1 research outputs found
Plasmonic Nanosnowmen with a Conductive Junction as Highly Tunable Nanoantenna Structures and Sensitive, Quantitative and Multiplexable Surface-Enhanced Raman Scattering Probes
The
precise design and synthesis of plasmonic nanostructures allow
us to manipulate, enhance, and utilize the optical characteristics
of metallic materials. Although many multimeric structures (e.g.,
dimers) with interparticle nanogap have been heavily studied, the
plasmonic nanostructures with a conductive junction have not been
well studied mostly because of the lack of the reliable synthetic
methods that can reproducibly and precisely generate a large number
of the plasmonic nanostructures with a controllable conductive nanojunction.
Here, we formed various asymmetric Au–Ag head–body nanosnowman
structures with a highly controllable conductive nanojunction and
studied their plasmon modes that cover from visible to near-infrared
range, electromagnetic field enhancement, and surface-enhanced Raman
scattering (SERS) properties. It was shown that change in the plasmonic
neck region between Au head and Ag body nanoparticles and symmetry
breaking using different sizes and compositions within a structure
can readily and controllably introduce various plasmon modes and change
the electromagnetic field inside and around a nanosnowman structure.
The charge-transfer and capacitive coupling plasmon modes at low frequencies
are tunable in the snowman structure, and subtle change in the conductive
junction area of the nanosnowman dramatically affects the resulting
electromagnetic field and optical signal. The relationships between
the electromagnetic field distribution and enhancement in the snowman
structure, excitation laser wavelength, and Raman dye were also studied,
and it was found that the strongest electromagnetic field was observed
in the crevice area on the junction and synthesizing a thinner and
sharper neck junction is critical to generate the stronger electromagnetic
field in the crevice area and to obtain the charge-transfer mode-based
near-infrared signal. We have further shown that highly reproducible
SERS signals can be generated from these nanosnowman structures with
a linear dependence on particle concentration (5 fM to 1 pM) and the
SERS-enhancement factor values of >10<sup>8</sup> can be obtained
with the aid of the resonance effect in SERS. Finally, a wide range
of LSPR bands with high tunability along with high structural reproducibility
and high synthetic yield make the nanosnowman structures as very good
candidates for practically useful multiple-wavelength-compatible,
quantitative and sensitive SERS probes, and highly tunable nanoantenna
structures