Experimental and theoretical studies of 1-alkanethiols SAMs of various chain-lengths on gold nanoparticles and their effect on SERS, stability and surface properties

Abstract

1-alkanethiol SAMs on AuNPs have shown great potential towards the development of new functional materials. This is mainly due to the formation of dense, tightly bonded and well-ordered systems on the surface of AuNPs. This work showcases how the chain-length of 1-alkanethiols affects the stability and surface properties of AuNPs and the SERS effect. Using experimental and theoretical studies (by means of DFT), this work shows the interaction between 1-alkanethiols of 3 different chain-lengths and AuNPs. The effects on the optical properties, surface charge, stability and SERS were also investigated. The red shift of surface plasmon resonance band was observed as a result of the interaction between AuNPs and 1-alkanethioals. The Zeta potential indicated a strong electrostatic repulsion between AuNPs which was reduced after functionalizing with 1-alkanethiols. The long chain alkanethiol was found to strongly reduce the surface charge due to strong interaction with AuNPs. The calculated nucleophilic centre cross-sections for all alkanethiols were found to increase with the chain-length, indicating a strong interaction existed between long chain alkanethiol and AuNPs. The SERS data shows an increase in Raman intensities of all 1-alkanethiols adsorbed on the surface of AuNPs. Both the experimental and theoretical data shows that the alkanethiol with short chain-length possesses the strongest Raman signal enhancement.