The rich chemistry of transition metals permits them to undergo a great variety of reactions when found in biological environments. As such, metals fulfil multiple fundamental tasks in life organisms, and the homeostasis of bio-metals (i.e. Fe, Zn and Cu) is highly regulated. Equally, numerous anthropogenic metallic devices such as inorganic complexes or metal nanomaterials are currently being developed as biomedical or biotechnological tools. However, the same varied reactivity shown by metals makes challenging to explore their fate and mechanisms of action in biological samples, hampering their development into clinical or industrial use. Synchrotron-based X-ray imaging and spectroscopic techniques can provide valuable insight on the distribution and chemical properties of complexes and nanomaterials in biological environments, as they allow direct detection of metals and can reach subcellular spatial resolution. This can prompt dramatic improvements in the design and development of new and more effective metal-based drugs and medical nanodevices. My work during the last few years has been focused on exploring the potential of such techniques to understand the biological behaviour of metal-based systems at tissue or cellular level, by addressing several complex questions.