Rapid assessment of antiviral activity and cytotoxicity of silver nanoparticles using a novel application of the tetrazolium-based colorimetric assay.

This study centers on the development of a new screening tool for simultaneously evaluating the antiviral and cytotoxic properties of antiviral agents against an HIV-1-based, pseudotyped virus particle engineered to encode antibiotic resistance. The traditional colony-forming-unit assay for quantifying this type of virus was impractical as a screening tool due to the cumbersome nature of the setup and high costs in labor and supplies. Therefore, a smaller-scale and higher-throughput means of scoring antiviral activity was successfully developed and used to evaluate a specific batch of 25-nm silver nanoparticles (AgNPs). The new assay employed a unique application of the traditional cell proliferation/cytotoxicity test that is based on the chemical 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, which produces a colorimetric readout. The AgNPs showed a half maximal inhibitory concentration against the virus of 11.2±0.6 μg/ml (p<0.0001) with no significant toxicity against the cells. Because the virus was engineered to undergo only the first half of its replication cycle, the observed AgNP inhibition must have occurred at one of the early stages of infection. Overall, the new assay was very efficient and will be useful for testing different viral pseudotypes, screening different types of nanomaterials, and investigating other antiviral agents.