Microbial fuel cells (MFCs) hold considerable potential in bioelectricity generation and bioremediation, and their operational processes are highly sensitive to pH fluctuations. Therefore, online pH monitoring is crucial for optimizing the performance of MFCs. Existing pH meters often fall short in meeting the specific demands associated with online pH monitoring. In this study, we designed a novel voltammetric pH sensor based on electrochemically in situ-synthesized graphene-modified screen-printed electrodes. By surface coupling with the hydrogen-bond carrier alizarin safirol SE, the sensor achieves excellent linearity in pH detection within the range of 4.0 to 9.0, with a sensitivity of 70.7 mV per pH unit. The measurement cycle could be controlled within 15 s. This study successfully demonstrated in situ long-term pH dynamic monitoring in a seawater-based MFC constructed using coastal activated sludge, yielding ideal results. Notably, the incorporation of the aforementioned hydrogen-bond carrier enhanced the proton diffusion rate at the graphene interface, thereby improving the performance of the voltammetric pH sensor. Furthermore, this study revealed the considerable potential of this strategy for improving the reference system, which is expected to further substantially enhance the long-term sensing performance of this strategy. In addition, this strategy provides a new approach for long-term in situ online pH monitoring and thereby contribues to the future development of MFCs.

Seawater chlorophyll-a sensors are essential tools for marine ecological monitoring, enabling the detection of spatial and temporal variations in chlorophyll-a concentration. However, these sensors are susceptible to measurement drift, which can compromise data reliability. This study proposes a metrological approach for evaluating sensor performance using fluorescein sodium as a reference standard. Sensor performance was assessed in terms of linear response range, accuracy, precision, and stability. Results indicated a strong positive correlation between fluorescence intensity and fluorescein concentration. Based on the fitted calibration curve, indication error and standard deviation were calculated. The linear response range was determined by controlling the correlation coefficient, whereas stability was assessed through repeated measurements over different time periods. Within the linear range of 0 to 200 μg/L, the maximum measurement error was ≤2.00 μg/L, and the relative standard deviation was <0.20%. The sensor exhibited consistent performance from 2021 to 2022. Maintaining consistent pipetting accuracy was identified as a critical factor for ensuring measurement reliability.