In this paper, we report a facile route to synthesize mitochondria-targeted core–shell nanoparticles (NPs). Firstly, PLL-coated NPs are prepared by a one-step reprecipitation-encapsulation method assisted by positively charged poly-L-lysine (PLL). The effect of the molecular weight of PLL on the formation of particles is studied in terms of morphology, size and zeta potential, and medium-sized PLL (MH-PLL) is proved to be the optimum one. By means of crosslinking with different amounts of glutaraldehyde, amino groups in MH-PLL-NPs are characterized by zeta potential and fluorescamine assay, respectively. The results indicate that in the PLL shell, only a small portion of amino groups (surface amino groups, SAGs) are available for conjugation, while the other groups exclusively contribute to zeta potential. Subsequently, a known mitochondriotropic ligand, triphenylphosphonium (TPP), is conjugated with SAG via a carbodiimide reaction, which is evaluated by NMR and absorption spectra, respectively. The TPP-MH-PLL-NPs exhibit a low cytotoxic effect tested by the MTT method, as well as efficient cellular uptake microscopically observed after a fluorescent dye, coumarin 6, is incorporated. Most importantly, the TPP-conjugated NPs can selectively target mitochondria, demonstrated by the merged z-stacked images in co-localization experiments with MitoTracker-stained mitochondria. Given that many hydrophobic species could be loaded into the particle core, TPP-MH-PLL-NPs are very promising as mitochondria-targeted nanocarriers for imaging or anti-cancer therapies.

Ratiometric fluorescent core–shell nanoparticles (NPs) with good biocompatibility are successfully prepared by a one-step reprecipitation–encapsulation method for sensing dissolved oxygen. The particle core comprises the oxygen probe platinum(II) octaethylporphine (PtOEP), the reference dye coumarin 6 (C6) and a third fluorophore dinaphthoylmethane (DNM). Upon single 381 nm excitation, C6 gives oxygen-insensitive referenced green fluorescence via intraparticle FRET from DNM, whilst PtOEP yields highly oxygen-sensitive red phosphorescence with a quenching response of 94%. The fluorescence quenching of the NPs against oxygen follows a linear Stern–Volmer behavior, which is fundamental for practical sensing. Moreover, positively charged poly-L-lysine molecules are in situ self-assembled onto the surface of NPs during synthesis. The resultant core–shell NPs with functional groups exhibit low cytotoxic effects as well as effortless cellular uptake, indicating targeted intracellular oxygen sensing is very promising using the oxygen nanosensors.