Macroporous silicon was prepared through an anodization process; the prepared samples showed an average pore size ranging from 4 to 6 microns, and the depth of the pores in the silicon wafer was approximately 80 microns. The prepared samples were tested for hydrogen peroxide (H2O2) concentrations, which can be used for industrial and environmental sensing applications. The selected H2O2 concentration covered a wide range from 10 to 5000 μM. The tested samples showed a linear response through the tested H2O2 concentrations with a sensitivity of 0.55 μA μM–1∙cm–2 and lower detection limits of 4.35 μM at an operating voltage of 5 V. Furthermore, the electrode exhibited a rapid response with a response time of ca. two seconds. Furthermore, the prepared sensor showed a reasonable stability over a one-month time period.

For highly sensitive pH sensing, an electrolyte insulator semiconductor (EIS) device, based on ZnO nanorod-sensing membrane layers doped with magnesium, was proposed. ZnO nanorod samples prepared via a hydrothermal process with different Mg molar ratios (0–5%) were characterized to explore the impact of magnesium content on the structural and optical characteristics and sensing performance by X-ray diffraction analysis (XRD), atomic force microscopy (AFM), and photoluminescence (PL). The results indicated that the ZnO nanorods doped with 3% Mg had a high hydrogen ion sensitivity (83.77 mV/pH), linearity (96.06%), hysteresis (3 mV), and drift (0.218 mV/h) due to the improved crystalline quality and the surface hydroxyl group role of ZnO. In addition, the detection characteristics varied with the doping concentration and were suitable for developing biomedical detection applications with different detection elements.

No abstract

Multilayers zinc oxide thin films were synthesized by the sol–gel spin coating process to fabricate sensing membranes in an electrolyte-insulator-semiconductor (EIS) sensor for pH detection. The effect of various layers (single, three and five layers) on the crystallinity, morphological and optical properties of ZnO films were investigated by XRD, FE-SEM, and Photoluminescence respectively. The ZnO thin films grown were polycrystalline with hexagonal wurtzite structure. The films were not smooth, with grains and porosity in between them, and become denser as film thickness increased. The PL spectra exhibit two main emission peaks at near band edge 360-380 nm region (strong and sharp UV radiation) and 450–600 nm region (broad blue, green, and yellow radiation). Sensitivity, linearity was measured to determine the sensing and reliability performance of fabricated devices. The result confirmed that, the sensitivity for the three samples increased with increased layer from 48.3 mV/pH to 82.58 mV/pH. Compared to single and three layers of the ZnO electrolyte-insulator-semiconductor (EIS), ZnO grown with five layers exhibits a higher sensitivity of 82.58 mV/pH in solutions from pH 2–12 and linearity of 99.015 %. This is due to the increased of ZnO thickness, which produces dense surface and a well-crystallized grain structure.