Flexible Force Sensor Based on a PVA/AgNWs Nanocomposite and Cellulose Acetate.

Nanocomposites are materials of special interest for the development of flexible electronic, optical, and mechanical devices in applications such as transparent conductive electrodes and flexible electronic sensors. These materials take advantage of the electrical, chemical, and mechanical properties of a polymeric matrix, especially in force sensors, as well as the properties of a conductive filler such as silver nanowires (AgNWs). In this work, the fabrication of a force sensor using AgNWs synthesized via the polyol chemical technique is presented. The nanowires were deposited via drop-casting in polyvinyl alcohol (PVA) to form the active (electrode) and resistive (nanocomposite) sensor films, with both films separated by a cellulose acetate substrate. The dimensions of the resulting sensor are 35 mm × 40 mm × 0.1 mm. The sensor shows an applied force ranging from 0 to 3.92 N, with a sensitivity of 0.039 N. The sensor stand-off resistance, exceeding 50 MΩ, indicates a good ability to detect changes in applied force without an external force. Additionally, studies revealed a response time of 10 ms, stabilization of 9 s, and a degree of hysteresis of 1.9%. The voltage response of the sensor under flexion at an angle of 85° was measured, demonstrating its functionality over a prolonged period. The fabricated sensor can be used in applications that require measuring pressure on irregular surfaces or systems with limited space, such as for estimating movement in robot joints.

Quantification of hCG Hormone Using Tapered Optical Fiber Decorated with Gold Nanoparticles.

In this study, a novel technique for the quantification of the human chorionic gonadotropin (hCG) hormone using localized surface plasmons and a tapered optical fiber decorated with gold nanoparticles (Au-NPs) is reported. The tapered optical fiber fabrication process involves stretching a single-mode optical fiber using the flame-brushing system. The waist of the tapered optical fiber reaches a diameter of 3 µm. Decoration of the taper is achieved through the photodeposition of 100 nm Au-NPs using the drop-casting technique and a radiation source emitting at 1550 nm. The presence of the hCG hormone in the sample solutions is verified by Fourier-transform infrared spectroscopy (FTIR), revealing the presence of bands related to functional groups, such as C=O (1630 cm-1), which are associated with proteins and lipids, components of the hCG hormone. Quantification tests for hormone concentrations were carried out by measuring the optical power response of the tapered optical fiber with Au-NPs under the influence of hCG hormone concentrations, ranging from 1 mIU/mL to 100,000 mIU/mL. In the waist of the tapered optical fiber, the evanescent field is amplified because of localized surface plasmons generated by the nanoparticles and the laser radiation through the optical fiber. Experimental results demonstrated a proportional relationship between measured radiation power and hCG concentration, with the optical power response decreasing from 4.45 mW down to 2.5 mW, as the hCG hormone concentration increased from 1 mIU/mL up to 100,000 mIU/mL. Furthermore, the spectral analysis demonstrated a spectral shift of 14.2 nm with the increment of the hCG hormone concentration. The measurement system exhibits promising potential as a sensor for applications in the biomedical and industrial fields.

Effect of Chitosan Nanoparticles Incorporating Antioxidants from Salvia hispanica L. on the Amaranth Flour Films.

Research background: Amaranth (Amaranthus hypochondriacus) flour produces films with excellent barrier properties against water vapor, allowing food preservation, but the mechanical properties are poor compared to synthetic films. One strategy to improve these properties is the incorporation of nanoparticles. The particles can also serve as a vehicle for the addition of antioxidant agents into the films. The objective of this work is to optimize the formulation for the preparation of amaranth flour films treated with antioxidant chia (Salvia hispanica L.) extract-loaded chitosan particles using response surface methodology (RSM). Experimental approach: Chitosan nanoparticles with the extract were synthesized by ionic gelation, and the films were made by the casting method. Three independent variables were assigned: amaranth flour (4-6%), glycerol (25-35%) and chitosan nanoparticles loaded with the chia extract (0-0.75%). We then evaluated the physical (thickness), mechanical (tensile strength, Young´s modulus and elongation), barrier (water vapor permeability, moisture and water solubility) and antioxidant properties of the films. The experimental results of the properties were analyzed using a Box-Behnken experimental design generating 15 runs with three replicates at the central point. Results and conclusions: Second and third order polynomial models were obtained from the ANOVA analysis of the evaluated responses, and high coefficients of determination were found (0.91-1.0). The water vapor permeability of the films was 0.82-2.39·10-7 (g·mm)/(Pa·s·m2), tensile strength was 0.33-1.63 MPa and antioxidant activity 2.24-5.65%. The variables had different effects on the films: glycerol negatively affected their properties, and the permeability values increased with increased amaranth flour content. The nanoparticles improved the mechanical, barrier and antioxidant properties of the films compared to the films without nanosystems. The optimal formulation was 4% amaranth flour, 25% glycerol and 0.36% chitosan nanoparticles. The optimized films had better mechanical (1.62 MPa) properties, a low water vapor permeability value (0.91·10-7 (g·mm)/(Pa·s·m2)) and moderate antioxidant activity (6.43%). Novelty and scientific contribution: The results show the effect of chitosan nanoparticles on the properties of amaranth flour films for the first time. The resulting equations are useful in the design of food packaging.

