Sensor Response Research Articles

A sensing material-free and simple readout MEMS sensor for detecting helium

Abstract In this work, we report a method that enables a standard electrostatic MEMS device to perform complex sensing functionalities, such as detecting the presence of helium without a sensing material or a conditioning circuit. Helium is a noble, odorless, non-reactive gas that is very challenging to detect. It is used in critical applications such as storing nuclear fuel waste inside a dry cask. In these applications, its leakage from the dry cask may indicate the cask's safe operation's degradation. A departure from the common practice of exciting the MEMS around its mechanical resonance, the method is based on exciting the MEMS around its electrical resonance circuit. This method shows that the tiny difference between the air dielectric constant (1.00059) and helium (1.000067) corresponding to only a few Femtofarad level capacitances produces a 25 mV difference without a conditioning circuit. Simulation results confirmed those findings and explored the sensor response at different operation conditions. This method eliminates the need for a heated microstructure and the need for absorption material. This method is not limited to gas sensing. It can be applied to other sensing mechanisms, such as acceleration and pressure measurements, and eliminate the complex circuit to read small capacitance in these applications.

A Rhodamine-Based Ratiometric Fluorescent Sensor for Dual-Channel Visible and Near-Infrared Emission Detection of NAD(P)H in Living Cells and Fruit Fly Larvae.

The detection and dynamic monitoring of intracellular NAD(P)H concentrations are crucial for comprehending cellular metabolism, redox biology, and their roles in various physiological and pathological processes. To address this need, we introduce sensor A, a near-infrared ratiometric fluorescent sensor for real-time, quantitative imaging of NAD(P)H fluctuations in live cells. Sensor A combines a 3-quinolinium electron-deficient acceptor with a near-infrared rhodamine dye, offering high sensitivity and specificity for NAD(P)H with superior photophysical properties. In its unbound state, sensor A emits strongly at 650 nm and weakly at 465 nm upon 400 nm excitation. Upon binding to NAD(P)H, it shows a fluorescence increase at 465 nm and a decrease at 650 nm, enabling accurate ratiometric measurements. Sensor A also exhibits ratiometric upconversion fluorescence when excited at 800 or 810 nm, offering additional flexibility for different experimental setups. The sensor's response relies on the reduction of the 3-quinolinium acceptor by NAD(P)H, forming a 1,4-dihydroquinoline donor that enhances fluorescence at 465 nm and quenches the near-infrared emission at 650 nm through photoinduced electron transfer. This mechanism ensures high sensitivity and reliable quantification of NAD(P)H levels while minimizing interference from sensor concentration, excitation intensity, or environmental factors. Sensor A was validated in HeLa and MD-MB453 cells under various metabolic and pharmacological conditions, including glucose and maltose stimulation and treatments with chemotherapeutic agents. Co-localization with mitochondrial-specific dyes confirmed its mitochondrial targeting, enabling precise tracking of NAD(P)H fluctuations. In vivo imaging of Drosophila larvae under nutrient starvation or chemotherapeutic exposure revealed dose-dependent fluorescence responses, highlighting its potential for tracking NAD(P)H changes in live organisms. Sensor A represents a significant advancement in NAD(P)H imaging, providing a powerful tool for exploring cellular metabolism and redox biology in biomedical research.

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

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

A Large Voltage Responsivity Pyroelectric Sensor Based on Hot-Pressed Lead Zirconate Titanate Ceramic

In this article, hot-pressed PZT ceramics were used as a sensitive element material and made into a pyroelectric chip. Three current mode sensors were fabricated using a pyroelectric chip of different thicknesses (80 μm, 40 μm, and 30 μm). The voltage responsivity of sensors reached the order of magnitude of 105. The size effect resulting from varying the thickness was studied. The results indicate that as the thickness decreases, the performance significantly increases. When the modulation frequency is 10 Hz, the specific detectivity of the sensor with a 30 μm PZT ceramic pyroelectric chip reaches 5.3 × 108 cm·Hz1/2/W.

Ppb-Level Self-Calibrating Ozone Detection Using a T-Type Multipass Enhanced Photoacoustic Sensor with a 9.46 μm Quantum Cascade Laser.

