Surface Acoustic Wave Resonator Chip Setup for the Elimination of Interfering Conductivity Responses

A surface acoustic wave (SAW) resonator chip setup is presented that eliminates interfering signal responses caused by changes in the electrical environment of the surrounding media. When using a two-port resonator, applying electrically shielding layers between the interdigital transducers (IDTs) can be challenging due to the limited dimensions. Therefore, a layered setup consisting of an insulating polymer layer and a conductive gold layer was preferred. The SAW resonators were provided with polycarbonate housings, resulting in SAW resonator chips. This setup enables easy application of a wide range of coatings to the active part of the resonator surface, while ensuring subsequent electrical and fluidic integration of the resonator chips into a microfluidic array for measurements. The signal responses of uncoated SAW resonators and those with polymer coatings with and without a gold layer were tested with aqueous potassium chloride (KCl) solutions up to 3 mol/L, corresponding to conductivities up to 308 mS/cm. The use of a polymer coating at the thickness of the first Love mode resonance and a conductive gold layer completely reduced the electrical impact on the SAW resonator signal response, making small signals resulting from changes in viscosity and density of the KCl solutions visible.

A Liquid Crystal-Modulated Metastructure Sensor for Biosensing

In this paper, a liquid crystal-modulated metastructure sensor (MS) is proposed that can detect the refractive index (RI) of a liquid and change the detection range under different applied voltages. The regulation of the detection range is based on the different bias states of the liquid crystal at different voltages. By changing the sample in the cavity that is to be detected, the overall electromagnetic characteristics of the device in the resonant state are modified, thus changing the position of the absorption peaks so that different RI correspond to different absorption peaks, and finally realizing the sensing detection. The refractive index unit is denoted as RIU. The range of the refractive index detection is 1.414-2.828 and 2.121-3.464, and the corresponding absorption peak variation range is 0.8485-1.028 THz and 0.7295-0.8328 THz, with a sensitivity of 123.8 GHz/RIU and 75.6 GHz/RIU, respectively. In addition, an approach to optimizing resonant absorption peaks is explored, which can suppress unwanted absorption generated during the design process by analyzing the energy distribution and directing the current flow on the substrate. Four variables that have a more obvious impact on performance are listed, and the selection and change trend of the numerical values are focused on, fully considering the errors that may be caused by manufacturing and actual use. At the same time, the incident angle and polarization angle are also included in the considered range, and the device shows good stability at these angles. Finally, the influence of the number of resonant rings on the sensing performance is also discussed, and its conclusion has guiding value for optimizing the sensing demand. This new liquid crystal-modulated MS has the advantages of a small size and high sensitivity and is expected to be used for bio-detection, sensing, and so on. All results in this work were obtained with the aid of simulations based on the finite element method.

Smart Superhydrophobic Textiles Utilizing a Long-Range Antenna Sensor for Hazardous Aqueous Droplet Detection plus Prevention

This paper demonstrates the feasibility of a long-range antenna sensor embedded underneath a liquid repellent fabric to be employed as a wearable sensor in personal protective fabrics. The sensor detects and monitors hazardous aqueous liquids on the outer layer of fabrics, to add an additional layer of safety for professionals working in hazardous environments. A modified patch antenna was designed to include a meandering-shaped resonant structure, which was embedded underneath the fabric. Superhydrophobic fabrics were prepared using silica nanoparticles and a low-surface-energy fluorosilane. 4 to 20 μL droplets representing hazardous aqueous solutions were drop-cast on the fabrics to investigate the performance of the embedded antenna sensor. Long-range (S₂₁) measurements at a distance of 2-3 m were performed using the antenna sensor with treated and untreated fabrics. The antenna sensor successfully detected the liquid for both types of fabrics. The resonant frequency sensitivity of the antenna sensor underneath the treated fabric exhibiting superhydrophobicity was measured as 370 kHz/μL, and 1 MHz/μL for the untreated fabric. The results demonstrate that the antenna sensor is a good candidate for wearable hazardous aqueous droplet detection on fabrics.

