Dark modes in symmetric bulk Dirac semimetal dimers excited by cylindrical vector beams

Dark plasmonic modes with sharp spectral resonance peak and exceptionally high quality factor makes it essential for applications in bio-chemical sensing and fluorescence enhancement. Here, we investigate the mid-infrared spectral responses of bulk Dirac semimetal (BDS) dimers under focused azimuthally polarized and radially polarized cylindrical vector beams (CVB). Through numerical simulations, we obtained direct excitation of dark modes and revealed how the beams manipulate the dipole hybridization to produce these modes. By tuning Fermi energy of BDS, the resonant wavelength of the dark modes can be further adjusted. Our results may find the application of CVB in plasmonic sensing.

Single-Molecule Detection of SARS-CoV-2 by Plasmonic Sensing of Isothermally Amplified Nucleic Acids

Single-molecule detection of pathogens such as SARS-CoV-2 is key to combat infectious diseases outbreak and pandemic. Currently colorimetric sensing with loop-mediated isothermal amplification (LAMP) provides simple readouts but suffers from intrinsic non-template amplification. Herein, we report that plasmonic sensing of LAMP amplicons via DNA hybridization allows highly specific and single-molecule detection of SARS-CoV-2 RNA. Our work has two important advances. First, we develop gold and silver alloy (Au-Ag) nanoshells as plasmonic sensors that have 4-times stronger extinction in the visible wavelengths and give 20-times lower detection limit for oligonucleotides than Au nanoparticles. Second, we demonstrate that the diagnostic method allows cutting the complex LAMP amplicons into short repeats that are amendable for hybridization with oligonucleotide-functionalized nanoshells. This additional sequence identification eliminates the contamination from non-template amplification. The detection method is a simple and single-molecule diagnostic platform for virus testing at its early representation.Table of Content