This study proposes a facile method for synthesis of Au-coated magnetic nanoparticles (AuMNPs) core/shell nanocomposites with nanoscale rough surfaces. MnFe2O4 nanoparticles (NPs) were first modified with a uniform polyethylenimine layer (2 nm) through self-assembly under sonication. The negatively charged Au seeds were then adsorbed on the surface of the MnFe2O4 NPs through electrostatic interaction for Au shell formation. Our newly developed sonochemically assisted hydroxylamine seeding growth method was used to grow the adsorbed gold seeds into large Au nanoparticles (AuNPs) to form a nanoscale rough Au shell. Au-coated magnetic nanoparticles (AuMNPs) were obtained from the intermediate product (Au seeds decorated magnetic core) under sonication within 5 min. The AuMNPs were highly uniform in size and shape and exhibited satisfactory surface-enhanced Raman scattering (SERS) activity and strong magnetic responsivity. PATP was used as a probe molecule to evaluate the SERS performance of the synthesized AuMNPs with a detection limit of 10(-9) M. The synthesized AuMNPs were conjugated with Staphylococcus aureus (S. aureus) antibody for bacteria capture and separation. The synthesized plasmonic AuNR-DTNB NPs, whose LSPR wavelength was adjusted to the given laser excitation wavelength (785 nm), were conjugated with S. aureus antibody to form a SERS tag for specific recognition and report of the target bacteria. S. aureus was indirectly detected through SERS based on sandwich-structured immunoassay, with a detection limit of 10 cells/mL. Moreover, the SERS intensity at Raman peak of 1331 cm(-1) exhibited a linear relationship to the logarithm of bacteria concentrations ranging from 10(1) cells/mL to 10(5) cells/mL.

A nanotechnique to assemble silver nanocrystals and control the gaps precisely in the sub-10 nm regime is demonstrated on an active coating exhibiting surface-enhanced Raman scattering ͑SERS͒. The silver nanocrystal superlattice coating boasts a high SERS enhancement factor, large dynamic range, and universal SERS activity. The observed SERS efficiency can be explained in terms of interparticle-coupling-induced Raman enhancement.

A simple method for improving surface-enhanced Raman scattering (SERS) performance of aligned silver nanorod (Ag NR) array was investigated. This method was to construct a kind of hybrid substrate by grafting Au@Ag core-shell nanoparticles (NPs) into Ag NR array using poly (2-vinylphridine) (P2VPy) as a bridging agent. The hybrid substrate yielded excellent SERS performance as its detection limit improved from 10 À6 M to 10 À8 M using trans-1,2-bis(4-pyridyl) ethylene (BPE) as probe molecule, which was increased by two orders of magnitude compared with Ag NR array substrate. The signi¯cant improvement of SERS performance of Ag NR arrays was attributed to the addition of Au@Ag core-shell NPs. As a result of surface plasmon resonance generated by the interaction of electromagnetic (EM) (IAEM)¯led between NP and NR structures, increasing hotspots were found at the connections of NPs and NRs, the gaps of adjacent rods, and the gaps of two particles consequently. These results were validated by the¯nite di®erence time domain (FDTD) calculation. Besides, hybrid substrate shows good performance in stability and reproducibility. The proposed method was simple and robust, which promoted SERS performance of Ag NR array e®ectively, showing great potential in the application of SERS substrate fabrication and SERS-based bio-chemical sensing.

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This article presents a facile and generally applicable methodology for the morphology diversification of two-dimensional (2D) nanostructure arrays by modifying angle-resolved heterogeneous shadow mask (AR-HSM). Colloid spheres are used to prepare scalable well-organized monolayer film by self-assembly method and then etched in oxygen plasma to reduce size. Subsequently, the heterogeneous layer is generated by tilted metal deposition technique, then utilized as shadow mask in the substrate etching process, and finally removed by wet etching technique. As a result, the controllable fabrication of a series of complex morphologies, ranging from the crescent structure to the hoof-like structure and the stripes with apexes, is realized. The morphology of the nanostructure array is depend on the profile of the heterogeneous shadow mask (HSM) which is correlated to the incidence angle of the metal vapor. Therefore, a theoretical model is built for the prediction and design of the nanostructure morphology. This AR-HSM aided approach provides a novel and accessible route for the diversification of nanostructure morphology; and can be readily extended to other functional substrates which may be applied in photovoltaic devices or bio-chemical sensors.

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