Washington: Researchers have developed a chip-based technology that can be integrated into a portable instrument for use in field situations where rapid, accurate detection of Ebola infections is needed to control outbreaks.
Laboratory tests using preparations of Ebola virus and other hemorrhagic fever viruses showed that the system has the sensitivity and specificity needed to provide a viable clinical assay, researchers said.
The current gold standard for Ebola virus detection relies on a method called polymerase chain reaction (PCR) to amplify the virus's genetic material for detection. Because PCR works on DNA molecules and Ebola is an RNA virus, the reverse transcriptase enzyme is used to make DNA copies of the viral RNA prior to PCR amplification and detection.
"Compared to our system, PCR detection is more complex and requires a laboratory setting," said senior author Holger Schmidt, professor of Optoelectronics at University of California, Santa Cruz.
"We're detecting the nucleic acids directly, and we achieve a comparable limit of detection to PCR and excellent specificity," Mr Schmidt said. In laboratory tests, the system provided sensitive detection of Ebola virus while giving no positive counts in tests with two related viruses, Sudan virus and Marburg virus.
Testing with different concentrations of Ebola virus demonstrated accurate quantification of the virus over six orders of magnitude. Adding a "preconcentration" step during sample processing on the microfluidic chip extended the limit of detection well beyond that achieved by other chip-based approaches, covering a range comparable to PCR analysis.
"The measurements were taken at clinical concentrations covering the entire range of what would be seen in an infected person," Mr Schmidt said.
Mr Schmidt's lab at UC Santa Cruz worked with researchers at Brigham Young University and UC Berkeley to develop the system. Virologists at Texas Biomedical Research Institute in San Antonio prepared the viral samples for testing.
The system combined a microfluidic chip for sample preparation and an optofluidic chip for optical detection.
The microfluidic chip was made of a silicon-based polymer, polydimethylsiloxane (PDMS), and had microvalves and fluidic channels to transport the sample between nodes for various sample preparation steps.
The targeted molecules - in this case, Ebola virus RNA - were isolated by binding to a matching sequence of synthetic DNA (called an oligonucleotide) attached to magnetic microbeads.
The microbeads were collected with a magnet, nontarget biomolecules were washed off, and the bound targets were then released by heating, labelled with fluorescent markers, and transferred to the optofluidic chip for optical detection. The study was published in the journal Scientific Reports.
