Facile Synthesis of Bile Salt Encapsulated Gold Nanoparticles and Its Use in Colorimetric Detection of DNA

A novel way to synthesize gold nanoparticles (AuNPs) using naturally occurring bile salts, namely, sodium cholate (NaC) and sodium deoxy cholate (NaDC), as reducing and capping agents at room temperature has been reported. Variations of NaC concentration provided good control over the size and shape of the AuNPs, allowing us to tune the color of NPs from green to red. While the hydroxyl group of bile salt reduced the Au3+ ions, the carboxylate group binds strongly to the surface of the NPs. The optical properties, size, and shape of the NPs were analyzed using UV–visible spectroscopy and transmission electron microscopy (TEM). The interaction of NaC on the AuNP surface was studied using cyclic voltammetry, FT-IR, and thermogravimetric analysis (TGA). The combination of steady-state and time-resolved quenching studies using fluorescent probes confirmed the hydrophobic interaction between NaC micelles and AuNPs. The color change properties associated with the aggregation of NPs were used for the colorimetric detection of plant-associated Gemini viruses using degenerate probes. The assay was completed within 20 min, and ≥600 pmol of the target DNA could be detected by UV–visible spectroscopy.