As the backbone of proteins, amino acids play a vital role in all biological processes. It is well-known that the efficacies of cold atmospheric pressure plasma on amino acids are substantial, especially in plasma medicine. This study evaluated the chemical effects of the dielectric barrier discharge (DBD) plasma-constituted from a mesh and plate electrodes-on L-Cysteine powder in a dry treatment. This amino acid allows various covalent modifications due to its simple and diverse structure. We aimed to produce more diverse and higher masses of chemical products by adding dimethyl sulfoxide (DMSO) and hydrogen peroxide (H2O2) into the plasma of Ar and Air by the bubbling method. Fourier transform infrared spectroscopy and Liquid chromatography-mass spectroscopy (LCMS/MS) identified the resulting product patterns. Scanning electron microscopy and ultraviolet–visible spectroscopy to determine any modifications after exposure to the plasma studied the structural changes of cysteine. Results showed that changes in the amino acid structure depend on reactive species. The results also indicated that cysteine powder treated with DBD plasma produced chemical products with a higher value of molecular masses some containing other amino acids. Since strong direct oxidation of cysteine was observed, it has been understood that several parameters of discharge must be taken to oversight the procedure of polymerization processes
