Ingestible, Biofriendly, and Flexible Flour-Based Humidity Sensors with a Wide Sensing Range

Abstract

Ecofriendly and biofriendly materials are highly appealing in electronic devices with the booming development of the Internet of Things. Humidity sensors perform an indispensable role in various fields such as monitoring industry processes and living systems. In this contribution, for the first time, edible and abundant material-flour has been introduced to the sensing layers for humidity detection. The ionic conductive K 2 CO 3 and hygroscopic glycerol (Gly) with biosafety were introduced to the sensing layer to promote a humidity sensing capability and longtime stability. The ingestible Gly-K 2 CO 3 flour-based humidity sensor using PLA as substrates displays an excellent sensing performance and wide humidity detecting range. Good linearity between capacitance and relative humidity (RH) has been achieved for the RH range from 6% to 94%. According to a wireless monitoring system, even at 250 kHz, the sensor can still monitor the nuance of the humidity difference between 40% and 43% and exhibited an ultrafast response time (0.3 s) and recovery time (0.7 s). Furthermore, the consistent and stable sensing performance after long-time measurements for 100 days and bending tests for 500 cycles also demonstrated a long-time humidity detecting stability and mechanical flexibility for the Gly-K 2 CO 3 flour-based humidity sensor. Humidity sensing mechanisms were thoroughly investigated through SEM-EDX, FTIR, XPS, and complex impedance spectroscopies. The enhanced sensing performance, wide humidity detecting range, and long-time stability are attributed to the ionic conductivity from K 2 CO 3 and the hydrogen-bond interaction between H 2 O and enormous hydrophilic groups, such as hydroxyl and amino groups in the flour-based networks and binary solvent.

In Situ All‐Weather Humidity Visualization by Using a Hydrophilic Sponge

“…[ 1–5 ] The different application scenarios need different monitoring techniques, for example, for earth humidity monitoring, such remote techniques as microwave, millimeter, and terahertz (THz), should be employed to provide all‐weather observations of the atmosphere on a global basis; [ 6,7 ] while in human daily lives for such fields as food storage, concrete structures, the internet of things (IoT), electronic devices, respiration monitoring, disease diagnosis, and treatment, the humidity monitoring and evaluating require the sensitive materials with the features of short response and recovery times, as well as diverse‐configuration compatibility, that can meet the spatial and temporal humidity gradients measurements. [ 8–15 ] To date, many efforts have been performed for the fabrication of sensitive materials, including metal oxides, ceramics, perovskites, carbon compounds, and organic polymers, to realize high‐performance humidity monitoring. [ 16–20 ] However, the complicated steps for device construction, the low flexibility, as well as the extreme dependence on external energy‐supply systems or coupled circuits, have obstructed to some extent the broad application of these reported sensor devices.…”

Thermally Degradable Inductors with Water-Resistant Metal Leaf/Oleogel Wires and Gelatin/Chitosan Hydrogel Films

“…Some ingestible sensors have shown a pH response on a sugar-based substrate, and a dietary sensor that attaches to food with silk has been reported . Edible materials have also been utilized for colorimetric indicators, flour-based humidity sensors, or chewing-gum-based personalized healthcare monitors …”

“…34 Some ingestible sensors have shown a pH response on a sugar-based substrate, 19 and a dietary sensor that attaches to food with silk has been reported. 35 Edible materials have also been utilized for colorimetric indicators, 36 flour-based humidity sensors, 37 or chewing-gum-based personalized healthcare monitors. 38 For the communications components, previous research has focused on inductors with harmless materials, such as gold leaf, 19 copper, 21 magnesium, 22,23 and zinc/iron, 24 gallium/ indium inductors with hydrogels for near-field communications, 25 or silk/Au-based split ring resonators.…”

Photoacid-Loaded Nanopores of Hollow Mesoporous Organosilica Capsules for Fluorescent Humidity Sensing

“…Fast and robust humidity sensing has wide applications in research, medical, and industrial scenes. − Among the abundant diversity of strategies, the mainstream of reported strategies for humidity sensing is electronic-based sensing. The impedance, , capacitance, voltage, or current signals of a semiconductor can be slightly affected by water vapor in ambient air, which poses fundamental principles of electronic-based humidity sensors. Taking advantage of the ultra-sensitive detection of electronic signals, the electronic-based humidity sensing exhibits excellent sensitivity, fast response, and recovery.…”