Multifunctional dithioacetal-modified perylenediimide (DTPDI) is synthesized as a highly sensitive and selective fluorescent chemosensor for recyclable Hg2+ detection and an effective DNA carrier. The central PDI chromophore allows the tracing of cell uptake by fluorescence microscopy, dithioacetals enable the detection of Hg2+, and peripheral amine hydrochloride salts increase the water solubility and also serve as positive charges for noncovalent binding of negatively charged DNA. In addition to serve as a recyclable fluorescent probe for Hg2+ detection, DTPDI can be rapidly internalized into live cells with low cytotoxicity and high DNA delivery efficacy.