It is of great significance to sensitively and conveniently detect trace UO22+ ions in biological and environmental samples due to severe health risks. However, such suitable sensors are still scarce. In this work, DNAzyme-based hydrogels modified on Ag NP-grafted PAN nanorods array as flexible SERS biosensor have been developed for ultrasensitive UO22+ ion detection. They were first formed by the substrate strand and enzyme strand comprising the main cleavage-reaction stem-loop complex. Then, a UO22+ ions responsive smart hydrogel capsule was achieved by DNAzyme complex hybridized with DNA polyacrylamide chains. Raman reporter RhB was introduced and intentionally trapped inside the hydrogel. In the absence of UO22+ ions, a tiny Raman signal was presented because RhB was trapped inside the hydrogel and far away from SERS substrates. Conversely, the responsive hydrogel could be specifically attacked by UO22+ ions to release RhB, leading to a strong Raman signal. With the amplified signal procedure, this flexible SERS biofilm accomplished sensitive and selective detection of UO22+ ions with a wide linear range from 1 pM to 0.1 mu M and a low detection limit of 0.838 pM. This result is nearly five orders below the EPA-defined maximum contaminant level (180 nM). Furthermore, this biofilm gives full play to the advantages of a flexible biosensor. It can directly detect the aquatic products (such as fish and kelp) polluted by UO22+ ions, demonstrating that this flexible SERS biofilm has promising potential for applications in a rapid environmental safety inspection.