Proposal of De Novo Antigen Test for COVID-19: Ultrasensitive Detection of Spike Proteins of SARS-CoV-2

Polymerase chain reaction (PCR)-based antigen tests are technically difficult, time-consuming, and expensive, and may produce false negative results requiring follow-up confirmation with computed tomography. The global coronavirus disease 2019 (COVID-19) pandemic has increased the demand for accurate, easy-to-use, rapid, and cost-effective antigen tests for clinical application. We propose a de novo antigen test for diagnosing COVID-19 using the combination of sandwich enzyme-linked immunosorbent assay and thio-nicotinamide adenine dinucleotide (thio-NAD) cycling. Our test takes advantage of the spike proteins specific to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus. The limit of detection of our test was 2.3 × 10−18 moles/assay. If the virus has ~25 spike proteins on its surface, our method should detect on the order of 10−20 moles of virus/assay, corresponding to ~104 copies of the virus RNA/assay. The detection sensitivity approaches that of PCR-based assays because the average virus RNA load used for PCR-based assays is ~105 copies per oro- or naso-pharyngeal swab specimen. To our knowledge, this is the first ultrasensitive antigen test for SARS-CoV-2 spike proteins that can be performed with an easy-to-use microplate reader. Sufficient sensitivity can be achieved within 10 min of thio-NAD cycling. Our antigen test allows for rapid, cost-effective, specific, ultrasensitive, and simultaneous multiple measurements of SARS-CoV-2, and has broad application for the diagnosis for COVID-19

Synthesis of novel green phosphate pigments in imitation of natural ores

As novel green pigment, various sodium iron phosphates, Na4Fe7(PO4)6, NaFe4(PO4)3, and Fe3(PO4)2, imitated with Xenophillite and Vivianite, were synthesized using a hydrothermal process. The obtained powders were estimated with X-ray diffraction (XRD), Infrared (IR) spectra, ultraviolet–visible (UV–vis) reflectance spectra, and L*a*b* color space. The hydrothermal temperature and time, volume of water, phosphorus resource were studied in this process. All samples prepared in this work were dark green powders. The weak peaks of Na4Fe7(PO4)6 and Fe3(PO4)2 were observed in XRD patterns of all samples. Hydrothermal treatment of a long duration produced high greenish powders. The large volume of water used improved the greenish and bluish colors of the phosphate powders