A Prototype of the D4 Assay (IMAGE) Duke University Caption Cassio Fontes demonstrates a prototype of the D4 assay, which might be used to quickly test for COVID antigens, using blood drops and a hand-held scanner. Credit Michaela Kane, Duke University Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.