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Coherently embedded Ag nanostructures in Si: 3D imaging and their application to SERS.

ABSTRACT: Surface enhanced Raman spectroscopy (SERS) has been established as a powerful tool to detect very low-concentration bio-molecules. One of the challenging problems is to have reliable and robust SERS substrate. Here, we report on a simple method to grow coherently embedded (endotaxial) silver nanostructures in silicon substrates, analyze their three-dimensional shape by scanning transmission electron microscopy tomography and demonstrate their use as a highly reproducible and stable substrate for SERS measurements. Bi-layers consisting of Ag and GeOx thin films were grown on native oxide covered silicon substrate using a physical vapor deposition method. Followed by annealing at 800°C under ambient conditions, this resulted in the formation of endotaxial Ag nanostructures of specific shape depending upon the substrate orientation. These structures are utilized for detection of Crystal Violet molecules of 5 × 10(-10) M concentrations. These are expected to be one of the highly robust, reusable and novel substrates for single molecule detection.

SUBMITTER: Juluri RR

PROVIDER: S-EPMC3982172 | biostudies-other | 2014

REPOSITORIES: biostudies-other

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SERS-active substrate assembled by Ag NW-embedded porous polystyrene fibers.

Project description:Here we demonstrate a novel SERS-active substrate assembled by silver nanowire (Ag NW)-embedded porous polystyrene (PS) fibers. Ag NWs are synthesized through a glycerol-mediated solvothermal method firstly, then electrospun into PS porous fibers. The as-synthesized Ag NWs are embedded in PS fiber and aligned orderly along the axial direction. Porous structure appears in PS fiber due to the phase separation induced by rapid evaporation of solvents. Large amounts of holes not only greatly improve the sample collection efficiency of the SERS-active substrate, but also significantly facilitate the adsorption of target molecules on the surface of Ag NWs, thus increasing the probability of enhancement of target molecules. In addition, compared with polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP), PS has better solvent resistance. The detection limit of 4-aminothiophenol (4-ATP) on our fabricated electrospun fiber mats is 10-7 M, and the electrospun fiber mats showed good reproducibility of SERS signal detection. This study proposes a feasible strategy for the large-scale preparation of flexible SERS-active substrate assembled by Ag NW-embedded porous PS fibers. The produced flexible SERS substrates may have potential application in wearable sensors for the trace detection of chemical and biological molecules.

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Graphene-Ag Hybrids on Laser-Textured Si Surface for SERS Detection.

Project description:Surface-enhanced Raman scattering (SERS) has been extensively investigated as an effective approach for trace species detection. Silver nanostructures are high-sensitivity SERS substrates in common use, but their poor chemical stability impedes practical applications. Herein, a stable and sensitive SERS substrate based on the hybrid structures of graphene/silver film/laser-textured Si (G/Ag/LTSi) was developed, and a simple, rapid, and low-cost fabrication approach was explored. Abundant nanoparticles were directly created and deposited on the Si surface via laser ablation. These aggregated nanoparticles functioned as hotspots after a 30 nm Ag film coating. A monolayer graphene was transferred to the Ag film surface to prevent the Ag from oxidation. The SERS behavior was investigated by detecting R6G and 4-MBT molecules. The experimental results indicate that the maximum enhancement factor achieved by the G/Ag/LTSi substrate is over 10⁷ and less than 23% SERS signals lost when the substrate was exposed to ambient conditions for 50 days. The covering graphene layer played crucial roles in both the Raman signals enhancement and the Ag nanostructure protection. The stable and sensitive SERS performance of G/Ag/LTSi substrate evince that the present strategy is a useful and convenient route to fabricate large-area graphene-silver plasmonic hybrids for SERS applications.

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Distinctly Different Morphologies of Bimetallic Au-Ag Nanostructures and Their Application in Submicromolar SERS-Detection of Free Base Porphyrin.

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Project description:The formation of silver nanopetal-Fe3O4 poly-nanocrystals assemblies and the use of the resulting hetero-nanostructures as active substrates for Surface Enhanced Raman Spectroscopy (SERS) application are here reported. In practice, about 180 nm sized polyol-made Fe3O4 spheres, constituted by 10 nm sized crystals, were functionalized by (3-aminopropyl)triethoxysilane (APTES) to become positively charged, which can then electrostatically interact with negatively charged silver seeds. Silver petals were formed by seed-mediated growth in presence of Ag+ cations and self-assembly, using L-ascorbic acid (L-AA) and polyvinyl pyrrolidone (PVP) as mid-reducing and stabilizing agents, respectively. The resulting plasmonic structure provides a rough surface with plenty of hot spots able to locally enhance significantly any applied electrical field. Additionally, they exhibited a high enough saturation magnetization with Ms = 9.7 emu g-1 to be reversibly collected by an external magnetic field, which shortened the detection time. The plasmonic property makes the engineered Fe3O4-Ag architectures particularly valuable for magnetically assisted ultra-sensitive SERS sensing. This was unambiguously established through the successful detection, in water, of traces, (down to 10-10 M) of Rhodamine 6G (R6G), at room temperature.

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Project description: Not available

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Project description:The finite-difference time-domain (FDTD) method was employed to simulate the electric field distribution for noble metal (Au or Ag)/semiconductor (Ge or Si) substrates. The simulation showed that noble metal/Ge had stronger SERS enhancement than noble metal/Si, which was mainly attributed to the different dielectric constants of semiconductors. In order to verify the simulation, Ag nanoparticles with the diameter of ca. 40 nm were grown on Ge or Si wafer (Ag/Ge or Ag/Si) and employed as surface-enhanced Raman scattering substrates to detect analytes in solution. The experiment demonstrated that both the two substrates exhibited excellent performance in the low concentration detection of Rhodamine 6G. Besides, the enhancement factor (1.3 × 10(9)) and relative standard deviation values (less than 11%) of Ag/Ge substrate were both better than those of Ag/Si (2.9 × 10(7) and less than 15%, respectively), which was consistent with the FDTD simulation. Moreover, Ag nanoparticles were grown in-situ on Ge substrate, which kept the nanoparticles from aggregation in the detection. To data, Ag/Ge substrates showed the best performance for their sensitivity and uniformity among the noble metal/semiconductor ones.

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