A high-performance fluorescent probe for detection of cysteine in plasma constructed by combining Cu(I) and 2,5-dimercapto-1,3,4-thiadiazole

•Fluorescent probe DMTD-CuNPs was constructed by combining DMTD with Cu(I).•DMTD significantly increased the fluorescence intensity of DMTD-CuNPs at 515 nm.•Stokes shift 315 nm of probe reduces the self-quenching of probe fluorescence.•The probe has low detection limit, high sensitivity and good selectivity for Cys.•The probe can specifically detect Cys in plasma samples.