Fabrication and Evaluation of Plasmonic Nanopipettes for Near-Field Enhanced Raman Spectroscopy.

Plasmonic nanopipettes, which are functionalized with plasmonic nanomaterials, are widely used in near-field spectroscopy to enhance the optical processes. The fabrication and screening processes of these nanopipettes are critical for their intended applications. Here, an easy-to-implement fabrication scheme based on high-vacuum sputtered gold island films was reported. Additionally, the process of using surface-enhanced Raman spectroscopy (SERS) to evaluate the plasmonic enhancement of nanopipettes was described for near-infrared laser excitation, and it could be readily applied to other optical windows. These results indicated that the reported plasmonic nanopipettes can be used as Tip-SERS probes. Finally, the scanning ion-conductance microscopic tip-enhanced Raman spectroscopy (SICM-TERS) was demonstrated with the optimized plasmonic nanopipette. Together with density functional theory simulation, the observed near-field Raman spectra were analyzed and assigned. These plasmonic nanopipettes can be used to investigate a range of surface science problems in heterogeneous electrochemical interfaces, as well as in soft and biomimetic materials.