Iodoacetyl-LC-Biotin (N-Iodoacetyl-N'-Biotinylhexylenediamine or N-Biotinyl-N'-(iodoacetyl)-1,6-hexanediamine) reacts with sulfhydryl groups to form stable thioether linkages. Iodoacetyl-LC-Biotin has an extended spacer arm that reduces steric hindrance. Iodoacetyl-LC-Biotin must be dissolved in an organic solvent, such as DMSO or DMF, then added to an aqueous biotinylation reaction. Iodoacetyl-LC-Biotin coupling reactions are most efficient when reacted at at pH 7.5 - 8.5 in reduced light. The resulting biotinylated protein can then be detected when used in conjunction with streptavidin or Immobilized Streptavidin.