Biocompatible fluorescent core–shell nanoparticles for ratiometric oxygen sensing

Abstract

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.