Applications of gold nanoparticles in virus detection

Draz, Mohamed Shehata; Shafiee, Hadi

The colorimetric assay involves the ability of AuNPs to preferentially adsorb ssDNA over dsDNA and specifically sense the presence of the target DNA [54] . Specific, short ssDNA probes adsorb to the surface of AuNPs, resulting in an increased particle colloidal stability and an increased ability to withstand slightly elevated salt concentrations without significant aggregation or color changes. Upon addition, the target DNA specifically forms dsDNA with the adsorbed ssDNA probes, which then easily detach, leaving the AuNPs to aggregate due to the salt. The particle aggregation causes the red color of the solution to change to blue, indicating the presence of target SARS nucleic acids; this change can be directly assessed by the naked eye or precisely quantified by ultraviolet-visible (UV-vis) spectroscopy in correlation to the target DNA concentration (Fig. 5A ). In the electrochemical assay, AuNPs are applied to enhance the electrode conductivity and increase the surface area available for detection probe immobilization [72] . SARS-specific DNA-capturing probes are first immobilized on the surface of an electrode structured with AuNPs; then, they are allowed to hybridize with the biotinylated targets. Then, streptavidin-labeled alkaline phosphatase is applied to catalyze the indirect reduction and deposition of silver ions, which are eventually measured by anodic stripping voltammetry in correlation with the target DNA concentration (Fig. 5B) .