Sulfur-containing natural zwitterionic amino acids and derivative on gold: Study on physicochemical and anti-fouling properties

Abstract

Many researchers have found that the stability of SAMs is an issue for long-term biomedical applications. The surface functional group is not stable under ambient conditions. To address this problem, we use cysteine, natural sulfurcontaining zwitterionic compounds, and cysteine betaine which is the derivative of cycteine, with quaternary ammonium group at its terminal end, to decorate Au substrate by using the chemisorbing properties of the thiol group. By adding various different additives into the solution of alkanethiols during SAM formation to eliminate unbound thiol and to prevent the degradation processes of alkanethiol SAMs, we can decrease the film thickness and increase the wettability. Furthermore, we also compared their physical and chemical properties of amino acids SAMs on Au that were stored under different conditions for various lengths of time. Based on the above, our study aims to investigate the influence of different SAMs condition and chemical structure for anti-fouling properties. Contact angle analysis indicated that after degradation, the photooxidation sample decreased relative to that of the freshly prepared SAMs. X-ray photoelectron spectroscopy (XPS) not only used to detect the chemical elements of SAMs on Au substrates, but also detect the changes in the chemical state of the surface oxidized atoms. The bacterial adhesion tests revealed the excellent anti-fouling properties of zwitterionic amino acids SAMs. And adopt MTT assay to assessing cell viability.