CruzQuench™ 5 maleimide is designed to be a superior quencher to Cy5, CFLsm5 and Cy5.5. CQ5 has (a). much stronger absorption; (b). much higher quenching efficiency; and (c). versatile reactive forms with desired solubility for labeling oligonucleotides and peptides. This CQ5 product is primarily used for labeling peptides. It is also used for post-labeling of thiol-modified oligonucleotides.