Changqian Cao

Magnetoferritin nanoparticles for targeting and visualizing tumour tissues

Engineered nanoparticles have been used to provide diagnostic, therapeutic and prognostic information about the status of disease. Nanoparticles developed for these purposes are typically modified with targeting ligands (such as antibodies, peptides or small molecules) or contrast agents using complicated processes and expensive reagents. Moreover, this approach can lead to an excess of ligands on the nanoparticle surface, and this causes non-specific binding and aggregation of nanoparticles, which decreases detection sensitivity. Here, we show that magnetoferritin nanoparticles (M-HFn) can be used to target and visualize tumour tissues without the use of any targeting ligands or contrast agents. Iron oxide nanoparticles are encapsulated inside a recombinant human heavy-chain ferritin (HFn) protein shell, which binds to tumour cells that overexpress transferrin receptor 1 (TfR1). The iron oxide core catalyses the oxidation of peroxidase substrates in the presence of hydrogen peroxide to produce a colour reaction that is used to visualize tumour tissues. We examined 474 clinical specimens from patients with nine types of cancer and verified that these nanoparticles can distinguish cancerous cells from normal cells with a sensitivity of 98% and specificity of 95%.

Magnetic characterization of noninteracting, randomly oriented, nanometer-scale ferrimagnetic particles

determined by AC susceptibility is (9.2 ± 7.9) × 10 10 Hz. The extrapolated Mrs/Ms and Bcr/Bc at 0 K are 0.5 and 1.12, respectively, suggesting that the ferrimagnetic HFn cores are dominated by uniaxial anisotropy. The calculated effective magnetic anisotropy energy constant Keff =1 .2 ×1 0 5 J/m 3 , which is larger than previously reported values for bulk magnetite and/or maghemite or magnetoferritin and is attributed to the effect of surface anisotropy. These data provide useful insights into superparamagnetism as well as biomineralization of ultrafine ferrimagnetic particles.

Enhanced magnetic resonance imaging and staining of cancer cells using ferrimagnetic H-ferritin nanoparticles with increasing core size

Purpose This study is to demonstrate the nanoscale size effect of ferrimagnetic H-ferritin (M-HFn) nanoparticles on magnetic properties, relaxivity, enzyme mimetic activities, and application in magnetic resonance imaging (MRI) and immunohistochemical staining of cancer cells. Materials and methods M-HFn nanoparticles with different sizes of magnetite cores in the range of 2.7–5.3 nm were synthesized through loading different amounts of iron into recombinant human H chain ferritin (HFn) shells. Core size, crystallinity, and magnetic properties of those M-HFn nanoparticles were analyzed by transmission electron microscope and low-temperature magnetic measurements. The MDA-MB-231 cancer cells were incubated with synthesized M-HFn nanoparticles for 24 hours in Dulbecco’s Modified Eagle’s Medium. In vitro MRI of cell pellets after M-HFn labeling was performed at 7 T. Iron uptake of cells was analyzed by Prussian blue staining and inductively coupled plasma mass spectrometry. Immunohistochemical staining by using the peroxidase-like activity of M-HFn nanoparticles was carried out on MDA-MB-231 tumor tissue paraffin sections. Results The saturation magnetization (Ms), relaxivity, and peroxidase-like activity of synthesized M-HFn nanoparticles were monotonously increased with the size of ferrimagnetic cores. The M-HFn nanoparticles with the largest core size of 5.3 nm exhibit the strongest saturation magnetization, the highest peroxidase activity in immunohistochemical staining, and the highest r2 of 321 mM−1 s−1, allowing to detect MDA-MB-231 breast cancer cells as low as 104 cells mL−1. Conclusion The magnetic properties, relaxivity, and peroxidase-like activity of M-HFn nanoparticles are size dependent, which indicates that M-HFn nanoparticles with larger magnetite core can significantly enhance performance in MRI and staining of cancer cells.

Identification of ferrous-ferric Fe3O4 nanoparticles in recombinant human ferritin cages.

Recombinant ferritin is an excellent template for the synthesis of magnetic nanoparticles. This paper describes carefully performed experiments both to identify ironoxides within nanoparticles and to measure the number of iron atoms in the cores of recombinant human H-chain ferritin (HFn), based on spectroscopy techniques. Using electron energy-loss spectroscopy (EELS) analysis, magnetite (Fe3O4) has been unequivocally identified as the ironoxide formed within HFn cores under special preparation conditions. Atom counting analysis by EELS and high-angle annular dark-field imaging further allowed the correlation of the particle sizes to the real Fe atom numbers in a quantitative manner. These results help clarify some structural confusion between magnetite and maghemite (γ-Fe2O3), and also provide standard data for the number of Fe atoms within Fe3O4 particles of a given size, whose use is not limited to cases of magnetite synthesized in the cores of recombinant human ferritin.