A first-principles study on the electronic and optical properties of ZnO nanowires toward detection of α-amino acids

Abstract

In this paper, ab initio calculations for the adsorption of six prevalent alpha-amino acids, as metabolite biomarkers, onto the zinc oxide nanowire (ZnONW) are accomplished by applying the SIESTA package. This study aims to assay the electronic and optical properties of the α-amino acid-adsorbed ZnONWs comparatively. The species of interest contain arginine, asparagine, cysteine, glycine, lysine, and proline as repetitive monomers in human cells. Representation of total and local density of states reveals strong chemisorption of the α-amino acids from the carboxylic end with the nanowire through n-type conduction in conjunction with the adsorption energy of lower than −0.816 eV and charge transfer of higher than 0.238 |e|, respectively. In particular, highly polarizable cysteine-adsorbed ZnONW with the maximum difference in isoelectric point of ZnO and cysteine shows the highest corresponding quantities equal to −2.825 eV and 0.543 |e|, respectively. In comparison with the pristine ZnONW, the higher the amount of charge transferred in α-AA-adsorbed ZnONW, the larger the shift in the conduction band edge to the lower energies. The calculation of the absorption coefficient for the α-amino acid-adsorbed ZnONWs implies the presence of an enhanced peak within the near-UV spectrum for the carboxyl-oriented arginine-, lysine-, and proline-ZnONW complexes, in addition to an attenuated peak within the visible spectrum for the carboxylic/thiol-oriented cysteine-ZnONW configuration. Subsequently, it is revealed that jointly exploring both electronic and optical properties of the specific cysteine-adsorbed nanowires is of utmost importance, which could provide further evidence for the early prognosis of cystinuria and other associated metabolic disorders.