D-Leu-Pro-Arg-Rh110-D-Pro is a substrate for Factor Xa I (FXIa) with binding affinity. D-Leu-Pro-Arg-Rh110-D-Pro consists of Rhodamine 110 linked to a peptide chain through a cleavable bond. Cleavable bond cleavage enhances fluorophore intensity. D-Leu-Pro-Arg-Rh110-D-Pro can be used to detect FXIa activity.