Synchrotron infrared nanospectroscopy on a graphene chip

A recurring goal in biology and biomedicine research is to access the biochemistry of biological processes in liquids that represent the environmental conditions of living organisms. These demands are becoming even more specific as microscopy techniques are fast evolving to the era of single cells analysis. In the modality of chemical probes, synchrotron infrared spectroscopy (µ-FTIR) is a technique that is extremely sensitive to vibrational response of materials, however, the classical optical limits prevent the technique to access the biochemistry of specimens in the subcellular level. In addition, due to the intricate environmental requirements and strong infrared absorption of water, µ-FTIR of bioprocess in liquids remains highly challenging. In phase with those challenges, on-chip liquid cells emerge as a versatile alternative to control the water thickness while providing a biocompatible chemical environment for analytical analyzes. In this work we report the development of a liquid platform specially designed for nanoscale infrared analysis of biomaterials in wet environments. A key advantage of our designed platform is the use of graphene as the optical window that interfaces wet and dry environments in the liquid cell. By combining near-field optical microscopy and synchrotron infrared radiation, we measure nanoscale fingerpint IR absorbance of a variety of liquids often used in biological studies. Further, we demonstrate the feasibility of the platform for the chemical analysis of protein clusters immersed in water with a clear view of the proteins secondary structure signatures. The simplicity of the proposed platform combined to the high quality of our data make our findings a template for future microfluidic devices targeting dynamical nanoscale-resolved chemical analysis.