This mechanism was demonstrated by Elechiguerra et al. for HIV-1 exposed to 1–10 nm Ag NPs157 and by Orlowski et al. for HSV-2 exposed to 13, 33, and 46 nm Ag NPs coated with tannic acid.161 Elechiguerra et al. found that the optimal size of Ag NPs was around 10 nm, with larger or smaller NP sizes showing weaker physical interaction with the virus.