3-D pillar-and-scaffold nanostructures for integrating nitrogen-vacancy doped nanodiamonds.

Three-dimensional (3-D) scaffolds made of polymers are relevant for cell culture and sensor immobilization to convert biological signals into optical signals for detection. We present a computational study of 3-D pillar-and-scaffold nanostructures designed for embedding the negatively charged nitrogen vacancy (NV-) color centers in nanodiamonds, focusing on light confinement and emission enhancement. To develop optically active platforms for quantum sensing, we analyze the electric field profiles in both pillar-without-scaffold and pillar-and-scaffold dielectric structures at the zero phonon line of the NV- in nanodiamonds. The results reveal that scaffold edges significantly improve field confinement by modifying the local electromagnetic environment. To further enhance resonance effects in low-index materials, a partial silver coating was applied, enabling the excitation of surface plasmon polaritons and leading to stronger field localization. Coupling of the NV- center in nanodiamond with a pillar-and-scaffold structure at optimal field hotspot locations leads to a higher Purcell factor in dielectric pillar-and-scaffold and metal-coated pillar-and-scaffold structures compared to pillar-without-scaffold structures. Both dielectric and metal-coated pillar-without-scaffold structures exhibit a flat optical response with minimal emission enhancement. In comparison, dielectric and metal-coated pillar-and-scaffold structures support well-defined resonance modes and exhibit significantly higher theoretical decay rates, with the metal-coated structures showing the strongest enhancement due to plasmonic field amplification. We have fabricated 3-D pillar scaffolds with silver coating using two-photon polymerization, showing an experimental unloaded Q-factor of up to 17 in the spectral range of the NV-. These findings highlight the potential of plasmon-based pillar-and-scaffold platforms for higher-sensitivity 3-D quantum sensing using NV- color centers.