In this work, a "turn-on" fluorescence biosensor based on FAM-ssDNA/DFNS@DA complex was developed for rapid and straightforward detection of nucleic acid sequences. The combination of the unique structure of DFNS and the fluorescence quenching by PDA coating allowed us to construct the fluorescence sensor that can tolerate various interfering molecules in biological samples. The release of the fluorophore labeled ssDNA upon target recognition leads to effective fluorescence recovery, enabling rapid and specific detection of the nucleic acid targets. The proposed method for DNA/RNA analysis can be implemented using the generic platform of PDA-coated DFNS without complicated material synthesis. Given that short ssDNA sequences are widely used as labels and probes in biological assays, the analytical platform demonstrated in this work can be combined with antibodies and aptamers to detect a wide variety of biological targets including cellular metabolites, proteins and whole cells.