It is critical to design and synthesize plasmonic nanostructures that can generate very strong and quantitative surface-enhanced Raman scattering (SERS) signals that could be amplified by multiple laser wavelengths to realize the full potential of SERS nanoprobes. Here, we report the synthesis of Au-nanobridged nanogap cucumbers (Au-NNCs) from DNA-modified Au nanorods and comparison of their SERS signals with three different Raman dyes with our recently reported Au-nanobridged nanogap spheres (Au-NNSs). Although the Au-NNSs generate highly stable and reliable signals, these spherical nanogap structures with a smooth surface produce strong SERS signals (SERS enhancement factor at~10 8 ) only with 633 nm excitation laser. The Au-NNCs with a bumpy surface generated up to~3-,~23-, and~130-fold higher SERS signals with 514, 633, and 785 nm excitation laser wavelengths, respectively, compared to the Au-NNSs.Keywords: Surface-enhanced Raman scattering, Nanogap, Core-shell particle, Gold nanorod, Multiple laser wavelength compatibility Plasmonic signal enhancements from gold and silver nanoparticles (AuNPs and AgNPs) have been studied for various applications including surface-enhanced Raman scattering (SERS), 1-7 localized surface plasmon resonance (LSPR), 8,9 colorimetric assay, 10,11 nanoatenna, 12,13 and plasmonic biosensors. 14,15 In the case of SERS, there have been intense research efforts to design and synthesize SERS-active nanostructures that generate stable, reproducible, and strong SERS signals in a controllable fashion for the practical use. [16][17][18][19][20][21] It is now widely known that plasmonic hot spots, formed between plasmonic structures, are responsible for very strong electromagnetic field enhancement that can amplify SERS signals. [22][23][24][25][26] However, controlling and generating these plasmonic nanogaps, especially of~1 nm, in solution is highly challenging, and, therefore, obtaining reliable and quantitative signals from these SERS nanoprobes is not completely addressed yet. Typically, the plasmonic coupling becomes exponentially stronger from~1-nm or smaller plasmonic gap. 16,22,[25][26][27] As a step forward, we recently showed that a high-yield synthesis of Au-nanobridged nanogap particles (Au-NNPs) with~1 nm interior plasmonic gap from DNAmodified AuNPs (DNA-AuNPs) is possible. Although the hollow interior nanogap generates highly uniform and reproducible Au SERS signals from >90% of particles with a narrow distribution of enhancement factors (EFs) from 1.0 × 10 8 to 5.0 × 10 9 , 16 there is still much room for improvement in SERS enhancement, and strong SERS signals from the AuNNPs were obtained only when a 633 nm laser was used as an excitation source. Getting higher SERS intensity and obtaining strong SERS signals from different excitation laser wavelengths are important for more versatile and multiplexed sensing applications of these interior nanogap probes and, in particular, near-infrared (NIR) laser-based in vivo bioimaging and therapeutic applications: radiation in the NIR...

We report here a self-organized electroless deposition of copper in an ultrathin layer CuSO4 of electrolyte. Microscopically the branching rate of the copper deposits is significantly decreased, forming an array of smooth polycrystalline filaments. Compared with a conventional electrodeposition system, no macroscopic electric field is involved and the thickness of the electrolyte layer is greatly decreased. Therefore the electroless deposition takes place in a nearly ideal, two-dimensional diffusion-limited environment. We suggest that restriction of the thickness of the electrolyte film is responsible for the generation of smoother branches of the electrodeposits. Our data also show that even in a diffusion-limited scenario the aggregate morphology is not necessarily very ramified and fractal-like.

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