Self-assembled monolayer film of concave star-shaped Au nanocrystals as highly efficient SERS substrates.

The concave star-shaped Au nanocrystals with ten sharp tips endowed them with 12-fold higher SERS enhancements than Au nanospheres. • Au nanocrystals with sharp tips were prepared using pentatwinned Au NSs as seed. • Au nanocrystals provided a broad spectral range from VIS to NI region. • Monolayers of Au nanocrystals displayed strong shape-dependent SERS activity. • Concave nanostars was 12-fold higher SERS enhancement than Au NSs. In this work, various geometries of Au nanocrystals with sharp tips including decahedra, concave star, and spindle were synthesized through Ag underpotential deposition-dominated growth approach based on utilizing a novel type of Au nanoseed (i.e., pentatwinned Au nanospheres). These as-prepared Au nanocrystals exhibited a broad localized surface plasmon resonance (LSPR) tunability from visible to near-infrared region. Furthermore, we fabricated the monolayer film based on Au nanocrystals with different morphologies through liquid/liquid interface self-assembly technique, which displayed strong shape-dependent surface enhanced Raman scatting (SERS) performance. More significantly, concave star-shaped Au nanocrystals with ten sharp tips endowed them with 12-fold higher SERS enhancements than Au nanospheres, which was in line with the simulation results by finite difference time domain (FDTD) method. Our study provides a novel route for fabrication of Au nanocrystals with diversified structures, and the efficient SERS substrates have great prospect for the applications in ultrasensitive chemical and biological sensing. [ABSTRACT FROM AUTHOR]