Nanomaterials designed for biomedical applications are expected to establish contact with physiological fluids, which contain a wide variety of biomolecules and cellular entities. It is now well-accepted that when a nanomaterial comes into contact with a biological fluid, its nature and physico-chemical properties can be affected by the formation of the so-called protein corona, which leads to a modification of its expected behaviour, fate and pharmacological profile. As a consequence, the protein corona has been studied extensively during the last decade, aiming to describe and define the effect of nanomaterial parameters on the composition of the corona. Similarly, numerous investigations have been performed to understand the effect of the corona itself on a wide range of biological processes. The protein corona has become a critical parameter to be described and understood before the translation of any nanomaterial to biomedical applications. Among the myriad of available nanomaterials designed and engineered today, gold nanoparticles have attracted a lot of attention due to their plasmonic properties, which confer them interesting optical and thermal characteristics. Due to these properties, gold-based nanostructures have been proposed for several biomedical uses such as drug delivery, biosensing, imaging and disease treatment. Therefore, it is vital to get a deeper understanding on the protein corona formed around this type of nanomaterial. In this PhD thesis, we focused on the study of the protein corona formed on the surface of gold nanoparticles of different sizes and shapes functionalized with carboxylic polyethylene glycol. Protein corona composition was quantitatively and qualitatively evaluated for gold nanospheres, gold nanorods and gold nanostars of different dimensions. In addition, the in vivo protein corona on gold nanoparticles was isolated and analysed for the first time. Lastly, the potential of gold nanoparticles as optoacoustic imaging contrast agents was studied. For this purpose, optoacoustic signals generated by different gold nanoparticles was measured in the absence and presence of protein corona. General results revealed the nanoparticle features strongly affect protein corona composition, which additionally has an impact on the optoacoustic performance of this nanomaterial type.