Highly sensitive and selective colorimetric detection of sulphide using Ag–Au nanoalloys: a DFT study

Abstract

A density functional theory approach is applied to investigate the sensing mechanism for the colorimetric detection of sulphide (S) among sulphide species, such as S, SH, cysteine (Cys), and H₂S, using Ag–Au nanoalloys. By exploring the adsorption of sulphide species on the Ag₄₂Au₁₃ and Ag₅₅ clusters, it is found that the adsorption strength of those sulphide species on the Ag₄₂Au₁₃ cluster is stronger than those on the Ag₅₅ cluster, corresponding to the higher sensitivity of the Ag₄₂Au₁₃ cluster compared with the Ag₅₅ one for the colorimetric detection of sulphide species. In addition, it is found that the adsorption strength of the Ag₄₂Au₁₃ and Ag₅₅ clusters towards sulphide species follows the order of S > SH > Cys > H₂S, indicating that both the Ag₄₂Au₁₃ and Ag₅₅ clusters possess high selectivity for the colorimetric detection of S over other sulphide species. By investigating the coverage effect of S on the Ag₄₂Au₁₃ cluster, it is found that increasing the coverage of S leads to the decrease of the adsorption strength. Our theoretical results are expected to provide new guidelines for rational design of more powerful adsorption-based colorimetric sensors for detecting S using Ag–Au nanoalloys.