Array For Monitoring Research Articles

Ultrasensitive and selective CuAlO2 sensor toward H2S based on surface sulfuration-desulfuration reaction

Exploring novel sensing materials with extraordinary specificity/selectivity is essential to construct artificial gas molecules recognition chips (sensor arrays) for future environment and health monitoring. Herein, we reported the excellent H2S sensing properties of a p-type delafossite CuAlO2 sensor. Without complex size, morphology or defect control procedures, irregularly shaped CuAlO2 particles (size ranging from tens of nm to several μm) synthesized by a simple sol-gel route, exhibit an ultrahigh response (4600) toward (10 ppm) H2S molecules at 160 °C. Tiny responses (< 2) toward (100 ppm) NH3, NO2 and diverse volatile organic compounds (VOCs) molecules indicate an excellent selectivity. In addition to well-known surface oxygen involved gas/oxide charge interaction, quasi-operando spectroscopy (combing XPS, Raman, GC-MS, UPS etc.) analyzing suggests the surface sulfuration of CuAlO2 (S:CuAlO2 possessing a higher EV position than CuAlO2), which would act as a chemically switched ‘gate’ and effectively modulate the resistance of sensing channel, and thus contributes ultrahigh electrical response toward H2S. The reversible S doping-detaching and unique S:CuAlO2/CuAlO2 band alignment make delafossite CuAlO2 as an alternative novel H2S sensor with fantastic response and selectivity, and open up new opportunities for future applications.

Wearable multiplexed biosensor system toward continuous monitoring of metabolites

Comprehensive metabolic panels are the most reliable and common methods for monitoring general physiology in clinical healthcare. Translation of this clinical practice to personal health and wellness tracking requires reliable, non-invasive, miniaturized, ambulatory, and inexpensive systems for continuous measurement of biochemical analytes. We report the design and characterization of a wearable system with a flexible sensor array for non-invasive and continuous monitoring of human biochemistry. The system includes signal conditioning, processing, and transmission parts for continuous measurement of glucose, lactate, pH, and temperature. The system can operate three discrete electrochemical cells. The system draws 15 mA under continuous operation when powered by a 3.7 V 150 mAh battery. The analog front-end of the electrochemical cells has four potentiostats and three multiplexers for multiplexed and parallel readout from twelve working electrodes. Utilization of redundant working electrodes improves the measurement accuracy of sensors by averaging chronoamperometric responses across the array. The operation of the system is demonstrated in vitro by simultaneous measurement of glucose and lactate, pH, and skin temperature. In benchtop measurements, the sensors are shown to have sensitivities of 26.31 μA mM−1·cm−2 for glucose, 1.49 μA mM−1·cm−2 for lactate, 54 mV·pH−1 for pH, and 0.002 °C-1 for temperature. With the custom wearable system, these values were 0.84 ± 0.03 mV μM−1·cm−2 or glucose, 31.87 ± 9.03 mV mM−1·cm−2 for lactate, 57.18 ± 1.43 mV·pH−1 for pH, and 63.4 μV·°C−1 for temperature. This miniaturized wearable system enables future evaluation of temporal changes of the sweat biomarkers.

An Enhanced Time-Reversal Imaging Algorithm-Driven Sparse Linear Array for Progressive and Quantitative Monitoring of Cracks

A Lamb wave and linear piezoelectric lead zirconate titanate (PZT) array-based monitoring method for the detection and quantification of crack damage is presented in this paper. Because existing PZT array arrangements are not suitable for quantitative monitoring of crack damage both in orientation and in length, a sparse linear PZT array is introduced and applied to collect crack reflections. Based on this new array, a method for estimating crack orientation is proposed. An amplitude spectrum as a function of angle is mapped using time delayed and summed signals. By finding the peaks in the spectra, the central actuator element and corresponding orientation angle are determined. Furthermore, the time of flight imaging method is modified to display and evaluate cracks quantitatively. Validating experiments are conducted on a T6061 aluminum plate, monitoring and evaluating single and connected cracks with various orientations in different locations. As suggested by the experiments, the orientation of most cracks can be well recognized and all cracks can be quantitatively displayed by the proposed methods.

