<p>Being enlightened by Fenton-like reaction, a novel chemically driven redox-cycling system has been developed without the participation of additional reducing agents. In this chemically driven cycling system, terephthalic acid (TA) was selected as fluorescence substrate to trap the generated hydroxyl radicals (·OH) to produce 2-hydroxyterephthalic acid (TAOH), which possessed high fluorescence intensity. On one hand, Cu⁺ triggered a Fenton-like reaction with H₂O₂ to yield Cu²⁺ and ·OH. But on the other&#xa0;hand, the generated Cu²⁺ could react with H₂O₂ to produce Cu⁺ and O₂^·− (further converted into ·OH). The regenerated Cu⁺ could take turns reacting with H₂O₂ to produce more ·OH and form more TAOH. As a result, a kind of chemical redox-cycling signal amplification reaction was touched off. On the basis of copper based metal–organic frameworks (Cu-MOFs) and signal amplified strategy, a magnetic separated-mode fluorescent biosensor was designed for the sensitive determination of DNA. The method allowed ultrasensitive detection of target DNA H1N1 with a linear range from 5&#xa0;pM to 10&#xa0;nM, and with a limit of detection of 2 pM. This magnetic separated-type system could effectively minimize the background signals by reducing the mutual interferences between nucleic acids hybridization and fluorescence signal conversion.</p> Graphical Abstract <p></p>