Seo Sujin, Chang Te-Wei, Liu Gang Logan
Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA.
Micro and Nano Technology Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA.
Sci Rep. 2018 Feb 14;8(1):3002. doi: 10.1038/s41598-018-19256-7.
Unique colorimetric optical properties of nanomaterials can effectively influence the light absorption or emission of molecules. Here, we design plasmonic substrate for surface-enhanced Raman scattering (SERS) by inducing three-dimensional (3D) hot spots on the sensing surface. The 3D hot spots are formed by the self-assembly of plasmonic nanoparticles (NPs) on a 3D plasmonic nanocup array structure. This 3D hot spot formation on the periodic nanocup arrays achieves much higher SERS enhancement factor than the 2D NP arrays, which have been conventionally sought SERS substrates. We also utilize the colorimetric properties of the nanocup arrays for an additional degree of SERS enhancement. Colorimetry, achieved by tunable plasmon resonance wavelength by controlling dielectric property on the nanocup array surface, eases the modulation of the plasmonic resonance condition without modifying the nanostructure design. By continuously monitoring the shifts of the plasmon resonance condition and its effect on the light absorption and emission of the nearby molecules, we verify that larger SERS enhancement is achieved when the plasmon resonance wavelength is matched with the Raman excitation wavelength. The ease of plasmon resonance tuning of this nanocup array-nanoparticle hybrid structure allows versatile SERS enhancement for a variety of different Raman measurement conditions.
纳米材料独特的比色光学特性能够有效影响分子的光吸收或发射。在此，我们通过在传感表面诱导三维（3D）热点来设计用于表面增强拉曼散射（SERS）的等离子体基底。3D热点是由等离子体纳米颗粒（NP）在三维等离子体纳米杯阵列结构上自组装形成的。在周期性纳米杯阵列上形成的这种3D热点实现了比二维NP阵列更高的SERS增强因子，二维NP阵列一直是传统的SERS基底。我们还利用纳米杯阵列的比色特性来进一步增强SERS。通过控制纳米杯阵列表面的介电性质实现可调谐等离子体共振波长的比色法，在不改变纳米结构设计的情况下简化了等离子体共振条件的调制。通过持续监测等离子体共振条件的变化及其对附近分子光吸收和发射的影响，我们证实当等离子体共振波长与拉曼激发波长匹配时可实现更大的SERS增强。这种纳米杯阵列 - 纳米颗粒混合结构的等离子体共振调谐的简便性使得在各种不同的拉曼测量条件下都能实现通用的SERS增强。
