Magnetite-nanoparticle-encapsulated pH-responsive polymeric micelle as an MRI probe for detecting acidic pathologic areas

Nanometer-sized particles are increasingly used for biomedical applications, ^[1] as polymeric micelles to carry hydrophobic imaging markers and/or drugs for disease diagnosis and therapy.^[2] Usually, these polymeric micelles in an aqueous medium are composed of a hydrophobic core and a hydrophilic corona, sometimes conjugated with active-targeting ligands (e.g., antibody, peptides, nucleic acids) that can target the biomarker of a disease.^[2a-c] On the other hand, some polymeric micelles alone, not conjugated with a targeting ligand, can also target the pathologic tissue by a stimuli-response mechanism, with which pH, temperature, or redox can be a stimulus condition.^[3] In this context, a pH-responsive polymeric micelle is utilized to be reactive in an acidic-pH environment, in which it is then dissolved. We envisioned that if we encapsulate magnetite nanoparticles (Fe₃O₄), which are frequently used as a contrast agent for magnetic resonance imaging (MRI), into the pH-responsive polymeric micelle, the resulting Fe₃O₄- nanoparticle-loaded pH-responsive polymeric micelle could be used as a contrast agent for MRI to target and, simultaneously, image the pH-stimuli tissue, such as cancerous tissue. Herein, we report a facile and powerful pH-responsive polymeric micelle that can well encapsulate Fe₃O₄ nanoparticles, and its potential applications in medicine for diagnostic imaging of acidic pathologic areas.