Tunable Layered Gold Nanochips for High Sensitivity and Uniformity in SERS Detection

Reasonable design and controllable fabrication of plasmonic substrates are the keys to achieving surface-enhanced Raman spectroscopy (SERS) detection with high sensitivity and uniformity. The coupling of the two main modes of surface plasmon, the localized surface plasmon resonance (LSPR) mode and the surface plasmon polariton (SPP) mode, has been proven to be an appealing way to obtain excellent SERS responses. Nevertheless, it remains an obstacle to further improve the LSPR-SPP coupling efficiency due to the dramatic nonuniformity of the nanostructure obtained by traditional wet chemical methods. Here, we report a controllable electron-beam lithography (EBL) process for the fabrication of layered Au nanochips. For the optimized Au CFN (cap and film nanostructure) structure, benefiting from the remarkable electric field enhancement induced by the effective LSPR-SPP coupling at the junction of the Au cap and Au film structure, an improved SERS performance with an enhancement factor (EF) of 2.8 x 106 and a low detection limit of 10-13 M are achieved using 4-nitrothiophenol (4-NTP) as the probe molecule. In addition, the Au CFN substrate exhibits a high uniformity over a large area. Such a new strategy for the design of plasmonic substrates with superior LSPR-SPP can be in various SERS detection scenarios.