The delivery of fluorescent agents or probes to cells and tissues by using nanoparticles is currently receiving a growing interest because such nanodimensional structures can conveniently allow the preparation of small tools to spy at cellular mechanisms without interferences. We describe here the synthesis and characterization of fluorescently labeled cationic core-shell nanoparticles (NPs), made up of a core of polymethylmethacrylate (PMMA), surrounded by a shell bearing cationic groups, modified for nanosensing purposes. In particular, the NPs have been characterized as potential intracellular nanocarriers of molecular beacons (MB) for tumor mRNA sensing. Survivin targeting MBs have been used with Atto647N and Blackberry 650 as fluorophore/quencher pair. The MB was anchored to the surface of the PMMA nanoparticles via a commercial sulfhydryl-reactive heterobifunctional crosslinker and the achieved nanomaterials have been then characterized in vitro.