Biotin-XX hydrazide, also known as Biotin-(AC5)2-hydrazide, is a carbonyl-reactive biotinylation reagent featuring two aminohexanoic acid spacers. This compound demonstrates a heightened efficacy in binding to avidin.

Biotin-XX hydrazide contains two aminohexanoic acid spacers which greatly enhances the efficiency of formation of the complex between the biotinylated antibody (or other biotinylated protein) and the avidin–probe conjugate, where the probe can be a fluorochrome or an enzyme[1].