An electrochemical zinc oxide (ZnO) pH sensor is proposed and prototyped using a flexible printed circuit board (FPCB). The device is resistant to acidic and alkaline solutions and exhibits excellent electrical conductivity. The sensing film was deposited by radio-frequency sputtering, providing a dense ZnO layer, and (3-aminopropyl)triethoxysilane (APTES) was used to enhance the chemical stability of the ZnO in acidic solutions. The proposed pH sensor has an average sensitivity of 37.52 mV/pH, linearity of 0.995, and a repeatable RSD value of 2.4%. Testing was conducted with Carmody’s buffer pH 2–10 and a voltage-time measurement system. The stability of the prototype was determined by the measurement of the drift and hysteresis effects.

In this study, we deposited zinc oxide (ZnO) and aluminum-doped zinc oxide (AZO) on the electroless nickel immersion gold (ENIG) of a flexible printed circuit board (FPCB) as a potentiometric pH sensor. The sensing films of the pH sensor were fabricated by a radio frequency (RF) sputtering system and analyzed by field emission scanning electron microscope (FE-SEM) and X-ray photoelectron spectroscopy (XPS). In the pH 2 to 10 buffer solutions, it was observed that the characteristics of the pH sensor through the voltage–time (V-T) measurement system include average sensitivity and linearity, drift effect, and repeatability. According to the experimental results, the pH sensors in this study could exhibit good characteristics.

We improve photovoltaic performance by incorporating graphene quantum dots (GQDs) into dye-sensitized solar cells (DSSCs). GQD can emit green fluorescence (∼530 nm) in the ultraviolet wavelength range (∼340 nm), and this characteristic is applied to enhance the light absorption ability of N719 dye. Using GQDs as auxiliary sensitizers to achieve co-sensitization with N719 dye can enhance the photovoltaic performance of DSSCs. We observed the photoresponse characteristics of DSSCs with different sensitization effects by incident photon-to-current conversion efficiency (IPCE). According to the results, the photoelectric conversion efficiency of DSSCs using the GQD+N719 co-sensitized photoanode was increased to 5.14%, which is a 20% improvement.

This study prepared an enzymatic potentiometric uric acid sensor based on zinc oxide (ZnO) and uricase. Also, we develop a potentiometric differential measurement system. We applied Nafion, APTES, and glutaraldehyde to immobilize the enzyme and increase sensitivity to prevent enzyme leakage. Thus, the uric acid sensor was integrated into FPCB which could provide flexibility to the sensor. In the uric acid concentration range of 2 mg/dL-10 mg/dL, we analyzed the characteristics of sensors with the voltage-time measurement system, measuring the average sensitivity, linearity, response time, limit of detection (LOD), and interference effects. The modification of Nafion and uricase improved the performance of the uric acid sensor.

An enzymatic glucose biosensor based on magnesium oxide (MgO) film potential measurement is proposed, in which glucose oxidase (GOD) is used to enhance the glucose sensing performance. And according to the chemical properties of MgO, GOD was immobilized on the working electrode using (3-aminopropyl)triethoxysilane and glutaraldehyde. The top layer of the sensor is Nafion to enhance the selectivity of glucose. The film substrate of the sensor adopts a flexible printed circuit board with excellent chemical properties, and MgO is deposited on the working electrode by a radio frequency sputtering process. The MgO coated on the film has a thickness of about 100 nm, measured by field emission scanning electron microscopy. X-ray photoelectron spectroscopy analysis confirmed that the sensor mainly comprises MgO elements. The sensing capability of this sensor pair is the potentiometric measurement by time-voltage (V-T) measurement method. The glucose concentration measurement range is linear from 2 mM to 10 mM. Regarding average sensitivity, linearity, response time, interference effect, and limit of detection, multiple experimental results show that the MgO enzymatic glucose biosensor has excellent average sensing performance compared with traditional glucose biosensors.

In this study, the standard industrial flexible printed circuit board (FPCB) was employed to fabricate the potentiometric enzymatic dopamine biosensor. The aluminum-doped zinc oxide (AZO) was used to make the sensing films of the dopamine sensor. This sensing film was prepared by a radio frequency (R.F.) sputtering system. The thickness and surface morphology of the AZO films were observed by the field emission scanning electron microscope (FE-SEM), and the elemental composition and oxidation state of the films were analyzed through X-ray electron spectroscopy (XPS). Tyrosinase was used as the enzyme of the sensor, which was immobilized on AZO film with (3-Aminopropyl)triethoxysilane (APTES) and glutaraldehyde. After the sensor was prepared, we integrated the sensor and the readout circuit board through the FPCB connecter and then measured the sensing characteristics of the dopamine sensor in the dopamine concentration range of 1 μM - 10 mM. The sensing characteristics mostly include average sensitivity and linearity, limit of detection, interference effect, response time, reproducibility, flexibility, and life time. Based on the experiment results, the dopamine sensor in this study has good sensing characteristics. Through the enzyme, the sensor has good selectivity for dopamine in the presence of other relatively high concentrations interfered with biomolecules.