Water-dispersible magneto-fluorescent nanocomposites for NIR imaging and magnetic separation of mitochondria

Reproducible synthetic methods for quantum dots (QDs) and magnetic NPs (MNPs) with high physical and optical properties often recruit different types of organic surface passivation ligands, including oleic acid and oleylamine. In the absence of adequate surface passivation by an inorganic shell deposition on the QD core or organic amphiphilic polymers/ligands, there is no straightforward and universally applicable method for producing magneto-fluorescent nanocomposites (MFNs), which impedes in various biomedical applications. A simple phase transfer method was developed for the fabrication of submicron MFNs (300-400 nm) containing QDs and MNPs in the water phase, without the removal of these original ligands, which frequently results in a reduction in PL stability, quantum yield (QY) and magnetic properties dramatically. It has been established that the preservation of the optical and magnetic properties of water-soluble submicron MFNs is attributable to the presence of original oleylamines on the surface of as-synthesized QDs and MNPs. This is achieved by a process of transimination and self-healing imine formation. In addition, the termination reaction utilizing urea and a tertiary amine enables the preservation of QD and MNPs within the MFNs' inner hydrophobic compartment and the colloidal stability of MFNs during repeated cycles of magnetic separation. The application of these MFNs, in conjunction with mitochondria targeting moiety conjugation, intracellular delivery and subcellular organelle targeting, was demonstrated. The enrichment of mitochondria was achieved by means of a magnetically-driven separation process, utilizing TPP-conjugated MFNs, thus circumventing the necessity for centrifugal steps, which are known to be deleterious to biological samples.