posted on 2023-12-13, 17:34authored byHaoyu Guan, Guoqiang Fang, Xinxin Li, Haoyu Dong, Siqingaowa Han, Xiang Lin, Li Wang
The
plasmon coupling properties of assembled metal nanogap
structures
are highly sensitive to the distance, shape, orientation, and configuration
of faceted nanoparticles. However, the orientation control of nanoparticles
is usually limited to in-plane configurations. In this paper, Au@Ag
nanocubes (NCs) with sharp edges and corners were assembled on a polystyrene
(PS) microsphere array as a hierarchical surface-enhanced Raman spectroscopy
(SERS) substrate via a facile self-assembly technique. The Au@Ag NC
monolayer undergoes an out-of-plane reconstruction and forms V-shaped
nanogaps under the modulation of the PS microsphere array curved surface.
This unique V-shaped nanogap can generate electromagnetic fields stronger
than those of traditional parallel gaps and make it easier for target
molecules to diffuse into the nanogaps. The three-dimensional (3D)
SERS substrates have a wider spectral response and 20 times higher
SERS activity than those of the Au@Ag NC monolayer films on flat substrates.
The high sensitivity was demonstrated by the detection limit down
to 10–9 M for 4-MBA with a substrate enhancement
factor up to 3.1 × 107. Furthermore, the optimized
3D SERS substrate was applied to determine As5+ in water
with detection limits as low as 10–8 M assisted
by machine learning, indicating that the 3D SERS substrates have promising
applications in food safety, environmental monitoring, and biological
diagnosis.