Fluorescent nanoparticles for ratiometric pH-monitoring in the neutral range

This article describes the synthesis and characterisation of poly(acrylamide) nanoparticles (NPs) with a covalently immobilised pH-sensitive fluorophore. With a pK(a) 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 z-potential are synthesised and evaluated.