"Pomegranate-Like" Plasmonic Nanoreactors with Accessible High-Density Hotspots for in Situ SERS Monitoring of Catalytic Reactions.

Noble metal nanoparticles (NPs) have enabled surface-enhanced Raman scattering (SERS) for in situ monitoring of NPs-catalyzed reactions. However, it still remains a great challenge to ensure that analytes without plasmonic metal surface-affinity groups (such as thiol and amino groups) can be located into hotspots and detected by SERS. Here, we report a novel sacrificial template method for the fabrication of "pomegranate-like" plasmonic nanoreactors (PPNs), in which high-density embedded AuNPs simultaneously generated SERS enhancement and catalytic performance. Once the analytes entering PPNs are catalyzed and meanwhile located into the hotspots, in situ SERS monitoring of catalytic reactions can be achieved. The intense hotspots of localized electric fields of PPNs were evaluated by finite-difference time-domain simulation. By using PPNs as a substrate, SERS signals of molecules without Au surface-affinity groups were obtained, such as p-naphthoquinone and 4-nitrophenol. The PPNs showed high catalytic activities in the reduction of 4-nitrothiophenol to 4-aminothiophenol and 4-nitrophenol to 4-aminophenol, respectively. Besides, the SERS spectra of both 4-nitrophenol and 4-aminophenol during the reduction reaction of 4-nitrophenol with NaBH4 were first obtained, demonstrating their utilization in the detection of catalytic reactions.