Highly fluorescent core-shell silica nanoparticles made by the modified Stöber process (C dots) are promising as tools for sensing and imaging subcellular agents and structures but will only be useful if they can be easily delivered to the cytoplasm of the subject cells. This work shows that C dots can be electrostatically coated with cationic polymers, changing their surface charge and enabling them to escape from endosomes and enter the cytoplasm and nucleus. As an example of cellular delivery, we demonstrate that these particles can also be complexed with DNA and mediate and trace DNA delivery and gene expression.