Long-term Stability Of Sensors Research Articles

Hydrodynamics-engineered polyaniline nanofibers on graphene nanosheets for high-performance pH sensors

Real-time sweat monitoring in the human body using wearable sensors is promising for noninvasive and continuous healthcare applications. For reliable and accurate sweat analysis, further improvement in the response time and long-term stability of sensors is required. This paper reports an electrochemical pH sensor based on polyaniline/graphene (PANi-Gr) with rapid electron and ion transfer. The implementation of the Taylor–Couette flow approach allowed the efficient exfoliation of graphite into Gr nanosheets and the rapid polymerization of aniline monomers on the Gr surface, resulting in nanofiber PANi-deposited Gr nanocomposites. PANi-Gr had a large surface area and porous structure, which are favorable for rapid and stable electrochemical reactions. The screen-printed PANi-Gr-based pH sensor exhibited a Nernstian sensitivity of 61.91 mV/pH, rapid response time of <1 s, and long-term stability upon monitoring with minimal potential drift (0.04 mV h−1) under strong acidic and basic conditions. Furthermore, the on-body performance of the wearable pH sensor integrated with a wireless electronic device was analyzed via the noninvasive real-time monitoring of human sweat pH during stationary cycling. The developed sensor can be used in wearable real-time sweat monitoring devices for medical and healthcare applications.

Evaluation of VIIRS Thermal Emissive Bands Long-Term Calibration Stability and Inter-Sensor Consistency Using Radiative Transfer Modeling

This study investigates the long-term stability of the Suomi National Polar-orbiting Partnership (S-NPP) Visible Infrared Imaging Radiometer Suite (VIIRS) moderate-resolution Thermal Emissive Bands (M TEBs; M12–M16) covering a period from February 2012 to August 2020. It also assesses inter-sensor consistency of the VIIRS M TEBs among three satellites (S-NPP, NOAA-20, and NOAA-21) over eight months spanning from 18 March to 30 November 2023. The field of interest is limited to the ocean surface between 60°S and 60°N, specifically under clear-sky conditions. Taking radiative transfer modeling (RTM) as the transfer reference, we employed the Community Radiative Transfer Model (CRTM) to simulate VIIRS TEB brightness temperature (BTs), incorporating European Centre for Medium-range Weather Forecasts (ECMWF) reanalysis data as inputs. Our results reveal two key findings. Firstly, the reprocessed S-NPP VIIRS TEBs exhibit a robust long-term stability, as demonstrated through analyses of the observation minus background BT differences (O-B ∆BTs) between VIIRS measurements (O) and CRTM simulations (B). The drifts of the O-B BT differences are consistently less than 0.102 K/Decade across all S-NPP VIIRS M TEB bands. Notably, observations from VIIRS M14 and M16 stand out with drifts well within 0.04 K/Decade, reinforcing their exceptional reliability for climate change studies. Secondly, excellent inter-sensor consistency among these three VIIRS instruments is confirmed through the double-difference analysis method (O-O). This method relies on the O-B BT differences obtained from daily VIIRS operational data. The mean inter-VIIRS O-O BT differences remain within 0.08 K for all M TEBs, except for M13. Even in the case of M13, the O-O BT differences between NOAA-21 and NOAA-20/S-NPP have values of 0.312 K and 0.234 K, respectively, which are comparable to the 0.2 K difference observed in overlapping TEBs between VIIRS and MODIS. These disparities are primarily attributed to the significant differences in the Spectral Response Function (SRF) of NOAA-21 compared to NOAA-20 and S-NPP. It is also found that the remnant scene temperature dependence of NOAA-21 versus NOAA-20/S-NPP M13 O-O BT difference after accounting for SRF difference is ~0.0033 K/K, an order of magnitude smaller than the corresponding rates in the direct BT comparisons between NOAA-21 and NOAA-20/S-NPP. Our study confirms the versatility and effectiveness of the RTM-based TEB quality evaluation method in assessing long-term sensor stability and inter-sensor consistency. The double-difference approach effectively mitigates uncertainties and biases inherent to CRTM simulations, establishing a robust mechanism for assessing inter-sensor consistency. Moreover, for M12 operating as a shortwave infrared channel, it is found that the daytime O-B BT differences of S-NPP M12 exhibit greater seasonal variability compared to the nighttime data, which can be attributed to the idea that M12 radiance is affected by the reflected solar radiation during the daytime. Furthermore, in this study, we’ve also characterized the spatial distributions of inter-VIIRS BT differences, identifying variations among VIIRS M TEBs, as well as spatial discrepancies between the daytime and nighttime data.

