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• It was the first application of GaON in PEC immunosensors. • An effectively cascade-like energy band edge level was obtained, which can effectively amplified PEC response. • The BiVO 4 /GaON/CdS label-free PEC immunosensor was successfully developed for determination of procalcitonin. In this paper, GaON with excellent photoelectrochemical (PEC) performance was adopted in PEC immunosensor for the first time. Based on CdS sensitized BiVO 4 /GaON composite material, a label-free PEC immunosensor was successfully developed for determination of procalcitonin (PCT). Firstly, BiVO 4 nanoarray was prepared by electrodeposition. Then GaON was added to form the BiVO 4 /GaON composite material, due to the greatly increasing charge transfer efficiency, the PEC signal increased by about 3 times. At last, CdS grew in situ on BiVO 4 /GaON composite that further expanded the light absorption range and improved the light utilization, and the PEC signal further increased again. This PEC immunosensor has a good linear relationship of 0.1 pg mL−1 - 50 ng mL−1 and the detection limitation of 0.03 pg mL−1 is calculated. Importantly, the BiVO 4 /GaON/CdS immunosensor platform showed good specificity and stability, and serum sample analysis have been performed with satisfactory results. [ABSTRACT FROM AUTHOR]

• The signal indicator and matrix, Fe 3 S 4 -Pd, displayed excellent electrocatalytic activity for H 2 O 2 redox reaction. • Magnetic glassy carbon electrode was used to firmly immobilized the magnetic Fe 3 S 4 -Pd to achieve satisfied stability. • PBG nanomaterial played a role as the electron blocking label that realized a sensitive variation of current signal. • The signal-off sensing platform was successfully constructed, with a low detection limit of 130 fg/mL. Herein, a sandwich-type electrochemical (EC) immunosensor is proposed based on a special signal-off mode for the sensitive detection of procalcitonin (PCT) by utilizing Fe 3 S 4 loaded with Pd nanoparticles (Fe 3 S 4 -Pd) as a signal indicator and matrix and functionalized pineal mesoporous bioactive glass (PBG) as the label for signal amplification. Fe 3 S 4 -Pd not only shows excellent electrocatalytic activity for the H 2 O 2 redox reaction but is also firmly immobilized on a magnetic glassy carbon electrode due to its excellent magnetic properties; because of the above features, this immunosensor exhibits excellent sensitivity and stability, respectively. Glutaraldehyde is used as a cross-linking agent to bond the secondary antibodies (Ab 2) with PBG. It is worth mentioning that the electron transfer rate between the electrolyte and electrode is decreased significantly by PBG-Ab 2 ; thus, a sensitive variation in the current signal is observed, and a further improvement in the sensitivity of the immunosensor is realized. More importantly, the proposed signal-off sensing system has a wide linear detection range of 500 fg/mL to 50 ng/mL for PCT and a low detection limit of 130 fg/mL, which promotes it as a promising detection method for the sensitive detection of other biomarkers. [ABSTRACT FROM AUTHOR]