Bright photon upconversion in LiYbF4:Tm3+@LiYF4 nanoparticles and their application for singlet oxygen generation and in immunoassay for SARS-CoV-2 nucleoprotein.

Photon upconversion is an intensively investigated phenomenon in the materials sciences due to its unique applications, mainly in biomedicine for disease prevention and treatment. This study reports the synthesis and properties of tetragonal LiYbF4:Tm3+@LiYF4 core@shell nanoparticles (NPs) and their applications. The NPs had sizes ranging from 18.5 to 23.7 nm. As a result of the energy transfer between Yb3+ and Tm3+ ions, the synthesized NPs show intense emission in the ultraviolet (UV) range up to 347 nm under 975 nm excitation. The bright emission in the UV range allows for singlet oxygen generation in the presence of hematoporphyrin on the surface of NPs. Our studies show that irradiation with a 975 nm laser of the functionalized NPs allows for the production of amounts of singlet oxygen easily detectable by Singlet Oxygen Sensor Green. The high emission intensity of NPs at 800 nm allowed the application of the synthesized NPs in an upconversion-linked immunosorbent assay (ULISA) for highly sensitive detection of the nucleoprotein from SARS-CoV-2, the causative agent of Covid-19. This article proves that LiYbF4:Tm3+@LiYF4 core@shell nanoparticles can be perfect alternatives for the most commonly studied upconverting NPs based on the NaYF4 host compound and are good candidates for biomedical applications.

Digital and Analog Detection of SARS-CoV-2 Nucleocapsid Protein via an Upconversion-Linked Immunosorbent Assay.

The COVID-19 crisis requires fast and highly sensitive tests for the early stage detection of the SARS-CoV-2 virus. For detecting the nucleocapsid protein (N protein), the most abundant viral antigen, we have employed upconversion nanoparticles that emit short-wavelength light under near-infrared excitation (976 nm). The anti-Stokes emission avoids autofluorescence and light scattering and thus enables measurements without optical background interference. The sandwich upconversion-linked immunosorbent assay (ULISA) can be operated both in a conventional analog mode and in a digital mode based on counting individual immune complexes. We have investigated how different antibody combinations affect the detection of the wildtype N protein and the detection of SARS-CoV-2 (alpha variant) in lysed culture fluid via the N protein. The ULISA yielded a limit of detection (LOD) of 1.3 pg/mL (27 fM) for N protein detection independent of the analog or digital readout, which is approximately 3 orders of magnitude more sensitive than conventional enzyme-linked immunosorbent assays or commercial lateral flow assays for home testing. In the case of SARS-CoV-2, the digital ULISA additionally improved the LOD by a factor of 10 compared to the analog readout.

Research on Unrealistic Optimism among HoReCa Workers as a Possible Future Hotspot of Infections

As we are facing a new surge of the highly infectious delta variant of COVID-19, there is an urgent need for research to reduce the harm before this next wave hits. In the present paper, we present data that is alarming. We have found that HoReCa (hotels, restaurants, and catering services) workers, who are highly exposed to many new social interactions in close contact, present an unrealistic optimism (UO) bias: they perceive themselves as less at risk to this virus in comparison to others. From the literature, we already know that individuals holding this view are less involved in preventive actions and present more risky behaviors. In the face of the delta variant, this leads to the conclusion that restaurants will be new hot spots. What is more, we found that these unrealistic expectations are more pervasive: workers of the restaurant industry estimate low chances of bankruptcy, which may lead to unrealistic salary expectations, leading owners to a new upcoming wave of crisis: COVID-19 and bankruptcy—both of which may be caused by their workers.

Using social media to assess recreation across urban green spaces in times of abrupt change

For most of the world’s population, urban green spaces (UGS) offer the easiest form of contact with nature. Such environments deliver a wide variety of Recreational Ecosystem Services (RES) to visitors. This paper explores RES delivery in different types of UGS, differentiated with respect to their naturalness and distance from the city centre. Furthermore, it investigates how the identified use patterns are affected by an abrupt change in access. We extract data from Instagram, posted at the beginning of the COVID-19 pandemic, for Warsaw, Poland, and use it to measure both the intensity of use of UGS, and the experience of Instagram users. Furthermore, we compare these data with data from the same period for the previous year (2019). Our results indicate that, in typical conditions, the wilder the area, the fewer visitors. RES patterns changed, however, when access to UGS was restricted. The recent COVID-19 outbreak showed that soon after restrictions on visiting UGS were lifted, recreation shifted towards wilder green areas. Moreover, users became more oriented to wild nature. We conclude that the number of visitors, and the pattern of recreational use of UGS, are highly dependent on the character of green spaces across the urban wilderness continuum, and that they are influenced by abrupt changes in access.