Herein, a multifunctional electrochemiluminescence (ECL) and photoelectrochemical (PEC) biosensor based on exchange of Ag⁺ with CdTe QDs was developed for dual-mode detection of thrombin. First, CdTe QDs assembled on an electrode displayed superior ECL and PEC signals. At the same time, C-rich hairpin (HP) DNA linked to silicon spheres loaded a large amount of Ag⁺, and the specific binding of thrombin to an aptamer led to the release of DNA P; then, DNA P interacted with HP DNA to produce numerous Ag⁺ ions by an enzyme-digestion amplification reaction. Ag⁺ underwent ion exchange with CdTe QDs to generate AgTe/CdTe QDs, resulting in much reversed PEC and changed ECL signals for dual-mode detection of thrombin. This work takes advantage of outstanding multi-signals of QDs coupled with convenient ion exchange to achieve multi-mode detection of the target, avoiding false positive or false negative signals generated in the traditional detection process, and thus can be used for the rapid detection of various biomolecules in actual samples.