"The present thesis is focused in two main subjects; the photochemical and chemical synthesis of silver and gold nanoparticles (NPs) and their functionalization in order to study their interaction with cell cultures. The techniques used for the characterization of nanomaterials are described; electronic microscopies for the evaluation of size and shape, UV-Vis spectroscopy for the optical characterization and Raman spectroscopy for the evaluation of the functionalization of the NPs. The use of photochemical methods for the synthesis of silver NPs allowed us to have control over the size and morphologies of the NPs obtained; which is essential for several applications. The results will show an exhaustive study on the photochemical synthesis of silver NPs; power radiation, different reagents and temperature were analyzed as parameters and the optimal conditions for the photochemical synthesis of decahedral NPs were obtained. The extension of the photochemical synthesis of silver NPs by using two light sources is also presented; this allowed to tune the optical properties of the silver NPs in a wider range and to obtain a variety of morphologies. We believe that, with the use of different light sources, this photochemical method can be extended so that other morphologies and the optical properties of the NPs can be tuned in a wider range. On the other hand, the functionalization of the NPs is necessary to control their interaction with other materials; in the case of biological applications the surface chemistry plays an important role on how the biological samples behave in their presence. Finally, some preliminary results on the interaction of NPs and cell cultures are presented; the silver and gold NPs, synthesized in our lab, were functionalized expecting to reduce their toxicity in cell cultures. Our experiments were focused in the study of the toxicity of the NPs capping molecules. We find that with the capping molecules we propose in this work, there was no sign of toxicity in HeLa cell cultures. With the results obtained it is clear that these NPs have the potential to be used for photothermal therapies, as markers or in applications were the interaction of the NPs with live cells is necessary."