“(We) took advantage of the fact that nanoparticles have different colors if you make them different sizes,” said Hamad-Schifferli, of the Massachusetts Institute of Technology (MIT), who presented the device at the 250th National Meeting & Exposition of the American Chemical Society (ACS). “If you put nanoparticles on the antibodies that are inside the test, it gives rise to a different color on the test line.”
According to the Centers for Disease Control and Prevention, the 2014 Ebola outbreak in West Africa killed nearly 11,300 people in Guinea, Sierra Leone and Liberia. Total suspected cases numbered close to 28,000.
“Our main goal is to get this into the hands of as many people as possible,” Hamad-Schifferli said.
She emphasized the test wasn’t designed as a replacement for PCR (polymerase chain reaction) and ELISA (enzyme-linked immunosorbent assay) tests, which are more accurate, but require laboratory settings. Rather, the new test is meant as a first screening for areas without running water or electricity.
According to ACS, PCR and ELISA “are bioassays that detect pathogens directly or indirectly, respectively.”
The test uses silver nanoparticles. Slight changes in size elicit different colors. Red was assigned to Ebola, green to dengue fever and orange to yellow fever. The colored nanoparticles are attached to antibodies that bind to a biomarker of interest. According to Hamad-Schifferli, the blood sample is introduced to a “cotton weave pad,” and wicks through the device as results develop. The results are read from a nitrocellulose membrane, the paper part of the device.
She reported the sensitivity and specificity of the test as 97% accurate. The test takes 10 min to complete.
At $5 per strip, the total test costs $20, but Hamad-Schifferli said mass production could reduce the cost. Currently, the research team is consulting with companies about making the product commercially available.
While the test performs well in the lab setting, the team, comprised of people from MIT, Harvard Medical School and the U.S. Food and Drug Administration, found problems with humidity and temperatures of 36 C. By using foil packs as a sealing, the test was stable for three months in the aforementioned environment. Once opened, it must be used immediately, Hamad-Schifferli said.
Tests have been deployed to clinical settings in Colombia, Honduras and Africa. Hamad-Schifferli said it would be a few months before her team receives feedback regarding the test’s performance in the field.
Source:http://www.rdmag.com/articles/2015/08/paper-based-tests-infectious-diseases
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