A sensitive, real-time, and accurate ozone (O3) sensor system is developed based on the combination of multipass enhanced photoacoustic (MPPA) and direct multipass absorption spectroscopy with a mid-infrared quantum cascade laser (QCL). The QCL with an emission wavelength of 9.46 μm was used to probe the O3 absorption lines without interference from the absorption of water and carbon dioxide in the flowing mixtures. The MPPA sensor was constructed with a T-type cell composed of a vertical cylinder and a horizontal cavity which were designed as an acoustic resonator and for multipass absorption enhancement, respectively. By periodically on-off switching the modulation of the laser wavelength, rapidly switched measurements of direct absorption and PA spectra can be achieved for real-time and accurate calibrations of the second harmonic (2f) PA signals with the direct absorbance spectra of O3. Moreover, a detection limit of O3 of 6 ppb at an average time of 300 s was achieved, and a short sensor response time of 16 s was also obtained in the flow mixtures with a flow rate of 50 sccm. This work provides a reliable method for O3 detection with capabilities of parts-per-billion-level sensitivity and on-site real-time concentration calibration, thus holding promise for in situ ozone monitoring under various environments.

Copper-Substituted Calcium Orthophosphate (CaxCu1-x)HPO4.nH2O for Humidity Detection

Calcium orthophosphate material (Ca1-xCux)HPO4.nH2O (0.4 ≤ x ≤ 1) with the gradual replacement of Ca2+ with Cu2+ ions were synthesized by a chemical precipitation technique. Samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Then, the prepared powders were deposited onto an alumina substrate with interdigitated Pt electrodes by the spin coating method and polyvinyl alcohol (PVA) as a binder. Successively, the sensors were investigated from 0% to 90% at room temperature under various conditions, including humidity, nitrogenous oxide, methane, carbon dioxide and ammonia. The results evidenced that at 90% RH, the sensitivity of sensors significantly increased with the increase in the Cu content. Moreover, the sensors exhibited good repeatability and, after 1 year of aging, the sensor response was equal to 34% that of the freshly prepared sensor. Finally, there was no interference in the presence of other gases (nitrogenous oxide 2.5 ppm, methane 10 ppm, carbon dioxide 500 ppm and ammonia 4 ppm).

Fully printed field-effect transistor humidity sensor with chitosan/polyvinyl alcohol/nano carbon powder for enhanced moisture sensitivity.

With the advancement of flexible electronics, the demand for low-cost, high-performance flexible humidity sensors for wearable devices has increased significantly. However, commercial humidity sensors require complex preparation methods and are expensive. Therefore, we report polyvinyl alcohol/chitosan/nano carbon powder (PVA/CS/NCP) humidity-sensitive composite materials, which were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and contact angle measurements. A resistive humidity sensor was fabricated using screen printing, and the device showed a good response at 33%RH-98%RH humidity, and at 98% RH, the sensor achieved a response of 1.74. A fully printed field-effect transistor (FET) humidity sensor was prepared by integrating an ion gel transistor with a CS/PVA/NCP humidity-sensitive resistor to improve the response. The comparison reveals a significant improvement in the FET humidity sensor's response, reaching 6.27at 98% RH. In addition, both types of sensors exhibit less hysteresis and good repeatability. Lastly, we tested the constructed humidity sensors under non-contact and variable breathing conditions, laying the groundwork for future wearable applications.

Enhanced ammonia gas sensing response of Al-hyperdoped black silicon sensor at room temperature

Enhanced ammonia gas sensing response of Al-hyperdoped black silicon sensor at room temperature

Deformation energy facilitated high response and low temperature operation of NO2 sensor using branched nanorods of Bi2S3

Deformation energy facilitated high response and low temperature operation of NO2 sensor using branched nanorods of Bi2S3

Dynamic monitoring and characteristic analysis of a long-span operational bridge from high-rate sensor responses using RAAVMD approach

Dynamic monitoring and characteristic analysis of a long-span operational bridge from high-rate sensor responses using RAAVMD approach

Adaptive sensor placement selection and response reconstruction for bridge structural health monitoring

Abstract Bridge structural health monitoring (SHM) measures the real-time responses of bridges via instrumented sensors. This paper focuses on the bridge displacement reconstruction at unmeasured locations of interest (LoIs) using measurements from sensors. Increasing the number of sensors on the bridge can capture more structural information. However, considering the complex structure and scale of bridges, minimizing the number of sensors and selecting the critical sensing locations (CSL) to place sensors for measurements are significant in bridge SHM. To achieve efficient bridge SHM under limited number of sensors, this paper proposes an adaptive sensor selection and reconstruction neural network (ASSRNN) for determining the CSLs and reconstructing at all LoIs. In particular, a novel adaptive location selection mechanism (ALSM) as well as a unified network model and its learning process is proposed. In the experiments, the proposed model is validated based on a real-world case study of a long-span bridge in California, USA. Through the comparison of different sensor placement schemes. The experimental results show that the proposed model is effective and accurate in reconstructing the structural displacement responses via adaptive sensor selection for bridge SHM.

