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

Abstract

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 T 1 -weighted magnetic resonance imaging (MRI) ability, suggesting their great potential in the application of multienzyme catalysis and MRI.

Prussian blue nanozymes with enhanced catalytic activity: size tuning and application in ELISA-like immunoassay

“…Oppositely, Jia et al observed that slight growth of prussian blue nanoparticles accompanied the addition of excessive amounts of oxalic acid [43]. Probably, the larger aging time is the reason for this result [34]. Citric acid allows for the regulation of nanoparticle size in a wider range in comparison with oxalic acid.…”

“…The size of "artificial peroxidase" nanozymes can be controlled by tuning synthesis conditions: pH, temperature, ionic strength, and so on Alteration of various synthesis parameters (temperature [28,29], pH [30,31], presence of chelating agent [32,33,34], ratio of reactants [35], addition of organic solvent [36,37]) enables manipulating the size of prussian blue nanoparticles prepared by traditional double precursor method or hydrothermal single precursor method. We determined the influence of most of these factors on the diameter and yield of 'artificial peroxidase' nanozymes.…”

“…Syntheses were performed on different days using freshly prepared salt solutions to closely imitate real-world situation. The size of nanoparticles was assessed by DLS, which is known to overestimate the mean diameter of nanoparticles (in comparison with TEM) [34]. TEM analysis showed that "artificial peroxidase" nanoparticles have an irregular shape and are rather disordered assemblies of smaller nanoparticles (Figure S11).…”

“…Probably, carboxylic acids somehow enhance the catalytic activity of prussian blue nanoparticles. Recently, Feng et al prepared prussian blue nanoparticles in the presence of citric acid with various sizes and crystallinity by regulating the regime of reagents addition [34]. Authors demonstrated that more amorphous nanoparticles possessed better peroxidase-and catalase-like activity, which is also true for other nanomaterials [61].…”

“…On the other hand, citric acid facilitated the preparation of prussian blue nanoparticles with perfect crystallinity [40]. Evidently, the morphology of prussian blue nanoparticles depends on both concentration of chelating agent and aging time [34,64]. Synthesis in the presence of hydrogen peroxide also decreased the crystallinity of prussian blue analogs [65].…”