Electrochemical live monitoring of tumor cell migration out of micro-tumors on an innovative multiwell high-dense microelectrode array

Understanding of cell migration and spreading out of tumor tissue is of great interest concerning the mechanism and causes of tumor malignancy and metastases. Although there are methods available for studying cell migration on monolayer cell cultures like transwell assays, novel techniques for monitoring cell spreading out of 3D organoids or tumor tissue samples are highly required. In this context, we developed an innovative high-dense microelectrode array for impedimetric monitoring of cell migration from 3D tumor cultures. For a proof of concept, a strongly migrating breast cancer cell line (MDA-MB-231) and two malignant melanoma cell lines (T30.6.9, T12.8.10ZII) were used for generating viable micro-tumor models. The migration propensity was determined by impedimetric monitoring over 144 hours, correlated by microscopy and validated by transwell assays. The impedimetric analysis of covered electrodes and the relative impedance maximum values revealed extended information regarding the contribution of proliferative effects. More strikingly, using reference populations of mitomycin C treated spheroids where proliferation was suppressed, distinction of proliferation and migration was possible. Therefore, our high-dense microelectrode array based impedimetric migration monitoring has the capability for an automated quantitative analysis system that can be easily scaled up as well as integrated in lab on chip devices.

Combined calorimetric gas- and spore-based biosensor array for online monitoring and sterility assurance of gaseous hydrogen peroxide in aseptic filling machines

A combined calorimetric gas- and spore-based biosensor array is presented in this work to monitor and evaluate the sterilization efficacy of gaseous hydrogen peroxide in aseptic filling machines. H2O2 has been successfully measured under industrial conditions. Furthermore, the effect of H2O2 on three different spore strains , namely Bacillus atrophaeus, Bacillus subtilis and Geobacillus stearothermophilus, has been investigated by means of SEM, AFM and impedimetric measurements. In addition, the sterilization efficacy of a spore-based biosensor and the functioning principle are addressed and discussed: the sensor array is convenient to be used in aseptic food industry to guarantee sterile packages.

Sensors array for monitoring and automation of the electrochemical recovery of metals from waste printed circuit boards

Sensors array for monitoring and automation of the electrochemical recovery of metals from waste printed circuit boards

A self-powered gas sensor based on PDMS/Ppy triboelectric-gas-sensing arrays for the real-time monitoring of automotive exhaust gas at room temperature

A new self-powered active gas sensor for real-time monitoring of automotive exhaust gas was devised. The pipe-shaped device was fabricated from polydimethylsiloxane/polypyrrole (PDMS/Ppy) triboelectric gas-sensing unit arrays. The gas-sensing units can actively convert the mechanical energy of gas flow into a triboelectric current. The output current signal depends on the species and concentrations of the target chemical gases (CO, NH3, NO) in the gas flow, and thus can be used as a sensing signal. The device consists of seven gas-sensing units with different Ppy derivatives. As the different sensing units respond to the gases in different ways, the device can differentiate between gas species. The working mechanism is attributed to the coupling effect between the triboelectric effect of PDMS/Ppy and the gas-sensing properties of Ppy. The device can be installed in the tailpipe of an automobile, and can thus analyze the exhaust gas in real time without the need for any external electrical power. The results of the present study spur a new research direction for the development of automotive exhaust gas monitoring systems, thus playing an important role in the detection of air pollution.

Bioimpedance Sensor Array for Long-Term Monitoring of Wound Healing from Beneath the Primary Dressings and Controlled Formation of H2O2 Using Low-Intensity Direct Current.

