Protein-Based Flexible Moisture-Induced Energy-Harvesting Devices As Self-Biased Electronic Sensors

Abstract

Thin protein films of gelatin molecules grown on flexible substrates have been utilized to fabricate moisture-induced energy-harvesting devices, which work as self-biased sensors. Adsorbed water molecules from ambient moisture generate protons inside the film. A proton transfer path is formed through the hydrogen-bonded water molecules with protein around 55% relative humidity condition, and the protons are transferred due to the gradient of absorbed water molecules within the protein films. The devices are capable of harvesting electric power up to 5.5 μW/ cm 2 with an induced voltage of 0.71 V. Our findings not only provide a futuristic clean power generation concept from protein film as flexible power generator but also demonstrate the use of the energy-harvesting devices as self-biased electronic sensors for various flexible and wearable applications. The devices showed exceptional performance as humidity sensors and have been used for flexible healthcare applications, such as continuous monitoring of breathing pattern and lateral mapping of moisture levels at the finger tip for monitoring the wound healing process. Nevertheless, the diode-like response of the devices with humidity has been found to be suitable as a self-biased humidity-controlled electronic switch.

Moisture‐Enabled Electricity Generation: From Physics and Materials to Self‐Powered Applications

“…Some biomaterials including proteins nanowires and biological nanofibers of cellulose, chitin, silk fiboin, and amyloid have been developed to enable the generation of electricity in a moist environment. [40,90]…”

“…An electrical power of up to 5.5 µW cm −2 with an induced voltage of 0.71 V can be generated under a RH of 90%. [40] As polymers have been widely used in sensing, energy storage, information storage, and packaging engineering, future studies of moisture-induced electricity generators can be focused on the design, construction, and application of devices with hybrid functionalities. [187][188][189][190] For example, polymeric electrolytes exhibit ionic conductivity and can be used to construct energy storage devices such as supercapacitors.…”

“…This is necessary when an electronic component having high power consumption is first switched on (Figure 16b). [40,186] By connecting MEGs to memristors, the generators can also be used in self-powered information storage systems. An application of breath-powered reading was reported by Zhao et al, using a GO-based write-once-read-many memory in a self-powered word display.…”

“…For example, thin biodegradable protein films of gelatin, derived from collagen taken from animal body parts, can easily absorb water molecules from humidity because they contain a high concentration of amino acids with functional groups like –NH 2 , and –COOH. [ 40 ] Protons can be generated within the protein film from self‐ionization of water molecules and are then transferred through a conducting path formed by hydrogen‐bonded water molecules on the gelatin macromolecules (Figure 13i). An electrical power of up to 5.5 µW cm −2 with an induced voltage of 0.71 V can be generated under a RH of 90%.…”

“…Over the past 5 years, these processes have been used in MEGs to harvest electrical energy from moisture or water vapor in graphene, [ 38 ] carbon black (CB), [ 29 ] metallic oxide nanowires, [ 39 ] and a range of proteins. [ 40 ] The output power density in these devices is typically ≤1 mW cm −2 . Power outputs at this level facilitate the establishment of self‐powered systems for applications in healthcare, [ 39 ] environmental monitoring, [ 41 ] and smart tracking.…”