Wrinkled Nanoporous Gold Films with Ultrahigh Surface-Enhanced Raman Scattering Enhancement
WPI Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan. ACS Nano
(Impact Factor: 12.88).
06/2011; 5(6):4407-13. DOI: 10.1021/nn201443p
Amplified by plasomonic nanostructured metals, Raman intensity of organic molecules and biomolecules can be dramatically improved, particularly at "hot spots" where intense electromagnetic fields are produced in the vicinity of narrow nanogaps between metallic nanostructures. Therefore, developing new substrates with a high density of "hot spots" has been the recent topic of intense study. Here we report wrinkled nanoporous gold films that contain abundant Raman-active nanogaps produced by deformation and fracture of nanowire-like gold ligaments. This novel nanostructure yields ultrahigh surface enhanced Raman scattering for molecule detection.
Available from: Pham Khac Duy
- "The use of the WAC scheme clearly contributed to the reproducibility of the SERS spectra, even among 5 separately prepared substrates. The calculated SERS enhancement factor  was 4 × 10 6 relative to the intensity of a normal 2-NpSH spectrum (concentration: 300 mM). The decreased intensity resulting from the use of the substrate prepared with 360 s of electrodeposition was expected because of the less characteristic, blunt-edged structure of the nanodendrites formed under this condition. "
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ABSTRACT: A carbon fiber cloth (CFC)-supported Au nanodendrite (CFC-AuND) prepared by simple electrodeposition of Au onto CFC has been demonstrated. The motivation of employing CFC was to fully incorporate its useful characteristics of flexibility, porosity, and conductivity in the development of substrates versatile for both surface-enhanced Raman scattering (SERS) and electrochemical measurements. To improve sample representation in SERS measurement, a wide area coverage (WAC) scheme able to cover an area of 28.3 mm2 (illumination diameter: 6 mm) was used to compensate for the variation in Raman intensities of analytes adsorbed at different locations on the substrate. When a 1 nM 2-naphthalenethiol sample was measured using CFC-AuND, the corresponding Raman peaks were clearly observed and the substrate-to-substrate reproducibility of five separately prepared substrates was acceptable, with the relative standard deviation (RSD) of 8.5%. In addition, since the substrate was physically flexible, its SERS performance was not seriously degraded even after moderate bending. Next, the CFC-AuND substrate was used for the electrochemical detection of Hg(II) in aqueous samples by means of stripping voltammetry. The limit of detection (LOD) was 0.09 ppb and the substrate-to-substrate reproducibility was also superior, with RSDs below 3.6%. Overall, the results of the present work demonstrate the potential of CFC-AuND as a rugged, field-usable, cost-effective substrate for SERS and electrochemical measurements.
- "The dependence of the enhancement effect on the detailed preparation procedure is supported by further contributions   . Zhang et al.  for example, found a 100 times higher enhancement effect on wrinkled nanoporous gold films. Also, the enhancement effect on np-Au films obtained after dealloying of Au–Ag alloys is strongly affected by residual Ag . "
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ABSTRACT: Photothermal processing of nanoporous gold with a microfocused continuous-wave laser at λ = 532. nm provides a facile means in order engineer the pore and ligament size of nanoporous gold. In this report we take advantage of this approach in order to investigate the size-dependence of enhancement effects in surface-enhanced Raman spectroscopy (SERS). Surface structures with laterally varying pore sizes from 25. nm to ≥200. nm are characterized using scanning electron microscopy and then functionalized with N719, a commercial ruthenium complex, which is widely used in dye-sensitized solar cells. Raman spectroscopy reveals the characteristic spectral features of N719. Peak intensities strongly depend on the pore size. Highest intensities are observed on the native support, i.e. on nanoporous gold with pore sizes around 25. nm. These results demonstrate the particular perspectives of laser-fabricated nanoporous gold structures in fundamental SERS studies. In particular, it is emphasized that laser-engineered porous gold substrates represent a very well defined platform in order to study size-dependent effects with high reproducibility and precision and resolve conflicting results in previous studies.
Available from: Yasushi Inouye
- "However, their in-plane structural features and smooth ligament surfaces resulted from chemical etching constrain the local electromagnetic field strength below the limit for SERS-based single molecule detection212223. The SERS performances of nanoporous metal films can be further improved by introducing 3D quasi-periodic wrinkles through thermal contraction of pre-strained polymer substrates (Fig. 1a)242526. Using this procedure detailed in the Method section, rich SERS-active nanostructures at the ridges of the wrinkles, such as nanogaps and nanotips, are produced by deformation and failure of metal ligaments during film shrinking. "
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ABSTRACT: Detecting and identifying single molecules are the ultimate goal of analytic sensitivity. Single molecule detection by surface-enhanced Raman scattering (SM-SERS) depends predominantly on SERS-active metal substrates that are usually colloidal silver fractal clusters. However, the high chemical reactivity of silver and the low reproducibility of its complicated synthesis with fractal clusters have been serious obstacles to practical applications of SERS, particularly for probing single biomolecules in extensive physiological environments. Here we report a large-scale, free standing and chemically stable SERS substrate for both resonant and nonresonant single molecule detection. Our robust substrate is made from wrinkled nanoporous Au₇₉Ag₂₁ films that contain a high number of electromagnetic "hot spots" with a local SERS enhancement larger than 10⁹. This biocompatible gold-based SERS substrate with superior reproducibility, excellent chemical stability and facile synthesis promises to be an ideal candidate for a wide range of applications in life science and environment protection.
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