The amine functional group at one end of the PEG linker molecule allows for selective and covalent attachment to other molecules with complementary functional groups, such as carboxylic acids or activated esters, aldehydes and epoxides. The biotinyl functionality is used to attach avidin or streptavidin containing substrates. Pegylation by binding of biotinyl PEG to avidin and streptavidin is very specific and fast.