Dicoumarol assisted synthesis of water dispersible gold nanoparticles for colorimetric sensing of cysteine and lysozyme in biofluids

Abstract

The important roles of cysteine (Cys) and lysozyme (Lys) in biological systems have attracted great interest in their detection in various biofluids. Here, we report the use of dicoumarol (DIC) as a novel reducing and stabilizing agent for the synthesis of water-dispersible DIC-decorated gold nanoparticles (Au NPs) for the sensitive and selective colorimetric determination of Cys and Lys in biofluids. The characteristic surface plasmon resonance (SPR) peak at 525 nm and solution color of DIC–Au NPs undergo dramatic changes on exposure to Cys and Lys, yielding new absorption peaks appearing at 666 and 570 nm for Cys and Lys and concomitant color change from cherry red to blue for Cys and to purple for Lys, respectively. The high degree of DIC–Au NPs aggregation induced by Cys and Lys was observed at 0.4 M of NaCl. Based on this finding, we propose a method to detect Cys and Lys by the naked eye and UV-visible spectrometry. The proposed sensor quantitatively measured Cys and Lys concentrations within the dynamic range of 10–90 μM (R² = 0.9942) and 100–800 nM (R² = 0.9961) with limits of detection of 2.2 × 10⁻⁶ and 8.7 × 10⁻⁹ M for Cys and Lys, respectively. This probe was successfully applied to detect Cys and Lys in human urine and plasma and Lys in egg white, demonstrating its great value for practical application in biological systems.