One step surface modification of gold nanoparticles for surface-enhanced Raman spectroscopy

Abstract

One of the drawbacks of surface enhanced Raman spectroscopy is that molecule of interest needs to be adsorbed or at least present near the surface of the substrates in order to achieve high enhancement. Unfortunately, majority molecules have no suitable functional groups interacting with the surface of the substrates and suffer poor SERS enhancement. In this work, one-step surface modification of gold nanoparticles (AuNPs) using linking molecules (LM) was demonstrated to attract the target molecules (TM) closer to the surface of AuNPs, hence lead to higher SERS enhancement. Here, 2-mercaptoethanol was employed as the linking molecule for its strong adsorption on AuNPs surface through a thiol group on one end and the intermolecular interaction between the LM and the TM through the hydroxyl group at the other end. Three target molecules were tested. For benzoic acid, no intensity difference was observed on the AuNPs modified with LM compared with the non-modified original ones. Interestingly, two times higher enhancement was observed from cyclohexanol TM on the modified surface. As much as four times higher enhancement was achieved with the modified Au surface from 1,3-cyclohexanediol. The stronger the interaction between the LM and TM is, the higher the SERS enhancement factor is. Also, the enhancement is highly dependent on the surface coverage of the LM. This simple modification method is important for most molecules which do not strongly interact with commonly used SERS substrates like Au or Ag nanoparticles and enables their possible characterization or detection using SERS.