Controllable formation of polydopamine on carbon dots for ultrasensitive detection of alkaline phosphatase and ratiometric fluorescence immunoassay of benzocaine

•PDA’s triple roles of quencher, AA recognizer, and signal reporter were harnessed.•Fluorogenic substate AAP-CDs-DA was used in ultrasensitive ratiometric ALP sensing.•An ultrasensitive RF-ELISA was developed to detect benzocaine (LOD at fg/mL level).•The RF sensing platform exhibits good universality in food safety detection.