Adsorption of PEO-PPO-PEO triblock copolymers on a gold surface

Water-soluble triblock copolymers of Poly(ethylene oxide) and Poly(propylene oxide) (PEOn-PPOm-PEOn) are nonionic amphiphilic macromolecules, commercially available under the names of Pluronics and Poloxamers. Recently interest has been focused on studying their roles in reducing nonspecific protein adsorption and cell adhesion on biomaterial/biosensor surfaces. Although the ability of the adsorbed PEO-PPO-PEO triblock copolymer to reduce protein adsorption has been observed frequently, its detailed mechanism of functioning is yet to be clarified. In order to delineate this detailed mechanism, one first needs to know the adsorption behavior of Pluronics on various substrates. Although gold is a commonly used substrate for the probes of various biosensors, there is no direct data reporting the adsorption behavior of Pluronics on it. In this study, we use surface plasma resonance (SPR) technique and Ellipsometry to detect the adsorption isotherms of various Pluronics on a gold surface. The adsorption isotherm of Pluronics of P103, P104 and F108 all exhibit two plateaus that corresponding to the desorption of the EO and the micellization in bulk solution. At bulk concentration of 1 × 10−2 mg/ml, the total adsorbed amount of the copolymer increases with the increase of the molar mass of the polymer and with the decrease of the EO/PO ratio that suggests the strong influence of the hydrophobic PPO on the adsorbed amount of the polymer. At the CMC, the plateau value of adsorbed amount of Pluronics on Au is independent of molar mass and EO/PO ratio of copolymer. Protein adsorption on gold surfaces modified with various Pluronics shows good correlation between the amounts of protein adsorbed and the value of the reduced surface coverage, σ* of the Pluronic adlayer. In general, by increasing σ*, the nonspecific adsorption of human serum albumin can be reduced.