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 and extended 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 1 pg/ml for Immunoglobulin G (IgG); for resonant imaging, we demonstrate a spatial resolution below 1 µm 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.
Bibliographical noteFunding Information:
The authors D.C., G.P. and T.F.K. acknowledge financial support by the EPSRC of the UK (Grants EP/P02324X/1 and EP/P030017/1). E.M. acknowledges the funding from São Paulo Research Foundation (FAPESP) (Grant #2020/00619-4). Prof. T.F. Krauss acknowledges a Royal Society Wolfson Merit Award. Mr. George Duffett contributed to the development of the LABVIEW code for the characterization of the optical devices.
© Crown 2021