Bioengineers at the University of Washington have devised a way to use smartphone cameras for imaging diagnostics, paving the way to test for afflictions such as influenza and sexually transmitted infections without costly equipment. The technique, presented this month in Analytical Chemistry, could one day allow many medical tests that occur in the lab to take place in homes or doctors’ offices.
“Cell phones are ubiquitous,” says graduate student and lead author Kamal Shah. “We thought we could leverage the cameras on smartphones to implement a capability that we don’t normally think of cell phones for—their ability to quantitatively image.” Although others have attempted to co-opt the phones’ imaging capabilities, Shah’s device makes strides in both sensitivity and cost.
The team began by developing a lateral flow immunoassay, more commonly known as a test strip. This type of rapid diagnostic test is already widely used outside of labs. (The home pregnancy test is one example.) Typically, these tests work by allowing antibodies labeled with colored particles to bind to a molecule in a sample, such as a protein associated with a virus. If the molecule is present, the colored particles show up as a line on the test strip.
These tests diagnose a range of conditions, including HIV, malaria, and influenza, and are especially useful for reaching communities where medical facilities are scarce. But the device isn’t sensitive enough to detect many diseases that cause big problems at low concentrations. “Even influenza can be too low,” says senior author, Paul Yager, a bioengineer at the University of Washington.
For more sensitive read-outs, tests can instead include fluorescent labels—molecules that glow when light is directed at them. But these tests typically require specialized fluorescence readers in labs. Some groups have gotten around this issue by attaching filters to smartphones that enhance the camera’s ability to pick up light emitted by the fluorescent labels independently from the light used to excite the labels. The filters, however, can be expensive.
The University of Washington team instead selected quantum dot fluorescent labels that they excite with UV light. These tiny crystals and UV light each emit light at such dramatically different wavelengths that the smartphone’s own camera can distinguish the difference.
The team plugs a UV LED light directly into a phone’s USB port. Inspired by selfie sticks, they designed a single button that at once turns on the light and activates the camera shutter. The parts for the attachment cost less than ten dollars.
If a picture of a test strip shows a line, in addition to the control line, the test is positive. The team then determines the ratio of light emitted by the quantum dots to background noise using an image processing program. This ratio helps standardize results across phone models and can also offer a quantitative measurement of the pathogen’s concentration.
When testing for influenza A, their system was as sensitive as laboratory-based gel imaging of quantum dots and ten times more sensitive than imaging the more traditional gold nanoparticles on a laboratory scanner.
The work sets a benchmark for outperforming more traditional lateral flow immunoassays that use gold nanoparticles, says chemist Russ Algar of the University of British Columbia, who was not connected to the study. “The conclusions of the paper will excite people and be pointed to as evidence that smartphone imaging is not a gimmick and that the fluorescence mode of measurements should be pursued as a future biomedical technology.”
Sindy Tang of Stanford University, a specialist in microfluidics and lab-on-a-chip systems who was not involved in the study, was impressed that the authors achieved “such a high sensitivity and limit of detection basically comparable to a lab-based instrument.” Tang lauds the set-up’s low cost, but would still like to see the cost of reagents in point-of-care assays, such as antibodies and, in this case, quantum dots, addressed further. This would make the tests even more widely available, she notes.
Other research teams, including Algar’s, are experimenting with quantum dots and smartphone imaging. And while many of these groups use filters, Algar says these attachments aren’t always pricey. His group has designed a device that requires a filter, but uses the camera’s own flash to excite the fluorescent labels. “Both approaches have value,” he says, “and it would be great to eliminate the need for both external filters and external light sources.”
Yager is now focused on releasing another form of smartphone-imaged assay through a new startup called AssureDx. He and his colleagues are still considering their first target, which could be viral or bacterial. Yager believes the technology in the current paper also has commercialization potential if the medical diagnostics community is open to quantum dots. “If you are willing to go to the quantum dots, you can do this with a cellphone,” he says, “the cellphone you have in your pocket today.”