Water-durability and high-performance all-fiber humidity sensor using methyldiethanolamine-photopolymer-PDMS structure

In the context of optical fiber humidity sensing, the long-term stability of sensors in high humidity and dew environments such as bathrooms or marine climates remains a challenge, especially since many humidity sensitive materials are water soluble. In this study, we use methyldiethanolamine, pentaerythritol triacrylate and Eosin Y to form a liquid-solid structure humidity sensitive component, the outermost layer is coated with PDMS passivating layer to ensure the stability and durability of the humidity sensor under the conditions of dew and high humidity. The liquid microcavity of the sensor consists of methyldiethanolamine-pentaerythritol triacrylate composite solution, and the sensitivity is several times higher than that of the liquid-free cavity sensor. The sensitivity of the sensor to temperature is verified (0.43 nm/°C and 0.30 nm/°C, respectively) and temperature crosstalk is compensated using a matrix. The compact structure allows for ultra-fast response (602 ms) and recovery time (349 ms). Our work provides a promising platform for efficient and practical humidity and other gas monitoring systems.

Integration of buried dual-junction photodetection with ratiometric FRET-based biosensing: Results and design considerations

Fluorescence-based sensing powers laboratory-based bioanalytical systems. However, translating fluorescence-based bioanalytical sensing to benchtop or portable commercial platforms poses several technical challenges, including long-term sensor stability and fabrication complexity. To overcome such challenges, we designed, fabricated, and validated a novel ratiometric fluorescence assay which can be integrated with a commercial LED and a microfabricated dual-wavelength detector. With our integrated system, we were able to achieve direct, light intensity-independent, ratiometric sensing of a small molecule (tartaric acid) through a single detection window without complex electronic circuitry. We also present the integrated spectral effects between the buried dual-junction (BDJ) photodetector and the Förster resonance energy transfer (FRET) system over the relevant wavelength range. These results demonstrate both the feasibility and path to the development of an integrated sensing device which couples chemical and electronic systems.

Long-term Stability Enabling Technology of Silicon-Based Piezoresistive MEMS Pressure Sensor

Silicon-based piezoresistive microelectromechanical systems (MEMS) pressure sensor is one of the best studied and commercialized devices among all MEMS devices due to simple structure, easy reading circuit, strong batch fabrication capability and low price. The biggest technical bottleneck of this sensor for high-end applications such as aerospace is long-term stability after packaging. Therefore, long-term stability improvement technologies, as the common key technologies, have been widely concerned by academia and industry. In this paper, three common enabling technologies including pulsating fatigue, thermal-cold cycling and vibration aging are adopted to evaluate the effect of long-term stability of silicon-based piezoresistive MEMS pressure sensors by using control variable method and orthogonal test (OT) method. The comparative test results indicate that all these three technologies can improve the long-term stability of the pressure sensor. In addition, an optimized combination of environmental stress parameters is found to improve the stability more than 90% higher than before the test. The long-term stability of the sensors through the optimal parameter combination aging method is better than the original factory method. The research results can be used for reference to improve the long-term stability of various silicon-based pressure sensors.

