FT-IRRAS spectroscopic studies of the interaction of avidin with biotinylated dendrimer surfaces

Abstract

The interaction of avidin with biotin on a functional Au surface containing fourth generation amine-terminated polyamidoamine (G4-NH 2 PAMAM) dendrimers was investigated through the use of Fourier transform infrared reflection–adsorption spectroscopy (FT-IRRAS). The first step in the fabrication of the functional surfaces used was the construction of an aldehyde-terminated self-assembled monolayer (SAM) through the treatment of Au-coated glass slides with ethanol solutions of self-synthesized 2-hydroxypentamethylene sulfide (HPMS). The as-formed aldehyde-terminated monolayer was subsequently immersed in methanol solutions of G4-NH 2 PAMAM dendrimer to obtain well-organized primary amine-terminated surfaces. Biotinylation of the amine-terminated layers thus obtained was accomplished by use of the N-succinimidyl ester of biotin. Each step of the synthetic process, as well as the performance of final surface for protein recognition was monitored by FT-IRRAS. In particular, the molecular recognition ability was examined and quantified by use of an alkyne dicobalt hexacarbonyl probe coupled with avidin. Non-specific adsorption of avidin was determined by exposure of the amine-terminated and/or biotinylated surfaces to solutions of biotin-saturated avidin. The results indicate that the biotinylated G4-NH 2 PAMAM dendrimer layers formed according to this procedure have a high capacity for binding avidin with relatively high specificity. The performance of these layers (i.e. both binding capacity and specificity) improve substantially when 6-mercapto-1-hexanol (MH) is present as a co-adsorbent during the formation of the initial aldehyde-terminated layers. This effect can be attributed to the dilution of the initial aldehyde-terminated SAM, leading to a more favorable spatial arrangement of the subsequent biotinylated surfaces.