5(6)-Carbonylated rhodamine 110 X NHS ester is an active ester-based fluorescent reagent derived from 5(6)-carbonylated rhodamine 110 X. The NHS ester is highly reactive, allowing it to form stable amide bonds through covalent coupling with primary amine groups in proteins, peptides, aminoglycosides, nucleic acids, and other molecules (Ex/Em = 496/522 nm).