Study on the interactions of sulfur-containing amino acids with the pristine and defective graphene surfaces

The cysteine and methionine are two kinds of sulfur-containing amino acids in human body, which play important roles in biological activities. The adsorption mechanism of two amino acids on the pristine and defective graphene surfaces was studied in detail using density functional theory (DFT) method. Two adsorption systems are mainly considered: two amino acids lie flat on the pristine and defective graphene surfaces; two amino acids are vertically placed on the pristine and defective graphene surfaces, and the sulfur-containing group is close to the surface. The results showed that the initial configurations of cysteine and methionine have some influence on their interactions. There are high adsorption energies when two amino acids lie flat on pristine and defective graphene surfaces. In addition, the adsorption energy showed that two types of amino acids can better bind to the defective graphene surfaces. At the same time, the results indicated that interactions of methionine with the pristine and defective graphenes are greater than those of cysteine with the pristine and defective graphenes. The simulation results are expected to provide useful guidance for the graphene-based sensor on the sulfur-containing amino acids. (authors)