Preparation, characterization, resistance to protein adsorption, and specific avidin-biotin binding of poly (amidoamine) dendrimers functionalized with oligo(ethylene glycol) on gold

Protein-resistant films derived from the fifth-generation poly(amidoamine) dendrimers (PAMAM G5) fUnctionalized with oligo(ethylene glycol) (OEG) derivatives consisting of various ethylene glycol units (EG(n) = 3,4, and 6) were prepared on the self-assembled monolayers (SAMs) of 11-mercaptoundecanoic acid (MUA) oil gold Substrates. The resulting films were characterized by ellipsornetry, contact angle goniometry, and X-ray photoelectron spectroscopy (XPS). About 35% of the peripheral amines of the dendrimers were reacted with N-hydroxysuccinimideterminated EG(n) derivatives (NHS-EG(n)). The dendrimer films showed improved stability over octadecanethiolate SAMs on gold in hot solvents, attributed to the formation Of Multiple amide bonds per PAMAM unit with underlying NHS-activated MUA monolayer. The EG(n)-attached PAMAM surfaces with n = 3 reduced the adsorption of fibrinogen to similar to 20% monolayer. whereas 2-3% for n = 4 or 6. The dendrimer films with various densities of EG,, molecules on PAMAM surfaces were prepared by immersion ofthe NI-IS-terminated MUA-functionalized gold substrates in ethanolic Solutions containing PAMAM and NHS-EG,, Of Various mole ratios. The density (r) of the EG,, molecules on the PAMAM Surfaces is consistent with the mole ratio (r ') of NHS-EG(n)/free amine of PAMAM in solutions. The resistance to protein adsorption of the resulting surfaces is correlated with the surface density and the length of the EG chains. At their respective r. the EG(n)-modified dendrimer films resisted similar to 95% adsorption of fibrinogen on gold Surfaces. Finally, the specific binding of avidin to the 5% and similar to 40% biotinylated EG(3) dendrimers (surface density of biotin with respect to the total number of terminal amino groups on PAMAM G5) gave rise to about 50% and 100% surface coverage by avidin, respectively. (c) 2005 Elsevier Inc. All rights reserved.