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Self-powered wearable sensing systems have attracted great attention for their application in continuous health monitoring, which can reveal real-time physiological information on the body. Here, an innovative self-powered sound-driven humidity sensor for wearable intelligent dehydration monitoring system has been proposed. The sensor is primarily comprised of PTFE membrane, ZnO nanoarrays and Ti thin film. The piezoelectric/triboelectric effect of ZnO nanoarrays/PTFE membrane is coupled with the humidity sensing process. Sound wave can drive PTFE membrane to vibrate, and the contact and separation between PTFE and ZnO can generate electrical signals through piezoelectric/triboelectric effect. At the same time, the surface of the nanostructures can absorb the water molecules, which will influence the electrical output of the device. The device can convert sound energy into electrical output without any external electricity power supply, and the outputting voltage decreases with increasing relative humidity, acting as the sensing signal. The sensor has been integrated with data processing unit and wireless transmission module to form a self-powered wearable intelligent dehydration monitoring system, which can actively monitor the humidity of exhaled breath and transmit the information to the mobile phone. The results can open a possible new direction for the development of sound-driven gas sensors and will further expand the scope for self-powered nanosystems., (© 2023 IOP Publishing Ltd.)

Neonatal jaundice refers to the abnormality of bilirubin metabolism for newborns, and wearable transcutaneous bilirubin meters for real-time measuring the bilirubin concentration is an insistent demand for the babies' parents and doctors. In this paper, a self-powered wearable biosensor in a baby diaper for real-time monitoring neonatal jaundice has been realized by the hydrovoltaic-biosensing coupling effect of ZnO nanoarray. Without external power supply, the system can work independently, and the hydrovoltaic output can be treated as both the power source and biosensing signal. The working mechanism is that the hydrovoltaic output arises from the urine flowing on ZnO nanoarray and the enzymatic reaction on the surface can influence the output. The sensing information can be transmitted through a wireless transmitter, and thus the parents and doctors can treat the neonatal jaundice of babies in time. This work can potentially promote the development of next generation of biosensors and physiological monitoring system, and expand the scope of self-powered technique and smart healthcare area.

The emerging multifunctional flexible electronic-skin for establishing body-electric interaction can enable real-time monitoring of personal health status as a new personalized medicine technique. A key difficulty in the device design is the flexible power supply. Here a self-powered wearable noninvasive electronic-skin for perspiration analysis has been realized on the basis of a piezo-biosensing unit matrix of enzyme/ZnO nanoarrays. The electronic-skin can detect lactate, glucose, uric acid, and urea in the perspiration, and no outside electrical power supply or battery is used in the biosensing process. The piezoelectric impulse of the piezo-biosensing units serves as the power supply and the data biosensor. The working mechanism can be ascribed to the piezoelectric-enzymatic-reaction coupling effect of enzyme/ZnO nanowires. The electronic-skin can real-time/continuously monitor the physiological state of a runner through analyzing the perspiration on his skin. This approach can promote the development of a new-type of body electric and self-powered biosensing electronic-skin.

Highly stable piezo-immunoglobulin-biosensing has been realized from a SiO2/ZnO nanowire (NW) nanogenerator (NG) as a self-powered/active biosensor. The piezoelectric output generated by the SiO2/ZnO NW NG can act not only as a power source for driving the device, but also as a sensing signal for detecting immunoglobulin G (IgG). The stability of the device is very high, and the relative standard deviation (RSD) ranges from 1.20% to 4.20%. The limit of detection (LOD) of IgG on the device can reach 5.7 ng mL(-1). The response of the device is in a linear relationship with IgG concentration. The biosensing performance of SiO2/ZnO NWs is much higher than that of bare ZnO NWs. A SiO2 layer uniformly coated on the surface of the ZnO NW acts as the gate insulation layer, which increases mechanical robustness and protects it from the electrical leakages and short circuits. The IgG biomolecules modified on the surface of the SiO2/ZnO NW act as a gate potential, and the field effect can influence the surface electron density of ZnO NWs, which varies the screening effect of free-carriers on the piezoelectric output. The present results demonstrate a feasible approach for a highly stable self-powered/active biosensor.

