of the SEIRA signal is due to the first 10 nm, where a SEIRA spectrum of oriented HA proteins specifically interacting with the tBLM is detected (highlighted region in red and using square box). When IAV is not interacting directly, an isotropic SEIRA spectrum of the entire virus is detected, which resembles a bulk ATR-IR spectrum. B: Magnification of the membrane-interacting HA (PDB -6Y5G) that is detected using SEIRA; random/turn regions are in blue, αhelices in red, and β-sheets in orange. C: The amide I of specifically interacting IAV (Figure ) was modelled using three Gaussians at 1679, 1657, and 1635 cm -1 , which can be assigned to random/turn regions (blue), α-helices (red), and βsheets (orange), respectively. yields three underlying bands at 1679, 1657, and 1635 cm -1 (Figure ) that can be assigned to turn/random regions, α-helices and β-sheets, respectively, with a very similar composition of roughly 50%, 25% and 25%. It is worth noting that this suggests that the observed spectra in Figure have rather minor contributions due to the neuraminidase protein, a β-sheet-rich protein in the IAV envelope, which also binds sialic acids but as part of viral release. Contrasting the case of specific binding, at distances >10 nm the electromagnetic field is considerably weakened but non-zero. Consequently, the electromagnetic field interacts with all constituents of virus particles at larger distances, which is detected as a spectrum similar to the one obtained from ATR-IR.