Scheme 1.

Different strategies used for biotin and BG conjugation to vectors; a) Biconjugation method: Use of commercial NHS ester—BG for conjugation to amines of the vector, and maleimide‐biotin for conjugation to thiol. b–d) Monoconjugation method: Synthesized maleimide‐benzylguanine‐biotin molecules for conjugation to thiol of the vector. Different PEG linker sizes were tested in order to avoid steric hindrance between vector, the BG reaction with the SNAP‐tag, and streptavidin binding to the biotin moiety.