The identification of a suitable non-fluorescent molecule that can be oxidized by G-quadruplexes into a fluorescent product will be important for several fields such as bioanalyte sensing and cancer therapeutic discovery. Herein, we demonstrate that 2′,7′-dichlorodihydrofluorescein diacetate is a superior reducing substrate for the fluorometric detection of bioanalytes using peroxidase-mimicking G-quadruplexDNAzymes.