Graphene Langmuir-Schaefer films Decorated by Pd Nanoparticles for NO2 and H2 Gas Sensors

Abstract NO2 and H2 gas sensing by few-layer graphene (FLG) were studied in dependence on the annealing and decoration of graphene by palladium nanoparticles (NPs). Graphene was deposited onto SiO2 (500 nm)/Si substrates by a modified Langmuir-Schaefer technique. A solution of FLG flakes in 1-methyl-2-pyrrolidone was obtained by a mild sonication of the expanded milled graphite. FLG films were characterized by atomic force microscopy, X-ray diffraction, Raman spectroscopy, and the Brunnauer-Emmett-Teller method. Average FLG flake thickness and lateral dimension were 5 nm and 300 nm, respectively. Drop casting of Pd NP (6–7 nm) solution onto FLG film was applied to decorate graphene by Pd. The room temperature (RT) resistance of the samples was stabilized at 15 kΩ by vacuum annealing. Heating cycles of FLG film revealed its semiconducting character. The gas sensing was tested in the mixtures of dry air with H2 gas (10 to 10 000 ppm) and NO2 gas (2 to 200 ppm) between RT and 200 °C. The response of 26 % to H2 was achieved by FLG with Pd decoration at 70 °C and 10 000 ppm of H2 in the mixture. Pure FLG film did not show any response to H2. The response of FLG with Pd to 6 ppm of NO2 at RT was ≥ 23 %. It is 2 times larger than that of the pure FLG sample. Long term stability of sensors was studied.

Enhanced Performance Stability of Iridium Oxide-Based pH Sensors Fabricated on Rough Inkjet-Printed Platinum.

Today, electrochemical sensors are used for a broad range of applications. A fundamental challenge is still the achievement of long-term sensor stability by ensuring good adhesion between the deposited sensing layer and the substrate material, e.g., a metal electrode. Until now, the most applied strategy to overcome this problem is to increase the surface roughness of the metal layer by mechanical etching or by electroplating of additional material layers, which both imply an increase in manufacturing steps and thus the final cost of the overall device. Alternatively, to overcome these adhesion problems, we propose the direct printing of a novel platinum nanoparticle ink, which is compatible with low-cost additive digital inkjet and with flexible low-cost substrates. This water-based platinum ink has two unique features: it leads to highly rough surfaces, which promotes the adhesion of deposited sensing material, and it is a highly low-temperature curing ink, compatible with polymeric substrates that cannot withstand high temperatures. Based on this concept, we report about a long-term stable and highly sensitive solid-state pH sensor functionalized by anodic electrodeposited iridium oxide on a rough nanostructured platinum printed layer. The sensors showed an excellent reproducibility with a linear super-Nernstian response (71.3 ± 0.3 mV/pH unit) in a wide pH range (pH 2-11). Long-term stability tests for over 1 year of application demonstrate an excellent mechanical sensor layer stability, which is correlated to the distinct roughness of the printed platinum layer. This novel approach is useful to simplify the fabrication process and with that the sensor costs.

Sensor and microelectronic elements based on nanoscale granular systems

Specific effects observed in small metal particles due to their distinction from bulk material as well as phenomena inherent to an ensemble of these particles coupled by electron tunneling have attracted considerable attention to nanosized systems. Electron and photon emission was revealed as a power was fed into the metal nanoparticle films deposited on insulating substrates either by passage of an electrical current in the film plane or by laser irradiation in the infrared and visible range. The electrical conductivity of metal nanoparticle films close to the percolation threshold is sensitive to temperature, substrate bending and adsorption of various gases. Besides, the current–voltage characteristics of the conduction current of a system consisting of a metal nanoparticle film and an adsorbate exhibit a voltage-controlled negative resistance region. These peculiar properties enable nanosized particle systems to be used for various applications. The present review deals with a variety of sensors for physical properties and microelectronics elements based on nanoparticle films. The mechanisms underlying the special properties are discussed. Some technological methods ensuring better parameter definition and long-term stability of sensors are also described.

