Advanced Sensor Research最新文献

A new hybrid ultrasound luminescent chemical imaging technique is described along with a pH sensor to image chemical concentrations at the surface of implanted medical devices. The purpose is to detect and study local biochemistry during infection. The sensor comprises a mechanoluminescent film (SrAl₂O₄:Eu, Dy microphosphors embedded in a biocompatible polymer film) and a pH indicator dye. A focused ultrasound beam generates green luminescence at the ultrasound focal point. By pulsing the ultrasound ON and OFF, the modulated luminescence can be distinguished from persistent luminescence, for high spatial resolution imaging. A red fluorescent dye and the pH indicator dye bromothymol blue are added to the coating to modulate the red-light transmittance via pH dependent absorbance. Acidosis is observed as an increase in red luminescence intensity in spectroscopy and imaging. The films are sensitive to biologically relevant changes in pH (6.0–8.0) and can be imaged through optically scattering media to mimic tissue. The images have a knife edge spatial resolution of ≈3 mm through optically scattering phantoms, limited by the focused ultrasound spot size. This novel technique may permit the elucidation of implant infection at the implant surface and can be further developed for the measurement of other relevant chemical species in the future.

In this work, cost-effective and do-it-yourself capacitive pressure sensors are fabricated using readily available commercial components. The sensors are created in a single-step process -by simply applying electrically conductive paint onto both sides of a porous melamine sponge. These sensors exhibit a wide-range pressure sensing capability, spanning from 10 Pa to 100 kPa. The sensors showcase an impressively low limit of detection, detecting pressures as low as 10 Pa, and exhibit a moderate response time of 123 ms. Moreover, the sensors display remarkable repeatability and stability over 10 000 loading and unloading cycles without experiencing fatigue. Notably, these exceptional qualities come at an exceptionally low material cost, with the sensor measuring 20 × 20 × 2 mm. To showcase their potential applications, the fabricated sensors are successfully employed in real-time human motion detection, proximity detection, and wearable keyboard applications.

Sensors, functioning as primary conveyors of perceptual data, stand ready to illuminate the landscape of the intelligent era. Barium titanate, an exceedingly pivotal class of ferroelectric materials for sensor applications, has attracted considerable attention from both commercial and industrial sectors in recent years. Against this backdrop, this paper embarks on a comprehensive examination of sensors founded upon barium titanate across a spectrum of applications. Our investigation commences with a historical analysis of ferroelectric materials, with a specific emphasis on the developmental trajectory of barium titanate. Subsequently, an in-depth exposition elucidates the attributes and manufacturing processes linked to barium titanate materials, providing readers with insight into the structural and manufacturing aspects of these materials. Ultimately, we introduce a diverse array of sensors tailored to distinct functions within a myriad of domains.

Citrate is a key metabolite and nutrient in humans. Its level is associated with many diseases from tumor growth to bone diseases. Detection of citrate has relied on its high negative charge, metal chelating properties and as an enzyme substrate. In this work, the capture-selection method is used to isolate DNA aptamers for citrate. After 18 rounds of selection, a highly converged library is obtained and the first two sequences reached 99.6% of the library. Using the most abundant sequence named CA1, thioflavin T fluorescence spectroscopy and isothermal titration calorimetry show dissociation constants of 7.4 and 4.4 µm citrate, respectively. CA1 does not require sodium for binding but requires 1.0 mm magnesium. Among the tested carboxylate molecules, only citrate can bind to the aptamer. A light-up fluorescence strand displacement biosensor is developed and it can detect citrate in simulated urine with a detection limit of 1.1 µm. This short 42-nucleotide aptamer can be readily adapted to other types of sensing mechanisms for the detection of citrate.

Epidermal electronics that can monitor physiological signals such as surface electromyogram (sEMG) signals attract widespread attentions in personalized healthcare, human–machine interfaces (HMI) and virtual/augmented reality (AR/VR). However, conventional electromyographic electrodes suffer from skin discomfort, susceptibility to motion artifact interference, and short service lifetime. Here, an organohydrogel-based sEMG electrode endows with high conductivity, low modulus and long-term stability is developed by doping partially reduced graphene oxide (pRGO) into highly cross-linked organohydrogel network. The as-fabricated polyacrylamide/sodium alginate/tannic acid/partially reduced graphene oxide (PAM/SA/TA/pRGO) organohydrogel possesses farewell conductivity (4.22 S m⁻¹) while preserving tissue-like compliance (Young's modulus ≈32 KPa), excellent stretchability (≈600%), high adhesion as well as superior anti-drying properties. In addition, a stretchable sEMG electrode for long-term reliable service is fabricated via immobilizing the organohydrogel electrodes onto a flexible very high bond (VHB) substrate. As a result, the integrated electrodes show high signal-to-noise ratio (SNR) (35.15 db) comparable to that of the commercial electrodes. Furthermore, with assistance of deep learning, the proposed sEMG electrodes obtain high identification accuracy of 97.11% in distinguishing sophisticated gestures. This system can be further exploited for real-time tele-operations and offers broad prospects in human–machine immersive interactive application.

