Viral infections affect millions of people every year, yet broad-spectrum virucidal therapies are not available. Antiviral substances in current use act on specific viral mechanisms against only a small number of viruses. Virustatic materials interfere with the viral infection cycle before the cells become infected. By targeting highly conserved attachment receptors, they can be broad-spectrum and non-toxic. However, their reversible virus binding renders them ineffective in-vivo and therapeutically irrelevant. Broad-spectrum virucidal substances that irreversibly inhibit viral infectivity do exist, but are too toxic for therapeutic applications. An ideal antiviral method would be broad-spectrum, virucidal instead of virustatic and therefore irreversible, and non-toxic. The scientific literature describes gold-nanoparticles (NPs) with 2-mercaptoethanesulfonate (MES) ligands as virustatic since these NPs only bind reversibly to viral attachment ligands. In our research group, we postulated that by lengthening the ligands to 11-mercapto-1-undecanesulfonate (MUS), their binding would be stronger and induce a force on the viruses sufficient to damage the virus irreversibly. Virological testing indicated that these MUS NPs do exhibit a virucidal effect against a wide range of viruses. The present study was able to show the structural damage to viruses in their near-native state imaged in cryo-electron microscopy (cryoEM). We found that while virustatic MES NPs attach only in small numbers to the viruses virucidal MUS NPs avidly attach to viruses and show a clear progression towards fully NP-covered viruses, which we interpret as the morphology of the virucidal endpoint. The analysis of the immediate interaction of virucidal NPs and viruses showed that virucidal NPs bind to proteins vital to the viral infection cycle: (1) Virucidal NPs bind to glycoproteins on the viral envelope that exert a force onto the viral envelope leading to envelope breakage. (2) Virucidal NPs attach to released viral capsids that break upon interaction with virucidal NPs and become fully NP covered, which is the morphology of the virucidal endpoint. This project provided an opportunity to advance the field of NPs â based antivirals. It is the first study to provide a solution-state visualisation of the interaction of viruses and virucidal NPs. The study further offers important insight to the association of single NPs with viral proteins of the envelope and virus capsid as well as their effect upon them, and offers a new approach for the future of broad-spectrum non-toxic virucidal therapies. Keywords Nanoparticles, Viruses, CryoEM, CryoET, broad-spectrum antivirals, virustatic, virucidal, HSPG, HSV