On the other hand, Au may be a promising SERS substrate material because 1) it has excellent stability, reusability and biocompatibility and 2) an Au nanolayer thinner than 5 nm can not influence the sensitivity of Ag-based SERS substrates 15. To overcome this problem, many nanolayer shells on Ag cores (such as Ag/carbon, Ag/Au and Ag/SiO 2) were fabricated to improve the Ag nanostructure’s time-stability 12, 13, 14. These factors should favor Ag dendritic nanostructures to be used as high-active SERS substrates 2, 8.Īlthough Ag nanostructures possess high SERS properties in SERS applications, they have poor time-stability since their surface is highly sensitive to oxidation. Thus a large amount of ‘hot spots’ would exist in the spaces at the end of branches or among adjacent Ag branches. Actually, the strong electromagnetic (EM) coupling can be formed in the space between two adjacent branches from the coupling of SPR. Compared to other structures, Ag dendrites possess many multi-level branching nanostructures, thus allowing a large specific surface area and the corresponding complex nanostructure may be more favorable to absorption of probe molecules 10, 11. Many different Ag structures and substrates, which exhibit strong and tunable surface plasmon resonance (SPR) from the visible to the near-infrared spectral regimes 8, 9, have been proposed as effective enhancers of the weak basic Raman signals from the probe molecules. Recently, the SERS technique has been recognized as one of the most powerful and sensitive spectroscopic tools in the biological, clinical, chemical and environment fields because it can provide rich structural information in a non-destructive manner 2, 4, 5, 6, 7. Surface enhanced Raman scattering (SERS) has been explored as an effective molecular imaging optical modality due to its inherent ability to generate enhanced Raman signal of analyte when it is in close proximity to nano-roughened noble metal surfaces like silver (Ag) or gold (Au) 1, 2, 3. Finite-difference time-domain simulations were carried out to investigate the influence of Au nanolayer on Ag dendrites, which showed that the local electric fields and enhancement factor are hardly affected when a 4 nm Au nanolayer is coated on Ag dendrite surface. We have also experimented on fast detection of Cd 2+ at 10 −8 M concentration by decorating single-stranded DNA containing adenine and guanine bases on the surface of this dendrite. Six-month-duration stability tests showed that the core-shell dendrite substrate is much more stable than the Ag dendrite substrates. After four repeatable experiments, the substrate SERS function did not decrease at all, indicating that the dendrite should be of great significance to SERS application because it can save much resource.

With the help of sodium borohydride in water, Au surface absorbates such as thiophene, adenine, rhodamine, small anions (Br – and I –) and a polymer (PVP, poly(N-vinylpyrrolidone)) can be completely and rapidly removed. Ag dendrites were grown on Si wafer by the hydrothermal corrosion method and Au nanofilm on the surface of Ag dendritic nanostructure was then fabricated by chemical reduction. Surface enhanced Raman scattering (SERS) substrate based on fabricated core-shell dendrite was achieved.

Core shell