In this article, we present the design, fabrication and characterization of a microfluidic device and a dedicated electronic system to perform 8 multiplexed electrochemical measurements of synthetic miRNA strands, as well as the biochemical protocols developed for the functionalization of the electrodes and the quantification experiments. The outcomes of this work highlight that the parallelization of eight microchannels containing 2-electrode cells driven by the dedicated electronics offers a solution as robust as a conventional 3-electrode cell and commercially available potentiostats. In addition, this solution presents the advantage of simultaneously reduce the microfabrication complexity, as well as offering an integrated; multiplexed and portable system for the quantification of miRNA. The results presented demonstrate that the system shows a linear response on concentrations down to 10⁻¹⁸ mol/L of perfect matched reporter and capture sequences of synthetic miRNA.

In this manuscript, a pyroelectrically-charged flexible polydimethylsiloxane (PDMS) piezoelectret force sensor is reported. The proposed pyroelectric charge trapping approach supports low power operation, small footprint, uniform charge distribution, and chip-scale integration for recharging capability. Various flexible porous PDMS membranes (150 mm in diameter, ~100 µm-thick) are fabricated using a water-in-PDMS emulsion technique for controlled pore size (0.6 – 142 µm) and their piezoelectric coefficients are measured to be 70–170 pC/N, representing increases of 100% to 450% after charging. Finally, the charged membranes were used as a pressure sensor array, allowing the recording of a human step.

Texture detection is one of the essential features requested for artificial tactile sensing to push the demand for flexible low-cost tactile sensors in the robotics sector. In this manuscript, we demonstrate the ability of a ferroelectret-based pressure sensor together with a patterned elastomer layer to detect surface textures. The ferroelectret sensor was fabricated using fluorinated ethylene propylene (FEP) sheets bonded with a patterned adhesive layer to create cavities, integrated with the elastomer bumped surface, and finally charged using a pyroelectric method developed by our group. The ferroelectret-based sensor showed a linear response to the applied force in the range of 0.5 to 2 N, a piezoelectric coefficient of 150.1 ± 3.2 pC/N in the range of 10–80 Hz, and a flat dynamic response in the range of 10–1000 Hz. The tactile sensing characterization of the sensor, performed at different scanning speeds (10 to 30 mm/s) and gratings with different periodicities (0 to 0.8 mm), showed that the fundamental frequencies observed ranged from 12 Hz to 75 Hz, as expected from the model. These results lay the foundation for the adoption of such sensors in different applications that need fine tactile information, such as an autonomous or teleoperated robotic hand, prostheses, and wearable devices.

In this article, a pyroelectrically charged fluorinated ethylene propylene (FEP) piezoelectret force sensor is reported. The proposed pyroelectric charging technique provides reproducible and tunable charge generation. Pyroelectric charging is simple and compact when compared to other ferroelectret charging methods, such as corona discharge and dielectric barrier discharge and irradiation, which require high-voltage sources, sharp tips, and vacuum setups. In this pyroelectric charging study, temperature ramp rates of 1 °C/s ( dT $=15^{\circ }\text{C}$ ), 2 °C/s ( dT $=30^{\circ }\text{C}$ ), and 4 °C/s ( dT $= 60\,\,^{\circ }\text{C}$ ) are applied to a lithium niobate pyroelectric crystal using a programmable temperature control system. The effects of the temperature ramp applied to the pyroelectric crystal and the number of temperature ramps on the piezoelectret charging are assessed. The pyroelectrically charged FEP piezoelectrets show ${d}_{{33}}$ piezoelectric coefficients up to 68.6 pC/N. The output of the FEP sensors is linear with the force and independent of frequency in the range of 45–505 Hz. The charge retention was assessed, showing no degradation of the piezoelectric activity up to 66 h. Finally, the FEP ferroelectret sensors were used in a pressure sensor array, allowing the recording of a human step (gait analysis experiment).

The growing demand for continuous cardiac signal monitoring has propelled the development of highly sensitive flexible sensors with reduced power requirements. Proposed flexible ferroelectrets/piezoelectrets are voided polymers that can be polarized/poled, acquiring a piezoelectric behavior that is suited for sensing applications. Here, ferroelectret preparation was achieved by laser-patterning of an adhesive-coated polypropylene (PP) spacer with low Young’s modulus, resulting in improved piezoelectric coefficient while avoiding high-temperature thermal bonding between the different ferroelectret layers. The spacer pattern and thickness were optimized and compared to a suitable analytical model. The optimized piezoelectret showed a low compressive modulus (~300 kPa), a maximum dynamic piezoelectric coefficient d ₃₃ = 81 ± 5 pC/N and a quasi-static piezoelectric coefficient of ~8552 pC/N. In the short term, the sensors were stable in a wide range of temperature and relative humidity, but after 70 days at room temperature the d ₃₃ decreased to ~36 % of the initial value. Finally, the optimized ferroelectret device was demonstrated in the measurement of the human pulse and extraction of cardiovascular parameters (heart rate and carotid-femoral pulse wave velocity).

Magnetic sensor systems integrate a sensing element and magnetic field generators to determine their relative position or to measure movement. Typically, the magnetic fields are produced by permanent magnets, which have high intensity but are hard to machine into custom shapes. However, novel solutions using magnetic polymer composites (MPCs) have emerged as field generators due to their low cost, weight and patterning freedom. Here, we present a finite element model developed in COMSOL Multiphysics that allows the design of complex magnetization patterns on these polymer composites, taking into account the geometries of the parts and the magnetic properties of the materials employed. The model, together with the characterization protocol of the materials, has proved to be capable of predicting the magnetization of polymer composites at different temperatures. In addition, the model incorporates the properties of the magnets used during the magnetization process, such as the size, shape and magnetization, as well as the properties of the surrounding elements. This new model facilitates the design of new polymeric parts with complex shapes and magnetization patterns that can be employed as field generators in magnetic sensing systems.