A scalable and autoclavable oxygen nanosensor platform for metabolic monitoring of Saccharomyces cerevisiae in a bioreactor and other in situ systems.

Polymer-encapsulated dye nanoparticle sensors are a valuable approach to achieving in situ analyte measurements with luminescence; however, typical emulsion-based nanosensors are poorly suited for large-scale biological samples due to limitations of synthesis scalability and stability. Branched polyethylenimine (PEI) is a versatile polymer scaffold ideal for constructing nanoparticles with various covalently conjugated moieties due to their high density of reactive primary amines, high water solubility, and biological stability. In this work, we used branched polyethylenimine as a scaffold-based approach for making a stable and scalable ratiometric oxygen sensor. Pt (II) tetracarboxyporphine was usedas an oxygen-sensing dye and coumarin 343 as a reference dye, all covalently linked to the PEI scaffold producing a product that could withstand sterilization procedures and easily be scaled. To minimize toxicity from the PEI scaffold, we conjugated it with 2000MW PEG.Theapplicability of the sensors was demonstratedin a 200mL Saccharomyces cerevisiae yeast culture, using orthogonal luminescent and electrochemical oxygen measurements to validate sensor response and measure the metabolic activity of the yeast in our culture. This approach was able to match the sensitivity of our electrochemical measurements while improving upon drawbacks of other luminescent methods of oxygen detection, demonstrating effective monitoring for at least 20h. Our scaffold-based approach is a modular and easily translatable technology that could be useful in various biotechnological applications.

Interfacial Engineering Facilitates Real-Time Detection of Dual Hazardous Gases at ppb Levels via Single-Step Hydrothermal Nanoarchitectonics of Self-Assembled PbSnS/SnO2 Heterostructures.

Next-generation real-time gas sensors are crucial for detecting multiple gases simultaneously with high sensitivity and selectivity. In this study, ternary metal sulfide (PbSnS)-incorporated metal oxide (SnO2) heterostructures were synthesized via a one-step hydrothermal method. Characterizations such as X-ray diffraction, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy confirmed the successful formation of PbSnS/SnO2 heterostructures. Subsequently, thin films based on PbSnS/SnO2 heterostructures were fabricated and employed for the detection of real-time dual hazardous oxidizing gases at room temperature. The sensor response for NO2 gas was found to be 1.04 at 25 parts per billion (ppb) with a limit of detection (LOD) of 18.17 ppb, while for O3 gas, the sensor response was 1.03 at 15 ppb with an LOD of 7.34 ppb. Moreover, high selectivity for detecting two oxidizing gases in real time by using differential analysis of the gas sensing curve has been reported. Furthermore, density functional theory calculations corroborated the sensing mechanism, elucidating that the Pb atom in PbSnS/SnO2 is primarily responsible for the adsorption of NO2 gas, whereas SnO2 in PbSnS/SnO2 is responsible for the adsorption of O3 gas. These findings demonstrate the potential of PbSnS/SnO2 heterostructures for advanced gas sensing applications, offering insights into their fundamental sensing mechanisms.

Pyridinium surfactants can modulate the UV response of methyl green dye‐doped polymeric films for sensor development

