In this paper, we fabricated p-Co₃O₄/n-TiO₂ heterostructures and investigated their gas sensing properties. The structural and morphological characterization were performed by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy analysis (XPS). The electrical properties of the heterostructure were studied within the temperature range from 293 K to 423 K. Changes in electrical properties and sensing behavior against reducing and oxidizing gases were attributed to the formation of p–n heterojunctions at the Co₃O₄ and TiO₂ interface. In comparison with sensing performed with pristine TiO₂ nanotubes (NTs), a significant improvement in H₂ sensing at 200 °C was observed, while the sensing response against NO₂ decreased for the heterostructures. Additionally, a response against toluene gas, in contrast to pristine TiO₂ NTs, appeared in the Co₃O₄/TiO₂ heterostructure samples.

Pristine and chromium (Cr) doped WO₃ nanoflakes (NFs) with various concentrations were successfully fabricated by a facile hydrothermal technique on alumina (Al₂O₃) substrates. The structural, optical, and morphological properties of these NFs were investigated by x-ray diffraction, scanning electron microscopy, transmission electron microscopy, UV-Visible diffusion reflectance spectroscopy (UV–Vis DRS), and x-ray photoelectron spectroscopy. Gas sensor tests were performed against various volatile organic compounds such as ethanol, xylene, toluene, and isopropanol gases in the temperature range between 50 °C and 250 °C. According to the results of these tests, the isopropanol sensing ability of WO₃ NFs is enhanced with Cr-doping due to the increasing active adsorption sites on the surface and improved surface reactions with the decreasing band gap energy. The highest isopropanol sensing response which was calculated to be 77.1 has been obtained by nominally 2% Cr doping at the optimal operating temperature of 150 °C.

Pristine and WO3 decorated TiO2 nanorods (NRs) were synthesised to investigate n-n-type heterojunction gas sensing properties. TiO2 NRs were fabricated via hydrothermal method on fluorine-doped tin oxide coated glass (FTO) substrates. Then, tungsten was sputtered on the TiO2 NRs and thermally oxidised to obtain WO3 nanoparticles. The heterostructure was characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) spectroscopy. Fabricated sensor devices were exposed to VOCs such as toluene, xylene, acetone and ethanol, and humidity at different operation temperatures. Experimental results demonstrated that the heterostructure has better sensor response toward ethanol at 200 °C. Enhanced sensing properties are attributed to the heterojunction formation by decorating TiO2 NRs with WO3.

In this letter, we present the first example of a zinc oxide (ZnO) thin film grown by atomic layer deposition method (ALD) on a quartz crystal microbalance (QCM) for the detection of human transferrin (hTF) molecule. Morphological, structural, and optical properties of ZnO thin film were investigated by scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, X-ray diffraction spectroscopy, ultraviolet–visible spectroscopy, and photoluminescence. For biosensor measurements, ZnO/QCM sensors were modified with antitransferrin to obtain selectivity against hTF. Mass-sensitive biosensor tests were carried out using two different measurement methods: dip–dry and flow-cell. It was observed that antitransferrin immobilized ZnO/QCM sensor detected hTF molecule in the range of 100–1000 ng. Moreover, the sensors exhibited better performance in the dip–dry method than the flow-cell method. ZnO-coated QCM exhibited good mass-sensitive performance, which make it a suitable sensor platform for biosensor applications.

In this study, surface acoustic wave (SAW) sensor platforms were fabricated with various electrode structure design on piezoelectric substrates using micro electro-mechanical system (MEMS) fabrication techniques. After the fabrication and characterization of SAW sensor platforms, ZnO nanorods sensing layer was coated on devices by seed-mediated hydrothermal method for using in volatile organic compounds (VOCs) pollutant detection at room temperature. Sensor tests were performed against acetone, hydrogen cyanide (HCN), hydrogen sulfide (H₂S), ammonia, and relative humidity in the concentration range between a few particles per million (ppm) and particle per billion (ppb). In the ppb regime, the highest sensor response was observed to be 13.113 Hz for 750 ppb acetone at room temperature, with an approximate response and recovery time as 29.97 and 30.01 minutes, respectively. The gas sensing characteristics of ZnO based SAW sensor was investigated in detail regarding the various sensing mechanism parameters such as mass-sensitivity and elasticity effect.