Long term stability of metal oxide-based gas sensors for e-nose environmental applications: An overview

The e-nose technology has enormous potentialities for in site monitoring of off-odours. However a number of limitations are associated with the properties of chemical sensors, the signal processing performances and the real operating conditions of the environmental field. The field experience of the research group included testing of a large amount of sensors in different sensor technologies and among those the metal oxide-based gas sensors (Figaro type) are the best gas sensors for long term application, as stated during more than 1 year of field testing. To be usable for the off-odours field measurement, the e-nose has to deal with the lack of long term stability of these sensors. The drift and the sensors replacement have to be considered. In order to appraise the time evolution of the sensors and the effect on the results of an electronic nose, experimentation has been performed during more than 3 years on two identical sensor arrays. The two arrays contain the same six Figaro sensors and are in the same sensor chamber of the e-nose system. Both arrays have worked continuously, without break. This paper presents the drift of some TGS sensors for 7 years as well as the difference in the temporal behaviour of identical sensors and the consequence on the e-nose results after the sensor replacement in the sensors array. A correction of the drift and of the replacement effect is applied and the classification results are exposed, with and without correction.

Ring Laser Measurements of Ground Rotations for Seismology

Abstract Since the discovery of the wave nature of light, optical interferometry has assumed an important place in high precision metrology. This is mostly due to the inherent high sensor resolution for operational wavelengths in the vicinity of several hundred nanometers. In this context, interferometers in the Michelson configuration are most prominently used in gravitational wave antennas, such as the large projects VIRGO, LIGO, TAMA, and GEO600. In the Sagnac configuration they are used for high resolution rotation monitoring such as the precise observation of Earth rotation. Modern large-scale ring lasers reach a sensitivity for the measurement of rotation of 1 prad/sec (with approximately 1 hr of averaging). Because of the comparatively short wavelengths employed, optical interferometers are extremely sensitive to small mechanical perturbations of the entire apparatus. These can be caused by deformations, thermal or mechanical stress, and instabilities in the alignment of the optical components at the level of about λ /100. Ring lasers suitable for geophysical applications require a sensor resolution in the range of 10 -8 rad/sec and below. This demands a scale factor of the instrument that is only achievable with mechanical dimensions of the interferometer on the order of about 1 m 2 or larger. At the same time the necessary mechanical rigidity of the entire instrument has to be on the order of 5 nm. Currently, this has only been achieved with monolithic ring lasers made from blocks of Zerodur and installed in a temperature stabilized underground environment. However if long-term sensor stability is not required, compromises can be made and, in particular for studies of regional seismic events, it becomes feasible to build a heterolithic rotation sensor in a simpler and much cheaper way. Here, we report the design and first results from the GEOsensor, which has been specifically constructed for studies in rotational seismology. The sensor is operated at the Pinon Flat Seismological Observatory in Southern California.

Comparative study of nanocrystalline SnO 2 materials for gas sensor application: Thermal stability and catalytic activity

In this paper we discuss thermal stability of tin dioxide nanoparticles and long-term stability of the SnO 2-based gas sensors. Relying on laser-spark element analysis and XRD analysis we compare crystallite growth kinetics of synthesized and commercial (Sigma–Aldrich) SnO 2 with different impurity level. We found that commercial SnO 2 nanopowder has lower thermal stability in comparison with synthesized one, resulting in higher crystallite growth rate and poly-dispersed particle size after annealing. A special attention is drawn to discussion of catalytic activity of the nanocrystalline materials. Using IR spectroscopy we studied chemical composition of the annealed materials, which allowed us to reveal in the synthesized SnO 2 intensive formation of Sn–OH bonding during annealing. We performed temperature programmed reduction (TPR) analysis to compare the catalytic activity of the materials with and without deposited Pd on SnO 2. Long-term stability of the sensors made on the basis of synthesized and commercial SnO 2 was measured as a sensor signal deviation during 590 h of operation in 0.2, 0.6 and 1.0 vol. % of propane in air (50% RH at 20 °C).

