Addressable Graphene Encapsulation of Wet Specimens on a Chip for Combinatorial Optical, Electron, Infrared and X-ray based Spectromicroscopy Studies

Abstract: Label-free spectromicroscopy methods offer the capability to examine complex cellular phenomena. Electron and X-ray-based spectromicroscopy methods, though powerful, have been hard to implement with hydrated objects due to the vacuum incompatibility of the samples and due to the parasitic signals from (or drastic attenuation by) the liquid matrix surrounding the biological object of interest. Similarly, for many techniques that operate at ambient pressure, such as Fourier Transform Infrared spectromicroscopy (FTIRM), the aqueous environment imposes severe limitations due to the strong absorption by liquid water in the infrared regime. Here we propose a microfabricated multi-compartmental and reusable hydrated sample platform suitable for use with several analytical techniques, which employs the conformal encapsulation of biological specimens by atomically thin graphene. Such an electron, X-ray, and infrared transparent, molecularly impermeable as well as mechanically robust enclosure preserve the hydrated environment around the object for a sufficient time to allow in-situ examination of hydrated bio-objects with techniques operating both in ambient or high vacuum conditions. An additional hydration source, made by hydrogel pads patterned near/around the specimen and co-encapsulated, has been added to further extend the hydration lifetime. Scanning electron and optical fluorescence microscopies, as well as synchrotron radiation-based FTIR and X-ray fluorescence microscopies, have been used to test the applicability of the platform and for its validation with yeast, A549 human carcinoma lung cells and micropatterned gels as biological object phantoms.