In this study, the potentiometric arrayed glucose biosensors, which were based on zinc oxide (ZnO) or aluminum-doped zinc oxide (AZO) sensing membranes, were fabricated by using screen-printing technology and a sputtering system, and graphene oxide (GO) and Nafion-glucose oxidase (GOx) were used to modify sensing membranes by using the drop-coating method. Next, the material properties were characterized by using a Raman spectrometer, a field-emission scanning electron microscope (FE-SEM), and a scanning probe microscope (SPM). The sensing characteristics of the glucose biosensors were measured by using the voltage–time (V-T) measurement system. Finally, electrochemical impedance spectroscopy (EIS) was conducted to analyze their charge transfer abilities. The results indicated that the average sensitivity of the glucose biosensor based on Nafion-GOx/GO/AZO was apparently higher than that of the glucose biosensor based on Nafion-GOx/GO/ZnO. In addition, the glucose biosensor based on Nafion-GOx/GO/AZO exhibited an excellent average sensitivity of 15.44 mV/mM and linearity of 0.997 over a narrow range of glucose concentration range, a response time of 26 s, a limit of detection (LOD) of 1.89 mM, and good reproducibility. In terms of the reversibility and stability, the hysteresis voltages (V_H) were 3.96 mV and 2.42 mV. Additionally, the glucose biosensor also showed good anti-inference ability and reproducibility. According to these results, it is demonstrated that AZO is a promising material, which could be used to develop a reliable, simple, and low-cost potentiometric glucose biosensor.

A flexible urea sensor based on urease-magnetic beads (MBs) and graphene oxide (GO) has been synthesized on nickel oxide (NiO) as matrix. The flexible urea sensor was constructed by sputtering technology and screen-printing technology. A sequential titrating of GO and magnetic beads over the surface on NiO film was adopted for the sensor preparation by the covalent binding with urease. The electrochemical impedance, response time and drift effect of the urea sensor based on MBs, GO and NiO were recorded using electrochemical impedance spectroscopy (EIS) and voltage-time (V-T) measurement system.

Two types of urea biosensors were integrated with a wireless measurement system and microfluidic measurement system. The two biosensors used were (i) a magnetic beads (MBs)-urease/graphene oxide (GO)/titanium dioxide (TiO₂)-based biosensor and (ii) an MBs-urease/GO/ nickel oxide (NiO)-based biosensor, respectively. The wireless measurement system work exhibited the feasibility for the remote detection of urea, but it will require refinement and modification to improve stability and precision. The microchannel fluidic system showed the measurement reliability. The sensing properties of urea biosensors at different flow rates were investigated. From the measurement results, the decay of average sensitivity may be attributed to the induced vortex-induced vibrations (VIV) at the high flow rate. In the aspect of wireless monitoring, the average sensitivity of the urea biosensor based on MBs-urease/GO/NiO was 4.780 mV/(mg/dl) and with the linearity of 0.938. In the aspect of measurement under dynamic conditions, the average sensitivity of the urea biosensor based on MBs-urease/GO/NiO were 5.582 mV/(mg/dl) and with the linearity of 0.959. Both measurements performed NiO was better than TiO₂ according to the comparisons.

In this work, the flexible arrayed urea biosensor is composed of silver paste electrodes by screen printing technology. The sensing film is made of the nickel oxide (NiO) by radio frequency (R. F.) sputtering system, and then modified by Au nanoparticles (Au NPs) and graphene oxide (GO). The average sensitivity, response time, interference effect and electrochemical impedance of urea biosensors are analyzed by voltage-time (V-T) measurement system and electrochemical impedance spectroscopy (EIS). The surface morphology of the biosensor is analyzed by scanning electron microscope (SEM). The results show that the flexible arrayed urea biosensor has excellent average sensitivity over a wide concentration range (0.01 mM–100 mM) of 57.16 mV/decade, linearity of 0.998, response time of 25 s, limit of detection (LOD) of 7.64 μM, and excellent selectivity.

In this study, the characteristics and stability of the nickel oxide (NiO) based uric acid biosensors modified with graphene and magnetic beads (MBs) were investigated. The sensitivity and linearity of the different membranes were compared by using the voltage-time (V-T) measurement system. Then, the electrochemical impedance spectroscopy (EIS) was used to prove that adding the modification could reduce the impedance of the thin films and improve the electron transfer feature. Furthermore, we successfully fabricated the MBs-uricase/rGO/NiO films as a sensing membrane for the NiO based biosensor, which was suitable for measuring the uric acid in this study. Thus, the NiO based uric acid biosensor showed the relatively higher average sensitivity and linearity of 38.279 mV/(mg/dL) and 0.966, respectively. Finally, in terms of stability, an investigated into both the interference effect and lifetime of the uric acid biosensor was conducted, and the satisfying stability in this regard was also shown.