This article describes the synthesis and characterisation of poly(acrylamide) nanoparticles (NPs) with a covalently immobilised pH-sensitive fluorophore. With a pKa of 6.7, good photostability, emission in the visible spectral range and large Stokes' shift the naphthalimide-based pH-indicator is well suited for bio-analytical applications. Additionally, the nanosensors contain a pH-insensitive reference fluorophore that allows the ratiometric monitoring of pH e.g. inside living cells. In order to enhance the cellular uptake and endosomal escape of the beads, novel core–shell nanoparticles bearing a positive ζ-potential are synthesised and evaluated.
