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

TL;DR

This paper demonstrates the design and characterization of circular V-groove plasmonic metasurfaces on single-crystal gold microplates, showing their potential for high-sensitivity optical sensing, including detection of malaria biomarkers.

Contribution

It introduces a novel fabrication of whispering-gallery metasurfaces with tunable Fano resonances and evaluates their sensing capabilities through simulations and modeling.

Findings

Narrow Fano-like reflectance minima with weak azimuthal dependence

Bulk sensitivities up to ~598 nm RIU$^{-1}$ and figures of merit up to ~33

Estimated detection limit for malaria biomarker at 0.016 nM

Abstract

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 \textit{Plasmodium 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.