Determination of blood glucose parameter from human blood serum by using a quartz crystal microbalance sensor coated with phthalocyanines compounds

Determining the blood glucose level is important for the prevention and treatment of diabetes mellitus. We developed a sensor system using Quartz Crystal Microbalance (QCM) to determine the blood glucose level from human blood serum. This study consists of two experimental stages: artificial glucose/pure water solution tests and human blood serum tests. In the first stage of the study, the QCM sensor with the highest performance was identified using artificial glucose solution concentrations. In the second stage of the study, human blood serum measurements were performed using QCM to determine blood glucose levels. QCM sensors were coated with phthalocyanines (Pcs) by jet spray method. The blood glucose values of 96 volunteers, which ranged from 71 mg/dL to 329 mg/dL, were recorded. As a result of the study, human glucose values were determined with an average error of 3.25%.

Mobile Acoustic Wave Platform Deployment in the Amazon River: Impact of the Water Sample on the Love Wave Sensor Response

This paper presents an experimental platform allowing in situ measurement in an aqueous medium using an acoustic Love wave sensor. The aim of this platform, which includes the sensor, a test cell for electrical connections, a microfluidic chip, and a readout electronic circuit, is to realize a first estimation of water quality without transportation of water samples from the field to the laboratory as a medium-term objective. In the first step, to validate the ability of such a platform to operate in the field and in Amazonian water, an isolated and difficult-to-access location, namely, the floodplain Logo Do Curuaï in the Brazilian Amazon, was chosen. The ability of such a platform to be transported, installed on site, and used is discussed in terms of user friendliness and versatility. The response of the Love wave sensor to in situ water samples is estimated according to the physical parameters of Amazonian water. Finally, the very good quality of the acoustic response is established, potential further improvements are discussed, and the paper is concluded.

Exploiting Direct Laser Writing for Hydrogel Integration into Fragile Microelectromechanical Systems

The integration of chemo-responsive hydrogels into fragile microelectromechanical systems (MEMS) with reflective surfaces in the micron to submicron range is presented. Direct laser writing (DLW) for 3D microstructuring of chemoresponsive "smart" hydrogels on sensitive microstructures is demonstrated and discussed in detail, by production of thin hydrogel layers and discs with a controllable lateral size of 2 to 5 µm and a thickness of some hundred nm. Screening results of polymerizing laser settings for precision microstructuring were determined by controlling crosslinking and limiting active chain diffusion during polymerization with macromers. Macromers are linear polymers with a tunable amount of multifunctional crosslinker moieties, giving access to a broad range of different responsive hydrogels. To demonstrate integration into fragile MEMS, the gel was deposited by DLW onto a resonator with a 200 nm thick sensing plate with high precision. To demonstrate the applicability for sensors, proof of concept measurements were performed. The polymer composition was optimized to produce thin reproducible layers and the feasibility of 3D structures with the same approach is demonstrated.

An LC Wireless Microfluidic Sensor Based on Low Temperature Co-Fired Ceramic (LTCC) Technology

This work reports a novel wireless microfluidic biosensor based on low temperature co-fired ceramic (LTCC) technology. The wireless biosensor consists of a planar spiral inductor and parallel plate capacitor (LC) resonant antenna, which integrates with microchannel bends in the LTCC substrate. The wireless response of the biosensor was associated to the changes of its resonant frequency due to the alteration in the permittivity of the liquid flow in the microchannel. The wireless sensing performance to different organic liquids with permittivity from 3 to 78.5 was presented. The measured results are in good agreement with the theoretical calculation. The wireless detection for the concentration of glucose in water solution was investigated, and an excellent linear response and repeatability were obtained. This kind of LC wireless microfluidic sensor is very promising in establishing wireless lab-on-a-chip for biomedical and chemical applications.