AbstractConcerns about ultraviolet radiation (UV‐R) are increasing due to climate change. The effects of UV‐R on living organisms depend on exposure duration and intensity, making it crucial to monitor UV‐R levels. In this study, we investigated the role of surfactants as photosensitizing or stabilizing agents in a colorimetric sensor based on a polymeric film doped with methyl green dye. The films were synthesized using the casting technique from a filmogenic solution containing either carboxylated polyvinyl alcohol (P1) or hydroxylated polyvinyl alcohol (P2). We evaluated the impact of surfactant structure (dodecylpyridinium chloride, C12; hexadecylpyridinium chloride, C16; or sodium dodecyl sulfate, SDS) and concentration on the colorimetric response of the films to UV‐R. Color changes were monitored using the CIELab system. The results showed that, under UV‐R exposure for up to 5 h, films without surfactants did not lose their blue hue (negative b* parameter in CIELab). While SDS stabilized the dye in the polymeric matrix, films containing pyridinium surfactants (C12 or C16) changed color from blue to pale yellow (positive b* parameter in CIELab). The color change, which was modulated by surfactant concentration, was attributed to radical reactions involving the pyridinium surfactants, influenced by their hydrophobicity and the polymer structure. These results represent a significant advancement in colorimetric sensors for UV‐R, as they allow for the modulation of the sensor's response time through surfactant concentration in the polymeric film.

BiOI: Self‐Powered Humidity Sensor and Breath Monitor

AbstractThe self‐powered, adaptable, quick, and precise humidity sensors are required to measure humidity in the microenvironment. Here, a simple one‐step wet chemical method is presented to prepare stacked layered bismuth oxyiodide (BiOI) nanoplates. The remarkable response and self‐powered behavior of BiOI nanoplates‐based humidity sensors are demonstrated for the first time. The humidity sensing characteristics of BiOI are examined within the range of 30–80% relative humidity (RH) at an operating temperature of 323 K. The highest sensitivity level of 39 kΩ per %RH is determined for a relative humidity of 75.5%. A successful attempt is made to use this sensor as a human breathing process monitor. The sensor response times at room temperature in this test are 3.04(9) s at 0 V and 3.31(7) s at 20 V, whereas the recovery times are estimated to be 6.57(6) s at 0 V and 6.42(4) s at 20 V. Future advancements in sensing devices utilizing BiOI hold the potential to yield highly responsive, ultrafast sensors with simplified device geometries, and self‐powered.

CuO Nanowire Humidity Sensors Enhanced by Au Nanostructure Prepared on TSV Substrate

Abstract The authors studied the growth of cupric oxide nanowires (CuO NWs) on through-silicon via (TSV) substrates and the subsequent fabrication of humidity sensors utilizing these CuO NWs. We also explored the effect of annealing gold nanoparticles (Au NPs) deposited on CuO NWs through sputtering with varying thicknesses of the Au film (1–5 nm) to enhance the humidity response. The morphology and crystallography of both CuO NWs and Au NPs were characterized using multi-function environmental field-emission scanning electron microscopy and X-ray diffraction techniques. The results indicate that the resistance of the CuO NWs increased with increasing relative humidity, attributed to the p-type conductivity of CuO. Adding the Au NPs further augmented the humidity response. Interestingly, an increase in the initial thickness of the Au film led to a proportional increase in the average diameter of the annealed Au NPs, ranging from 11 to 31 nm for Au film thicknesses of 1–5 nm. Notably, the sample with 11 nm Au NP/CuO NWs exhibited superior sensor response compared to the samples of other thicknesses.

Photocatalytic Organic Semiconductor-Bacteria Imprinted Polymers for Highly Selective Determination of Staphylococcus aureus at the Single-Cell Level.

This work utilized a combination of photocatalytic organic semiconductors and bacteria to create a photocatalytic organic semiconductor-bacterial biomixture system based on a bacteria imprinted polymers (OBBIPs-PEC) sensor, for the detection of S. aureus with high sensitivity in "turn-on" mode at the single-cell level. This outstanding sensor arises from an integration of two different types of semiconductor materials to form heterojunctions. As well this sensor involves combining a semiconductor material with cationic side chains and an electron transport chain within a natural cellular environment, in which the cationic side chain of poly(fluorene-co-phenylene) organic semiconductor at 2-(4-mesyl-2-nitrobenzoyl)-1,3-cyclohexanedione (PFP-OC@MNC) demonstrated the ability to penetrate the cell membrane of S. aureus and interact with specific binding sites through electrostatic interactions. As the cavities in the BIPs were occupied by S. aureus, during light irradiation, the electrons stimulated by the photoexcitation process in the manufactured PFP-OC@MNC semiconductors were successfully transmitted to S. aureus, where these electrons played a role in the regeneration of NADH and FADH2, and then the presence of S. aureus acted as a proficient electron acceptor for photoexcited electrons; thereby the PEC response of the OBBIPs-PEC sensor was significantly enhanced. Of note, it exhibited high selectivity for S. aureus over other bacteria and maintained excellent performance in complex matrices, distinguishing S. aureus with concentrations as low as 10 CFU/mL. This work dramatically reduces the influence of interference factors in the traditional mode and offers a powerful way for microorganism detection in food and environmental fields.

