Flexible Humidity Sensor with High Sensitivity and Durability for Respiratory Monitoring Using Near-Field Electrohydrodynamic Direct-Writing Method

Abstract

The humidity of breath can serve as an important health indicator, providing crucial clinical information about human physiology. Significant progress had been made in the development of flexible humidity sensors. However, improving its humidity sensing performance (sensitivity and durability) is still facing many challenges. In this work, near-field electrohydrodynamic direct writing (NFEDW) was proposed to fabricate humidity sensors with high sensitivity and durability for respiration monitoring. Due to the applied electric field, dense carbon nanotube/cellulose nanofiber (CNT/CNF) networks formed during the printing process that enhance the sensitivity of the sensor. The prepared sensor showed excellent humidity responses, with a maximum response value of 61.5% (ΔR/R 0 ) at 95% relative humidity (RH). Additionally, the sensitivity film prepared by the NFEDW method closely fits the poly(ethylene terephthalate) (PET) substrate, endowing the sensor with outstanding bending (with a maximum curvature of 4.7 cm −1 ) and folding durability (up to 50 times). The sensitivity of the prepared sensor under different simulated conditions, namely, nose breathing, mouth breathing, coughing, yawning, breath holding, and speaking, was excellent, demonstrating the potential of the sensor for the real-time monitoring of human breath humidity. Thus, the high-performance flexible humidity sensor is suitable for human respiration and health monitoring.

Design of Ti3C2Tx/SnO2-Selective Ethanolamine Sensor

“…This is because the unfavorable reaction originated from the exposed Ti atoms on Ti 3 C 2 T x and the dissolved oxygen molecules in ambient air. 51 Ti 3 C 2 T x nanostructure is easily oxidized and degraded under aerobic or humidity conditions. Consequently, we further explore the humidity sensitivity of the Ti 3 C 2 T x /SnO 2 sensor by exposing the sensor to 100 ppm of EA at different relative humidity (38−83% RH).…”

“…As shown in Figure a, as the relative humidity increases, the EA response decreases from 20 to 4.5. We assumed that water molecules occupy the active sites on Ti 3 C 2 T x /SnO 2 , and Ti 3 C 2 T x /SnO 2 nanocomposites even begin to degrade at high humidity, resulting in lower response values. ,− Furthermore, we investigated the baseline resistance/response value of the sensor with an increase in humidity (Figure S4). At first, as the relative humidity increases, the baseline resistance value and response value to EA gradually decrease.…”

Multi-layered micro-patterns co-printed with Ag@CuO nano-ink for flexible devices

“…For this reason, most of the laser energy absorbed by the copper oxide particles on the upper layer was transmitted to the silver layer, which increased the rate of sintering, and 1CuO@2Ag was completely solidified. In addition, according to previous studies [33][34][35][36], copper oxide can absorb up to 90% of the laser energy and reflects only 10% of the laser energy. However, if the silver layer was printed as the upper layer, most of the laser energy was reflected, as shown in figures 3(a) and (b).…”

Flexible Humidity Sensor Based on a Graphene Oxide–Carbon Nanotube-Modified Co3O4 Nanoparticle-Embedded Laser-Induced Graphene Electrode

“…Humidity sensors employ various working mechanisms and are capable of generating multiple physical signals. With respect to distinct measurement techniques, humidity sensors can be classified into a range of types, including resistive, − capacitive, − impedance, , and voltage. , Traditional humidity sensors are predominantly constructed on rigid substrates, resulting in limited comfort during use and inability to adapt to surfaces with complex geometries. , The emergence of flexible and soft electronic technology in recent years has revolutionized the wearable applications, giving rise to flexible humidity sensors that cater to novel requirements like breath monitoring …”