Chronic wounds impose a significant financial burden for the healthcare system. Currently, assessment and monitoring of hard-to-heal wounds are often based on visual means and measuring the size of the wound. The primary wound dressings must be removed before assessment can be done. We have developed a quasi-monopolar bioimpedance-measurement-based method and a measurement system to determine the status of wound healing. The objective of this study was to demonstrate that with an appropriate setup, long-term monitoring of wound healing from beneath the primary dressings is feasible. The developed multielectrode sensor array was applied on the wound area and left under the primary dressings for 142 h. The impedance of the wounds and the surrounding intact skin area was measured regularly during the study at 150 Hz, 300 Hz, 1 kHz, and 5 kHz frequencies. At the end of the follow-up period, the wound impedance had reached the impedance of the intact skin at the higher frequencies and increased significantly at the lowest frequencies. The measurement frequency affected the measurement sensitivity in wound monitoring. The skin impedance remained stable over the measurement period. The sensor array also enabled the administration of periodical low-intensity direct current (LIDC) stimulation in order to create an antimicrobial environment across the wound area via the controlled formation of hydrogen peroxide (H2O2).

Clinical assessment of a non-invasive wearable MEMS pressure sensor array for monitoring of arterial pulse waveform, heart rate and detection of atrial fibrillation

There is an unmet clinical need for a low cost and easy to use wearable devices for continuous cardiovascular health monitoring. A flexible and wearable wristband, based on microelectromechanical sensor (MEMS) elements array was developed to support this need. The performance of the device in cardiovascular monitoring was investigated by (i) comparing the arterial pressure waveform recordings to the gold standard, invasive catheter recording (n = 18), (ii) analyzing the ability to detect irregularities of the rhythm (n = 7), and (iii) measuring the heartrate monitoring accuracy (n = 31). Arterial waveforms carry important physiological information and the comparison study revealed that the recordings made with the wearable device and with the gold standard device resulted in almost identical (r = 0.9–0.99) pulse waveforms. The device can measure the heart rhythm and possible irregularities in it. A clustering analysis demonstrates a perfect classification accuracy between atrial fibrillation (AF) and sinus rhythm. The heartrate monitoring study showed near perfect beat-to-beat accuracy (sensitivity = 99.1%, precision = 100%) on healthy subjects. In contrast, beat-to-beat detection from coronary artery disease patients was challenging, but the averaged heartrate was extracted successfully (95% CI: −1.2 to 1.1 bpm). In conclusion, the results indicate that the device could be useful in remote monitoring of cardiovascular diseases and personalized medicine.

Cascaded amplifying circuits enable ultrasensitive cellular sensors for toxic metals.

Cell-based biosensors have great potential to detect various toxic and pathogenic contaminants in aqueous environments. However, frequently they cannot meet practical requirements due to insufficient sensing performance. To address this issue, we investigated a modular, cascaded signal amplifying methodology. We first tuned intracellular sensory receptor densities to increase sensitivity, and then engineered multi-layered transcriptional amplifiers to sequentially boost output expression level. We demonstrated these strategies by engineering ultrasensitive bacterial sensors for arsenic and mercury, and improved detection limit and output up to 5,000-fold and 750-fold, respectively. Coupled by leakage regulation approaches, we developed an encapsulated microbial sensor cell array for low-cost, portable and precise field monitoring, where the analyte can be readily quantified via displaying an easy-to-interpret volume bar-like pattern. The ultrasensitive signal amplifying methodology along with the background regulation and the sensing platform will be widely applicable to many other cell-based sensors, paving the way for their real-world applications.

A Highly Sensitive Pressure-Sensing Array for Blood Pressure Estimation Assisted by Machine-Learning Techniques.

This work describes the development of a pressure-sensing array for noninvasive continuous blood pulse-wave monitoring. The sensing elements comprise a conductive polymer film and interdigital electrodes patterned on a flexible Parylene C substrate. The polymer film was patterned with microdome structures to enhance the acuteness of pressure sensing. The proposed device uses three pressure-sensing elements in a linear array, which greatly facilitates the blood pulse-wave measurement. The device exhibits high sensitivity (−0.533 kPa−1) and a fast dynamic response. Furthermore, various machine-learning algorithms, including random forest regression (RFR), gradient-boosting regression (GBR), and adaptive boosting regression (ABR), were employed for estimating systolic blood pressure (SBP) and diastolic blood pressure (DBP) from the measured pulse-wave signals. Among these algorithms, the RFR-based method gave the best performance, with the coefficients of determination for the reference and estimated blood pressures being R2 = 0.871 for SBP and R2 = 0.794 for DBP, respectively.

