Quantitative analysis of COOH-terminated alkanethiol SAMs on gold nanoparticle surfaces

Kien Cuong Nguyen

Abstract

Surface-functionalization of a self-assembled monolayer (SAM) can be achieved by introducing functional molecules at the terminal. To immobilize biomolecules on a gold substrate, COOH-terminated alkanethiol SAMs are preferably employed. Thiol molecules adsorption on gold surface was performed using thioglycolic acid (TGA, HS-CH₂-COOH) monomers and a self-assembled technique.

Characterization by Fourier transform infrared (FTIR) spectroscopy revealed gold–sulfur (Au–S) bonding through confirming the presence and disappearance of thiol molecules on the Au surface before and after the sample's immersion in the TGA solution. Moreover, FTIR spectra also proved the presence of carboxyl molecules (C = O; OH) at the free end on the gold nanoparticle (AuNP) surface. Quantitative analysis of the carboxyl molecules interacted with methylene blue (MB) ones, and then identification by UV-Vis absorption spectroscopy showed that the average density of the carboxyl molecules on the free end of the alkanethiol SAM was about 3.9 × 10¹⁴ molecules per cm²