Hydrothermal vs. microwave carbon dots-gold nanozymes: Interface morphology driven selective SERS detection of Hg²⁺...

Hydrothermal and microwave routes are the two primary routes for carbon dots (CDs) preparation. However, how the structural differences induced by these pathways affect the interfacial architecture and sensing functions of CDs-based composites remains underexplored. Here, we demonstrate that hydrothermal and microwave synthesis structure CDs to form distinct interfaces on gold nanoparticles (AuNPs), modulating their nanozyme activity and surface-enhanced Raman scattering (SERS) performance. Hydrothermal synthesis yields polymer-like CDs forming a dense coating on AuNPs, conferring excellent colloidal stability, synergistic nanozyme activity, and selective recognition of Hg²⁺. In contrast, microwave synthesis produces graphene-like CDs that anchor sparsely onto AuNPs, maximizing electromagnetic hotspots for superior SERS activity. These two interfacial configurations allow catalytic and SERS functions to be respectively optimized-a trade-off difficult to resolve in a single composite. We also observed that trace HAuCl₄ treatment could partially restore the activity of deactivated nanozymes. By elucidating correlations between synthetic pathways, CDs architecture, and interfacial performance, this work establishes a synthesis-interface-function framework for designing Au@CDs with high activity and stability, enables selective SERS detection of Hg²⁺ with excellent anti‑interference performance against CH₃Hg⁺, and offers a regeneration strategy for deactivated materials.