Influence of molecular assembly and NaCl concentration on gold nanoparticles for colorimetric detection of cysteine and glutathione

Abstract

We have investigated the influence of reagents concentrations, temperature and time on the UV–visible spectra and morphology of Au NPs by using tryptophan (Trp), ascorbic acid (AA), hydroxyl amine (HA) as reducing and capping agents. The AA-Au NPs acted as a colorimetric probe for selective sensing of cysteine (Cys) and glutathione (GSH). Various experimental parameters such as effect of temperature, time and reagents concentrations are investigated for the synthesis of controlled size water dispersible Au NPs with SPR band at 565, 527 and 530nm using Trp, AA and HA as reducing agents. The synthesized Au NPs were characterized by UV–visible spectrometry, FT-IR, dynamic light scattering (DLS) and transmission electron microscopic (TEM) techniques, respectively. Among three Au NPs, AA-Au NPs effectively acted as a colorimetric probe for parallel sensing of Cys and GSH, resulting a change in their SPR band from 527nm to 715nm and to 668nm for Cys and GSH, respectively. The sensitivity of the probe was greatly improved for the detection of Cys and GSH in the presence of 0.4mM NaCl. These novel multifunctional organic molecules-based Au NPs preparations offer many advantages, including simplicity of preparation, multifunctional (reducing and capping agents) and acted as a probe for colorimetric sensing of Cys and GSH.