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.

Potentiometric biosensors based on flexible arrayed silver paste electrode and copper-doped zinc oxide sensing film modified by iron-platinum nanoparticles (FePt NPs) are designed and manufactured to detect lactate in human. The sensing film is made of copper-doped zinc oxide (CZO) by a radio frequency (RF) sputtering system, and then modified by iron-platinum nanoparticles (FePt NPs). The surface morphology of copper-doped zinc oxide (CZO) is analyzed by scanning electron microscope (SEM). FePt NPs are analyzed by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The average sensitivity, response time, and interference effect of the lactate biosensors are analyzed by voltage-time (V-T) measurement system. The electrochemical impedance is analyzed by electrochemical impedance spectroscopy (EIS). The average sensitivity and linearity over the concentration range 0.2–5 mM are 25.32 mV/mM and 0.977 mV/mM, respectively. The response time of the lactate biosensor is 16 s, with excellent selectivity.

In this study, a novel low unity-gain frequency and low power consumption instrumentation amplifier (UGFPCIA) was designed and applied to the readout circuit of the potentiometric biosensor measurement system. The proposed UGFPCIA was developed using the Taiwan Semiconductor Manufacturing Company (TSMC) 0.18- $\mu \text{m}$ process technology, and simulated in a Laker analog design environment, and had a 1.5-V supply voltage for reduced power consumption. The uric acid (UA) biosensor based on RuO ₂ thin film was fabricated in this study. The sensing characteristics of the RuO ₂ UA biosensor were measured by the proposed UGFPCIA and the LT1167, a commercial instrumentation amplifier; then, their readout circuits were compared. According to the chip measurement results, the proposed UGFPCIA achieved a common-mode gain of −54 dB and a unity-gain frequency (UGF) of 588 kHz. Its power consumption was $397.92~\mu \text{W}$ . Moreover, the measurement results showed that the sensitivity and linearity of the flexible arrayed RuO ₂ UA biosensor were 7.15 mV/(mg/dL) and 0.997, respectively. The LT1167 used a 2.3-V minimum supply voltage, while the proposed UGFPCIA used a 1.5-V minimum supply voltage; the power consumption is 84% lower than the former. This indicates that UGFPCIA was more stable during the measurement process and consumes lesser power.

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.

Dye-sensitized solar cells (DSSCs) are low-cost solar cells belonging to the thin-film photovoltaic cell type. In this study, we studied the photovoltaic performances of DSSCs based on titanium dioxide (TiO₂) nanofibers (NFs) containing silver (Ag) nanoparticles (NPs) under low illumination. We used the sol-gel method with the electrospinning technique to prepare the TiO₂ NFs containing Ag NPs. Herein, we used two ways to add TiO₂/Ag NFs to modify the photoelectrode successfully and enhance the performance of DSSCs. One way was that the TiO₂/Ag NFs were mixed with pristine TiO₂; the other way was that the TiO₂/Ag NFs were seeded beside the TiO₂ colloid layer as an additional layer on the photoelectrode of the DSSC. According to this experiment, the photovoltaic conversion efficiency of the DSSC which had TiO₂/Ag NF seeded as an additional layer on the photoelectrode (5.13%) was increased by 28% compared to the DSSC without the photoelectrode modification (3.99%). This was due to the suppression of electron recombination and the more effective utilization of the light radiation by adding the TiO₂/Ag NFs. Because of the good conductivity of Ag, the electrons were quickly transported and electron recombination was reduced. In addition, the photovoltaic conversion efficiency of the DSSC which had TiO₂/Ag NF seeded as an additional layer on the photoelectrode increased from 5.13% to 6.23% during the decrease in illumination from 100 mW/cm² to 30 mW/cm²; however, its photovoltaic conversion efficiency decreased to 5.31% when the illumination was lowered to 10 mW/cm².