Graphene-Based Platform for Infrared Near-Field Nano-Spectroscopy of Water and Biological Materials in an Aqueous Environment

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.