Expanding Mn loading capacity of BSA via mild non-thermal denaturing and cross-linking as a tool to maximize the relaxivity of water protons.

Development of nanoparticles (NPs) serving as contrast enhancing agents in MRI requires a combination of high contrasting effect with the biosafety and hemocompatibility. This work demonstrates that bovine serum albumin (BSA) molecules bound to paramagnetic Mn ions are promising building blocks of such NPs. The desolvation-induced denaturation of BSA bound with Mn ions followed by the glutaraldehyde-facilitated cross-linking provides the uniform in size 102.0 ± 0.7 nm BSA-based nanoparticles (BSA-NPs) loaded with Mn ions, which are manifested in aqueous solutions as negatively charged spheres with high colloid stability. The optimal loading of Mn ions into BSA-NPs provides maximum values of longitudinal and transverse relaxivity at 98.9 and 133.6 mM s, respectively, which are among the best known from the literature. The spin trap EPR method indicates that Mn ions bound to BSA-NPs exhibit poor catalytic activity in the Fenton-like reaction. On the contrary, the presence of BSA-NPs has an antioxidant effect by preventing the accumulation of hydroxyl radicals produced by HO. The NPs exhibit remarkably low hemolytic activity and hemagglutination can be avoided at concentrations lower than 110 μM. Thus, BSA-NPs bound with Mn ions are promising candidates for combining high contrast effect with biosafety and hemocompatibility.