As an important branch of modern science and technology, flexible sensor combines the functions of traditional sensors with the characteristics of flexible materials to meet the needs of modern electronic devices for lightweight, flexible and wearable characteristics. However, flexible sensors are faced with problems such as poor stability and weak anti-interference ability in extreme environments. Here, a strategy of combining thermoplastic polyurethane and conductive carbon black is adopted to obtain conductive elastic film with good conductivity and excellent mechanical properties (TPU@CB film). TPU@CB film exhibits very good mechanical strength (8 MPa). When TPU@CB film is assembled into a sensor, it exhibits wide detection range (600%), low detection limit (0.05%) and short response time (15 ms). Notably, the TPU@CB film demonstrates clear detection capabilities for both ECG and EMG signals of the human body when utilized as an electrode patch. Thanks to lithography, TPU@CB film is machined into strain gauge shape. TPU@CB strain gauge achieves a high signal-to-noise ratio and can detect a wide range of frequency vibrations from 0 to 900 Hz, as well as accurately detect the speed of the motor. This provides a feasible way to promote the development of flexible electronics.

The visible light localization system holds great promise as a highly accurate indoor positioning method. However, it still suffers deficiencies including high latency and power consumption, and large area cost. To address these issues, a high energy efficient spiking localization system inspired by the biological spatial representation system is presented. This system utilizes an optical neuromorphic sensor, consisting of a compact NbO_x-based threshold switching memristor and a photoresistor. The key lies in the system's ability to convert analog light information into electrical spikes, resembling the behavior of sensory neurons, which enables the encoding of light illuminance through spiking frequency. Consequently, the system achieves high uniformity, high linearity (≈10%), and high sensitivity (≈1.1 kHz Lux⁻¹ and ≈72.7 kHz cm⁻¹ for light illuminance and distance detection, respectively), indicating its potential suitability for visible light localizations. By leveraging a spiking neural network classifier, the system successfully distinguishes locations with different illuminances. After 150 epochs, it achieves an accuracy of 97%, showcasing the feasibility of using the spiking localization system in real-world applications. The approach of spike-based light positioning is a leap forward toward the development of future compact, highly energy-efficient visible light localization systems.

Flexible pressure sensors employing porous polymer materials are renowned for their superior sensing capabilities, attributed to the inherently low stiffness of porous polymers. The practical utilization of such sensors hinges on the development of a straightforward, cost-effective, and patternable method for preparing porous polymer materials. In this research, a novel laser thermoforming process is introduced to craft a porous Polydimethylsiloxane (PDMS) film, leveraging carbon black (CB) as an endothermic agent and glucose as a porogen. The resulting porous PDMS film serves as the foundation for a remarkably sensitive flexible piezoresistive sensor. Owing to the inherent flexibility endowed by the porous structure, the porous PDMS-based pressure sensor achieves a remarkable sensitivity of 109.4 kPa⁻¹ within 0–200 Pa, an effective measurement span of 0–100 kPa, rapid response and recovery times of 79 and 55 ms, and impressive stability over 5000 cycles. The sensor's utility extends to applications such as human pulse monitoring, Morse coding, and robot claw sensing, underscoring its promise in the realm of flexible electronics. In summary, the laser thermoforming process realizes the one-step, economical, and patternable preparation of porous polymer materials, and introduces a novel avenue for the realization of high-performance flexible sensors based on thermally cured porous polymers.

Capacitive pressure sensors based on porous foams have been demonstrated for various biomedical applications (0–10 kPa). Many different methods for fabricating porous foams have been reported. In this work, for the first time, the incorporation of silica nanoparticles are reported into the templating process of porous foams fabricated through a combination of particle and emulsion templating, in order to enhance the formation of smaller microstructures in polydimethylsiloxane foams. The foams are coated with graphene, and pressure sensors developed using these foams showed increased sensitivity, up to 4.08 kPa⁻¹. The incorporation of nanoparticles also improves the linearity of the sensitivity, giving a linear sensitivity for the pressure sensors over a pressure range of 0–6 kPa. Further, these pressure sensors have a low limit of detection of ≈13 Pa. These results indicate that incorporation of suitable nanoparticles in the templating of foams is a promising strategy for developing foam-based pressure sensors with high and linear sensitivity.

Epidermal electronics is an emerging wearable platform that involves attaching deformable forms of devices to the skin. Epidermal electrodes represent a vital component of this technology, as they provide a direct electronic interface with the skin for sensing and stimulation. However, most of the current electrodes are built on non-permeable elastomer substrates, which can limit their long-term, continuous operations in a non-invasive manner. Fortunately, recent advancements in conductive materials and fabrication techniques have enabled high-performance epidermal electrodes that are comfortable to wear. In order to track the latest progress, this review article first introduces the designs of permeable structures and the preparation of conductive electrodes. The subsequent discussion elaborates on effective strategies to achieve desirable properties, such as high conductivity, stretchability, skin adhesion, and biocompatibility. The emerging applications of permeable epidermal electrodes are also summarized. Finally, this review concludes with the current challenges and future directions of breathable epidermal electrodes.