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In-vitro monitoring conformational changes of polypeptide monolayers using infrared plasmonic nanoantennas Rostyslav Semenyshyn, Mario Hentschel, Christoph Stanglmair, Tanja Teutsch, Cristina Tarin, Claudia Pacholski, Harald Giessen, and Frank Neubrech Nano Lett., Just Accepted Manuscript • DOI: 10.1021/acs.nanolett.8b02372 • Publication Date (Web): 02 Aug 2018 Downloaded from http://pubs.acs.org on August 3, 2018
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TOC Graphic 43x29mm (300 x 300 DPI)
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Nano Letters
Figure 1. Chip-level based SEIRA for in-vitro monitoring conformational changes of polypeptides. A monolayer of poly-L-lysine (PLL) as a model system for polypeptides is immobilized in the plasmonic hotspots of gold (Au) nanoantennas. The amide vibration of PLL is enhanced if the plasmon is resonantly matched to the molecular vibration. By adding external stimuli, the secondary structure can be reversibly changed from the α to the β state resulting in different substructures of the amide vibration. The experiments are performed in aqueous solution. 57x38mm (300 x 300 DPI)
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Figure 2. IR optical properties of the poly-L-lysine model system and functionalization scheme. (a) PLL molecules are immobilized on a gold surface using a mixed monolayer of MUA and MUoL. The intermolecular distance between PLL molecules, which can be adjusted by the composition of MUA/MUoL, and their distance to the gold surface is crucial for conformational changes. (b) Reflectance spectra of resonant nanoantenna arrays in D2O are taken before (red) and after (green) functionalization with MUA/MUoL and poly-L-lysine (see illustrations). After molecular adsorption, the resonance frequency is shifted and the amide I vibration is enhanced by the plasmonic nearfields. SEM image depicts an exemplary antenna array; the scale bar is 1 µm. 124x152mm (300 x 300 DPI)
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Nano Letters
Figure 3. In-vitro monitoring of PLL conformational changes. Baseline-corrected SEIRA signals (right) of nanoantennas functionalized with PLL under different external stimuli. (a) After functionalization, PLL molecules are in a random mixture of α-helix to β-sheet as evidenced by the vibrational substructure of the amide band. (b) If the basicity is increased to a pD-value of 12, the vibrational signature of the β-sheet state (1618 cm-1) vanishes and only the α-helix state (1644 cm-1) signature remains. (c) SDS forces a transition of the polypeptides back to the β-sheet state. (d) A second increase in basicity (pD of 12) switches the vast majority of molecules back to the α-helix state. The vertical dashed lines indicate amide vibration of PLL in the α-helix and β-sheet states. 157x326mm (300 x 300 DPI)
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Figure 4. Principal component analysis (PCA) of PLL structural changes. The first and second principal components and their scores are determined. (a) The first principal component resembles intensity changes of the resonantly scattered light. The second principal component represents the changes of molecular vibration under the external chemical stimuli. Most of the variability of each spectrum can be accounted for by a linear combination of the first and second principal components with scores, shown in (b) in 2dimensional space. This presentation depicts the clustering of the dataset and thus represents the different conformational states of PLL. Particularly, the clusters 2 and 4 (light and dark green) are the one group attributed to α-helix, whereas 3rd cluster is the group attributed to the β-sheet state, and 1st – a mixture of both α-helix and β-sheet. 134x183mm (300 x 300 DPI)
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