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 in the era of single cell analysis. In the modality of chemical probes, synchrotron infrared spectroscopy (µ-FTIR) is a technique that is extremely sensitive to vibrational responses of materials; however, the classical optical limits prevent the technique to access the biochemistry of specimens at the subcellular level. In addition, due to the intricate environmental requirements and strong infrared absorption of water, µ-FTIR of bioprocesses in liquids remains highly challenging. In phase with these challenges, on-chip liquid cells emerge as a versatile alternative to control the water thickness while providing a biocompatible chemical environment for analytical analyses. 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 an optical window that interfaces wet and dry environments in the liquid cell. By combining near-field optical microscopy and synchrotron infrared radiation, we measure the nanoscale fingerprint 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 with the high quality of our data makes our findings a template for future microfluidic devices targeting dynamic nanoscale-resolved chemical analysis.

Apparent Softening of Wet Graphene Membranes on a Microfluidic Platform.

Graphene is regarded as the toughest two-dimensional material (highest in-plane elastic properties) and, as a consequence, it has been employed/proposed as an ultrathin membrane in a myriad of microfluidic devices. Yet, an experimental investigation of eventual variations on the apparent elastic properties of a suspended graphene membrane in contact with air or water is still missing. In this work, the mechanical response of suspended monolayer graphene membranes on a microfluidic platform is investigated via scanning probe microscopy experiments. A high elastic modulus is measured for the membrane when the platform is filled with air, as expected. However, a significant apparent softening of graphene is observed when water fills the microfluidic system. Through molecular dynamics simulations and a phenomenological model, we associate such softening to a water-induced uncrumpling process of the suspended graphene membrane. This result may bring substantial modifications on the design and operation of microfluidic devices which exploit pressure application on graphene membranes.