Viral binding and membrane fusion are essential steps in viral infection, mediated by viral proteins that bind to host cell receptors and facilitate the fusion between viral and host membranes. Targeting these steps for the development of new antiviral strategies requires methods that enable investigating virus-membrane interactions under in-situ conditions, while providing mechanistic insights on a molecular level. Here, we demonstrate the use of surface-enhanced infrared absorption (SEIRA) spectroscopy combined with tethered bilayer lipid membranes (tBLMs) for the label-free detection of virus-membrane interactions, using the Influenza A/X-31 virus (IAV) as a model. Exploiting the nanometer-scale surface-sensitivity of SEIRA, we detect the vibrational fingerprint of IAV's hemagglutinin (HA) glycoprotein, as it specifically binds to sialic acid receptors of the ganglioside GD1a in the tBLM, mimicking the host membrane. Triggering viral fusion via a pH change, we identify structural changes of HA engaging with the host membrane model. Moreover, by constructing the tBLM from deuterated lipids, we utilize the vibrational isotope effect and distinguish between viral and model membrane, providing a basis to track lipid mixing. This approach establishes a powerful tool for spectroscopic studies of the function and inhibition of viral proteins, while still embedded in intact virus particles.
