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Accurate detection of L -Cysteine (Cyst) is critical because it is a recognized marker associated with diseases such as liver damage and kidney failure. Photoelectrochemical (PEC) sensor is an emerging strategy for biochemical analysis. However, the sensitivity of PEC sensor is limited by the high recombination rate of photogenerated electron-hole pairs. In this study, Au-mediated Z-scheme TiO 2 -Au-BiOI (HTNTs-Au-BOI) photoelectrochemical sensing platform for Cyst detection is proposed. Au NPs with plasmon resonance effect not only boost the light absorption but also facilitate the formation of Z-heterojunction HTNTs-Au-BOI through its own mediating effect. The Z-heterostructure with built-in electric field dramatically suppress the recombination of photogenerated electron-hole pairs and improve the sensitivity of the sensor. Meanwhile, the dual-specificity of Bi-S and Au-S bonds achieves a highly selective and sensitive detection of Cyst. The PEC sensor shows a wide linearity detection range of 80 nM-200 μM with a detection limit of 70 nM. The sensor also shows good results in the detection of serum samples, with a relative standard deviation (RSD) of 0.68–7.3 %. [Display omitted] • The Z-scheme TiO 2 -Au-BiOI is constructed using the mediation of Au NPs. • Au NPs with plasmonic resonance effect can significantly enhance the light absorption of TiO 2 -Au-BiOI. • Z-scheme HTNTs-Au-BiOI with built-in electric field suppress the recombination of photogenerated electron-hole pairs. • The dual-specificity of Bi-S and Au-S bonds achieve a highly selective and sensitive detection of Cyst. [ABSTRACT FROM AUTHOR]

Investigation of the mechanism of oxygen vacancy-regulated photoelectrochemical sensors for highly sensitive and selective determination of biomolecules containing electron-donating groups is an innovative research field. In this study, oxygen vacancy-regulated TiO 2 nanotube arrays (Ov-TNTs) with high photoelectrochemical activity were synthesized and applied to defect tetracycline hydrochloride (TC). The synergistic effect of oxygen vacancies and Ti3+ droves Ov-TNTs with a narrow energy band to generate more photogenerated carriers under irradiation. The photocurrent response of the oxygen vacancy-regulated photoelectrochemical sensor decreased with increasing TC concentration, which could be mainly attributed to adsorption of TC, which consumed part of the oxygen vacancies on the surface of Ov-TNTs. This system had excellent linearity in the range of 0.1–1000 nM with a detection limit of 0.33 nM (S/N = 3). In addition, the sensor was highly selective for TC determination due to the mutual electrostatic interaction between negatively charged TC-containing electron-donating groups (-NH 2 and -OH) and positively charged Ov-TNTs. This study provided a foundation for developing an oxygen vacancy-regulated adsorptive photoelectrochemical sensor. • The introduction of oxygen vacancies drives TNTs with narrow energy band to generate more photogenerated carriers. • Oxygen vacancies can be used as electron traps for preferential adsorption of TC molecules with electron-donating groups. • The photoelectrochemical sensor exhibits superior sensitivity and selectivity for TC detection. • The mechanism investigation shows that the adsorption of TC on the surface of Ov-TNTs decreases the oxygen vacancies and Ti3 + concentration, resulting in the gradual recovery of photocurrent to pure TNTs. [ABSTRACT FROM AUTHOR]