Detection of Off‐Resonance Single‐Walled Carbon Nanotubes by Enormous Surface‐Enhanced Raman Scattering

Abstract The resonant Raman spectroscopy can only detect on‐resonance single‐walled carbon nanotubes (SWNTs) within the laser resonance window. In principle, surface‐enhanced Raman scattering (SERS) spectroscopy can expand the resonance window. However, detection of off‐resonance SWNTs by SERS remains challenging due to the difficulties in locating the SWNTs exactly at the hot spots with enormous SERS enhancements. Here, polyhedral gold nanocrystals (AuNCs) are in situ prepared on SWNTs for SERS detection via a facile ultrasonic spray pyrolysis method. The fact that the edges of the AuNCs attach to the SWNTs ensures the location of SWNTs perfectly at the SERS hot spots. Consequently, the enormous SERS enhancement enables a maximum enhancement factor of (3.4 ± 0.6) × 10⁴ for an individual SWNT, which is about two orders of magnitude higher than the maximum reported in literatures. The detection ratio of SWNTs is also dramatically increased from 33% without SERS to 76% with SERS. The existence of the polyhedral AuNCs suppresses the antenna effects of the SWNTs and allows effective enhancements of the SWNTs under various polarization conditions. The enormous enhancements also enable the detection of several new Raman bands of the SWNTs.