Graphened IR Screens: A New Spectroscopic Platform For Bio-Species
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Graphened IR Screens: A New Spectroscopic Platform For Bio-Species Amrita Banerjee, Dieter Moeller and Haim Grebel Electronic Imaging Center, New Jersey Institute of Technology, Newark, NJ 07102, U.S.A. ABSTRACT Metallo-dielectric screens are periodic structures, which are at resonance with the infrared (IR) wavelength of interest: a standing wave of surface charges is formed at resonance conditions, which enables transmission or, reflection of certain IR bands. Graphene is a monolayer thick crystal of carbon. It is chemically inert and exhibits very large electronic mobility. Recently, we succeeded in fabricating mono and a few-layered suspended graphene on top of these screens. We combined these two unique components in fabricating novel platforms, which enhance IR signals of soft bio-species. Specifically, we used these platforms to examine IR spectra of a model protein, cytochrome c from a bovine heart tissue. Clear Raman signal variation as a function of platform orientation has been demonstrated. Accentuation of the IR absorption spectra was shown as well.
INTRODUCTION Free standing metal meshes have been investigated as filters in the visible to the THz spectral region for astronomy and remote sensing applications [1]. Commercially available squared shaped meshes are mainly used as band pass and band reject (notch) filters [2]. In general, these filters are able to separate desired IR signals from more energetic short wavelength radiation, allow for color temperature measurements, provide order sorting for grating spectrometers, and improve the signal-to-noise ratio of Fourier transform spectrometers (FTIR) [3]. The meshes are made of periodic structures, which are at resonance with certain IR wavelength of interest. A standing wave of surface charges is formed at resonance conditions, which enables transmission or, reflection of certain IR bands. Graphene is a monolayer thick crystal of carbon. Graphene is chemically inert and exhibits large electronic mobility [4, 5]. Recently, we succeeded in fabricating mono and a fewlayered graphene into films on solid and perforated substrates [6, 7]. By combining the properties of IR screens and graphene, we hope to fabricate new spectroscopic platforms, which enhance IR and Raman signals of molecules and specifically, bio-species. Raman spectroscopy is a widely used spectroscopic tool to detect molecular vibrations. Raman signals are typically weak and many attempts have been made to enhance these signals. We hypothesize that Raman signals can be enhanced by the use of IR screens coated with a few layer of graphene and, specifically, by those screens at resonance with the vibration frequency of the molecule. We have successfully made graphenated metal screens with biotinylated lipid bilayers and conjugated streptavidin and we studied protein binding to the lipid bilayers - a building block of cell membranes [8]. Infrared spectroscopy is a complementary spectroscopic tool to Raman. The absorption of the biotinylated lipid bilayer has exhibited strong dep
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