Seed-mediated tuning of branch size in vertically aligned branched silver nanoplates for large-area and highly sensitive SERS substrates

Abstract

In this work, we report a solution-based, scalable, and low-cost strategy for fabricating large-area, vertically aligned branched silver nanoplates (BANs) on glass substrates (GS), addressing a key challenge in surface-enhanced Raman spectroscopy (SERS) substrate design: achieving simultaneous morphological controllability, large-area uniformity, and high signal reproducibility using simple wet-chemical routes. By tuning the concentrations of AgNO₃ and citrate ions in a seed-mediated growth process, the branch size of Ag nanoplates can be precisely controlled over a wide range (40–394 nm), enabling regulation of interbranch spacing during vertical assembly. Notably, reducing the branch size (<100 nm) leads to the formation of a high density of ultrasmall plasmonic nanogaps, resulting in enhanced plasmonic coupling and uniformly distributed SERS hot spots across large areas. Benefiting from this tunable hierarchical architecture, the optimized GS–BAN substrate exhibits a high analytical enhancement factor (AEF) of 7.7 × 10⁸ and an ultralow detection limit of 10⁻¹¹ M for rhodamine 6G (R6G), along with excellent signal reproducibility, as evidenced by a relative standard deviation (RSD) of 6.82%. These results demonstrate that branch-size engineering effectively overcomes uniformity and scalability limitations, while enhancing hot-spot density and analytical sensitivity, enabling reliable and large-area SERS platforms without complex fabrication processes.