Self-powered active biosensor has been realized from ZnO nanowire (NW) nanogenerator (NG). The piezoelectric output generated by ZnO NW NG can act not only as a power source for driving the device, but also as a biosensing signal. After immersing in 10(-3) g ml(-1) human immunoglobulin G (IgG), the piezoelectric output voltage of the device under compressive deformation decreases from 0.203±0.0176 V (without IgG) to 0.038±0.0035 V. Such a self-powered biosensor has higher response than transistor-type biosensor (I-V behavior). The response of self-powered biosensor is in a linear relationship with IgG concentration (logarithm, 10(-7)-10(-3) g ml(-1)) and the limit of detection (LOD) on IgG of the device is about 6.9 ng ml(-1). The adsorption of biomolecules on the surface of ZnO NWs can modify the free-carrier density, which vary the screening effect of free-carriers on the piezoelectric output. The present results demonstrate a feasible approach for actively detecting biomolecules by coupling the piezotronic and biosensing characteristics of ZnO NWs., (Copyright © 2014 Elsevier B.V. All rights reserved.)

The output of a piezoelectric nanogenerator (NG) fabricated using ZnO nanowire arrays is largely influenced by the density of the surface charge carriers at the nanowire surfaces. Adsorption of gas molecules could modify the surface carrier density through a screening effect, thus, the output of the NG is sensitive to the gas concentration. Based on such a mechanism, we first studied the responses of an unpackaged NG to oxygen, H2S and water vapor, and demonstrated its sensitivity to H2S to a level as low as 100 ppm. Therefore, the piezoelectric signal generated by a ZnO NWs NG can act not only as a power source, but also as a response signal to the gas, demonstrating a possible approach as a self-powered active gas sensor.

Room-temperature, high H2S sensing has been realized from a CuO/ZnO nanoarray self-powered, active gas sensor. The piezoelectric output of CuO/ZnO nanoarrays can act not only as the power source of the device, but also as the H2S sensing signal at room temperature. Upon exposure to 800 ppm H2S at room temperature, the piezoelectric output of the device greatly decreased from 0.738 V (in air) to 0.101 V. The sensitivity increased to 629.8, much higher than bare ZnO nanoarrays. As the device was exposed to H2S, a CuO/ZnO PN-junction was converted into a CuS/ZnO Ohmic contact, which greatly increased the electron density in the nanowire and enhanced the screen effect on the piezoelectric output. Our results can stimulate a research trend on designing new composite piezoelectric material for high-performance self-powered active gas sensors. [ABSTRACT FROM AUTHOR]

Ag/ZnO nanotetrapods are synthesized in mass production via a simple thermal-evaporation/hydrothermal route, and Ag nanoparticles are randomly coated on ZnO nanotetrapods. Ag/ZnO nanotetrapods can co-use the solar and mechanical energy to degrade various organic pollutants, and the solar-photocatalytic activity is significantly enhanced by the piezo-assistance. For instance, under ultrasonic stimulation (200 W) and solar illumination (500 W), Ag/ZnO nanotetrapods can completely degrade methyl orange (MO) within 25 min. The high piezo/solar-photocatalytic efficiency of Ag/ZnO nanotetrapods can be ascribed to the coupling of surface plasmon resonance and piezophototronic effect in the solar-photocatalytic process. The localized surface plasmon resonance effect of Ag nanoparticles can increase the visible light absorption. Ag/ZnO interface can facilitate the interfacial charge transfer and induce the separation of photo-induced charge carriers. The piezoelectric field originated from the deformation of ZnO nanotetrapods can further enhance the separation of photo-induced electron/hole pairs. Our results imply that Ag/ZnO nanotetrapods have great potentials of using sustainable energy in the nature for environmental remediation. [ABSTRACT FROM AUTHOR]

High and fast response of H 2 S sensing at room temperature has been realized from NiO/ZnO hetetojunction nanowire (NW) arrays as a self-powered gas sensor. The piezoelectric output generated by NiO/ZnO NW nanogenerator (NG) can act as both the power source and sensing signal. Upon exposure to 1000 ppm H 2 S at room temperature, the piezo-voltage of NiO/ZnO NW arrays decreases from 0.388 V (in dry air) to 0.061 V, and the response is approximately 10 times higher than that of bare ZnO NW arrays. Such a high performance can be attributed to the piezoelectric effect of ZnO and the conversion of NiO/ZnO PN-junctions. Our study confirms that introducing heterostructures into NG is a right direction for the development of self-powered gas sensors. [ABSTRACT FROM AUTHOR]

