Gold–Silver-Alloy Core-Expanded Nanocubes with Sub-5 nm Intragaps for SERS-Based Sensing

The strong electromagnetic field generated by localized hot spots within plasmonic nanogaps has attracted widespread research attention. Nevertheless, the controllable fabrication of nanoscale gaps has been lacking facile and effective strategies. In this work, we develop a straightforward, controllable approach for fabricating precise intragaps. The Au–Ag core-expanded nanocubes with tunable nanoscale intragaps are synthesized based on the synergistic effects of metal ion galvanic replacement and coreduction reactions. The growth process can be attributed to the selective deposition of atoms and the creation of growth sites by atomic migration. These plasmonic particles exhibit strong SERS activity with an enhancement factor of up to 4.89 × 1010 and a detection limit of 10–12 M for 4-ATP. FDTD simulations reveal that their excellent SERS performance can be ascribed to strong hot spots generated by nanogaps. Additionally, the size of the intragap can be controlled at the nanoscale by adjusting the shell thickness of the seed, which can further regulate the optical properties and SERS activity of the particles. This work will not only offer a facile and controllable method for the fabrication of plasma nanogaps but also provide a stable and powerful platform for molecular sensing and detection.