Molecular interactions of biomolecules with surface-engineered interfaces using atomic force microscopy and surface plasmon resonance

We have used albumin-modified atomic force microscope (AFM) tips to probe interactions with a range of hydrophilic polymer brush surfaces and protein. Copolymers of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) (Pluronics) adsorbed onto polymer interfaces have been shown in previous studies to modify adsorption properties of blood components [using surface plasmon resonance (SPR) and AFM]. Here we have employed protein-coated AFM probes to study a series of PEO PPO-PEO-coated interfaces prepared with a range of PEO and PPO molecular weights. Subsequent force-distance experiments have shown a good correlation between the forces of adhesion of an albumin-functionalized AFM probe with the various PEO-PPO-PEO surfaces and the adsorption trends of albumin onto these polymeric surfaces observed with SPR. The data suggest that the size of the hydrophobic PPO segment of the Pluronic is a major determinant of the polymer protein resistance properties. In addition, as the PEO layer density increased, a reduction of interaction force was measured because of the formation of a steric barrier from the PEO polymer brush. Such studies suggest that AEM may be employed as a novel method to assess "biocompatibility" and to rapidly screen surface-engineered surfaces with micrometer spatial resolution.