The test for Kaposi’s sarcoma
, a deadly skin cancer related to HIV infections, is usually too energy-intensive for remote regions of the world -- such as sub-Saharan Africa where its mortality rates are high. Late diagnosis of the disease is one of the reasons for its low survival rate.
For a less power-hungry method, engineers have remodeled the test to create a quick diagnostic using just the sun and a smartphone app.
“DNA tests are extensively used in medical diagnostics since they are sensitive and specific,” Cornell’s David Erickson
says in a news release
. “Some places in the developing world have limited infrastructure and unreliable electricity, and these kinds of tests usually hog energy.” Testing for the disease typically requires a human skin biopsy and the use of a technique called polymerase chain reaction (PCR)
to amplify traces of virus DNA. As New Scientist explains
, this is done in the presence of a primer, which is a bit of DNA that binds to pre-selected target sequences, acting as the starting point for the strand to be copied. Since the process must be repeated until there are enough copies to be detected, a lot of energy goes into driving the reaction, as well as heating and cooling the samples.
This new solar thermal PCR test (pictured) works without electricity and uses about 0.08 watts, which is a 100-fold reduction in power consumption compared with more conventional techniques of processing biopsies. That means a standard iPhone battery could provide about 70 hours of power for testing.
After medical technicians deposit the skin biopsy into the solar thermal PCR device, a completed diagnostic test can be conducted with a smartphone in about half an hour. Here’s the process, according to New Scientist
- The device uses a lens to focus the sun's rays into a disc of light where the edges are cooler than the center.
- A chip with a long microscopic channel etched onto it is placed under the light.
- The sample moves along this channel so that its temperature changes in cycles, alternating between the warmer center and the cooler edges. (This thermal cycling drives the PCR.)
- A dye called SYBR Green glows under blue light if amplified DNA from the virus is detected.
- A smartphone controlling the chip then reads the results.
The team is now testing the device in Uganda.
was published in Scientific Reports
Image: Cornell’s Li Jiang with the solar thermal PCR test by Jason Koski/University Photography