Application of a fluorescent biosensor based-on magneto-γ-Fe2 O3 -methyldopa nanoparticles for adsorption of human serum albumin.

Understanding and controlling the interaction between the polymer methyldopa (2-amino-3-(3,4-dihydroxyphenyl)-2-methyl-propanoic acid) (PMDP)-γ-Fe2 O3 nanoparticles and biological fluids is important if the potential of nanoparticles (NPs) in biomedicine is to be realized. Physicochemical studies on the interactions between proteins and NPs are influenced by the surface properties of the NPs. To identify the effects of the NP surface, interactions between human serum albumin (HSA) and PMDP-γ-Fe2 O3 NPs were investigated. Here, the adsorption of HSA onto small (10-30 nm diameter) PMDP-γ-Fe2 O3 NPs was quantitatively analyzed using spectroscopic methods. The fluorescence quenching data were checked for the inner-filter effect, the main confounding factor in the observed quenching. The binding constants, Ka , were calculated at different temperatures, using a nonlinear fit to the experimental data, and the thermodynamic parameters ∆H, ∆S and ∆G were given. The obtained thermodynamic signature suggests that hydrophobic interactions at least are present. This result indicates that the structure of the protein turns from a structureless denatured state at pH 3 into an ordered biologically active native state on addition of PMDP-γ-Fe2 O3 NPs. Copyright © 2015 John Wiley & Sons, Ltd.