We offer a variety of quenchers, fluorophores, and non-fluorescent modifications in the form of succinimidyl esters, carboxylic acids, and amines for post-synthesis labeling. These labeling reagents can be used to label peptides and proteins. BHQ® dyes are dark quenchers that are available as active esters for coupling to amine groups on peptide substrates. Our family of CAL Fluor® and Quasar® labels are designed with peptide labeling in mind and have been extensively performance tested in a variety of assay formats.