Polymer coated gold-ferric oxide superparamagnetic nanoparticles for theranostic applications

BACKGROUND: Engineered inorganic nanoparticles (NPs) are essential components in the development of nanotechnologies. For applications in nanomedicine, particles need to be functionalized to ensure a good dispersibility in biological fluids. In many cases however, functionalization is not sufficient: the particles become either coated by a corona of serum proteins or precipitate out of the solvent. We show that by changing the coating of magnetic iron oxide NPs using poly-l-lysine (PLL) polymer the colloidal stability of the dispersion is improved in aqueous solutions including water, phosphate buffered saline (PBS), PBS with 10% fetal bovine serum (FBS) and cell culture medium, and the internalization of the NPs toward living mammalian cells is profoundly affected. METHODS: A multifunctional magnetic NP is designed to perform a near-infrared (NIR)-responsive remote control photothermal ablation for the treatment of breast cancer. In contrast to the previously reported studies of gold (Au) magnetic (Fe(3)O(4)) core–shell NPs, a Janus-like nanostructure is synthesized with Fe(3)O(4) NPs decorated with Au resulting in an approximate size of 60 nm mean diameter. The surface of trisoctahedral Au–Fe(3)O(4) NPs was coated with a positively charged polymer, PLL to deliver the NPs inside cells. The PLL–Au–Fe(3)O(4) NPs were characterized by transmission electron microscopy (TEM), XRD, FT-IR and dynamic light scattering (DLS). The unique properties of both Au surface plasmon resonance and superparamagnetic moment result in a multimodal platform for use as a nanothermal ablator and also as a magnetic resonance imaging (MRI) contrast agent, respectively. Taking advantage of the photothermal therapy, PLL–Au–Fe(3)O(4) NPs were incubated with BT-474 and MDA-MB-231 breast cancer cells, investigated for the cytotoxicity and intracellular uptake, and remotely triggered by a NIR laser of ~ 808 nm (1 W/cm(2) for 10 min). RESULTS: The PLL coating increased the colloidal stability and robustness of Au–Fe(3)O(4) NPs (PLL–Au–Fe(3)O(4)) in biological media including cell culture medium, PBS and PBS with 10% fetal bovine serum. It is revealed that no significant (< 10%) cytotoxicity was induced by PLL–Au–Fe(3)O(4) NPs itself in BT-474 and MDA-MB-231 cells at concentrations up to 100 μg/ml. Brightfield microscopy, fluorescence microscopy and TEM showed significant uptake of PLL–Au–Fe(3)O(4) NPs by BT-474 and MDA-MB-231 cells. The cells exhibited 40 and 60% inhibition in BT-474 and MDA-MB-231 cell growth, respectively following the internalized NPs were triggered by a photothermal laser using 100 μg/ml PLL–Au–Fe(3)O(4) NPs. The control cells treated with NPs but without laser showed < 10% cell death compared to no laser treatment control CONCLUSION: Combined together, the results demonstrate a new polymer gold superparamagnetic nanostructure that integrates both diagnostics function and photothermal ablation of tumors into a single multimodal nanoplatform exhibiting a significant cancer cell death. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s12951-018-0405-7) contains supplementary material, which is available to authorized users.