Safranin and cysteine capped gold nanoparticles: spectroscopic qualitative and quantitative studies

Abstract

The interaction between cysteine and safranin with citrate capped gold nanoparticles was studied. All measurements were carried out using resonance light scattering (RLS), UV-vis. absorption and fluorescence spectrometry. The size and surface characteristics of safranin-capped gold nanoparticles in the solution containing cysteine were also investigated by dynamic light scattering (DLS) and transmission electron microscopy (TEM) techniques. The average diameter and surface potential of synthesized GNPs were 19.0 nm and −56.3 mV, respectively. Interaction of the GNPs and safranin or cysteine leads to increases in their sizes and surface potentials. The influence of parameters such as pH, ionic strength of the solution and safranin concentration on the spectrophotometric and spectrofluorimetric characteristics of GNPs was studied. This system was used for determining cysteine content of unknown solutions. In the optimum conditions (pH, 4; sodium chloride, 0.014 M and safranin, 9.0 × 10⁻⁶ M) two linear dynamic ranges (9.0 × 10⁻⁸–1.0 × 10⁻⁶ M and 5.0 × 10⁻⁶–9.0 × 10⁻⁵ M) with RSD less than 5% were obtained for cysteine. The limit of detection under the optimized conditions was 3.7 × 10⁻⁸ M of cysteine. Kinetic studies of safranin and cysteine adsorption on the surface of GNPs were carried out and their corresponding rate constants were also calculated using kinetic models.