Cerium (IV) oxide nanoparticles (CeO2 NPs or nano-ceria) are one of the most popular NPs used in both industry and medicine. Nowadays, CeO2 NPs could be considered as one of the NPs with better prospects for future applications in medicine. CeO2 NPs have the ability to change between oxidation states Ce(IV) and Ce(III) creating oxygen vacancies in their structure. This ability, in theory, could regulate oxidative stress (OS). However, there are many contradictory reports regarding the beneficial or adverse effects CeO2 NPs produce when internalised in the body. In addition, the mechanisms through which CeO2 NPs interact once internalised in the body are not yet totally understood.
This thesis analyses the interaction between CeO2 NPs and phospholipids (DOPC, DOPG, DOPE, DOPA and DOPS) using a biosensor able to mimic the cellular membrane. The working electrode of the electrochemical sensing device (ESD) consists of a mercury coated platinum electrode (Hg/Pt electrode) where phospholipids are deposited. CeO2 NPs with different size and shapes (spheres, cubes, needles and dots) are synthesised using wet-chemical and hydrothermal methods. Also, coated CeO2 NPs were synthesised using PVP, PEG, dextran and the CeO2 NPs were treated with PBS. The NPs were characterised using TEM, SAED, EDX, XRD, DLS and Z-Potential.
Results show the chemical behavior of the CeO2NPs is related to a large extent to the characteristics of the NPs surface, the characteristics of their dispersion media and the size of the NPs. CeO2 NPs (spheres, cubes, needles and dots) did not show an interaction with the phospholipid membrane (DOPC) when the system was under a continuous flow of phosphate saline buffer (PBS, pH 7.4) and citric-citrate buffer (CCB, pH 4.0, 5.0, 6.0). Nevertheless, an interaction was observed when the system was under a continuous flow of CCB (pH 3.0) and GLY (3.0). It was concluded that Ce3+ on the NPs surface can bind to the phosphate group of the phospholipid polar heads when the NPs are in GLY 3.0. Results also showed that citrate on the CeO2 NPs surface hampers the interaction with the phospholipid monolayer at pHs above 3.0. Additionally, at acidic pH (pH 3.0), the CeO2 NPs (spheres and cubes) were able to cross the phospholipid monolayer and directly interact with the Hg/Pt electrode showing a semiconductor effect. Needles, which were bigger in size, did not produce a semiconductor effect under the same conditions. The semiconductor effect decreases as size increases. The interaction of the coated CeO2 NPs with DOPC was found to be dependent on the coating agent. In this way, the interaction between DOPC and the NPs was produced by the coating agent, not the NPs. Finally, CeO2 showed to be inert when interacting with DOPA, DOPG and DOPE under a continuous flow of PBS. The only exception was the dots, which produced a significant interaction with DOPA under the same conditions.
