Due to their high surface/weight ratio and capacity to pass through cell membranes, carbon nanotubes (CNTs) have been extensively explored for drug and gene delivery applications.108 CNTs have been also successfully used for the delivery of antiviral agents. Compared to pristine materials, oxidized CNTs (ox-CNTs) showed an inhibitory activity for HIV viruses per se.109 This effect has been associated with the oxygenated groups that increase the hydrophilicity and the colloidal stability of the material. The antiviral efficiency has been correlated to the ox-CNT interaction with host cells.109 However, it is not clear how and what kind of mechanism blocks the viral machinery in host cells. Different anchoring strategies have been explored to link antiviral drugs onto CNT surface. For instance, ox-CNTs were covalently linked to 2-amino-3-nitro-1-(3,5-dimethylbenzyl)-aniline (CHI360) and N-(2-aminophenyl-3-nitro-)-3,5-dimethylbenzenesulfonamide (CHI415), two active non-nucleoside reverse transcriptase inhibitors for HIV treatment.109 Following the covalent conjugation, only a moderate antiviral effect was observed compared to pure drugs, indicating that most probably the NM cell trafficking played a key role on the virucidal activity.109 In another study, ox-CNTs functionalized with cyclodextrin were used for the delivery of acyclovir (a prodrug inhibitor of the viral DNA polymerases) for the treatment of HSV-1. Preliminary results showed that when acyclovir was delivered via the nanotubes, the viral antireplicative effect was higher than the free drug.110 More recently, a similar approach was applied to herpes virus using cyclodextrin and PEI-functionalized CNTs for co-delivery of cidofovir and plasmid DNA. However, the antiviral effect of the materials was not explained, and the transfection effect was not satisfactory.111 Functionalized CNTs have been also used for delivery of ribavirin in vivo using grass carp as an animal model for the study of grass carp reovirus. ox-CNTs were first functionalized via amidation with BSA, and then ribavirin was covalently bound to the protein via esterification (Figure 12).112