Interaction of Citrate-Capped Gold Nanoparticles with the Selected Amino Thiols for Sensing Applications

Abstract

The amino thiols, methionine, cysteine, and homocysteine are considered to be important biomarkers for various diseases. In the present study, the authors have demonstrated that the interactions of synthesized citrate-capped gold nanoparticles with these amino thiols at different pH values can be used to develop simple colorimetric methods for their detection in aqueous solutions. The aggregation of the gold nanoparticles by interactions with the thiol group was found to depend strongly on the pH of the amino thiols. At pH 10, the detection of cysteine was possible in the presence of homocysteine at low concentration and similarly homocysteine could be detected in the presence of cysteine at low concentration by thiol-induced aggregation of the gold nanoparticles. Cysteine and methionine were specifically detected by monitoring the aggregation of the gold nanoparticles through the UV–Visible spectra at pH 7 and pH 10 respectively. The increase in the mean hydrodynamic diameter of the particles confirmed the thiol-induced aggregation of the particles both at pH 7 and pH 10. The specific pH-based interactions can form a basis to design simple colorimetric sensors for the amino thiols using as-synthesized citrate-capped gold nanoparticles without further functionalization.