Detecting A Virus Visually

When a virus infiltrates a population, doctors want to quickly identify it to help contain the epidemic. For developing countries that don’t have access to expensive methods to detect viruses, such as nucleic acid amplification through the polymerase chain reaction (PCR), affordable pathogen detection techniques are needed. Researchers led by Xiaoyuan (Shawn) Chen of the National Institutes of Health have demonstrated one approach that may fit the bill: a nanoparticle-based sensor that signals a virus’s presence by changing color (Angew. Chem. Int. Ed. 2013, DOI: 10.1002/anie.201307952). The team incubates human throat swab samples with a solution of iron oxide beads and adds the mix to polystyrene plates. Both the plates and the beads are coated with virus-specific antibodies. Also attached to the beads are enzymes that convert thioesters to thiols. When the plates are rinsed, any virus particles present in the sample stay behind, trapped in the middle of a plate-bead sandwich. After the rinse, the thioester acetylthiocholine and gold nanoparticles are added to the plates. The bead-attached enzyme then converts the molecule to thiocholine, which bears a free SH group. When this group sticks to the gold nanoparticles, it causes them to aggregate and shift in color from red to purple. If a sample doesn’t contain virus, the enzyme-bearing beads simply wash away. By using this scheme, the team visually detected enterovirus 71, a pathogen that causeshand, foot, and mouth disease, at a concentration as low as 10,000 virus particles per mL of sample.