ZnO nanotower arrays decorated with cubic and tetrahedral shaped Ag-NPs as hybrid SERS-active substrates

Highlights: • The nanogaps between neighboring Ag-NPs and the corners of Ag-NPs provided massive hot-spots for the Ag-NPs/ZnO nanotower (AZT) substrates. • Ag-NPs with an average diameter of ~60 nm could improve the scattering efficiency. • The nanosteps of the nanotower simultaneously retained both Ag-NPs and R6G molecules to allow the R6G access the hot-spots region. • Stronger localized surface plasmon resonance (LSPR) can emerge at the tower tips due to more exposure to incident light than the side surface of nanotower. Ag/ZnO hybrid surface-enhanced Raman scattering (SERS) substrates laden with 3D hot-spots and electron transfer (ET) resonance, which can generate large Raman signals enhancement, have attracted extensive attention in recent years. This work fabricated the cube and tetrahedron shaped Ag-nanoparticles (Ag-NPs) with corners and an average particle size of ~60 nm by solvothermal method, then anchored the Ag-NPs on ZnO nanotower arrays with laminated nanosteps by drop-casting without surface modifiers to obtain the Ag-NPs/ZnO nanotower (AZT) SERS substrates. This AZT substrate manifests high SERS EF (6.9 × 10¹³) to rhodamine 6G (R6G) and a low detection limit (1 × 10⁻¹⁸ M). The high SERS sensitivity benefits from not only the combination of the two kinds of hot-spots, i.e. the nanogaps and the corners of Ag-NPs, but also the retaining of R6G molecules on the nanosteps of ZnO nanotowers, by which the R6G molecules can access the hot-spots regions. This study provides a bran-new approach for optimizing the performance of SERS substrates.