Surface-Enhanced Raman Spectroscopy on Two-Dimensional Networks of Gold Nanoparticle−Nanocavity Dual Structures Supported on Dielectric Nanosieves

Abstract

We report a facile method for the fabrication of 2-dimensional networks of Au nanoparticle-nanocavity dual structures supported on dielectric nanosieves. The optical extinctions of the as-fabricated network films were found to be dominated by optical transmission, a signature characteristic to nanocavities. The surfaces of the as-fabricated Au films were found to be hydrophobic toward water with a measured contact angle of 125.4°b ut quite wettable with ethanol with a contact angle of 9.5°at room temperature and are readily convertible to totally hydrophobic or hydrophilic when chemically modified with self-assembled monolayer of molecules with desired functional groups. High quality surface-enhanced Raman spectra (SERS) from a monolayer of self-assembled 4-mercaptobenzoic acid (4-MBA), an electrostatic double layer of 4-mercaptobenzoic acid and rhodamine-6G (4-MBA-R6G), and nonspecifically adsorbed R6G were obtained, respectively, demonstrating that the dual structured network films are active, stable, and uniform as substrates in SERS. Employing the SERS spectra from a monolayer of self-assembled 4-MBA, the enhancement factors of 10 6 and 10 5 were achieved with excitations at 632.8 and 785 nm, respectively. Discrete dipole approximation (DDA) calculations were conducted to examine the electric field intensity distributions on linearly and circularly aggregated nanoparticles, two typical local aggregation patterns of nanoparticles in the as-fabricated network films. The DDA calculations reveal an important relationship between three factors: the generation of the hottest E-field spot on a linear chain aggregate, the position of the extinction peak of the aggregate, and the excitation wavelength used. It was found that the hottest spot on a linear aggregate is generated only when the excitation wavelength is in resonance with the extinction peak of the aggregate. An "effective aggregation number" scale is proposed to measure the effectiveness of the aggregation of nanoparticles in 1-and 2-dimensions at a given excitation. A "hot-spot" delocalization picture is proposed for the nanocavities formed by circular aggregation of nanoparticles to account for the observed isotropic SERS on the as-fabricated films.

Synergistic Effects of Wrinkled Graphene and Plasmonics in Stretchable Hybrid Platform for Surface‐Enhanced Raman Spectroscopy

“…For instance, when the SERS substrate is stretched to 10%, it is noticed that the intensity of all the characteristic modes of R6G raises, while that of CuPc drops down. The enhancement performance of WG/Au NPs hybrid substrate for simultaneous detection of R6G and CuPc is affected by the plasmon resonance between the absorbates and SERS substrate, which can be tuned by the fabrication of morphology (such as size, shape, and distribution) of plasmonics . Here, the hybrid SERS substrate under different tensile strain exhibited different morphology, different resonance peak, and changed the intensity and peak position of characteristic modes of R6G and CuPc.…”

A sensitive DNA sensor based on an organic electrochemical transistor using a peptide nucleic acid-modified nanoporous gold gate electrode

“…It suggests that the deposited gold nanoparticles are in good crystalline structure, similar with that in the previous work. 27 Therefore, gold nanoparticles link with each other along the AAO substrate frames to form a compact structure. The peculiar structure suggests that electric properties of the as-fabricated nanoporous gold electrode would be affected not only by that of individual particles but also by their linear and ring-shaped aggregates.…”

Self-assembled Au nanoparticles network thin films at air-water interface and their SERS properties

“…由于未组装的Au纳米粒子在基质表 面随机分布并相互隔离, 不易产生更加有效的"热点 (Hot-spots)", 而Au纳米粒子网状结构其表面微结构和 微孔隙更易产生大量"Hot-spots", 有利于形成耦合的 电磁场, 使网状纳米金薄膜表现出显著的SERS效 应 [46] . 同时, 由纳米金粒子组装形成的网状结构薄膜 较大的表面积和粗糙表面能锚定和吸附更多的4-ATP 分子, 且纳米金粒子之间紧密的融合和链组装相互作 用可以提供更大的耦合电磁场效应, 从而具有较强的 表面增强拉曼效应 [47,48] . 另外, 随4-ATP浓度的增加 (10 −7~1 0 −3 mol/L), Au纳米粒子网状结构表面吸附的 4-ATP分子的谱峰强度明显增强(图S8).…”