Applications of gold nanoparticles in virus detection

Draz, Mohamed Shehata; Shafiee, Hadi

The AuNPs-fluorometric assays for HBV are performed through different schemes that basically depict the quenching efficiency of AuNPs in a manner remarkably similar to the traditional FRET protocol. Zheng et al. developed a multiplex detection system based on applying gold nanorods (AuNRs) as acceptors and QDs of different colors as donors to simultaneously detect HBsAg and HBV e antigen [62] . This assay follows the direct sandwich immunoassay format, and the presence of target antigens is manifested by the FRET-induced quenching of QD fluorescence in the formed sandwich nanostructure of AuNR-Ab1/Ag/QD-Ab2 (Fig. 9C ). Draz et al. further coupled multiple AuNP-peptide conjugateacceptors with single-core QD-antibody Fab conjugate-donors, forming a preassembled hybrid nanocluster plasmonic resonator complex for HBsAg and HBV particle detection (Fig. 9C) . This scheme follows a competitive assay format, and the addition of HBV target surface antigen or particles to the preassembled nanocluster releases the quenched fluorescence signal of the QDs in proportion to the In this assay, the target HBsAg is captured and labeled with AuNP-Ab/HRP, and the detection signal is measured by using an Ab-modified Au electrode to assess the reduction of H2O2 catalyzed by the bound HRP using differential pulse voltammetry (DPV) technique [76] . (B) Copper (Cu)-enhanced electrochemical immunoassay. AuNPs serve as a scaffold for a horseradish peroxidase (HRP) enzyme that catalyzes a redox reaction in the first scheme or enhances metal deposition in the second scheme [75] . (C) Fluorometric detection by the FRET-induced quenching of fluorophores on the surface of AuNPs. AuNPs and gold nanorods (AuNRs) are applied to quench the fluorescence of fluorophores, such as (i and ii) quantum dots (QDs) [62, 65] and (iii) fluorescein amidite (FAM) [61] , through a FRET-based interaction in the presence of the target virus. A similar AuNP FRET-based scheme has been reported for the detection of H1N1, which belongs to the family Orthomyxoviridae [63] . (D) Light-scattering assays using AuNP-antibody probes. (i) Light-scattering immunoassay of virus antigen based on using AuNPs with different sizes (10 nm and 50 nm) conjugated with antibodies (Abs) to sandwich target antigens and enhance the dynamic light scattering [51] . Additionally, this scheme has been reported with the use of AuNPs of the same size for H1N1 detection [53] . (ii) Plasmonic immunoassay based on allowing AuNR-Ab conjugates to interact with the target antigen, thus changing the AuNR localized surface plasmon resonance (LSPR) behavior [52] .