A water-soluble neutral fluorescent conjugated oligomer (FBT) is integrated with graphene oxide (GO) to form a hybrid nanoprobe with extremely low fluorescence background due to the robust quenching capability of GO. The contact between GO and FBT can be effectively shielded by Concanavalin A because of the strong specific protein-carbohydrate interaction, which ultimately allows light-up visual detection of lectin and Escherichia coli.