Highly Sensitive ZnO/Au Nanosquare Arrays Electrode for Glucose Biosensing by Electrochemical and Optical Detection

The fabrication of a ZnO/Au nanosquare-array electrode was successfully carried out for the detection of glucose concentration in biomedical applications. The fabrication of the ZnO/Au nanosquare array using an ultra-thin alumina mask (UTAM) based on the imprinted anodic aluminum oxide (AAO) template and the direct current (DC) sputtering method was able to produce a very well-ordered nanosquare arrangement with a side size of 300 nm and a thickness of 100 nm. Tests were done to evaluate the performance of the electrode by means of cyclic voltammetry (CV) which showed that the addition of glucose oxidase (GOx) increased the sensitivity of the electrode up to 1180 ± 116 μA mM^-1cm^-2, compared with its sensitivity prior to the addition of GOx of 188.34 ± 18.70 mA mM^-1 cm^-2. A i_ox/i_red ratio equal to ~1 between the peaks of redox reactions was obtained for high (hyperglycemia), normal, and low (hypoglycemia) levels of glucose. The ZnO/Au nanosquare-array electrode was 7.54% more sensitive than the ZnO/Au thin-film electrode. Furthermore, finite-difference time-domain (FDTD) simulations and theoretical calculations of the energy density of the electric and magnetic fields produced by the ZnO/Au electrode were carried out and compared to the results of CV. From the results of CV, FDTD simulation, and theoretical calculations, it was confirmed that the ZnO/Au nanosquare array possessed a significant optical absorption and that the quantum effect from the nanosquare array resulted in a higher sensitivity than the thin film.

PDMS-ZnO Piezoelectric Nanocomposites for Pressure Sensors

The addition of piezoelectric zinc oxide (ZnO) fillers into a flexible polymer matrix has emerged as potential piezocomposite materials that can be used for applications such as energy harvesters and pressure sensors. A simple approach for the fabrication of PDMS-ZnO piezoelectric nanocomposites based on two ZnO fillers: nanoparticles (NP) and nanoflowers (NF) is presented in this paper. The effect of the ZnO fillers' geometry and size on the thermal, mechanical and piezoelectric properties is discussed. The sensors were fabricated in a sandwich-like structure using aluminium (Al) thin films as top and bottom electrodes. Piezocomposites at a concentration of 10% w/w showed good flexibility, generating a piezoelectric response under compression force. The NF piezocomposites showed the highest piezoelectric response compared to the NP piezocomposites due to their geometric connectivity. The piezoelectric compound NF generated 4.2 V while the NP generated 1.86 V under around 36 kPa pressure. The data also show that the generated voltage increases with increasing applied force regardless of the type of filler.

Enhanced piezocapacitive response in zinc oxide tetrapod-poly(dimethylsiloxane) composite dielectric layer for flexible and ultrasensitive pressure sensor

We demonstrate polymeric piezocapacitive pressure sensors based on a novel composite dielectric film of poly(dimethylsiloxane) elastomeric silicone and zinc oxide tetrapod. With an appropriate loading of zinc oxide tetrapods, composite piezocapacitive pressure sensors show a 75-fold enhancement of pressure sensitivity over pristine devices, achieving a marked value as high as 2.55 kPa^-1. The limit of detection was estimated to be about 10 mg, corresponding to a subtle stimulus of only 1.0 Pa. Besides, versatile functionalities such as detection of finger bending/straightening, calligraphy writing, and air flow blowing have been investigated. It is expected that the proposed piezocapacitive pressure sensors incorporating stress-sensitive additives of zinc oxide nanostructures may provide a promising means for potential applications in ultrasensitive wearable, healthcare systems and human-machine interfaces.

Optimization of ZnO Nanorods Concentration in a Micro-Structured Polymeric Composite for Nanogenerators

The growing use of wearable devices has been stimulating research efforts in the development of energy harvesters as more portable and practical energy sources alternatives. The field of piezoelectric nanogenerators (PENGs) and triboelectric nanogenerators (TENGs), especially employing zinc oxide (ZnO) nanowires (NWs), has greatly flourished in recent years. Despite its modest piezoelectric coefficient, ZnO is very attractive due to its sustainable raw materials and the facility to obtain distinct morphologies, which increases its multifunctionality. The integration of ZnO nanostructures into polymeric matrices to overcome their fragility has already been proven to be fruitful, nevertheless, their concentration in the composite should be optimized to maximize the harvesters’ output, an aspect that has not been properly addressed. This work studies a composite with variable concentrations of ZnO nanorods (NRs), grown by microwave radiation assisted hydrothermal synthesis, and polydimethylsiloxane (PDMS). With a 25 wt % ZnO NRs concentration in a composite that was further micro-structured through laser engraving for output enhancement, a nanogenerator (NG) was fabricated with an output of 6 V at a pushing force of 2.3 N. The energy generated by the NG could be stored and later employed to power small electronic devices, ultimately illustrating its potential as an energy harvesting device.

Piezoelectric property comparison of two-dimensional ZnO nanostructures for energy harvesting devices

In this paper, experimental and theoretical studies of the piezoelectric effect of two-dimensional ZnO nanostructures, including straight nanosheets (SNSs) and curved nanosheets (CNSs) are conducted. The results show that the CNSs have a great advantage in piezoelectric property over the SNSs; the maximum output current of the NG based on CNSs was measured to be about 260 nA, much higher than that generated by SNSs. For comparatively analyzing the working mechanics of both NGs, the piezopotential distribution of both CNS and SNS structures was studied using the finite element method. The simulation result that the piezopotential generated by CNSs is always much larger than that generated by SNSs in the case of lateral bending, has more advantages for piezoelectric NGs than the SNSs. This work may provide guidance for structural optimization of piezoelectric nanogenerators and designing high-performance self-powered strain sensors.

In this paper, experimental and theoretical studies of the piezoelectric effect of two-dimensional ZnO nanostructures, including straight nanosheets (SNSs) and curved nanosheets (CNSs) are conducted.

ZnO-based nanostructured electrodes for electrochemical sensors and biosensors in biomedical applications

Fascinating properties of ZnO nanostructures have created much interest due to their importance in health care and environmental monitoring. Current worldwide production and their wide range of applications signify ZnO to be a representative of multi-functional oxide material. Recent nanotechnological developments have stimulated the production of various forms of ZnO nanostructures such as nano-layers, nanoparticles, nanowires, etc. Due to their enhanced sensing properties, improved binding ability with biomolecules as well as biological activities have enabled them as suitable candidates for the fabrication of biosensor devices in the biomedical arena. In this review, the synthesis of ZnO nanostructures, mechanism of their interaction with biomolecules and their applications as sensors in health care area are discussed considering the biosensors for molecules with small molecular weight, infectious diseases, and pharmaceutical compounds.

Fabrication of an Ag/Fe2O3/ZnO ternary composite with enhanced photocatalytic performance

A novel Ag/Fe₂O₃/ZnO ternary composite was fabricated using the chemical deposition and photochemical deposition methods.