Photo by Максим Кукушкин
Blood drop
Researchers say they have developed a point-of-care, paper-based test that quickly detects the presence of Zika virus in blood.
Currently, testing for Zika requires that a blood sample be refrigerated and shipped to a medical center or laboratory, delaying diagnosis and possible treatment.
The new test, on the other hand, does not require refrigeration and can produce results in minutes.
“If an assay requires electricity and refrigeration, it defeats the purpose of developing something to use in a resource-limited setting, especially in tropical areas of the world,” said Srikanth Singamaneni, PhD, of Washington University in St. Louis, Missouri.
“We wanted to make the test immune from variations in temperature and humidity.”
Dr Singamaneni and his colleagues described this test in Advanced Biosystems.
The researchers used the test on blood samples from 4 subjects known to be infected with Zika virus and samples from 5 subjects who did not have the virus.
The test showed positive results for the Zika-infected patients and negative results for controls. There were no false-positives.
How the test works
The test uses gold nanorods mounted on paper to detect Zika infection in the blood.
The test relies on a protein made by Zika virus that causes an immune response in infected individuals— ZIKV-nonstructural protein 1 (NS1). The ZIKV-NS1 protein is attached to gold nanorods mounted on a piece of paper.
The paper is then covered with protective nanocrystals. The nanocrystals allow the diagnostic nanorods to be shipped and stored without refrigeration prior to use.
To use the test, a technician rinses the paper with slightly acidic water, removing the protective crystals and exposing the protein mounted on the nanorods.
Then, a drop of the patient’s blood is applied. If the patient has come into contact with the virus, the blood will contain immunoglobulins that react with the ZIKV-NS1 protein.
“We’re taking advantage of the fact that patients mount an immune attack against this viral protein,” said study author Jeremiah J. Morrissey, PhD, of Washington University.
“The immunoglobulins persist in the blood for a few months, and when they come into contact with the gold nanorods, the nanorods undergo a slight color change that can be detected with a hand-held spectrophotometer. With this test, results will be clear before the patient leaves the clinic, allowing immediate counseling and access to treatment.”
The color change cannot be seen with the naked eye, but the researchers are working to change that. They’re also working on developing ways to use saliva rather than blood.
Although the test uses gold, the nanorods are very small. The researchers estimate the cost of the gold used in one of the assays would be 10 to 15 cents.
