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Register a new userDNA-functionalized gold nanoparticle assemblies for Surface Enhanced Raman Scattering
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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.
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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.
Ag nanorod arrays/dielectrics/mirror-structured multilayer thin-film are well known, highly sensitive surface-enhanced Raman scattering (SERS) substrates that enhance the Raman scattering cross-section by the interference of light. However, extracting biomarkers directly from human skin using these solid substrates is difficult. To overcome this problem, we propose a multilayer thin-film flake dispersion gel by centrifugal mixing of the multilayer thin-film and hydroxyethyl cellulose (HEC) gel. The multilayer thin-film was prepared by serial bideposition using the dynamic oblique angle deposition technique. The mixing process was optimized to obtain flakes of ~10 {mu}m so that the optical properties of the multilayer film can be preserved, and there is no risk of adverse effects on humans. The SERS features of the flakes dispersion gel were tested using 4, 4-bipyridine (BPY). The BPY molecules diffused through the highly porous gel within a few seconds, generating significant SERS signals. The multilayer film flakes dispersion gel showed a SERS signal about 20 times better than the gel-dispersed Ag nanorod arrays without a multilayer film structure. These SERS active flakes dispersion gel can be used directly on the skin surface to collect body fluids from sweat, for biomarker sensing.
Engineered electromagnetic fields in plasmonic nanopores enable enhanced optical detection and their use in single molecule sequencing. Here, a plasmonic nanopore prepared in a thick nanoporous film is used to investigate the interaction between the metal and a long-chain double strand DNA molecule. We discuss how the matrix of nanoporous metal can interact with the molecule thanks to: i) transient aspecific interactions between the porous surface and DNA and ii) optical forces exerted by the localized field in a metallic nanostructure. A duration of interaction up to tens of milliseconds enables to collect high signal-to-noise Raman vibrations allowing an easy label-free reading of information from the DNA molecule. Moreover, in order to further increase the event of detection rate, we tested a polymeric porous hydrogel placed beneath the solid-state membrane. This approach enables a slowdown of the molecule diffusion, thus increasing the number of detected interactions by a factor of about 20.
Surface enhanced Raman scattering (SERS) process results in a tremendous increase of Raman scattering cross section of molecules adsorbed to plasmonic metals and influenced by numerous physico-chemical factors such as geometry and optical properties of the metal surface, orientation of chemisorbed molecules and chemical environment. While SERS holds promise for single molecule sensitivity and optical sensing of DNA sequences, more detailed understanding of the rich physico-chemical interplay between various factors is needed to enhance predictive power of existing and future SERS-based DNA sensing platforms. In this work we report on experimental results indicating that SERS spectra of adsorbed single-stranded DNA (ssDNA) isomers depend on the order on which individual bases appear in the 3-base long ssDNA due to intra-molecular interaction between DNA bases. Furthermore, we experimentally demonstrate that the effect holds under more general conditions when the molecules dont experience chemical enhancement due to resonant charge transfer effect and also under standard Raman scattering without electromagnetic or chemical enhancements. Our numerical simulations qualitatively support the experimental findings and indicate that base permutation results in modification of both Raman and chemically enhanced Raman spectra.
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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