Applications of gold nanoparticles in virus detection

Draz, Mohamed Shehata; Shafiee, Hadi

Numerous AuNP-based scanometric, fluorometric, electrochemical, and colorimetric assays have been reported for the molecular detection of HCV (Table 1 ). In these assays, AuNPs are utilized for different sensing functions: 1) AuNPs have been modified with poly(dT)-tailed DNA and directly applied to label target DNA sequences terminally modified with a poly(dA)-tail in a LFA assay to allow the colorimetric detection of HCV (Fig. 7B) [55] . 2) AuNPs electrostatically or covalently modified with Cy3-tagged ssRNA sequences have been applied for the fluorometric detection of target HCV sequences, in which the fluorophores are quenched in a process analogous to FRET. The presence of Cy3 in the vicinity of the surface of AuNPs eventually results in Cy3-emission quenching. Upon hybridization with target viral RNA, the electrostatically adsorbed probes labeled with Cy3 are detached from the surface of the particles, releasing the quenched fluorescence. The covalently bound probes form rigid dsRNA with a linear configuration, causing Cy3 to move away from the particle surface and release the quenched emission [60] (Fig. 7C) . 3) AuNPs have also been applied to enhance electrical conduction and catalyze a reduction reaction on the surface of detection electrodes. A specifically designed hairpin DNA probe terminally modified with AuNPs and bound to the surface of a glassy carbon electrode is utilized to detect the amplified viral RNA. The presence of target DNA results in the formation of rigid dsDNA, and the hairpin conformation consequently changes, moving the AuNPs away from the electrode surface, which eventually appears as a detectable decline in the current value in proportion to the target DNA concentration [78] . 4) AuNPs decorated with a specific nucleic acid probe were used for colorimetric detection of HCV. The assay is based on using cationic AuNPs to induce the aggregation of AuNPs probes. In the absence of HCV, the cationic AuNPs electrostatically bind to negatively charged AuNPs-DNA probes causing their aggregation and change of the solution color to blue. The presence of HCV nucleic acid protects the probes and prevents their aggregation by cationic AuNPs and the solution color remains red. This assay was specific and showed a sensitivity of 93.3% and a detection limit of 4.57 IU/μL [13] .