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: Surface Enhanced Raman Spectroscopy (SERS) has a long history as an ultrasensitive platform for the detection of biological species from small aromatic molecules to complex biological systems as circulating tumor cells. Thanks to unique properties of graphene, the range of SERS applications has largely expanded. Graphene is efficient fluorescence quencher improving quality of Raman spectra. It contributes also to the SERS enhancement factor through the chemical mechanism. In turn, the chemical flexibility of Reduced Graphene Oxide (RGO) enables tunable adsorption of molecules or cells on SERS active surfaces. Graphene oxide composites with SERS active nanoparticles have been also applied for Raman imaging of cells. This review presents a survey of SERS assays employing graphene or RGO emphasizing the improvement of SERS enhancement brought by graphene or RGO. The structure and physical properties of graphene and RGO will be discussed too.

Replacing water with dimethyl sulfoxide (DMSO) completely reshapes the free-energy landscapes of solvated proteins. In DMSO, a powerful hydrogen-bond (HB) acceptor, formation of HBs between backbone NH groups and solvent is favored over HBs involving protein's carbonyl groups. This entails a profound structural disruption of globular proteins and proteinaceous aggregates (e.g., amyloid fibrils) upon transfer to DMSO. Here, we investigate an unusual DMSO-induced conformational transition of β 2amyloid fibrils from poly-L-glutamic acid (PLGA). The infrared spectra of β 2 -PLGA dissolved in DMSO lack the typical features associated with disordered conformation that are observed when amyloid fibrils from other proteins are dispersed in DMSO. Instead, the frequency and unusual narrowness of the amide I band imply the presence of highly ordered helical structures, which is supported by complementary methods, including vibrational circular dichroism and Raman optical activity. We argue that the conformation most consistent with the spectroscopic data is that of a PLGA chain essentially lacking nonhelical segments such as bends that would provide DMSO acceptors with direct access to the backbone. A structural study of DMSO-dissolved β 2 -PLGA by synchrotron small-angle X-ray scattering reveals the presence of long uninterrupted helices lending direct support to this hypothesis. Our study highlights the dramatic effects that solvation may have on conformational transitions of large polypeptide assemblies.

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