Transparent Conducting Oxide Plasmonics: Fano‐Type Graphene Coupling and Biomedical Applications

ABSTRACT

Heavily doped transparent conducting oxide (TCO) nanoparticles and their Au‐based core–shell hybrids provide sharp, tunable resonances across biological windows I and II (BW‐I and BW‐II). This study quantifies localized surface plasmon resonances, refractive‐index sensitivity, and figure of merit (FOM) of Ga‐doped ZnO (GZO), Al‐doped ZnO (AZO), and indium tin oxide (ITO) nanospheres in aqueous media . The key advance is demonstrating that bare TCOs offer competitive sensing, Au‐shell coating enables spectral tuning, and graphene integration yields electrically tunable Fano resonances . GZO nanoparticles exhibit narrow resonances spanning 1500–2200 nm with sensitivities up to ∼727 nm/RIU and average FOM of ∼2.5, exceeding conventional Au and Ag sensors. Coating GZO cores with ultrathin Au shells continuously blue‐shifts resonance across BW‐I and BW‐II, yielding shell‐thickness‐dependent sensitivities of ∼350–500 nm/RIU and FOM values of ∼1.25–2.25 RIU ^{− 1} for GZO–Au core–shell nanoparticles, rivaling noble‐metal benchmarks. Monolayer graphene encapsulation promotes strong plasmon–graphene mode hybridization, producing pronounced Fano resonances. In GZO–Au–graphene structures, co‐optimization of Au thickness (1–6 nm) and Fermi level (∼0.5–0.9 eV) produces sharp Fano dips electrically positioned from BW‐II into BW‐I. Findings establish TCO‐based nanostructures as promising low‐loss plasmonic platforms for deep‐tissue sensing, bioimaging, photothermal therapy.