A new probe/Cu²⁺ complex for the detection of his-tagged protein has been developed, based on an improved probe, Dansyl-Gly-Py (1), by closely mimicing the structure of a peptide, ATCUN. In aqueous solution, 1/Cu²⁺ has good selectivity to histidine and cysteine, and further can detect histidine-rich protein by releasing the quenched fluorescence of 1.