Self-Powered Biosensors for Monitoring Human Physiological Changes

Abstract

Human physiological signals have an important role in the guidance of human health or exercise training and can usually be divided into physical signals (electrical signals, blood pressure, temperature, etc.) and chemical signals (saliva, blood, tears, sweat). With the development and upgrading of biosensors, many sensors for monitoring human signals have appeared. These sensors are characterized by softness and stretching and are self-powered. This article summarizes the progress in self-powered biosensors in the past five years. Most of these biosensors are used as nanogenerators and biofuel batteries to obtain energy. A nanogenerator is a kind of generator that collects energy at the nanoscale. Due to its characteristics, it is very suitable for bioenergy harvesting and sensing of the human body. With the development of biological sensing devices, the combination of nanogenerators and classical sensors so that they can more accurately monitor the physiological state of the human body and provide energy for biosensor devices has played a great role in long-range medical care and sports health. A biofuel cell has a small volume and good biocompatibility. It is a device in which electrochemical reactions convert chemical energy into electrical energy and is mostly used for monitoring chemical signals. This review analyzes different classifications of human signals and different forms of biosensors (implanted and wearable) and summarizes the sources of self-powered biosensor devices. Self-powered biosensor devices based on nanogenerators and biofuel cells are also summarized and presented. Finally, some representative applications of self-powered biosensors based on nanogenerators are introduced.

Keywords: biosensor; health monitoring; nanogenerator; self-powered.

Figure 1

Physical signals (electrical, blood pressure, temperature) and chemical signals (saliva, blood, tears, sweat) that can be collected from the human body. (Figure 1 made by Figdraw).

Figure 2

Wearable biosensors and implantable biosensors. (a) A stretchable wearable sensor for motion monitoring [45]. Copyright 2019 American Chemical Society. (b) A soft and breathable electronic skin that can be worn on the arm for volleyball catch statistics [46]. Copyright 2021 American Chemical Society. (c) A wristband for gesture recognition and full keyboard letter input [47]. Copyright 2022 Wiley Online Library. (d) An implantable pressure sensor based on a piezoelectric film to monitor blood pressure changes [48]. Copyright 2016, Elsevier. (e) An implantable endocardial pressure sensor for monitoring heart rate arrhythmias, ventricular fibrillation, and premature ventricular contractions [49]. Copyright 2019, Wiley Online Library. (f) A spiral organogel sensor implanted in the patellar ligament to monitor knee flexion frequency and angle [50]. Copyright 2022 American Chemical Society.

Figure 3

Biosensors with their characteristics. (a) A hydrogel sensor that can monitor pulse, with stretchable and self-healing characteristics, and a notch that can self-heal within 5 min after being cut [52]. Copyright 2017, American Chemical Society. (b) A stretchable TENG and energy storage composite energy system that can drive an electronic meter with energy derived from the human body [51]. Copyright 2016 American Chemical Society. (c) A TENG with shape adaptation that heals itself 1 min after being cut [53]. Copyright 2021, MDPI. (d) A biodegradable water-soluble TENG that degrades in water and the natural environment [54]. Copyright 2019, American Chemical Society. (e) A self-healing hydrogel that completes self-healing within 2.5 min after being cut at room temperature and can be used as a touch- and pressure-sensing e-skin [55]. Copyright 2016, Science. (f) A biodegradable TENG that degrades and is reabsorbed in vivo after completing its task [56]. Copyright 2022, Elsevier.

Figure 4

Use of a nanogenerator as an energy supply device. (a) A stretchable high-performance PENG that can power an electronic watch [61]. Copyright 2018, Elsevier. (b) A highly biocompatible electronic skin powered using a PENG [62]. Copyright 2021, American Chemical Society. (c) A nestable arch-shaped flexible TENG that can light up six LED bulbs [69]. Copyright 2020, American Chemical Society. (d) A wearable multifunctional TENG with a 10 cm × 10 cm area that can drive 944 LEDs [70]. Copyright 2019, Elsevier. (e) A wearable self-powered sensor that uses PyNG for energy supply [75]. Copyright 2017, Elsevier. (f) A hybrid nanogenerator that integrates frictional, piezoelectric, and thermoelectric power to harvest energy from wind and water vapor [76]. Copyright 2018, American Chemical Society.

Figure 5

Application scenarios for biofuel cells. (a) A fabric-based flexible cell that relies on sweat to generate electricity [78]. Copyright 2020, Elsevier. (b) An epidermal biofuel cell that monitors sweat and derives energy from it [83]. Copyright 2021, Elsevier. (c) Image of microfluidic patch with embedded sensors and a lactate sensor [82]. Copyright 2019, Science. (d) A bracelet with six biofuel cells in series that derives energy from lactic acid in sweat [80]. Copyright 2021, Elsevier. (e) A contact biofuel cell that collects energy from lactic acid in sweat [81]. Copyright 2021, Elsevier. (f) A stretchable, soft biofuel cell that can be attached to human skin to convert lactic acid from sweat into energy [84]. Copyright 2019, Wiley Online Library. (g) A biofuel cell that can be printed onto stretchable, soft fabric with suitable fitting characteristics to harvest energy from sweat [79]. Copyright 2016, Royal Society of Chemistry. (h) A needle-shaped biofuel cell that converts glucose in mice into electricity [85]. Copyright 2020, Elsevier.

Figure 6

Practical applications of biosensors for human condition monitoring. (a) A nanogenerator pillow for monitoring human sleep state [86]. Copyright 2022, American Chemical Society. (b) A nanogenerator-based smart insole for gait monitoring and fall warning [87]. Copyright 2022, Wiley Online Library. (c) A flexible self-powered sweat sensor that detects Na, K, and pH in sweat [88]. Copyright 2022, Elsevier. (d) A nanogenerator-based blood-pressure-monitoring bracelet for monitoring the pulse wave signal of the wearer [89]. Copyright 2022, MDPI. (e) A self-powered smart Band-Aid for motion and human–computer interaction [90]. Copyright 2023, Elsevier. (f) A breathing alarm device that harvests human motion energy for power sensors [91]. Copyright 2022, Elsevier. (g) A multi-pathway respiratory sensor inspired by the gill slit structure of sharks for respiratory monitoring [93]. Copyright 2022, Elsevier. (h) A stretchable stress sensor based on the helical structure of TENG for respiratory monitoring for in vivo implantation [94]. Copyright 2022, American Chemical Society.