Superhydrophobic, stretchable kirigami pencil-on-paper multifunctional device platform.

Wearable electronics with applications in healthcare, human-machine interfaces, and robotics often explore complex manufacturing procedures and are not disposable. Although the use of conductive pencil patterns on cellulose paper provides inexpensive, disposable sensors, they have limited stretchability and are easily affected by variations in the ambient environment. This work presents the combination of pencil-on-paper with the hydrophobic fumed SiO2 (Hf-SiO2) coating and stretchable kirigami structures from laser cutting to prepare a superhydrophobic, stretchable pencil-on-paper multifunctional sensing platform. The resulting sensor exhibits a large response to NO2 gas at elevated temperature from self-heating, which is minimally affected by the variations in the ambient temperature and relative humidity, as well as mechanical deformations such as bending and stretching states. The integrated temperature sensor and electrodes with the sensing platform can accurately detect temperature and electrophysiological signals to alert for adverse thermal effects and cardiopulmonary diseases. The thermal therapy and electrical stimulation provided by the platform can also deliver effective means to battle against inflammation/infection and treat chronic wounds. The superhydrophobic pencil-onpaper multifunctional device platform provides a low-cost, disposable solution to disease diagnostic confirmation and early treatment for personal and population health.

A single-film fiber optical sensor for simultaneous measurement of carbon dioxide and relative humidity.

Colorimetric measurement is a versatile, low-cost method for bio-/chemical sensing and that has importance in biomedical applications. General carbon dioxide (CO2) sensors based on colorimetric change of a pH indicator report only one parameter at a time and are cross-sensitive to relative humidity (RH). This work describes a novel optical fiber sensor with a thin film on the distal end of the fiber, combining colorimetric measurement and a white light Fabry-Pérot interferometer (FPI) for the simultaneous measurement of CO2 and RH. The CO2 sensitive dye ion-pair: thymol blue and tetramethylammonium hydroxide are encapsulated inside organically modified silica forming an extrinsic FPI cavity (refractive index of 1.501 ± 0.02 and thickness of 5.83 ± 0.09 µm). The sensor reversibly responds to 0-6% CO2 and 0-90% RH with negligible cross-sensitivity and allows measurement of both parameters simultaneously. A sensitivity of ∼0.19 nm/%RH is obtained for RH measurement based on the wavelength shift of the FPI and there is a polynomial correlation between the average intensity of selected wavelengths and the concentration of CO2. The applicability of the sensor is demonstrated by measuring the CO2 and RH exhaled from human breath with a percent error of 3.1% and 2.2% respectively compared to a commercial datalogger. A simulation model is provided for the dye-encapsulated FPI sensor allowing simulation of spectra of sensors with different film thicknesses.

Effect of Peak Tracking Methods on FBG Calibration Derived by Factorial Design of Experiment.

We present a calibration procedure for a humidity sensor made of a fiber Bragg grating covered by a polyimide layer. FBGs being intrinsically sensitive to temperature and strain, the calibration should tackle three variables, and, therefore, consists of a three-variable, two-level factorial design tailored to assess the three main sensitivities, as well as the five cross-sensitivities. FBG sensing information is encoded in the reflection spectrum from which the Bragg wavelength should be extracted. We tested six classical peak tracking methods on the results of the factorial design of the experiment applied to a homemade FBG humidity sensor. We used Python programming to compute, from the raw spectral data with six typical peak search algorithms, the temperature, strain and humidity sensitivities, as well as the cross-sensitivities, and showed that results are consistent for all algorithms, provided that the points selected to make the computation are correctly chosen. The best results for this particular sensor are obtained with a 3 dB threshold, whatever the peak search method used, and allow to compute the effective humidity sensitivity taking into account the combined effect of temperature and strain. The calibration procedure presented here is nevertheless generic and can thus be adapted to other sensors.

Multi-Parameter Sensing in a Multimode Self-Interference Micro-Ring Resonator by Machine Learning.

A universal multi-parameter sensing scheme based on a self-interference micro-ring resonator (SIMRR) is proposed. Benefit from the special intensity sensing mechanism, the SIMRR allows multimode sensing in a wide range of wavelengths but immune from frequency noise. To process the multiple mode spectra that are dependent on multiple parameters, we adopt the machine learning algorithm instead of massive asymptotic solutions of resonators. Employing the proposed multi-mode sensing approach, a two-parameter SIMRR sensor is designed. Assuming that two gases have different wavelength dependence of refractive indices, the feasibility and effectiveness of the two-parameter sensing strategy are verified numerically. Moreover, the dependence of parameter estimation accuracy on the laser intensity noises is also investigated. The numerical results indicate that our scheme of multi-parameter sensing in a multimode SIMRR holds great potential for practical high-sensitive sensing platforms compared with the single-mode sensing based on whispering gallery mode (WGM) resonators.

Combined Long-Period Fiber Grating and Microcavity In-Line Mach-Zehnder Interferometer for Refractive Index Measurements with Limited Cross-Sensitivity.

