A simple and sensitive sandwich-type photoelectrochemical (PEC) biosensor with CuO NPs labeled antibody for detection of protein was constructed. The approach relies on antibodies modified by CuO NPs which could release copper ions. In the presence of the target protein, the released copper ions help form the trapping sites to interfere with quantum confinement of quantum dots (QDs) and thus blocked the escape of photoelectron, leading to a "signal off' PEC method for sensitive detection. This work opens a novel highly sensitive way to detect cancer biomarker carcinoembryonic antigen (CEA) and provides an efficient applicable tool for PEC bioanalysis. (C) 2015 Published by Elsevier B.V.