Microfluidics for rapid, portable detection of viruses

The announcement this week that a research team from Brown University has developed a potentially portable influenza detection array could mean a more effective way to detect and track dangerous viruses like H1N1 (swine flu) on the horizon. At the same time, it also could lead to a simpler, easier way for physicians to identify and treat seasonal influenza in their offices.

The research community has been pursuing both goals, and the biochip-based microfluidic array unveiled online in the Journal of Molecular Diagnostics potentially could meet those needs. It also could detect other pathogens, its inventors say.

“It’s a low-cost device for active, on-site detection, whether it’s influenza, HIV, or TB [tuberculosis],” Anubhav Tripathi, Brown University associate professor of engineering and the corresponding author in the paper, said in a press release.

The key to the portable array is a biochip developed by the Brown University biomedical engineers and colleagues at Memorial Hospital in Rhode Island. The biochip can detect influenza by amplifying RNA targets from the virus in question and then using tiny magnets in a microtube to separate that particular RNA sequence from the rest of the RNA strand.

The researchers call their assay SMART: “A Simple Method for Amplifying RNA Targets.”

“The SMART assay using a synthetic model influenza DNA target sequence served as a fundamental demonstration of the efficacy of the capture and microfluidic separation system, thus bridging our system to a clinically relevant detection problem,” the authors wrote.

The device, which measures less than two inches across, is made up of a series of four tubes with bulbs on the ends, all of which are etched into the biochip. The device includes multiple DNA probes attached to 2.8 micron magnetic beads with base letters that match the code in the targeted RNA sequence from the specific virus the test is designed to detect. Because the team inundates the bio sample with these magnetized DNA probes, all RNA molecules with the specific sought-after sequence will bind to a probe, Tripathi said, adding, “the device allows us to design probes that are both sensitive and specific.”

Once the RNA molecules have had an opportunity to attach themselves to the magnetized probes, the team uses a magnet to drag the probes through a tube that narrows to 50 microns. The probes, which move at the slow speed of 0.75 millimeters per second through the tube, then are deposited at a bulb at the end of the tube.

The combination of the magnetized probes and the dragging magnet, plus principles of microfluidics, serves to separate probes that have collected the sought-after RNA fragment from the rest of the sample. This allows clinicians to amplify the RNA, which then will allow them to more effectively use conventional techniques such as nucleic acid sequence-based amplification to analyze the samples.

The devices could be manufactured commercially, Tripathi said, and could contain more than four channels each, to amplify even more RNA. Eventually, the researchers say, the device could be carried in a first aid kit for use in the field.

That would be an improvement over other currently available pathogen-diagnostic detectors, which mainly must be used as desktop devices and don’t provide real-time results.

For example, the U.S. Food and Drug Administration in 2008 approved the Human Influenza Virus Real-Time RT-PCR Detection and Characterization Panel (rRT-PCR Flu Panel), which also can isolate and amplify viral RNA. The device, which at the time was lauded as a “significant achievement for public health surveillance” by then-Health and Human Services Secretary Mike Leavitt, can provide results in four hours. It also can differentiate between seasonal influenza and more virulent, dangerous varieties such as H1N1.

Meanwhile, another novel approach – using Google searches for terms like “flu symptoms” to detect flu outbreaks – allows public health officials to track the spread of seasonal influenza across the globe. Google Flu Trends, which launched in late 2008, now provides flu estimates for more than 20 countries. Google says the tool potentially can detect pandemic flu viruses by comparing historical flu rates with currently reported rates and identifying any unexpected increases.

Source: McCalla S. et al. A Simple Method for Amplifying RNA Targets (SMART). Journal of Molecular Diagnostics. Published online 13 June 2012.