Biotinylation of colloidal gold particles using interdigitated bilayers: a UV–visible spectroscopy and TEM study of the biotin–avidin molecular recognition process

The surface modification of colloidal gold particles with biotin groups using a technique based on interdigitated bilayers is described. The biotinylation of the colloidal particles is accomplished by a two-step process. The first step involves the self-assembly of a close-packed primary monolayer of octadecanethiol (ODT) molecules on the colloidal particle surface. Thereafter, a secondary monolayer of alkylbiotin molecules is self-assembled on the ODT-capped gold colloidal particles by interdigitation of the alkyl groups of the biotin molecules with the hydrocarbon chains of the primary monolayer. The resulting biotinylation of the colloidal particles is checked by the high-affinity biotin–avidin interaction, which leads to cross-linking of the colloidal particles and an easily measurable change in the optical properties of the sol. This approach may be important for the incorporation of molecules with functional groups that become inactive due to modification of the molecule with colloidal particle surface-anchoring groups such as thiol groups and thus shows scope for development.