Recent advances in nanoscience increasingly focus on simple and cost-effective strategies for assembling well-defined nanomaterials. Designing hybrid nanostructures that synergistically combine different nanoscale components to achieve enhanced or novel functionalities remains a significant challenge. Carbon Dots (CDs), a class of small (<10 nm) luminescent carbon nanoparticles, are particularly suited for such applications due to their strong light-harvesting and emission properties, coupled with high surface chemical versatility. These features make CDs ideal building blocks for functional nanohybrids.

Here, we investigate how the fluorescence of green-emitting CDs is modulated when coupled with plasmonic metallic nanoparticles (MNPs) featuring controlled surface charges. We examine the photophysical and photochemical response of binary CD–MNP hybrids both when the components are in close contact and when a polymeric spacer separates them. Nitrogen-doped CDs with strong visible-range absorption and emission were synthesized via a simple bottom-up approach. These CDs were self-assembled in solution with silver (AgNPs) or gold nanoparticles (AuNPs) engineered to bear either positive or negative surface charges. Steady-state and time-resolved optical measurements confirm successful CD–MNP coupling, revealing that the optical response critically depends on the interparticle separation. Close contact between CDs and MNPs leads to emission quenching via efficient photoinduced charge transfer, triggering emergent photocatalytic activity due to interfacial charge separation. In contrast, the presence of a polymeric spacer enhances CD emission, with the nature of plasmonic interactions determined by the metal type: AgNPs plasmonically couple to the CD absorption, while AuNPs couple to the CD emission band.

These findings highlight versatile strategies to tune CD optical properties through MNP coupling, opening avenues for novel applications in photonics and photochemistry.

Nanoscale, 2025, 17, 9380