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[Display omitted] • Zn-Fe 2 O 3 /CdIn 2 S 4 as sensing platform to provide a stable PEC signal. • Ag@CuWO 4 as an antibody marker, which greatly reduces the detection limit. • PEC sensor exhibited a low detection limit of 14.7 fg/mL for CEA. • Handheld workstation controlled by smartphone for on-site testing of CEA. Carcinoembryonic antigen (CEA) is expressed in many tumor cells and is an important cancer marker in human serum. To assess human health, a rapid and accurate real-time detection method should be established for the sensitive detection of CEA. In this work, real-time and on-site CEA detection was achieved by constructing sandwich-type photoelectrochemical (PEC) immunosensor and using a portable electrochemical workstation controlled by a smartphone. The employment of Zn-doped Fe 2 O 3 /CdIn 2 S 4 (Zn-Fe 2 O 3 /CdIn 2 S 4) is proposed for the first time as a sensing platform for PEC sensor. Due to its suitable band gap combination, a stepped electron transfer pattern provides a stable photocurrent response. Ag@CuWO 4 as an antibody marker can amplify the sensor signal due to its ability to form a Z-type electron transfer mode with CdIn 2 S 4. The Box-Behnken experiment was used to eliminate the interaction of experimental conditions and screen out the optimal experimental conditions for the immunosensor. In addition, the PEC immunosensor has a good linear relationship with CEA in the detection range of 100 fg/mL to 100 ng/mL, with a detection limit as low as 14.7 fg/mL (S/N = 3). The immunosensor has portable characteristics, good stability, reproducibility, specificity, and storage stability. It showed appreciable recoveries and low relative standard deviations in human serum sample analysis. This PEC assay paves a new point-of-care testing method for other cancer markers, particularly environmental contaminants. [ABSTRACT FROM AUTHOR]