Bioaffinity sensors for miRNA detection using polarization-independent metamaterials

We propose bioaffinity sensors for miRNA detection using a polarization-independent metamaterial consisting of four pairs of gold rods arranged with four-fold rotational symmetry. The metamaterial is designed to be sensitive to changes in refractive index near the surface of gold rods, where ligands and analytes are adsorbed, whereas previous metamaterials focus only on the bulk refractive index of the surrounding medium. We first simulated the electromagnetic field near the surface of gold rods by rigorous coupled-wave analysis to determine the dimensions of the metamaterial in consideration of sensitivity and fabrication limitations. The designed metamaterial was fabricated on a glass substrate using a lift-off process that combines electron-beam (EB) lithography and EB vapor deposition. The ability to detect miRNA was verified using dmiR-21, DNA with a sequence similar to miR-21, which is known as one of the cancer biomarkers. The peak shift in the reflectance spectra was observed in the presence of dmiR-21, which indicates the proposed sensor can detect an increase in miRNA triggered by the onset of cancers.