Optimal design of 3D borehole seismic arrays for microearthquake monitoring in anisotropic media during stimulations in the EGS collab project

Multiple U.S. national laboratories, universities and industrial collaborators are conducting collaborative research under the EGS Collab project supported by the U.S. Department of Energy, to understand the fracture creation and imaging during fracturing in enhanced geothermal systems. Microearthquake hypocenter locations and focal mechanisms are used to monitor hydraulic fracturing growth and characterization at the EGS Collab experimental site at the Sanford Underground Research Facility using seismic receivers in multiple monitoring wells. We develop a methodology for optimal design a 3D borehole seismic array for cost-effective seismic monitoring in anisotropic media using not only the relationship between receiver distributions and standard deviation errors of microearthquake hypocenter locations, but also that between receiver distributions and focal-mechanism inversion errors. Our results indicate that microearthquake hypocenter locations and focal mechanisms can be reasonably well reconstructed for the EGS Collab Experiment I using six monitoring wells, including four fracture-parallel monitoring wells and two orthogonal wells. Eight seismic receivers evenly distributed in four parallel monitoring wells or twelve receivers in all six monitoring wells are required for hypocenter location, and twelve receivers evenly distributed in six wells or sixteen receivers in four wells are needed for focal-mechanism inversion.

Minimally‐invasive Microneedle‐based Biosensor Array for Simultaneous Lactate and Glucose Monitoring in Artificial Interstitial Fluid

AbstractHere we report the first mediated pain free microneedle‐based biosensor array for the continuous and simultaneous monitoring of lactate and glucose in artificial interstitial fluid (ISF). The gold surface of the microneedles has been modified by electrodeposition of Au‐multiwalled carbon nanotubes (MWCNTs) and successively by electropolymerization of the redox mediator, methylene blue (MB). Functionalization of the Au‐MWCNTs/polyMB platform with the lactate oxidase (LOX) enzyme (working electrode 1) and with the FAD‐Glucose dehydrogenase (FADGDH) enzyme (working electrode 2) enabled the continuous monitoring of lactate and glucose in the artificial ISF. The lactate biosensor exhibited a high sensitivity (797.4±38.1 μA cm−2 mM−1), a good linear range (10–100 μM) with a detection limit of 3 μM. The performance of the glucose biosensor were also good with a sensitivity of 405.2±24.1 μA cm−2 mM−1, a linear range between 0.05 and 5 mM and a detection limit of 7 μM. The biosensor array was tested to detect the amount of lactate generated after 100 minutes of cycling exercise (12 mM) and of glucose after a normal meal for a healthy patient (10 mM). The results reveal that the new microneedles‐based biosensor array seems to be a promising tool for the development of real‐time wearable devices with a variety of sport medicine and clinical care applications.

Comprehensive characterization and material modeling for ceramic injection molding simulation performance validations

Powder injection molding is like the process of plastics injection molding capable of the mass production of highly functional complex 3D parts, just in ceramics and metals. The market for products made by powder injection molding is constantly growing. With this growth, the need for reliable process simulations arises. Simulation tools are widely used in the development of new products and are applied in powder and polymer injection molding to support the product design, shorten the development time, avoid errors, and help to optimize the mold and process design. However, material data for feedstocks and thus simulations of the powder injection molding process are hardly available yet. The present work introduces the necessary material data for establishing a material model for simulations. An extensive material characterization of ceramic feedstocks was conducted. The material investigations comprised the determination of basic, thermal, and rheological material properties to collect a comprehensive data set. The necessary measurements and tools are outlined and their results are discussed in detail with regard to powder content and in comparison to pure plastics. The gained data enabled to successfully create a material model for mold filling simulations. Powder injection molding experiments were carried out with a spiral test geometry. The mold was equipped with a sensor array for the process monitoring during injection. Furthermore, a simulation model of the test geometry was established. Finally, the results of the experiments and simulations are discussed and are compared to validate the performance of the simulations. The results showed the potential and limitations of process simulations and standard software applied in conventional and micro powder injection molding.

