In　this　work,　a　novel　fluorescent　biosensor　has　been　constructed　for　rapid　detection　of　Cu(II)　via　the　interaction　between　the　fluorophore　groups　on　the　surface　of　nitrogen-doped-carbon-dots　(N-CDs)　and　·OH　produced　from　the　catalytic　reaction　between　Cu　(II)　and　cysteine　(Cys).　Specifically,　Cu　(II)　can　catalyze　the　oxidation　of　Cys　to　form　cystine　(Cys–Cys)　and　hydrogen　peroxide　(H2O2),　and　Cu　(II)　can　also　catalyze　the　decomposition　of　H2O2　to　produce　hydroxyl　radicals　(·OH)　by　the　Fenton-like　reaction.　·OH　can　oxidize　and　destroy　the　surface　structure　of　N-CDs,　resulting　in　the　fluorescence　quenching　of　the　N-CDs.　Under　the　optimal　experimental　conditions,　the　linear　range　of　Cu　(II)　is　determined　to　be　0.05–25 μmol L−1,　and　the　limit　of　detection　is　23 nmol　L−1　with　the　limit　of　quantitation　of　77 nmol　L−1.　Besides,　some　characterizations　are　provided　to　verify　the　proposed　principle.　The　method　has　been　successfully　applied　for　the　detection　of　Cu　(II)　in　human　serum　and　environmental　water　with　high　sensitivity　and　higher　selectivity.　©　2021,　The　Nonferrous　Metals　Society　of　China.