Monitoring the Growth of a Microbubble Generated Photothermally onto an Optical Fiber by Means Fabry-Perot Interferometry.

In the present paper, we show the experimental measurement of the growth of a microbubble created on the tip of a single mode optical fiber, in which zinc nanoparticles were photodeposited on its core by using a single laser source to carry out both the generation of the microbubble by photothermal effect and the monitoring of the microbubble diameter. The photodeposition technique, as well as the formation of the microbubble, was carried out by using a single-mode pigtailed laser diode with emission at a wavelength of 658 nm. The microbubble's growth was analyzed in the time domain by the analysis of the Fabry-Perot cavity, whose diameter was calculated with the number of interference fringes visualized in an oscilloscope. The results obtained with this technique were compared with images obtained from a CCD camera, in order to verify the diameter of the microbubble. Therefore, by counting the interference fringes, it was possible to quantify the temporal evolution of the microbubble. As a practical demonstration, we proposed a vibrometer sensor using microbubbles with sizes of 83 and 175 µm as a Fabry-Perot cavity; through the time period of a full oscillation cycle of an interferogram observed in the oscilloscope, it was possible to know the frequency vibration (500 and 1500 Hz) for a cuvette where the microbubble was created.

Tapered Optical Fiber Functionalized with Palladium Nanoparticles by Drop Casting and Laser Radiation for H₂ and Volatile Organic Compounds Sensing Purposes.

A comparative study on the sensing properties of a tapered optical fiber pristine and functionalized with the palladium nanoparticles to hydrogen and volatile organic compounds (VOCs), is presented. The sensor response and, response/recovery times were extracted from the measurements of the transient response of the device. The tapered optical fiber sensor was fabricated using a single-mode optical fiber by the flame-brushing technique. Functionalization of the optical fiber was performed using an aqueous solution of palladium chloride by drop-casting technique assisted for laser radiation. The detection principle of the sensor is based on the changes in the optical properties of palladium nanoparticles when exposed to reducing gases, which causes a variation in the absorption of evanescent waves. A continuous wave laser diode operating at 1550 nm is used for the sensor characterization. The sensor functionalized with palladium nanoparticles by this technique is viable for the sensing of hydrogen and VOCs, since it shows an enhancement in sensor response and response time compared to the sensor based on the pristine optical microfiber. The results show that the fabricated sensor is competitive with other fiber optic sensors functionalized with palladium nanoparticles to the hydrogen.

Optical fiber sensor based on localized surface plasmon resonance using silver nanoparticles photodeposited on the optical fiber end.

This paper reports the implementation of an optical fiber sensor to measure the refractive index in aqueous media based on localized surface plasmon resonance (LSPR). We have used a novel technique known as photodeposition to immobilize silver nanoparticles on the optical fiber end. This technique has a simple instrumentation, involves laser light via an optical fiber and silver nanoparticles suspended in an aqueous medium. The optical sensor was assembled using a tungsten lamp as white light, a spectrometer, and an optical fiber with silver nanoparticles. The response of this sensor is such that the LSPR peak wavelength is linearly shifted to longer wavelengths as the refractive index is increased, showing a sensitivity of 67.6 nm/RIU. Experimental results are presented.

3D printed needleless injector based on thermocavitation: analysis of impact and penetration depth in skin phantoms in a repetitive regime.

A global issue that requires attention is the duality between the shortage of needles for regular vaccination campaigns and the exponential increase in syringe and needle waste from such campaigns, which has been exacerbated by the COVID-19 pandemic. In response to this problem, this study presents a 3D printed needleless injector based on thermocavitation. The work focused on investigating the interaction of the resulting liquid jets with skin phantoms at different concentrations (1-2%), emphasizing their impact and penetration depth in a repetitive regime. The injector was designed and fabricated from a semi-transparent polymer using a high-resolution 3D printer, allowing the ejection of liquid jets with velocities up to ~ 73 m/s. The impact of these jets on skin phantoms was evaluated using a high-speed camera. After 6 consecutive liquid jets (1% concentration), a maximum penetration depth of ~ 2.5 mm was achieved, delivering approximately 4.7 µL. For the highest concentration (2.0%) and the same number of shots, the penetration depth was reduced to ~ 0.6 mm with a delivered volume of ~ 0.7 µL. An important finding of this study is that the liquid jet with the highest pressure does not cause the maximum penetration depth, but is the result of a series of successive shots. In addition, the velocity and shape of the ejected jet are determined by the amount of solution and the meniscus formed inside the injector. These findings advance the development of precise and efficient thermocavitation-based injectors with broad potential applications in medical and pharmaceutical fields.