Wide subwavelength grating waveguide photonic integrated circuit sensor system

We are studying the viability of a chip-scale integrated photonics based sensor assay array for wearable soldier health monitoring and environmental hazard warning applications. We propose using label-free analyte capture material clad wide subwavelength grating (SWG) waveguides as the sensor elements in a multiplexed array to probe the myriad variety and concentration ranges of chemical hazards and biomarker health molecules expected in these applications. We present here the simulated behavior of both rectangular and tapered wide SWG geometries. We discuss their transmission spectra, effective index, bulk sensitivity, and cladding dependence on waveguide width alongside strip and slot waveguide geometries. Experimental transmission and effective index measurements validating our simulation techniques are also given.

Epidermis-Inspired Ultrathin 3D Cellular Sensor Array for Self-Powered Biomedical Monitoring

Sensing devices with wearability would open the door to many advanced applications including soft robotics, artificial intelligence, and healthcare monitoring. Here, inspired by the configuration of the human epidermis, we present a flexible three-dimensional (3D) cellular sensor array (CSA) via a one-step thermally induced phase separation method. The CSA was framed by the 3D cellular electret with caged piezoelectric nanoparticles, which was ultrathin (80 μm), lightweight, and highlyrobust. For biomedical sensing, the 3D-CSA holds a decent pressure sensitivity up to 0.19 V kPa-1 with a response time of less than 16 ms. Owing to its rigid structural symmetry, the 3D-CSA could be identically operated from itsboth sides.It was demonstrated to successfully measure the human heartbeat, detect the eyeball motion for sleeping monitoring, and tactile imaging. Mimicking the functionalities of the human skin with a self-powered operation feature, the 3D-CSA was expected to represent a substantial advancement in wearable electronics for healthcare.

Plasmonic 3D Semiconductor-Metal Nanopore Arrays for Reliable Surface-Enhanced Raman Scattering Detection and In-Site Catalytic Reaction Monitoring.

It is urgent to develop a rapid, reliable, and in-site determination method to detect or monitor trace amounts of toxic substances in the field. Here, we report an alternative surface-enhanced Raman scattering (SERS) method coupled with a portable Raman device on a plasmonic three-dimension (3D) hot spot sensing surface. Plasmonic Ag nanoparticles (AgNPs) were uniformly deposited on 3D TiO2 nanopore arrays as a sensitive SERS substrate, and further coated with graphene oxide (GO). We demonstrate the plasmon-induced SERS enhancement (5.8-fold) and the improvement of catalytic activity by incorporation of plasmonic AgNPs into the 3D TiO2 nanopore arrays. The modification of GO on the TiO2-Ag nanopore array further increases by a 6.2-fold Raman enhancement compared to TiO2-Ag while maintaining good uniformity (RSD < 10%). The optimized TiO2-Ag-GO substrate shows powerful quantitative detection potential for drug residues in fish scales via a simple scrubbing method, and the limit of detection (LOD) for crystal violet (CV) was 10-8 M. The SERS substrate also showed detection practicability of pesticide residues in banana peel with an LOD of 10-7 M. In addition, our TiO2-Ag-GO substrate exhibits excellent SERS self-monitoring performance for catalytic reduction of multiple organics in NaBH4 solution, and the substrate shows good recyclability of 6 cycles. Such a 3D TiO2-Ag-GO substrate is a promising SERS substrate with good sensitivity, uniformity, and reusability, and may be utilized for further miniaturization for point of analytical applications.

Design and laboratory testing of a MEMS accelerometer array for subsidence monitoring.

