Development of polarographic flexible dissolved oxygen intelligent sensors

Dissolved oxygen can play a key role in the production and living of aquatic ecosystems. New materials and artificial intelligence (AI) technologies can be expected to promote the process of smart fisheries in recent years. It is very necessary to equip it with light, small, soft, and biocompatible sensors. Flexible electronics and sensing technology can be combined to detect dissolved oxygen. In this study, a flexible dissolved oxygen sensor was prepared to measure the temperature function by magnetron sputtering. The inkjet was also dispensed on both sides of the flexible substrate material. A multi-layer structure of the planar electrode was then adopted for the vertical distribution of oxygen-permeable film to encapsulate the electrolyte and the planar electrode. The polarization voltage was determined for the dissolved oxygen sensor by the linear sweep voltammetry (LSV) scanning in the electrochemical workstation. The polarization time of the sensor was measured by the response experiment. In addition, a comparison was also made on the difference between the prepared and commercial electrodes. The surface morphology of dissolved oxygen and temperature sensors was characterized using optical microscopy. A series of tests were carried out on the linearity, sensitivity, response time, drift, stability, and mechanical bending properties of the sensor. Finally, the sensing circuit and intelligent processing were designed to verify the feasibility of the sensor in the detection of dissolved oxygen in aquaculture water. The experimental results showed that the optimal polarization voltage of the prepared dissolved oxygen sensor was −0.6 V and the polarization time was 42 s. There was less difference between the flexible sensor and commercial electrodes in CV scanning, indicating the better performance of ion diffusion. Both the dissolved oxygen sensor and the temperature sensor exhibited homogeneous and better surface morphology at high magnification. There was an excellent linear relationship between the collection current and the dissolved oxygen content (R²=0.994 5) at room temperature. The sensitivity of the sensor was −0.03 μA·L/mg, the response time was 16.8 s (the maximum difference of multiple measurements was 3.3 s), and the maximum difference within 7 days was 0.0195 μA. The resistance of the flexible temperature sensor shared a better linear relationship with temperature in the range of 0-150 ℃ and 0-30 ℃ ( R² were 0.994 9 and 0.997 6, respectively). The sensitivity of the sensor was −2.47 kΩ/℃, the response time was 3 s, and the hysteresis error was 2.17%. The flexible sensor maintained better performance for the measurement of dissolved oxygen and temperature in the range of 0-60°. The maximum error of the prepared sensor was less than 5% when detecting different content of dissolved oxygen in aquaculture water at various temperatures, compared with the commercial sensor. A better temperature compensation can be obtained to rapidly and accurately detect the content of dissolved oxygen and the temperature of the water body in fishery applications.