  Scattering scanning near-field optical microscopy (s-SNOM) has emerged as a
powerful nanoscale spectroscopic tool capable of characterizing individual
biomacromolecules and molecular materials. However, applications of
scattering-based near-field techniques in the infrared (IR) to native
biosystems still await a solution of how to implement the required aqueous
environment. In this work, we demonstrate an IR-compatible liquid cell
architecture that enables near-field imaging and nanospectroscopy by taking
advantage of the unique properties of graphene. Large-area graphene acts as an
impermeable monolayer barrier that allows for nano-IR inspection of underlying
molecular materials in liquid. Here, we use s-SNOM to investigate the tobacco
mosaic virus (TMV) in water underneath graphene. We resolve individual virus
particles and register the amide I and II bands of TMV at ca. 1520 and 1660
cm$^{-1}$, respectively, using nanoscale Fourier transform infrared
spectroscopy (nano-FTIR). We verify the presence of water in the graphene
liquid cell by identifying a spectral feature associated with water absorption
at 1610 cm$^{-1}$.
