3D nanoflowers Fabricated by 396 nm LED-Induced photoreduction of silver ions onto gold nanoplates for SERS applications

In this paper, we demonstrate a simple and effective approach for the transformation of two-dimensional (2D) Au nanoplates into three-dimensional (3D) hierarchical nanostructures using 396 nm LED-assisted photoreduction. The reaction is carried out in an aqueous solution containing silver nitrate and ascorbic acid, where Au hexagonal nanoplates with edge lengths of ∼ 200–300 nm act as seeds for silver deposition. Under LED irradiation, these 2D nanoplates evolve into multifaceted 3D Ag@Au nanoflowers, ranging from 500–800 nm in size and composed of numerous thin petals (<50 nm) with sharp edges and corners. This structural evolution markedly increases the surface-to-volume ratio and produces abundant electromagnetic hotspots, making the nanoflowers highly promising plasmonic substrates. We propose that the transformation mechanism involves a synergistic interplay of kirigami-like cutting and origami-like folding processes. The kirigami-like behavior is associated with photoreduction-driven Ag deposition followed by a plasmonic induced photothermally enhanced Kirkendall effect, in which Ag atoms diffuse into the Au lattice, generating nanoscale voids and residual stress that compromise the integrity of the nanoplates. Simultaneously, hot electrons generated under UV LED irradiation accelerate Ag⁺ reduction and deposition. In parallel, the origami-like folding process may result from residual stress caused by lattice mismatch between Au and Ag across the nanoplate surfaces, promoting the upward bending and stacking of petal-like features. While this mechanistic hypothesis requires further validation, it provides a plausible explanation for the observed 2D-to-3D transformation. The resulting 3D Ag@Au nanoflowers exhibit broad optical absorption and strong surface-enhanced Raman scattering (SERS) activity. Using Rhodamine 6G as a probe molecule, we demonstrate significant SERS signal enhancement, highlighting the potential of these LED-driven nanostructures as efficient and cost-effective substrates for plasmon-enhanced sensing applications.