Assemblies of inorganic nanoparticles and carbon nanodots have emerged as promising candidates for hybrid materials in biomedical applications. In this work, the formation and properties of gold nanoparticles synthesized with the aid of carbon nanodots (CND) as reducing/stabilizing agents was investigated. Through careful modification of the reaction conditions, such as precursor concentrations and temperature, the size and shape of the particles can be controlled. In general, CNDs provide reductive sites at which gold seeds can be formed. As the gold nanoparticles grow, the CNDs form a polar solubilizing shell in the polar aqueous environment, yielding bulbous Au@pCND nanoclusters. In fact, charge-transfer interactions between the pCND shell and the Au core are implicit, as confirmed by steady state and time resolved absorption and fluorescence spectroscopies. Finally, this work demonstrated via in cell internalization tests that the size and the shape of the Au@pCND nanoclusters play a crucial role for the cancer cell toxicity. Also the Au@pCND prove to be good candidates as sensitizers in cancer radio-therapy.