The reversible binding of immunoglobulins G modified with adamantyl-end-capped poly(ethylene glycol)s to poly-β-cyclodextrin-coated gold surfaces and their interactions with specific target molecules: A surface plasmon resonance investigation

Adamantyl-end-capped poly(ethylene glycol)s (Ad-PEG) were coupled to immunoglobulins G (IgGs) using increasing molar ratios of Ad-PEG over IgG. The extent of modification of the Ad-PEG-IgGs was examined by electrophoresis and the effect of modification on their binding activity by enzyme-linked immunosorbent assays (ELISA). There was a graded increase in molecular weight at each Ad-PEG over IgG ratio for the modified IgG compared with the native one, and concurrently a graded decrease in binding activity with an increasing amount of coupling. After polymers of β-cyclodextrin (β-CD) were grafted to gold surfaces, inclusion of the adamantyl-modified IgGs into immobilized β-CD cavities was studied in real time by surface plasmon resonance (SPR). The resulting multilayered structures were highly stable in aqueous media and their ability to bind specific targets demonstrated by SPR. The binding capacities of the Ad-PEG-IgG layers were shown to decrease as the number of coupled Ad-PEG chains increased. These results were consistent with those of the ELISA. The initial poly-β-CD-coated surface could be regenerated by a two-step procedure using diluted chlorohydric acid and sodium dodecylsulfate (SDS) successively, or by a one-step procedure using SDS in acidic buffer.