Applications of gold nanoparticles in virus detection

Draz, Mohamed Shehata; Shafiee, Hadi

AuNPs are a leading class of metal nanostructures that is widely known for its chemical stability, water solubility, and broad size and shape controllability. AuNPs can range from 1 to 800 nm in size and have different morphological shapes, including spheres, rods, prisms, tetrapods, dog bones, cubes, shells and several hollow structures [42, 43] . The synthesis of AuNPs can be performed using different methods such as chemical reduction of salts, ultraviolet irradiation, lithography, aerosol technologies, laser ablation, ultrasonic fields, photochemical reduction of Au, and biological synthesis [9, 32] . AuNPs possess a high surface density of free electrons that results in inherent optical, electrical, and catalytic properties. The excitation of AuNPs with light can cause these free surface electrons, i.e., "plasmons," to oscillate to one side away from the atomic core, which remains as a positive charge on the other side, thereby creating a dipole or plasmon polariton [44, 45] . This dipole plasmon can change its direction in accordance with the frequency of incident light, and the resonance condition is reached when their frequency is approximately the same. This condition has been referred to as surface plasmon resonance (SPR). The most widely used AuNPs exhibit intense SPR bands that usually exist between 510-1100 nm and are known to be weakly dependent on the size of the AuNPs and the refractive index of the surrounding media but very sensitive to both the shape of the NPs and the interparticle distance [46] . The SPR of AuNPs has been observed to cause intense enhancing or quenching effects upon interactions with nearby photon emitters. These distance-dependent coupling effects are dipole-dipole interactions that usually include surface plasmon-mediated energy nanotransfer processes similar to fluorescence resonance energy transfer (FRET) and may be either destructive (resulting in quenched emission) or constructive (resulting in enhanced emission). Compared to other types of nanomaterials, metal nanoparticles, particularly AuNPs, constitute ideal tools in virus detection for numerous reasons, including the ease of synthesis, characterization, and surface modification, outstanding stability, biocompatibility, and exceptionally high absorption coefficients [47, 48] . Furthermore, as labeling agents, AuNPs are easily visualized due to their intense colors and are known to form stable and highly active bioconjugates with common targeting biomolecules, such as DNA and proteins, thereby enabling highly sensitive and specific sensing and detection applications [48] .