and increased healthcare costs. To address this gap, we designed a novel specialized portable skin-mounted flexible sensor system that allows remote signal acquisition of swallowing-related signals. Herein, we report technical details for the fabrication of the skin-mounted flexible sensor patch that is tailored for the human submental (under the chin) area, enabling the continuous, reliable monitoring of both muscles' activity (i.e., EMG signals) and laryngeal movements during swallowing events. The sensor patch is wired to a portable reusable wireless (Bluetooth) unit compatible with smart watches, phones, and tablets for post-data analysis and reporting through a cloud server, which would potentially enable telemonitoring of patients with dysphagia.

Antilope, A Portable Low-Cost Sensor System for the Assessment of Indoor and Outdoor Air Pollution Exposure

The increasing availability of low-cost sensors and open source projects make it easier than ever for a maker to build his own air quality node. Nonetheless, depending on one’s goal and its related data quality objective, to customize an existing project or to build a specific printed circuit board may still be very useful. In the framework of the Outdoor and Indoor Exposure project, a portable mini-station has been developed, tested and then used in two experiments: exposure assessment and complementary network measurement. The present paper focuses on the description of the equipment that was designed and prototyped, as well as on the tests that were made in the lab and in the field to evaluate its overall performance and that of its different sensors. Finally, we present what we consider to be its main drawbacks and our perspectives for further development and tests.

Kinematic Evaluation via Inertial Measurement Unit Associated with Upper Extremity Motor Function in Subacute Stroke: A Cross-Sectional Study.

Kinematic evaluation via portable sensor system has been increasingly applied in neurological sciences and clinical practice. However, conventional kinematic evaluation rarely extends the context beyond the motor impairment level. In addition, kinematic tasks with numerous items could be complex and time consuming that pose a burden to test applications and data processing. The study aimed to explore the correlation of finger-to-nose task (FNT) kinematics via Inertial Measurement Unit with upper limb motor function in subacute stroke. In this study, six FNT kinematic variables were used to measure movement time, smoothness, and velocity in 37 participants with subacute stroke. Upper limb motor function was evaluated with the Fugl-Meyer Assessment for Upper Extremity (FMA-UE), Action Research Arm Test (ARAT), and modified Barthel Index (MBI). As a result, mean velocity, peak velocity, and the number of movement units were associated with the clinical assessments. The multivariable linear regression models could estimate 55%, 51%, and 32% of variance in FMA-UE, ARAT, and MBI, respectively. In addition, age, gender, type of stroke, and paretic side had no significant effects on these associations. Results show that FNT kinematic variables measured via Inertial Measurement Unit are associated with upper extremity motor function in individuals with subacute stroke. The objective kinematic evaluation may be suitable for predicting clinical measures of motor impairment and capacity to understand upper extremity motor recovery and clinical decision making after stroke. This trial is registered with ChiCTR1900026656.

Fast SARS-CoV-2 virus detection using disposable cartridge strips and a semiconductor-based biosensor platform.

Detection of the SARS-CoV-2 spike protein and inactivated virus was achieved using disposable and biofunctionalized functional strips, which can be connected externally to a reusable printed circuit board for signal amplification with an embedded metal-oxide-semiconductor field-effect transistor (MOSFET). A series of chemical reactions was performed to immobilize both a monoclonal antibody and a polyclonal antibody onto the Au-plated electrode used as the sensing surface. An important step in the biofunctionalization, namely, the formation of Au-plated clusters on the sensor strips, was verified by scanning electron microscopy, as well as electrical measurements, to confirm successful binding of thiol groups on this Au surface. The functionalized sensor was externally connected to the gate electrode of the MOSFET, and synchronous pulses were applied to both the sensing strip and the drain contact of the MOSFET. The resulting changes in the dynamics of drain waveforms were converted into analog voltages and digital readouts, which correlate with the concentration of proteins and virus present in the tested solution. A broad range of protein concentrations from 1 fg/ml to 10 μg/ml and virus concentrations from 100 to 2500 PFU/ml were detectable for the sensor functionalized with both antibodies. The results show the potential of this approach for the development of a portable, low-cost, and disposable cartridge sensor system for point-of-care detection of viral diseases.

A Remote Sensor System Based on TDLAS Technique for Ammonia Leakage Monitoring.

The development of an efficient, portable, real-time, and high-precision ammonia (NH3) remote sensor system is of great significance for environmental protection and citizens’ health. We developed a NH3 remote sensor system based on tunable diode laser absorption spectroscopy (TDLAS) technique to measure the NH3 leakage. In order to eliminate the interference of water vapor on NH3 detection, the wavelength-locked wavelength modulation spectroscopy technique was adopted to stabilize the output wavelength of the laser at 6612.7 cm−1, which significantly increased the sampling frequency of the sensor system. To solve the problem in that the light intensity received by the detector keeps changing, the 2f/1f signal processing technique was adopted. The practical application results proved that the 2f/1f signal processing technique had a satisfactory suppression effect on the signal fluctuation caused by distance changing. Using Allan deviation analysis, we determined the stability and limit of detection (LoD). The system could reach a LoD of 16.6 ppm·m at an average time of 2.8 s, and a LoD of 0.5 ppm·m at an optimum averaging time of 778.4 s. Finally, the measurement result of simulated ammonia leakage verified that the ammonia remote sensor system could meet the need for ammonia leakage detection in the industrial production process.