Challenges and Promises of Electrochemical Detection and Sensing

The field of electrochemical detection and sensing is briefly surveyed. Some general problems are pointed out, e.g., the limited reproducibility of the sensor surface, difficulties with the long-term stability of sensors, or slow response of many electrochemical devices. On the other hand, promises and opportunities for the future involve further sensor miniaturization, combination of sensing and detection with chemometric techniques and/or with other measuring techniques, potentialities of in vivo measurements in biological objects, or mass production of simple and low cost single-use sensors.

Challenges and Promises of Electrochemical Detection and Sensing

The field of electrochemical detection and sensing is briefly surveyed. Some general problems are pointed out, e.g., the limited reproducibility of the sensor surface, difficulties with the long-term stability of sensors, or slow response of many electrochemical devices. On the other hand, promises and opportunities for the future involve further sensor miniaturization, combination of sensing and detection with chemometric techniques and/or with other measuring techniques, potentialities of in vivo measurements in biological objects, or mass production of simple and low cost single-use sensors.

A model for the relative environmental stability of a series of polyimide capacitance humidity sensors

A capacitance humidity sensor is used as a test device to characterize the performance of 13 polyimide films in relative humidity sensing applications. This sensor has a multilayer, free-standing film construction. It consists of a humidity sensitive polyimide dielectric core and conductive layers consisting of carbon filled polysulfone on each side of the polyimide film to form a capacitor. Thirteen polyimide films, including commercial polyimides and films of novel chemistry, are investigated to determine the long term stability of sensors using the films exposed to 85°C/85% RH for a total of 28 days. Differences in film chemistry are used to interpret trends in the environmental stability of the films.

Role of axial ligation on potentiometric response of Co(III) tetraphenylporphyrin-doped polymeric membranes to nitrite ions

Two types of Co(III) tetraphenylporphyrins, Co(III)TPPX (I) and Co(III)(N)TPPX (II), where X = C1 − or NO − 2 and N = C 5 H 5 N or C 6H 5CH 2C 5H 4N, are used as ionophores to prepare nitrite responsive polymeric membrane electrodes. The influence of the initial axial ligand (X − and N) on the operative ionophore mechanism of these metalloporphyrins within the solvent polymeric membranes is examined. Results from potentiometric and electrodialysis experiments suggest that in the presence of nitrite in the test sample and internal solution, both types of Co (III) porphyrins studied (I and II) act as neutral carriers and that the addition of lipophilic cationic sites (e.g., tridodecylmethylammonium ions (TDMA +)) to the organic membrane is essential to improve the selectivity and long term stability of sensors prepared with these species. Membranes formulated with (I) or (II) in the nitrite form along with TDMACl in plasticized PVC films exhibit the following selectivity sequence: SCN − > NO − 2 ~ C1O − 4 > Sal − > NO − 3 > Br − > C1 −. Membrane electrodes with added lipophilic cationic sites are shown to exhibit rapid, fully reversible and Nernstian response towards nitrite ions in the concentration range of 10 −1–10 −5 M, with good long term stability.

Oxygen Pressure as Biosensor for Rate Adaptive Cardiac Pacing

A new carbon based oxygen sensor for rate adaptive cardiac pacing has been developed. It measures oxygen partial pressure In mixed venous blood. The system was implanted in six sheep with a mean follow-up time of 261 days after implant. The sensor reacted in a physiological manner when the animals were at rest as well as during exercise. Long-term sensor stability and sensitivity were satisfactory, and we found excellent correlation with spontaneous heart rate variations and with oxygen saturation measurements. The sensor shows great promise although our experience is still limited and further development on the concept is on-going.

