One year into the COVID‐19 pandemic, diagnostic strategies, although central for contact tracing and other preventive measures, are still limited. To meet the global demand, lower cost and faster antigen tests for SARS‐CoV‐2 detection are a convenient alternative to the gold standard RT‐PCR assay. We tested laboratory‐based RT‐PCR RNA detection and two rapid antigen detection (RAD) tests, based on the immunochromatography test for nucleocapsid protein of SARS‐CoV‐2 (COVID‐19 Ag ECO Test, ECO Diagnóstica, Brazil, and Panbio^TM COVID‐19 Ag Rapid Test Abbott, Germany). Paired collection and testing were done in a small prospective open study in three clinical services in São Paulo, constituted of mostly symptomatic volunteers at collection (97%, 109/112) for a median of 4 days (IQR 3‐6), ranging from 1 to 30. Among the 108 paired RT‐PCR/RAD tests, results were concordant in 96.4% (101/108). The test's performance was comparable, with an overall sensitivity of 87% and a specificity of 96%. These observations add to other data that suggest that antigen tests may provide reasonable sensitivity and specificity and deserve a role to improve testing strategies, especially in resource‐limited settings.

Self-assembled thin films containing an inner monolayer of N,N′-bis(2-phosphonoethyl)-1,4,5,8-naphthalenetetracarboxylic diimide (PNDI) and an outer monolayer of the cationic protein cytochrome c (cyt c) were prepared on the surface of non-porous silica gel particles. Silica particles modified with PNDI alone or with cyt c alone were also prepared for comparison. The materials were characterized by elemental and thermogravimetric analysis, as well as UV-visible absorption, fluorescence and infrared spectroscopies. Binding of PNDI to the silica resulted in a low density, sub-monolayer coverage, in contrast to cyt c adsorption which gave a rather compact protein layer. The loading of cyt c found in the new materials (ca. 12 µmol g⁻¹) was higher than that found in the literature for porous silica gel. Irradiation of the materials at the imide absorption band resulted in the reduction of the cyt c heme iron, showing that the protein retained its activity upon binding to the modified silica gel surface. The proposed mechanism involves electron transfer from a photogenerated imide radical anion to the heme iron of the protein in the adjacent layer.