BiOBr_0.8I_0.2/CoS_x Nanostructure-Based Photoelectrochemical and Electrochemical Dual-Mode Sensing Platform for the Ultrasensitive and Highly Selective Detection of HER2

Sensitive and accurate detection of tumor markers is significant for early diagnosis and cancer treatment, but it remains challenging. A promising solution is to integrate different detection strategies into the same sensing platform. Herein, a BiOBr0.8I0.2/CoSx nanocomposite with high photoelectrochemical (PEC) and electrochemical (EC) activity is prepared by a hydrothermal method and afterward in situ visible light irradiation. The light irradiation makes BiOBr0.8I0.2/CoS turn into BiOBr0.8I0.2/CoSx (x = 1–2), and the photocurrent thus increases by 5 times. Compared with the BiOBr0.8I0.2, the photocurrent of the composite increased by 74 times due to the formation of a heterojunction and the enhanced sensitization of CoSx. Furthermore, the nanocomposite can exhibit a high cathodic signal. Therefore, it is used to construct a PEC and EC dual-mode sensing platform for the detection of human epidermal growth factor receptor-2 (HER2), by combining with the aptamer of HER2. Due to the steric hindrance of HER2, the PEC and EC signals change with HER2 concentration. Under the optimized conditions, the sensing platform shows quite low detection limits (0.31 and 1.06 pg/mL) and large linear ranges (0.001–10 and 0.005–15 ng/mL, for PEC and EC mode, respectively). It also demonstrates high selectivity, excellent stability, and good applicability. The sensing platform can also be applied to detect other markers by replacing the recognition element.