Circular V-grooves on single-crystal gold: optical properties and sensing feasibility

Single-crystal Au(111) microplates provide an ultra-smooth, low-defect platform for reproducible plasmonic nanocavities. Here we realize reflection-mode whispering-gallery metasurfaces comprising periodic arrays of circular V-groove cavities milled into optically thick Au microplates and characterize their visible–near-IR response. The measured spectra exhibit narrow, depth-tunable Fano-like reflectance minima with weak azimuthal dependence, reproduced by quarter-cell finite-element modeling consistent with strong gap-surface-plasmon confinement. For refractometric sensing, simulations yield bulk sensitivities up to $\sim 598$ nm RIU${}^{-1}$ and figures of merit up to $\sim 33$ (hexagonal lattice). As a model-based illustration, a functionalized architecture targeting $\mathit{\text{Plasmodium}}\mathit{\text{falciparum}}$ lactate dehydrogenase (PfLDH), a common malaria target of rapid diagnostic tests, gives an estimated limit of detection of $0.016$ nM ($\sim 0.56$ ng mL${}^{-1}$) under the adopted noise floor.