The in situ monitoring of displacement variation is important for studying the seabed subsidence mechanism. To meet the multi-point measurement requirements for vertical displacement in subsidence monitoring of the seabed surface, a Micro-Electro-Mechanical Systems accelerometer array was designed. By sensing the tilt angles, displacements on the array can be calculated. The subsidence is calculated as the difference in the displacements from the initial values. To improve the accuracy of the displacement calculation, a calibration model of the tilt angle was presented. The model parameters are computed through a least squares estimation method, which is solved by the Levenberg-Marquardt algorithm. Experimental results show that the calibration model performs excellently with the maximum error of tilt angle being less than 1° in the measurement range (-90°, 90°). The displacement measurement accuracy of the array (2.1 m long) is almost less than 1 cm. Thus, the results show a strong agreement between the detected data and actual deformation in the test.

Towards a minimally invasive device for continuous monitoring of beta-lactam antibiotics

Background: There is a need to develop novel mechanisms for monitoring and subsequently improving the precision of how we use antibiotics across care settings. We report the development of a microneedle array for the continuous monitoring of beta-lactam antibiotics. Methods & Materials: A surface modified microneedle array was developed for monitoring beta-lactam antibiotic concentrations in human interstitial fluid (ISF). The sensor was fabricated by anodically electrodepositing iridium oxide (AEIROF) onto a platinum surface on the microneedle followed by fixation of beta-lactamase enzyme within a hydrogel. Calibration of the sensor was performed to penicillin-G in buffer solution (PBS) and artificial ISF. Further calibration was undertaken using amoxicillin, ceftriaxone, and amoxicillin-clavulinate. Open-circuit potentials were recorded and data analysed using the Hill equation and log(concentration [M]) plots. Sensor performance during continuous monitoring in human tissue was modelled by development of a physiologically inspired calibration rig mimicking antimicrobial perfusion through tissue. The test rig was used to determine the diffusion (D) and partition coefficients (K) of penicillin-G within the test rig set at an initial flow rate of 10 μLmin−1. Results: The microneedle sensor demonstrated high reproducibility between penicillin-G runs in PBS with mean Km (± 1SD) = 4.4 ± 1.3 mM and mean slope function of log(concentration) plots 29 ± 1.80 mV/decade (r2 = 0.933). Response was reproducible after 28 days storage at 4 °C. In artificial ISF, the sensors response was Km (±1SD) = 7.7 ± 18.7 mM and a slope function of 34 ± 1.85 mv/decade (r2 = 0.995). Similar response was observed to amoxicillin. Ceftriaxone demonstrated a reduced but acceptable response. Addition of beta-lactamase inhibitor (clavulanic acid) inhibited response of the antimicrobial sensor to increasing concentrations of amoxicillin. Finally, the microneedle sensor was able to accurately respond to increasing and decreasing penicillin-G concentrations over a period of 2.5 hours on the test rig. Conclusion: Our results suggest that microneedle array based beta-lactam sensing may be a future application of this AEIROF based enzymatic sensor facilitating advanced control of antimicrobial delivery. Further work is now underway to evaluate the performance of microneedle sensing in humans receiving beta-lactam antibiotics and develop closed-loop-control systems for optimisation of dosing.

Highly-sensitive linear tactile array for continuously monitoring blood pulse waves

This work presents the development of a tactile sensing array for continuous blood pulse wave monitoring. The polymer-based sensing device consists of two polydimethylsiloxane layers, which were patterned with microdomes transferred from nylon membrane filters. The microdomes form interlocked structures, which enable the tunneling piezoresistive effect and provide ultra-high sensitivity. The sensing array was designed in an 8 × 1 linear configuration, and the length-width ratio of each sensing element is about 8. This design facilitates the acquisition of blood pulse wave signals on the skin above a radial artery. The measured relationship between resistance and pressure force indicates that the sensor exhibits very high sensitivity (−6.08 kPa−1). The array sensing results revealed that crosstalk between the sensing elements was nominal. In addition, the repeatability testing also showed that the performance of the sensor was quite stable after 10,000 loading-unloading cycles.