Hybrid plasmonic Bound State in the Continuum entering the zeptomolar biodetection range

Optical Bound States in the Continuum are peculiar localized states within the continuous spectrum that are unaffected by any far-field radiation and intrinsic absorption, therefore possessing infinite mode lifetime and Q-factor. To date they have been widely studied in dielectric structures whereas their exploitation in lossy media, i.e. plasmonic nanostructures, still remains a challenge. Here, we show the emergence of a hybrid BIC state in a 2D system of silver-filled dimers, quasi-embedded in a high-index dielectric waveguide. The hybrid BIC onset is found to be highly dependent on the bare modes' spectral and spatial overlap, but particularly on the plasmonic field's intensity. By tailoring the hybridizing plasmonic/photonic fractions we select an ideal coupling regime for which the mode exhibits both, high Q-factor values and strong near-field enhancement tightly confined in the nanogap and a consequently extremely small modal volume. We demonstrate that this optical layout can be exploited in a proof-of-concept experiment for the detection of TAR DNA-binding protein 43, which outperforms the sensitivity of current label-free biosensing platforms, reaching the zeptomolar range of concentration

Direct Band Gap Chalcohalide Semiconductors: Quaternary AgBiSCl₂ Nanocrystals

Heavy pnictogen chalcohalide semiconductors are coming under the spotlight for energy conversion applications. Here we present the colloidal synthesis of phase pure AgBiSCl2 nanocrystals. This quaternary chalcohalide compound features a quasi-two-dimensional crystal structure and a direct band gap, in contrast with the monodimensional structure and the indirect band gap peculiar to the orthorhombic, ternary Bi chalcohalides. Consistently, colloidal AgBiSCl2 nanocrystals exhibit photoinduced luminescence compatible with both band edge excitons and midgap states. This is the first observation of band edge emission in chalcohalide nanomaterials at large, although exciton recombination in our AgBiSCl2 nanocrystals mostly occurs via nonradiative pathways. This work further advances our knowledge on this class of mixed anion semiconductor nanomaterials and provides a contribution to establishing chalcohalides as a reliable alternative to metal chalcogenides and halides

Direct Band Gap Chalcohalide Semiconductors: Quaternary AgBiSCl₂ Nanocrystals

Heavy pnictogen chalcohalide semiconductors are coming under the spotlight for energy conversion applications. Here we present the colloidal synthesis of phase pure AgBiSCl2 nanocrystals. This quaternary chalcohalide compound features a quasi-two-dimensional crystal structure and a direct band gap, in contrast with the monodimensional structure and the indirect band gap peculiar to the orthorhombic, ternary Bi chalcohalides. Consistently, colloidal AgBiSCl2 nanocrystals exhibit photoinduced luminescence compatible with both band edge excitons and midgap states. This is the first observation of band edge emission in chalcohalide nanomaterials at large, although exciton recombination in our AgBiSCl2 nanocrystals mostly occurs via nonradiative pathways. This work further advances our knowledge on this class of mixed anion semiconductor nanomaterials and provides a contribution to establishing chalcohalides as a reliable alternative to metal chalcogenides and halides