A biocompatible fluorescent nanoprobe for the detection of reactive oxygen species in biological systems has been designed, synthesized and characterized, circumventing some of the limitations of the molecular probe diacetyl 2',7'-dihidrochlorodihydrofluorescein (DCFH-DA). It has been synthesized the nanoparticulate forme of DCFH-DA by convalently attaching the widely used fluorescent probe DCFH-DA to a mesoporous silica nanoparticle though a linker, The reactivity of nanoDCFH-DA has been tested toward several reactive oxygen species. In addition, it has been proven to slow down DCFH-DA reaction with molecular oxygen and it hampers from interactions with proteins. As a final piece of evidence, in vitro studies showed that the nanoprobe is internalized HeLa cancer cells, thus being capable of detecting intracellularly generated reactive oxygen species. To sum up, it can be stated that nanoDCFH-DA overcomes two major problems of free DCFH-DA, namely oxidation of the probe by air and interaction with proteins in biological systems. This 'nano' approach has thus proven useful to extend the utility of an existing and valuable fluorescent probe to complex biological systems.