Prussian Blue Nanoparticles Having Various Sizes and Crystallinities for Multienzyme Catalysis and Magnetic Resonance Imaging

Controllable synthesis of Prussian blue nanoparticles (PBNPs) is significant for their various applications. Further, exploration on the growth process of PBNPs (a kind of nanoparticle which usually undergoes an extremely complicated formation process) is instructive for controllable synthesis and will be an important supplement for crystallization theory. Herein, we developed a facile method to precisely and widely control the size and crystallinity of PBNPs. By simply tuning the prior addition volume of ferric chloride and citric acid mixture combining a double injection reaction, particles with a hydrodynamic size ranging from 120 to 40 nm were synthesized. Meanwhile, the crystallinity of the particles reduced as their size decreased. Unlike the common cognition that generation of PBNPs undergoes a nonclassical aggregation process, our results demonstrated that reaction rate dominated classical nucleation and nuclei enlargement, and the subsequent crystallization contributed to the formation of PBNPs. By carefully studying the crystallography state and transformation relationship of the as-prepared particles, PBNPs were generally divided into three categories: highly crystalline, partly crystalline, and highly amorphous PBNPs. Spectroscopy, enzymology, and magnetic measurements confirmed the size- and crystallinity-dependent physicochemical properties of the PBNPs. Smaller and amorphous PBNPs exhibited remarkably stronger peroxidase-like activity, catalase-like activity, and T1-weighted magnetic resonance imaging (MRI) ability, suggesting their great potential in the application of multienzyme catalysis and MRI.