Excessive　copper　ions　(Cu2+)　cause　serious　environmental　pollution　and　even　endanger　the　health　of　organisms.　Fluorescence　chemosensing　materials　are　widely　used　in　the　detection　of　metal　ions　due　to　their　simple　operation　and　high　sensitivity.　In　this　study,　SiO2-encapsulated　single　perovskite　quantum　dot　(PQD@SiO2)　core-shell　nanostructures　which　show　strong,　stable,　and　green　fluorescence　are　synthesized　and　composited　with　gold　nanoclusters　(AuNCs)　which　show　Cu2+-sensitive　and　red　light-emitting　fluorescence　to　obtain　a　visualized　ratiometric　fluorescence　sensor　(AuNCs/PQD@SiO2)　for　the　detection　of　Cu2+.　In　the　visualized　detection　of　Cu2+,　the　green　fluorescence　emitted　from　the　ion-insensitive　PQD@SiO2　component　is　used　as　a　reference　signal　and　the　red　fluorescence　emitted　by　ion-sensitive　AuNC　component　is　adopted　as　a　sensing　signal.　In　the　presence　of　Cu2+,　the　red　fluorescence　is　quenched　whereas　the　green　fluorescence　remains　stable,　which　results　in　a　visualized　fluorescence　color　change　from　orange-red　to　yellow　and　finally　to　green　with　increasing　Cu2+　concentration.　The　significant　change　in　the　fluorescence　color　of　AuNCs/PQD@SiO2　in　response　to　Cu2+　enables　a　rapid,　sensitive,　and　visualized　detection　of　Cu2+.　Further　accurate　and　sensitive　ratiometric　fluorescence　analysis　of　Cu2+　can　be　accomplished　by　measuring　the　ratio　of　fluorescence　intensities　at　643　and　520　nm　(I643/I520)　at　a　certain　Cu2+　level.　The　developed　AuNCs/PQD@SiO2-based　sensor　has　been　validated　by　its　satisfactory　application　in　the　detection　of　Cu2+　in　human　serum　and　environmental　water　samples.　This　journal　is　©　The　Royal　Society　of　Chemistry.