Ultrasensitive and recyclable SERS substrate based on Au-decorated Si nanowire arrays

Metallic nanoparticle (NP) decorated silicon nanowire (SiNW) heterostructures show significant promise in enhanced optical and opto-electrical properties due to the coupling of surface plasmon to nanowires. Here, recyclable Au-decorated silicon nanowire arrays (Au-SiNWAs) as surface-enhanced Raman scattering (SERS) substrates were successfully fabricated by a simple galvanic displacement reaction. The influence of different average size and aggregation level of Au NPs on SERS activity was explored. The SERS activity of the substrates strongly depends on the average size and aggregation level of Au NPs on the surface of the SiNWs, and the most optimal size and separation of AuNPs on the SiNWs can be achieved by controlling the reaction time. The optimized Au-SiNWA substrate exhibits ultrahigh sensitivity with an enhancement factor of 109, and is able to detect the analyte molecule at a concentration as low as 10(-11) M. More importantly, the SERS substrate is recyclable, as enabled by a self-cleaning function due to UV light photocatalytic degradation of the analyte molecules. The high sensitivity and recyclability of the Au-SiNWA SERS substrate is demonstrated by the detection of a model molecule rhodamine B (RhB). Our studies show that the unique Au-SiNWA SERS substrates have significant potential to put SERS into wider application.