High-Quality Resonances from Plasmonic Nanoparticle Lattices under Normal Incidence

Narrow plasmonic resonances in an asymmetric refractive index (RI) environment under normal incidence are desired for miniaturized sensors in clinical evaluation and lab-on-a-chip devices. We demonstrate that a thin alumina layer between Au nanoparticle (NP) lattices and a quartz substrate can induce total internal reflections and nonvanishing out-of-plane electric fields, resulting in ultranarrow quadrupole surface lattice resonances (SLRs). The SLRs show a line width below 1 nm with high-quality factors up to 1865 in simulations and up to 640 in experiments under normal incidence in the visible range. High-performance RI sensing based on SLRs is demonstrated for glucose in aqueous solutions and DMSO/water mixtures, which show a one magnitude improvement in the figure of merit compared with the Au NP lattices on the bare quartz substrate. This substrate modification opens a new avenue to design and generate high-quality plasmonic resonances for light-matter interactions and sensing applications.