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Register a new userGold on graphene as a substrate for surface enhanced Raman scattering study
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In this paper, we report our study on gold (Au) films with different thicknesses deposited on single layer graphene (SLG) as surface enhanced Raman scattering (SERS) substrates for the characterization of rhodamine (R6G) molecules. We find that an Au film with a thickness of ~7 nm deposited on SLG is an ideal substrate for SERS, giving the strongest Raman signals for the molecules and the weakest photoluminescence (PL) background. While Au films effectively enhance both the Raman and PL signals of molecules, SLG effectively quenches the PL signals from the Au film and molecules. The former is due to the electromagnetic mechanism involved while the latter is due to the strong resonance energy transfer from Au to SLG. Hence, the combination of Au films and SLG can be widely used in the characterization of low concentration molecules with relatively weak Raman signals.
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We synthesized three-dimensional nanoporous graphene films by a chemical vapor deposition method with nanoporous copper as a catalytic substrate. The resulting nanoporous graphene has the same average pore size as the underlying copper substrate. Our surface-enhanced Raman scattering (SERS) investigation indicates that the nanoporosity of graphene significantly improves the SERS efficiency of graphene as a substrate as compared to planar graphene substrates.
The graphene-enhanced Raman scattering of Rhodamine 6G molecules on pristine, fluorinated and 4-nitrophenyl functionalized graphene substrates was studied. The uniformity of the Raman signal enhancement was studied by making large Raman maps. The relative enhancement of the Raman signal is demonstrated to be dependent on the functional groups, which was rationalized by the different doping levels of pristine, fluorinated and 4-nitrophenyl functionalized graphene substrates. The impact of the Fermi energy of graphene and the phonon energy of the molecules was considered together for the first time in order to explain the enhancement. Such approach enables to understand the enhancement without assuming anything about the uniformity of the molecules on the graphene surface. The agreement between the theory and our measured data was further demonstrated by varying excitation energy.
The programmable assembly of DNA strands is a promising tool for building tailored bottom-up nanostructures. Here, we present a plasmonic nanosystem obtained by the base-pairing mediated aggregation of gold nanoparticles (NPs) which are separately functionalized with two different single-stranded DNA chains. Their controlled assembly is mediated by a complementary DNA bridge sequence. We monitor the formation of DNA assembled NP aggregates in solution, and we study their Surface Enhanced Raman Scattering (SERS) response by comparison with the single NP constituents. We interpret the revealed SERS signatures in terms of the molecular and NP organization at the nanoscale, demonstrating that the action of the DNA bridge molecule yields regular NP aggregates with controlled interparticle distance and reproducible SERS response. This demonstrates the potential of the present system as a stable, biocompatible, and recyclable SERS sensor.
Recently, studies have been carried out on attempts to combine surface-enhanced Surface-enhanced Raman spectroscopy (SERS) substrates that can be based on either localized surface plasmon (LSP) or surface plasmon polaritons (SPP) structures. By combining these two systems, the drawbacks of each other can be solved. However, the manufacturing methods involved so far are sophisticated, labor-intensive, expensive, and also technically demanding. We propose a facile method for the fabrication of a flexible plasmonic nanoslit SERS sensor. We utilized the pattern on periodic optical disks (DVD-R) as a cheap substitute for printing the periodic pattern on PDMS with soft imprint lithography. Ag nanoslit (AgNS) was fabricated by serial bideposition using a dynamic oblique angle deposition (DOD) technique. The nanoslit structures were physically and optically characterized, and the experimental results were compared to the numerical simulation studies; Monte Carlo and the finite-difference time-domain (FDTD) simulation. The Ag nanoslit structure showed an excellent SERS enhancement, and its biosensing capability was demonstrated by the sensing of bilirubin.
Nanofibers functionalized by metal nanostructures and particles are exploited as effective flexible substrates for SERS analysis. Their complex three-dimensional structure may provide Raman signals enhanced by orders of magnitude compared to untextured surfaces. Understanding the origin of such improved performances is therefore very important for pushing nanofiber-based analytical technologies to their upper limit. Here we report on polymer nanofiber mats which can be exploited as substrates for enhancing the Raman spectra of adsorbed probe molecules. The increased surface area and the scattering of light in the nanofibrous system are individually analyzed as mechanisms to enhance Raman scattering. The deposition of gold nanorods on the fibers further amplifies Raman signals due to SERS. This study suggests that Raman signals can be finely tuned in intensity and effectively enhanced in nanofiber mats and arrays by properly tailoring the architecture, composition, and light-scattering properties of the complex networks of filaments.
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