NEW YORK (360Dx) – A team of researchers at the University of Toronto have developed a compact and portable surveillance device that identifies populations vulnerable to vaccine-preventable diseases in areas that lack a centralized laboratory.
The team applied the digital microfluidics (DMF) platform for the first time outside the laboratory in Kenya in order to detect cases of measles and rubella in refugee populations.
In order to monitor and track infectious diseases in a population, health researchers typically perform serosurveys to determine the risks of outbreaks and evaluate the progress of immunization programs. Standard tests, however, need access to laboratories, freezers, and transportation, severely limiting their use in rural and remote locations .
In work described in a Science Translational Medicine study published today, Alphonsus Ng, one of the study's lead author and postdoctoral researcher at the University of Toronto, and his colleagues set out to improve infectious disease detection and surveillance in at-risk remote areas that could benefit from new testing methods.
The researchers therefore developed the Measles-Rubella Box (MR Box), a field-deployable, point-of-care system that relies on DMF, integrated with an instrument, to perform enzyme-linked immunosorbent assays. The immunoassay uses a finger prick of blood to quickly test for disease-specific antibodies.
During a press conference on Monday, the group explained that its overall goal was to validate the DMF platform in the remote setting, comparing the results to reference tests performed at the Kenya Medical Research Institute (KEMRI) The team used the system in a Kenyan refugee camp to test 144 children aged 9 to 59 months and caregivers for measles and rubella immunoglobulin G (IgG).
According to Darius Racks, one of the study's lead authors and postdoctoral researcher, the team encountered three major hurdles while building the shoebox-sized device, including figuring out how to "maintain a low manufacturing cost for the microfluidic cartridges, challenges of portability while maintaining accuracy, and developing a biochemical assay robust enough for the device."
To solve the manufacturing problem, the team turned to inkjet printing and hacked regular printers to produce electrodes using conductive inks. The researchers incorporated the printed devices — which dropped the overall cost by tenfold — into the inexpensive digital microfluidic cartridges and manipulated whole-blood samples into discrete fluid droplets.
Using the printers, the team developed the inkjet cartridges at $1.50 per assay, with a total price of $6.00 per cartridge. Rackus explained that the team is also seeking ways to prototype at-scale manufacturing methods, such as techniques involving a roll-coder — a metal drum that allows researchers to apply thin layers of different materials onto the flexible substrates. In a previous study published in the Royal Society of Chemistry, the team used roll-coders to effectively bring the cost of a DMF device down to about $1.00.
"If you apply scale to the lab-based printing, we hope that one day that these cartridges could be produced for pennies each," Rackus said.
In addition to low-cost cartridges, the team needed to develop portable instrumentation for the field. Digital microfluidics moves droplets by applying sequences of voltages to a set of electrodes, requiring research-grade equipment to maintain the chips. In order to develop equipment that was light and efficient, the team used laser-cut plastic and 3D printed parts to build the system.
The researchers also needed biochemical assays to test for immunity for measles and rubella. To do so, they attached viral proteins to magnetic beads, which mix and bind to the blood, eventually extracting the antibodies specific to the diseases. Since the platform contained a motorized magnet under the cartridge to hold the beads in place, the team was able to wash away the samples, leaving behind the beads and any captured antibodies behind.
According to Rackus, the platform introduces in a second antibody, which acts as a label for the captured antibodies, and one of the antibody's enzymes catalyzes a reaction that emits light. The team can measure how much light is emitted, which should be proportional to the concentration of the antibody that it is trying to measure.
In comparison to alternate strategies used for remote testing, the researchers noted in the study that the DMF can adapt to different combinations of rubella and measles tests performed on samples from two to four patients in each cartridge as needed. In addition, increases in sample throughput could be partnered with an increase in the number of assay types used on the same cartridge, such as DMF-based assays for conditions including malaria or bacterial infections. Finally, the flexibility of these cartridge types would allow for systems in the field to receive remote updates, revisions, and new assay protocols wirelessly based on optimization and development performed elsewhere.
Comparing reference data performed at KEMRI, the team found that the IgG assay had a clinical sensitivity of 86 percent for measles and 81 percent for rubella, in addition to specificity of 80 percent for measles and 91 percent for rubella respectively. The DMF platform also delivered results within 35 minutes.
Although the assay results did not match the accuracy of lab-based serosurveys, the team believes that the device represents a potentially useful tool for a range of global point-of-care health applications that require portable and low-cost blood analysis. The researchers have released the overall hardware instructions and software as open source so that other researchers can download and eventually improve the system's sensitivity and specificity.
In a follow-up interview following the the press conference, Rackus and University of Toronto doctoral candidate Julian Lamanna discussed potential future uses and areas where the research team could apply the MR Box for disease surveillance.
While researchers may use the DMF platform to diagnose a variety of infectious diseases in remote regions, Rackus explained that the team chose rubella and measles because they sought to help the World Health Organization achieve its goal of eradicating both diseases by 2020.
In addition to measles and rubella, the team is collaborating with Keith Parti, a professor at the University of Toronto, to develop a rapid molecular test for chikungunya, Zika, and dengue virus on the DMF platform.
"We are working with [Parti] to automate his test for a field trial that will likely take place in Brazil in the next 12 to 24 months or so," Lamanna said.
Rackus envisions that tests used on the DMF platform will potentially act as a decentralized testing network, replacing the need for a dedicated and costly lab in small towns or rural villages. Both Rackus and Lamanna noted that while the platform can be used for infectious disease detection, the main impetus for the new study was to demonstrate the device's utility for continual large-scale patient monitoring.
"We found that even when you've vaccinated and certified a region of the world to be disease free, you still need diagnostic and surveillance tools to monitor and continually demonstrate that the area is still [disease] free," Lamanna added.