Rapid Liquid Recognition and Quality Inspection with Graphene Test Papers

Electronic tongue is widely applied in liquid sensing for applications in various fields, such as environmental monitoring, healthcare, and food quality test. A rapid and simple liquid-sensing method can greatly facilitate the routine quality tests of liquids. Nanomaterials can help miniaturize sensing devices. In this work, a broad-spectrum liquid-sensing system is developed for rapid liquid recognition based on disposable graphene-polymer nanocomposite test paper prepared through ion-assisted filtration. Using this liquid-sensing system, a number of complex liquids are successfully recognized, including metal salt solutions and polymer solutions. The electronic tongue system is especially suitable for checking the quality of the foodstuff, including soft drinks, alcoholic liquor, and milk. The toxicants in these liquids can be readily detected. Furthermore, the novel material-structure design and liquid-detection method can be expanded to other chemical sensors, which can greatly enrich the chemical information collected from the electrical response of single chemiresistor platform.

Potential of Piezoelectric MEMS Resonators for Grape Must Fermentation Monitoring

In this study grape must fermentation is monitored using a self-actuating/self-sensing piezoelectric micro-electromechanical system (MEMS) resonator. The sensor element is excited in an advanced roof tile-shaped vibration mode, which ensures high Q-factors in liquids (i.e., Q ~100 in isopropanol), precise resonance frequency analysis, and a fast measurement procedure. Two sets of artificial model solutions are prepared, representing an ordinary and a stuck/sluggish wine fermentation process. The precision and reusability of the sensor are shown using repetitive measurements (10 times), resulting in standard deviations of the measured resonance frequencies of ~0.1%, Q-factor of ~11%, and an electrical conductance peak height of ~12%, respectively. With the applied evaluation procedure, moderate standard deviations of ~1.1% with respect to density values are achieved. Based on these results, the presented sensor concept is capable to distinguish between ordinary and stuck wine fermentation, where the evolution of the wine density associated with the decrease in sugar and the increase in ethanol concentrations during fermentation processes causes a steady increase in the resonance frequency for an ordinary fermentation. Finally, the first test measurements in real grape must are presented, showing a similar trend in the resonance frequency compared to the results of an artificial solutions, thus proving that the presented sensor concept is a reliable and reusable platform for grape must fermentation monitoring.

New Scalable Approach toward Shape Memory Polymer Composites via "Spring-Buckle" Microstructure Design

Shape memory polymers (SMPs) have attracted tremendous research interest since their discovery. However, most advances in research of SMPs are based on molecular designs, i.e., "bottom-up" strategies. Due to the viscoelasticity of polymers, slow and incomplete shape variations are inevitable for most existing SMPs. Here, we propose a simple and scalable approach to design and fabricate SMP composites (SMPCs) based on a "spring-buckle" microstructure design. Specifically, a highly elastic "spring" is employed as a basic skeleton for the SMPCs, onto which self-adhesive and stimuli-responsive "buckles" are installed as reversible switch units. The resultant SMPCs with such "spring-buckle" microstructure enable quick programming at ambient temperature and ultrafast (2-3 s) and nearly complete (∼100%) shape recovery triggered by organic solvents, benefiting from a unique capillary effect. This structural approach provides a novel design philosophy for shape memory materials and opens up new opportunities for their applications in sensor, actuator, aerospace, and other applications.

Graphene-Elastomer Composites with Segregated Nanostructured Network for Liquid and Strain Sensing Application

One of the critical issues for the fabrication of desirable sensing materials has focused on the construction of an effective continuous network with a low percolation threshold. Herein, graphene-based elastomer composites with a segregated nanostructured graphene network were prepared by a novel and effective ice-templating strategy. The segregated graphene network bestowed on the natural rubber (NR) composites an ultralow electrical percolation threshold (0.4 vol %), 8-fold lower than that of the NR/graphene composites with homogeneous dispersion morphology (3.6 vol %). The resulting composites containing 0.63 vol % graphene exhibited high liquid sensing responsivity (6700), low response time (114 s), and good reproducibility. The unique segregated structure also provides this graphene-based elastomer (containing 0.42 vol % graphene) with exceptionally high stretchability, sensitivity (gauge factor ≈ 139), and good reproducibility (∼400 cycles) of up to 60% strain under cyclic tests. The fascinating performances highlight the potential applications of graphene-elastomer composites with an effective segregated network as multifunctional sensing materials.