Optical detection of infectious SARS-CoV-2 virions by counting spikes.

Existing methods for the mass detection of viruses are limited to the registration of small amounts of a viral genome or specific protein markers. In spite of high sensitivity, the applied methods cannot distinguish between virulent viral particles and non-infectious viral particle debris. We report an approach to solve this long-standing challenge using the SARS-CoV-2 virus as an example. We show that wide-field optical microscopy with the state-of-the-art mesoscopic fluorescent labels, formed by a core-shell plasmonic nanoparticle with fluorescent dye molecules in the core-shell that are strongly coupled to the plasmonic nanoparticle, not only rapidly, i.e. in less than 20 minutes after sampling, detects SARS-CoV-2 virions directly in a patient sample without a pre-concentration step, but can also distinguish between infectious and non-infectious virus strains by counting the spikes on the lipid envelope of individual viral particles.

Ultra-bright and narrow-band emission from Ag atomic sized nanoclusters in a self-assembled plasmonic resonator.

We have proposed, implemented and investigated a novel, efficient quantum emitter based on an atomic-sized Ag nanocluster in a plasmonic resonator. The quantum emitter enables the realization of: (1) ultra-bright fluorescence, (2) narrow-band emission down to 4 nm, (3) ultra-short fluorescence lifetime. The fluorescence cross-section of a quantum emitter is on the order of σ ∼ 10-14 cm2, which is comparable to the largest fluorescence cross-sections of dye molecules and quantum dots, and enables a light source with a record high intensity known only for plasmon nanolasers. The results presented suggest a unique method for fabricating nanoprobes with high brightness and wavelength-tunable spectrally narrow fluorescence, which is needed for multiplex diagnostics and detection of substances at extremely low concentrations.

Resonant Concentration-Driven Control of Dye Molecule Photodegradation via Strong Optical Coupling to Plasmonic Nanoparticles.

Photobleaching is one of the basic chemical processes that occur naturally in organic molecules. In this work, we investigate the quantum dynamics of Cy 7.5 dye molecules optically coupled to Au nanorod particles and experimentally demonstrate the decrease of the photobleaching rate in this hybrid system. We discover the effect of a resonance-like behavior not observed before for any type of emitter─the photobleaching rate of the dye molecules reaches a minimum for a suitable number of molecules coupled to the nanoparticle. The manifestation of the effect is the consequence of shifts in the energy levels in the hybrid system caused by the change in the number of molecules coupled to a nanoparticle. The energy shifts are the prerequisite for the effective depopulation of the triplet level, which is responsible for the photodegradation mechanism. The discovered effect paves the way for increasing the efficiency of optoelectronic and photovoltaic devices.