Surface interactions relevant to cancer treatment - A study of fluorouracil reactions on diamond and graphite surfaces

Abstract

Fluorouracil (5-FU) is a chemotherapy drug with molecular formula C4H3FN2O2. The interaction between fluorouracil and nanocrystalline diamond, and between fluorouracil and graphite was studied with X-ray photoelectron spectroscopy (XPS). A film of 5-FU was deposited on the sample of interest and then heated stepwise. XPS-spectra were acquired at each temperature step. As the sample was heated, the molecules gradually evaporated off the sample, but a larger amount of fluorine atoms evaporated relative to nitrogen and oxygen. This was found for all the samples, and indicates that 5-FU reacts on the surface, in a reaction where fluorine is liberated from the rest of the molecule. Thus, diamond and graphite are not suitable as coating-materials for medical applications that involve fluorouracil.

The core levels of fluorine, nitrogen and oxygen shifted towards lower binding energy as the film thickness decreased, possibly due to doping mechanism on the film/substrate-interface. Angle-resolved photoelectron spectroscopy measurements were performed on a boron doped crystalline diamond, which clearly showed 2D-states crossing the valence band. As for boron, fluorine is a p-dopant, and similar features are likely to be found in a fluorine doped diamond.