Theoretical study on gold-coated iron oxide nanostructure: Magnetism and bioselectivity for amino acids

A fundamental understanding of the recent experiments of magnetic separation of amino acids using gold/iron oxide composite nanoparticles is provided for the first time by theoretically studying the interaction of gold-coated iron oxide cluster with sulfur-containing amino acids: cysteine, methionine, and taurine. We find, in agreement with experiments, that the interaction of cysteine is stronger than methionine, the interaction energies being 0.738 and 0.712 eV respectively. These energies are intermediate between van der Waals and covalent bonding and are ideal for effective binding and release in magnetic separation. On the other hand, we find that taurine, which is also a sulfur-containing amino acid, cannot bind to gold-coated iron oxide cluster. This selectivity can be used for the separation of taurine from the other two sulfur-containing amino acids. The present study provides insight on the mechanisms responsible for functionalizing iron oxide nanoparticles and may have far-reaching implications in biomedical research.