High sensitivity and fast response piezo-humidity sensing have been realized from Ga-doped ZnO nanowire (NW) nanogenerator (NG) as self-powered/active gas sensor. The piezoelectric output generated by Ga-doped ZnO NW NG can not only act as a power source for driving the device, but also as a sensing signal for detecting humidity. Upon exposure to 80% relative humidity (RH) at room temperature, the piezoelectric output of Ga-doped ZnO NWs decreases from 0.56 V (in 45% RH) to 0.12 V, and the sensitivity is up to 358, higher than that of undoped ZnO NWs. In addition, the response time of Ga-doped ZnO NWs is 5 s, much shorter than that of undoped ZnO NWs. Such high performance can be ascribed to that Ga 3+ ions can provide many donor defects and produce high local charge density/strong electrostatic field. The present results demonstrate a feasible approach for realizing high performance self-powered/active humidity sensor. [ABSTRACT FROM AUTHOR]

Room-temperature self-powered/active humidity sensing has been realized from Sb-doped ZnO nanowire (NW) arrays by coupling their piezoelectric and gas sensing characteristics. The piezoelectric output of the device acts as both the power source and the response signal against relative humidity (RH). Upon exposure to 70% RH, the piezoelectric output of Sb-doped ZnO NWs decreases from 1.35 V (10% RH) to 0.22 V, and the response is 83.70 (much higher than that of undoped ZnO). [ABSTRACT FROM AUTHOR]

High performance self-powered/active humidity sensors have been fabricated from Fe-doped ZnO nanoarrays. When the relative humidity (RH) is 60% at room temperature, the piezoelectric output voltage of the humidity sensor under compressive force decreases from 0.85 (at 5% RH) to 0.21 V. The self-powered humidity sensing performance of Fe-doped ZnO nanoarrays is much higher than that of undoped ZnO nanoarrays. Fe 3+ ions have small ionic radius and many positive charges (+3), thus the doping of Fe can lead to a high charge density, which can probably result in a large amount of adsorbed water molecules on the surface of Fe-doped ZnO NWs, enhancing the screening effect and decreasing the piezoelectric output. The present results demonstrate a new material system for high-performance self-powered/active humidity sensors. [ABSTRACT FROM AUTHOR]

Piezo/active humidity sensing of CeO 2 /ZnO and SnO 2 /ZnO nanoarray nanogenerators with high response and large detecting range have been realized. The piezoelectric output of the devices under external deformation is extremely sensitive to the humidity with a very large detecting range. The piezoelectric output of the devices can act not only as a power source, but also as a response signal to the relative humidity of the ambience. Such behavior can be attributed to the piezotronic effect of ZnO nanowires and the surface modification of CeO 2 or SnO 2 nanoparticles. Our study can open a new way for actively detecting humidity in the environment. [ABSTRACT FROM AUTHOR]

• ZnO/MoS 2 nanoarrays as sunlight photocatalysts have been synthesized on Ni foam. • The nanoarrays can generate piezoelectric field under flowing induced deformation. • The photocatalytic performances are significantly enhanced by piezoelectric field. • ∙ O H radical generated by ZnO/MoS 2 can be improved by piezoelectric field. • Piezoelectric field can convert Ⅱ-type into Z-scheme heterojunction of ZnO/MoS 2. Direct Z-scheme heterojunction of ZnO/MoS 2 nanoarray on Ni foam has been realized by flowing induced piezoelectric field for enhanced sunlight photocatalytic performances. The porous structure of Ni substrate can effectively induce applied deformation on nanorod arrays and generate built-in piezoelectric field by water flowing. Under sunlight irradiation for 50 min, the photocatalytic degradation efficiency of methyl orange is 50.6 %, and the degradation efficiency rapidly increases to 92.7 % under stirring-sunlight irradiation. The degradation rate increases with increasing stirring speed along an S-shaped relationship. In addition, the heterojunction photocatalyst also performs good repeatability in aqueous solution and even in alkaline solution. The role and amount of active radicals are investigated by radical scavenger experiments and electron spin resonance technique, indicating that only the amount of ∙ O H radicals can be significantly increased by flowing induced piezoelectric field. This interesting phenomenon can be attributed to that piezoelectric field converts Ⅱ-type heterojunction into Z-scheme configuration. [ABSTRACT FROM AUTHOR]