This work discusses sensing properties of a long-period grating (LPG) and microcavity in-line Mach-Zehnder interferometer (µIMZI) when both are induced in the same single-mode optical fiber. LPGs were either etched or nanocoated with aluminum oxide (Al2O3) to increase its refractive index (RI) sensitivity up to ≈2000 and 9000 nm/RIU, respectively. The µIMZI was machined using a femtosecond laser as a cylindrical cavity (d = 60 µm) in the center of the LPG. In transmission measurements for various RI in the cavity and around the LPG we observed two effects coming from the two independently working sensors. This dual operation had no significant impact on either of the devices in terms of their functional properties, especially in a lower RI range. Moreover, due to the properties of combined sensors two major effects can be distinguished-sensitivity to the RI of the volume and sensitivity to the RI at the surface. Considering also the negligible temperature sensitivity of the µIMZI, it makes the combination of LPG and µIMZI sensors a promising approach to limit cross-sensitivity or tackle simultaneous measurements of multiple effects with high efficiency and reliability.

Implementation of Simultaneous Multi-Parameter Monitoring Based in LC-Type Passive Wireless Sensing with Partial Overlapping and Decoupling Coils.

Inductor-capacitor (LC) passive wireless sensors are widely used for remote sensing. These devices are limited in applications where multiparameter sensing is required, because of the mutual coupling between neighboring sensors. This article presents two effective decoupling techniques for multiparameter sensing, based on partially overlapped sensors and decoupling coils, which, when combined, reduce the mutual coupling between sensors to near zero. A multiparameter LC sensor prototype with these two decoupling mechanisms has been designed, simulated, and measured. This prototype is capable of simultaneously measuring four parameters. The measurements demonstrate that the changes in capacitance in one individual sensor do not affect the measurements of the other sensors. This principle has been applied to simultaneous wear sensing using four identical wear sensors.

3D-Printing Techniques on the Development of Multiparameter Sensors Using One FBG.

We report the development of a fiber Bragg grating (FBG) sensor for multiparameter sensing using only one FBG. The FBG was half-embedded in a 3D-printed structure, which resulted in a division of the grating spectrum creating two peaks with different sensitivities with respect to different physical parameters. A numerical analysis of the proposed technique was performed using the coupled-mode theory with modified transfer matrix formulation. Then, experimental analyses were performed as function of temperature, strain and force, where the peaks showed different sensitivities in all analyzed cases. Such results enable the application of a technique for simultaneous measurement of multiple physical parameters using both peaks and the full width half maximum of the FBG embedded in a 3D structure. In the simultaneous multiparameter assessment, the proposed sensor system was able to estimate the three tested parameters (strain, temperature and force) with relative errors as low as 4%.

Multiparameter Sensing of Oxygen and pH at Biological Interfaces via Hyperspectral Imaging of Luminescent Sensor Nanoparticles.

Chemical dynamics in biological samples are seldom stand-alone processes but represent the outcome of complicated cascades of interlinked reaction chains. In order to understand these processes and how they correlate, it is important to monitor several parameters simultaneously at high spatial and temporal resolution. Hyperspectral imaging is a promising tool for this, as it provides broad-range spectral information in each pixel, enabling the use of multiple luminescent indicator dyes, while simultaneously providing information on sample structures and optical properties. In this study, we first characterized pH- and O2-sensitive indicator dyes incorporated in different polymer matrices as optical sensor nanoparticles to provide a library for (hyperspectral) chemical imaging. We then demonstrate the successful combination of a pH-sensitive indicator dye (HPTS(DHA)3), an O2-sensitive indicator dye (PtTPTBPF), and two reference dyes (perylene and TFPP), incorporated in polymer nanoparticles for multiparameter chemical imaging of complex natural samples such as green algal biofilms (Chlorella sorokiniana) and seagrass leaves (Zostera marina) with high background fluorescence. We discuss the system-specific challenges and limitations of our approach and further optimization possibilities. Our study illustrates how multiparameter chemical imaging with hyperspectral read-out can now be applied on natural samples, enabling the alignment of several chemical parameters to sample structures.

Ultrasensitive and Self-Powered Multiparameter Pressure-Temperature-Humidity Sensor Based on Ultra-Flexible Conductive Silica Aerogel.

The application of silica aerogel has been limited because of its poor mechanical properties. In order to expand the application scope of silica aerogel, this study fabricated an ultra-flexible conductive silica aerogel as a multiparameter sensor. The sample is fabricated by introducing poly (3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) on a base of ultra-flexible silica aerogel, which was prepared by a diene synthesis reaction at atmospheric pressure. The pressure, temperature, and humidity can be converted into electrical signals. The pressure sensitivity can reach up to 54.88 kPa-1, and the detection limit is as low as 5 Pa. The temperature resolution is up to 0.1 K, and the response time of humidity is within 4 s. More importantly, the developed multiparameter sensor can be self-powered to realize multiparameter sensing of pressure, temperature, and humidity. The ultra-flexible conductive silica aerogel is a promising candidate for monitoring human activities and fire-affected areas.