Evaluation of a Subcutaneous Glucose Sensor out to 3 Months in a Dog Model

To advance the feasibility of an implantable long-term glucose sensor with bioprotective sensor membranes and test protocols using a somatostatin analog (octreotide). Implantable sensors were constructed with one of eight bioprotective membranes and screened in vitro for stable response to glucose. Sensors were implanted subcutaneously into nondiabetic mongrel dogs and monitored at 4-min intervals via radiotelemetry. When implanted sensor responses showed evidence of tracking blood glucose after glucagon challenge (8-21 days postimplant), a glucose infusion protocol was used to assess performance. Sensor data were collected every 4 s after octreotide inhibition of endogenous insulin release. Reference plasma glucose samples were taken every 4-10 min. Preimplant in vitro testing of sensors verified linearity to 33.3 mM glucose and response times to 90% of equilibrium in 2-7 min. Ten implanted sensors tracked glucose for 20-114 days, during which 25 separate glucose infusion studies were conducted. The resulting regression data yielded a mean slope of 0.99 +/- 0.06, an intercept of 0.24 +/- 0.53 mM glucose, and a correlation coefficient 0.98 +/- 0.01. Long-term sensor stability was not judged adequate for clinical application, although two sensors tracked within +/- 15% for 33 and 42 days. In vivo oxygen delivery was shown to affect sensor performance. On explant, two of eight tested bioprotective membranes were found to be biostable and to fully protect the sensor's enzyme membrane. The foreign body capsule was adequately vascularized adjacent to the sensor up to 91 days postimplant. Sensor units eventually failed because of electronic problems (package leakage) or because of biodegradation or biofouling of test bioprotective membranes. Further development of this type of sensor may provide diabetic patients with a better means of monitoring blood glucose.

Introductory remarks on gas sensing

The progress of mankind can be seen, from a certain point-of-view, as a continuous effort of the human being to reproduce himself artificially in order to reduce his physical fatigue and to make himself more powerful. The most recent gigantic advances in his capability to elaborate signals and actuate actions mechanically seem to reward such a desire. However, robots still have problems in emulating the senses of taste and smell because of the impracticability in using traditional chemical analysis methodology to implement chemical sensors. That is why it makes sense to go deeper into the study of electric and ionic conduction in solids to detect gases. Possible mechanisms to be exploited take advantage of Nernst cells, and very recently a hydrogen sensor operating at room temperature has been developed for perspective applications in advance warning of possible earthquakes. A second possible mechanism deals with the high-temperature semiconductor-like properties of certain oxides, even if in such a case the gas selectivity and long-term sensor stability require improvement. Thirdly, MOSFET devices having a metal gate layer that selectively absorbs gases are under development.

Biological Oxygen Demand Sensor Using an Arsenic Resistant Bacterium

Various microbial biosensors, including BOD (biological oxygen demand) sensors, have been reported.''2 These are usually constructed by holding intact microorganisms, such as bacteria and yeasts, near the tip of an oxygen electrode. Since microorganisms consume organic compounds quantitatively, their concentrations can be determined by estimating the respiration activity of the immobilized microorganisms with the oxygen electrode. Many microorganisms have variants which show a resistance to toxic substances.3 We have studied the biaaccumulation of arsenic (As) by freshwater algae isolated from arsenic-polluted enviroments.4 In the course of our studies we isolated some bacteria contaminated with an algae culture containing As(V); one of them was identified as Pseudomonas putida. This bacterium is an aerobic heterotroph which exhibits extreme resistance to As(V); it can even multiply at concentrations above 5000 mg 1-' of inorganic As(V).5 It is known that ordinary bacteria become extinct when the surrounding As(V) level exceeds 1000 mg 1-' 3 P. putida ingests carbohydrates and proteins. Therefore, if the bacterium is empolyed in microbial sensors, BOD biosensing can be conducted in the presence of high levels of As(V). To our knowledge, microbial sensors have not yet' been studied regarding the use of resistant microorganisms. The use of such microorganisms is advantageous because long-term sensor stability can be envisaged, since other microorganisms hardly contaminate a microbial sensor when the latter is continuously used in a medium containing toxic substances; such contamination frequently causes serious problems in the operation of microbial sensors.6