A method is described for modulating the anodic photoelectrochemistry of netlike CdS quantum dots through the deposition and dissolution of the electron acceptor manganese dioxide (MnO) on the surface of the photoelectrode. Specifically, the photocurrent of a CdS-modified indium tin oxide (ITO/CdS) electrode is inhibited by chemical deposition of MnO. However, the photocurrent becomes recovered by oxidative removal of MnO with HO. This deposition-dissolution reaction modulates the photoelectrochemistry of CdS effectively. A bioassay for Escherichia coli (E. coli) O157:H7 is designed that uses the antimicrobial peptide magainin I as the recognition element. Glucose oxidase (GOx) acts as a catalytic label tracer to produce the signaling molecule HO in the microwell plates. The enzymatically generated HO etches the deposited MnO on the photoelectrode and thus enhances the photocurrent. This detection scheme does not cause any damage to biomolecules. It also avoids the adverse effects of immobilized biomolecules for retarding signal production and leads to improved detection when compared to conventional PEC configurations. E. coli can be detected in the 10 to 5.0 × 10 CFU·mL concentration range, and the limit of detection is 3 CFU·mL. Graphical abstractSchematic representation of the photoelectrochemical assay of E. coli through the deposition and dissolution of electron accepting manganese dioxide (MnO) on the surface of the photoelectrode.