PDA@ag Nanobowl SERS substrates with 3D continuous hot spots networks via an Interface-confined growth method for detection of pesticide residues.

The performance of surface-enhanced Raman scattering (SERS) hinges on plasmonic hot spots that are both abundant and spatially uniform. Here, we propose a ligand-regulated, interface-confined growth strategy: on a bowl-like mesoporous polydopamine (PDA) scaffold, the ammoniacal silver precursor [Ag(NH3)2]+ first forms a surface coordination layer with catechol and amine sites on PDA, lowering the activity of free Ag+ and enriching Ag(I) at the interface, thereby shifting nucleation from homogeneous in the bulk to interface-confined. The ensuing constrained growth suppresses coalescence/bridging and excessive coarsening, yielding Ag nanoparticle arrays with controlled size, tunable interparticle gaps, and high spatial uniformity, and producing dense yet discrete coverage across both the inner and outer interfaces of the bowl. The concave curvature and dual-interface connectivity provide continuous coupling pathways and abundant adsorption sites, establishing a three-dimensional continuous hot-spot network. Correlative multi-technique characterization and spectroscopic analyses (SEM, EDS mapping, UV-Vis, XPS) elucidate the structure-optical-performance relationship, revealing a sparse-to-dense optimal regime and a coalescence-induced degradation regime, and identifying a precursor concentration of 50 mM as the optimal window. The resulting substrate exhibits good reproducibility for R6G (RSD ≈ 10.99 %) and affords clear molecular fingerprinting and linear quantification for pesticide analysis, with limits of detection of 55 ng mL-1 for methyl parathion and 0.209 ng mL-1 for thiram. This template-free, mild, and generalizable strategy provides a scalable route to three-dimensional plasmonic SERS substrates, leveraging PDA surface chemistry to prevent Ag aggregation at the source while constructing continuous hot spots networks.