Dielectric Nanohole Array Metasurface For High-Resolution Near-Field Sensing and Imaging

Abstract

Dielectric metasurfaces support resonances that are widely explored both for far-field wavefront shaping and for near-field sensing and imaging. Their design explores the interplay between localised Mie resonances and extended Bragg resonances, with a typical trade-off between Q-factor and light localisation; high Q-factors are desirable for refractive index sensing while localisation is desirable for imaging resolution. Here, we show that a dielectric metasurface consisting of a nanohole array in amorphous silicon provides a favourable trade-off between these requirements. We have designed and realised the metasurface to support two optical modes both with sharp Fano resonances that exhibit relatively high Q factors and strong spatial confinement, thereby concurrently optimizing the device for both imaging and biochemical sensing. For the sensing application, we demonstrate a limit of detection (LOD) as low as 1pg/ml for Immunoglobulin G (IgG); for resonant imaging, we demonstrate a spatial resolution below 1µm and clearly resolve individual E.coli bacteria. The combined low LOD and high spatial resolution opens new opportunities for extending cellular studies into the realm of microbiology, e.g. for studying antimicrobial susceptibility.

Dielectric metasurface for high-precision detection of large unilamellar vesicles

“…In order to address these requirements, we have developed a dielectric metasurface based on a nanohole array geometry, which optimises the Q-factor, the resonance amplitude and the surface sensitivity. We have previously verified the surface sensitivity of this structure, which has enabled us to detect protein biomarkers down to 1 pg ml −1 (<10 fM) [21,22]. We now exploit this capability to detect EVs at low concentrations and verify an LOD < 10 3 EV ml −1 (<10 pM), which improves on the performance of the plasmonic and electrochemical sensors, while also offering the accurate detection of small changes in concentration.…”

“…The array is one of the family of structures supporting guided mode resonances. We chose the quasi-TM mode as most suitable for vesicle detection [21] because the mode is strongly confined to the silicon surface in the out-of-plane direction (figure 1(b)). The evanescent tail of the guided mode only extends approximately 100 nm into the medium, which leads to a strong interaction with the surface-bound vesicles that are of similar size.…”

“…The use of a-SiO x :H with its relatively high refractive index and low absorption loss in the near-infrared range (n = 2.4 and k ∼ 5 × 10 −4 at λ = 700 nm) allows us to obtain high Q-factors (Q ≈ 400) and strong resonance amplitudes (R max ≈ 0.6). We use a chirped configuration of the nanohole array by spatially tuning the period in order to simplify the readout system and to minimise the optical noise [21,23,24]. The period of the nanohole array is chirped from an initial value of Λ 1 = 410 nm to Λ 2 = 430 nm over a length of 500 µm.…”

High-quality-factor dual-band Fano resonances induced by dual bound states in the continuum using a planar nanohole slab

“…BICs reside inside the continuous spectrum of extended states but counterintuitively remain perfectly localized in space with theoretically infinite lifetime [8,9]. Although BICs are not observable from the continuous spectrum due to the non-radiative property, high-Q-factor Fano resonances can be achieved as BICs are transformed into quasi-BICs (QBICs) [10,11], potential applications include such as directional lasing [12], optical filters [13], nonlinear frequency conversion [14], ultra-sensitive sensors [15,16] and optical vortex beams [17].…”

Bloch mode engineering for photonic biosensors

“…If it has very high Q and small sensitivity, the resonance will barely shift. The FOM captures both effects by dividing the mode sensitivity by the resonance width, representing a good balance between both factors 81 :…”