Stable Electrochemical Determination of Dopamine by a Fluorine-Terminated {001}-Exposed TiO2 Single Crystal Sensor

Photochemical oxidation is able to effectively regenerate the fouled electrode in electrochemical pollutant monitoring, while its regeneration capacity is limited by the surface-bound hydroxyl radical speciation with low activity and mobility, which is attributed to the dissociated water adsorption on hydrophilic metal oxides. In this work, fluorine-terminated {001}-exposed TiO2 single crystals (F–TiO2) are rationally designed to construct an Au-based electrochemical sensor (Au/F–TiO2) for dopamine (DA) detection in different matrices. The Au/F–TiO2 sensor exhibits an efficient and stable detection capacity in both environmental and biological samples. A superior photochemical regeneration capacity is obtained on the Au/F–TiO2 electrode with much reduced matrix effects under UV irradiation. Spectral observation, crystallographic analysis, pollutant degradation performance, radical inhibition, and surface enhanced Raman scattering tests reveal that both the fluorine-terminated surface chemical features and the bulk-free radical speciation are mainly responsible for the superior photochemical regeneration capacity of the Au/F–TiO2 electrode. Even for the real biological samples, a stable electrochemical DA detection is also achieved on the Au/F–TiO2 sensor. Our work establishes a new approach to refine electrochemical sensors for stable monitoring and provides a robust photoactive electrode substrate with high efficiency and low cost for practical applications.