In this work, a unique, highly sensitive and selective fluorescence turn-on approach for cysteine detection using an ensemble of graphene oxide (GO) and metallized DNA is reported. The method is based on the extraordinarily high quenching efficiency of GO and the specific interaction between cysteine and metallized DNA via robust AgS bonds. In the presence of GO, the dye-labeled single-stranded DNA shows weak fluorescence, while it exhibits a dramatic fluorescence increase upon the formation of the double helix through the activated metallized DNA by cysteine. In addition, the protocol shows excellent selectivity for cysteine over various other amino acids found in proteins. Importantly, by exploring GODNA interactions and the thiol-mediated DNA hybridization, our sensing system can also be utilized to design the OR and INHIBIT logic gates using cysteine and DNA as inputs. To the author's knowledge, this method is the first example of combining GO and DNA metallization to fabricate a turn-on fluorescent sensor for cysteine and logic gates.