VRDye labeling kits are cost-effective alternatives to expensive, time-consuming, custom antibody labeling services. The High MW kits are optimized for labeling 1 mg of an IgG antibody. The High MW-Microscale kits are optimized for labeling 100 µg of an IgG antibody. These kits may also be used to label proteins spanning the molecular weight range of 50 kDa to 200 kDa. The visible dyes included in these kits are activated with N-hydroxysuccinimide (NHS) esters, which is the most commonly used reactive group for labeling proteins. NHS esters react with primary amines, forming stable, covalent bonds.