Home-based Waste Monitoring System using Internet of Things with Fuzzy Logic Method

The accumulation of waste in certain locations, especially in residential areas, due to the continuous accumulation of waste can cause environmental disturbances such as disease and unpleasant odors. This system is designed to find out whether the trash bin is full or not by applying fuzzy logic, if the status of the trash bin can be cleaned, it will be handled immediately so that the waste does not accumulate and disturb people around. This system can find out when the last time the waste was taken and the location of the trash bin as a prototype which can later be applied to areas with a wider range by cleaning service officers in Mamuju City. This system uses the HC-SR04 sensor to detect the distance of the waste to the sensor and uses the Load Cell sensor to detect the weight of the waste. Several tests were carried out, first by measuring the accuracy of each sensor used, the HC-SR04 sensor accuracy was obtained at 96.68% with an error of 3.32%. While the accuracy of the load cell sensor is 90.68% with an error of 9.32%. The second test calculates the sensor response time and Blynk notification response since the sensor detects waste, the average HC-SR04 sensor detection response is around 0.83 seconds. For the response time of incoming notifications when there is movement in the HC-SR04 sensor area has an average of 2.65 seconds. While the Load Cell sensor response time is only around 0.53 seconds. For Blynk notification response time since the Load Cell sensor detects it has an average of 2.51 seconds. The third test calculates the response time of the two sensors (HC-SR04 and Load Cell) and the Blynk notification response since the two sensors detected the waste, the average response time of the two sensors finished detecting only around 0.91 seconds. For the response time of the trash bin status condition, if there is movement in the area of the two sensors, the condition of the trash bin will change and display the status of Normal, Needs Cleaning and Highly Needs Cleaning with an average response time of 1.18 seconds. The system successfully sends notifications according to the fuzzy rules and expected to speed up the waste handling process

Sensorized laparoscopic surgical grasper with integrated capacitive force sensor for robot-assisted minimally invasive surgery

PurposeThis paper aims to introduce a sensorized surgical grasper with a novel flexible capacitive tactile force sensor integrated within the surgical grasper for minimally invasive surgery (MIS) and robot-assisted MIS (RMIS) procedures.Design/methodology/approachThe proposed sensor offers a unique configuration of sensing electrodes with one top excitation electrode and three bottom electrodes enabling the measurement of normal and shear forces without incorporating any complex decoupling algorithms. The design of the sensor is optimized using finite-element method simulations, ensuring efficiency and reliability.FindingsExperimental validation, real-time sensor response and application in lump detection through stiffness assessment demonstrate the decoupled force response (0–5 N normal range and 0–2 N shear range) with high sensitivity 0.0124/N, repeatability and hysteresis response with 5.65% and 4.7% errors respectively.Originality/valueThe compact design of the sensor makes it compliant with surgical graspers and therefore enhances the overall efficiency of robotic surgical procedures. The sensorized surgical grasper is fabricated using conventional machining and rapid prototyping techniques, presenting a cost-effective solution for adoption.

MOX Nanosensors to Detect Colorectal Cancer Relapses from Patient's Blood at Three Years Follow-Up, and Gender Correlation.

Colorectal cancer represents 10% of all the annual tumors diagnosed worldwide, being often not timely diagnosed, because its symptoms are typically lacking or very mild. Therefore, it is crucial to develop and validate innovative low-invasive techniques to detect it before becoming intractable. To this aim, a device equipped with nanostructured gas sensors has been employed to detect the airborne molecules of blood samples collected from healthy subjects, and from colorectal cancer affected patients at different stages of their pre- and post-surgery therapeutic path. Data was scrutinized by using statistical standard techniques to highlight their statistical differences, and through principal component analysis and support vector machine to classify them. The device was able to readily distinguish between the pre-surgery blood samples (i.e., taken when the patient had cancer), and the ones up to three years post-surgery (i.e., following the tumor removal) or the ones from healthy subjects. Finally, the correlation of the sensor responses with the patient/healthy subject's gender was investigated, resulting negligible. These results pave the path toward a clinical validation of this device to monitor the patient's health status by detecting possible relapses, to parallel to clinical follow-up protocols.