Enveloped viruses, such as HIV, Ebola and Influenza, are among the most deadly known viruses. Cellular membrane penetration of enveloped viruses is a critical step in the cascade of events that lead to entry into the host cell. Conventional ensemble fusion assays rely on collective responses to membrane fusion events, and do not allow direct and quantitative studies of the subtle and intricate fusion details. Such details are accessible via single particle investigation techniques, however. Here, we implement nano-infrared spectroscopic imaging to investigate the chemical and structural modifications that occur prior to membrane fusion in the single archetypal enveloped virus, influenza X31. We traced in real-space structural and spectroscopic alterations that occur during environmental pH variations in single virus particles. In addition, using nanospectroscopic imaging we quantified the effectiveness of an antiviral compound in stopping viral membrane disruption (a novel mechanism for inhibiting viral entry into cells) during environmental pH variations.

Infrared dielectric properties of muscovite mica, one of the first van der Waals crystals, exfoliated on silicon and SiO 2 substrates is studied using near-field nano-FTIR spectroscopy. The spectra of mica show strong thickness and wavelength dependence down to the monolayer-scale, with a prominent broad peak centered around ∼1080 cm −1 assigned to stretching vibrations of Si−O. We reveal that the infrared dielectric permittivity of mica is anisotropic, that is, has opposite signs along the inplane and out-of-plane axes, implying a Type I hyperbolic behavior in the range 920−1010 cm −1 and a Type II hyperbolic behavior in the range 1050−1130 cm −1 . Experimentally measured nano-FTIR spectra agree well with analytical model calculations based on an extended finite dipole model for layered systems of the tip−sample interaction when the out-of-plane dielectric values (instead of the in-plane dielectric values) were used in the calculations.

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