Nanoarchitectured peroxidase-mimetic nanozymes: mesoporous nanocrystalline α- or γ-iron oxide?

Nanozymes (nanoparticles with enzyme-like properties) have attracted considerable attention in recent years owing to their intrinsic enzyme-like properties and broad application in the fields of ELISA based immunoassay and biosensing. Herein, we systematically investigate the influence of crystal phases (γ-Fe2O3 and α-Fe2O3) of mesoporous iron oxide (IO) on their peroxidase mimetic activity. In addition, we have also demonstrated the applicability of these mesoporous IOs as nanozymes for detecting the glucose biomarker with a limit of detection (LOD) of 0.9 µM. Mesoporous γ-Fe2O3 shows high nanozyme activities (and magnetism) toward the catalytic oxidation of chromogenic substances, such as 3,3',5,5'-tetramethylbenzidine (TMB) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid)-ABTS, as well as for the colourimetric detection of glucose, compared to that of α-Fe2O3. We believe that this in-depth study of crystal structure based nanozyme activity will guide designing highly effective nanozymes based on iron oxide nanostructures for chemical sensing, biosensing and environmental remediation.

Mesoporous γ-Iron Oxide Nanoparticles for Magnetically Triggered Release of Doxorubicin and Hyperthermia Treatment.

Mesoporous iron-oxide nanoparticles (mNPs) were prepared by using a modified nanocasting approach with mesoporous carbon as a hard template. mNPs were first loaded with doxorubicin (Dox), an anticancer drug, and then coated with the thermosensitive polymer Pluronic F108 to prevent the leakage of Dox molecules from the pores that would otherwise occur under physiological conditions. The Dox-loaded, Pluronic F108-coated system (Dox@F108-mNPs) was stable at room temperature and physiological pH and released its Dox cargo slowly under acidic conditions or in a sudden burst with magnetic heating. No significant toxicity was observed in vitro when Dox@F108-mNPs were incubated with noncancerous cells, a result consistent with the minimal internalization of the particles that occurs with normal cells. On the other hand, the drug-loaded particles significantly reduced the viability of cervical cancer cells (HeLa, IC50 =0.70 µm), wild-type ovarian cancer cells (A2780, IC50 =0.50 µm) and Dox-resistant ovarian cancer cells (A2780/AD, IC50 =0.53 µm). In addition, the treatment of HeLa cells with both Dox@F108-mNPs and subsequent alternating magnetic-field-induced hyperthermia was significantly more effective at reducing cell viability than either Dox or Dox@F108-mNP treatment alone. Thus, Dox@F108-mNPs constitute a novel soft/hard hybrid nanocarrier system that is highly stable under physiological conditions, temperature-responsive, and has chemo- and thermotherapeutic modes of action.