Gold nanoparticles (AuNPs) are the most investigated nanomaterials for theragnosis applications. In a research field where live cell assays, as well as the tracking of nanomaterials into cell’s environment, are of extremely importance, water-soluble AuNPs have been intensively studied to overcome the toxic effects exerted by coatings. Unfortunately, AuNPs fluorescent tagging often fails due to self-quenching and a careful design must be carried out to keep optoelectronic properties and biocompatibility. In this work, the synthesis of fluorescent gold nanoprobes, able to enter within cell’s environment (biotags) and target the cell nucleus, was designed and the particles tracked by confocal laser scanning microscopy. The coating of AuNPs with maleimide poly(ethylene glycol) and fluorescent oligoaziridine biocompatible oligomers, resulted in robust, optical active biotags that open novel insights into cancer theragnosis.