SARS-CoV-2 antigen detection by saliva; an alternative to nasopharyngeal specimen: A cross-sectional study.

Background and Aims: Saliva samples are less invasive and more convenient for patients than naso- and/or oropharynx swabs (NOS). However, there is no US Food and Drug Administration-approved severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) rapid antigen test kit, which can be useful in a prolonged pandemic to reduce transmission by allowing suspected individuals to self-sampling. We evaluated the performances of High sensitive AQ+ Rapid SARS-CoV-2 Antigen Test (AQ+ kit) using nasopharyngeal swabs (NPs) and saliva specimens from the same patients in laboratory conditions. Methods: The real-time reverse transcription-polymerase chain reaction (rRT-PCR) test result was used for screening the inrolled individuals and compared as the gold standard. NP and saliva samples were collected from 100 rRT-PCR positives and 100 negative individuals and tested with an AQ+ kit. Results: The AQ+ kit showed good performances in both NP and saliva samples with an overall accuracy of 98.5% and 94.0%, and sensitivity of 97.0% and 88.0%, respectively. In both cases, specificity was 100%. AQ+ kit performance with saliva was in the range of the World Health Organization recommended value. Conclusion: xOur findings indicate that the saliva specimen can be used as an alternative and less invasive to NPs for quick and reliable SARS-CoV-2 antigen detection.

High-temperature and multichannel quantum anomalous Hall effect in pristine and alkali-metal-doped CrBr3 monolayers.

The realization of the high-temperature and multichannel quantum anomalous Hall effect (QAHE) has been a central research area in the development of low-power-consumption electronics and quantum computing. Recently discovered two-dimensional (2D) ferromagnetic (FM) materials provide unprecedented opportunities for the exploration of the high-temperature QAHE. Based on first-principles approaches, we first reveal that a FM CrBr3 monolayer harbors topologically nontrivial conduction bands with a high Chern number of C = 2. Then, we reveal that the interesting conduction bands can be moved downwards to the Fermi levels by electron and alkali-metal-doping; meanwhile, the QAHE characteristics can be preserved. Most strikingly, the Na-doped CrBr3 system possesses a higher Chern number of C = -4 with a transition temperature of ∼54 K, which is attributed to the constructive coupling effect of the quadratic non-Dirac and linear Dirac band dispersions. The present study, together with recent achievements in the field of 2D FM materials, provides an experimentally achievable guide for realizing the high-temperature and multichannel QAHE based purely on 2D FM systems.

Topological phase transition induced by px,y and pz band inversion in a honeycomb lattice.

The search for more types of band inversion-induced topological states is of great scientific and experimental interest. Here, we proposed that the band inversion between px,y and pz orbitals can produce a topological phase transition in honeycomb lattices based on tight-binding model analyses. The corresponding topological phase diagram was mapped out in the parameter space of orbital energy and spin-orbit coupling. Specifically, the quantum anomalous Hall (QAH) effect could be achieved when ferromagnetism was introduced. Moreover, our first-principles calculations demonstrated that the two systems of half-iodinated silicene (Si2I) and one-third monolayer of bismuth epitaxially grown on the Si(111)-√3 ×√3 surface are ideal candidates for realizing the QAH effect with Curie temperatures of ∼101 K and 118 K, respectively. The underlying physical mechanism of this scheme is generally applicable, offering broader opportunities for the exploration of novel topological states and high-temperature QAH effect systems.

Possible realization of the high-temperature and multichannel quantum anomalous Hall effect in graphene/CrBr3 heterostructures under pressure.

The recent studies of magno-assisted tunnelling in ferromagnetic van der Waals heterostructures formed by graphene and ultrathin CrBr3 films (D. Ghazaryan et al., Nat. Electron., 2018, 1, 344) offer broader opportunities for exploration of novel quantum phenomena, especially for realizing the graphene-based quantum anomalous Hall effect (QAHE). Based on first-principles approaches, we reveal that three types of graphene/CrBr3 (Gr/CrBr3) heterostructures exhibit metallic band behavior due to strong charge-transfer at the interfaces of these heterosystems. Remarkably, the pressure-induced QAHE can be achieved in Gr/CrBr3 and CrBr3/Gr/CrBr3 systems. Further low energy k·p model analyses show that the nontrivial topological properties are mainly attributed to the Rashba spin-orbit coupling (SOC), but not to the intrinsic SOC of graphene. Moreover, a multichannel device prototype is proposed in the superlattices composed of Gr/CrBr3 and normal insulator (such as hexagonal boron nitride) layers. Our work provides an experimentally feasible scheme for realizing the high-temperature and multichannel QAHE in graphene-based heterostructures.