O. Khatib, J. D. Wood, A. S. McLeod, M. D. Goldflam, M. Wagner, G. L. Damhorst, J. C. Koepke, G. P. Doidge, A. Rangarajan, R. Bashir, E. Pop, J. W. Lyding, M. H. Thiemens, F. Keilmann and D. N. Basov
ACS Nano, 2015, 9 (8), pp 7968–7975 (2015)
Scattering scanning near-field optical microscopy (s-SNOM) has emerged as a powerful nano-scale spectroscopic tool capable of characterizing individual biomolecules 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 nano-spectroscopy 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 nano-scale 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.