Scientists from Cornell University and Cornell Weill Medical College are developing a solar-powered, point-of-care PCR system that has the potential to enable electricity-free molecular diagnostics in resource-poor areas of the world.
So far, the researchers have used their prototype platform to successfully amplify genomic DNA extracted from Kaposi's sarcoma-associated herpesvirus, or KSHV, and are currently working to further optimize their system with an eye toward testing it in the field in the developing world.
In addition, the researchers are designing a syringe-based sample prep module for the system and would eventually like to move beyond tumor samples into other relevant sample types for infectious diseases. These next steps, however, would likely require additional funding or collaboration from an industry partner, David Erickson, an associate professor of mechanical and aerospace engineering at Cornell and a principal investigator on the project, told PCR Insider this week.
Erickson said that he and colleagues initiated their project when they were looking at ways to perform PCR-based diagnostics in resource-limited settings, particularly geographies without reliable electricity.
"One of the problems with PCR in those kinds of situations is that it actually consumes a fair bit of power," Erickson said. "We started looking to see what other sources of power might be available, and in the places we were looking, the one thing they mostly have in common is uniform, constant sunlight. So we started designing and developing a solar thermal PCR system that would be simple to use, be fixable in a situation where it broke down and you didn't have anything around, wouldn't take very much power, and would do things very efficiently."
Erickson, Cornell graduate student Li Jiang, and other colleagues presented an abstract on their technology last week at the Conference on Lasers and Electro Optics in San Jose, Calif.
In the system sunlight is focused through an adjustable lens onto an aluminum foil mask, which is composed of three nested rings and produces a specific pattern on a polydimethylsiloxane chip below it. A carbon black film in the chip absorbs this light and converts it into a thermal profile. The researchers can use thermocouples and a battery-powered smartphone and related application measure temperatures at points in the chip corresponding to the PCR steps of denaturation (95° C), annealing (60° C), and extension (75° C).
The user can then adjust the device’s tilt angle and chip-to-lens distance to achieve the desired temperatures. A continuous-flow PCR technique can quickly circulate the sample through each zone, achieving reactions as fast as 10 seconds per cycle. Detection of PCR products can be achieved using a nanoparticle-based colorimetric technology, and data can be read on a smartphone.
Erickson said that his group at Cornell's Ithaca, NY, campus is working with Ethel Cesarman, a professor of anatomic pathology and clinical pathology at the Cornell Weill Medical College campus in New York, to develop the sample processing portion of the system, a so-called "lab on a syringe."
"We're working with biopsy samples, and we take this lab on a syringe and process [the sample], and then we pump the remnants through the chip via that syringe," Erickson said. Sample prep would take place inside the syringe. "We haven't worked with other sample types yet. Biopsies are really [difficult], there is a lot of stuff in there, and the DNA-to-[background] ratio is quite low. We are thinking about working with other samples, but we kind of started driving down this road of biopsy-driven diagnostics."
As described in their CLEO abstract, Erickson and colleagues conducted preliminary amplification experiments using a 43-base-pair segment of genomic DNA extract from KSHV. They are working with this virus because KSHV tumors are difficult to distinguish from several other diseases with similar histologies, and in low-resource settings the tumors are often diagnosed incorrectly or far after they have significantly advanced.
They compared their solar-powered amplification with conventional PCR amplification using gel electrophoresis. They found that the gel bands for the two types of amplification matched, although the bands from the solar-powered amplification were less distinct.
In addition, they performed these amplification experiments in a laboratory under controlled temperature with simulated sunlight. However, they have also assessed the ability to created different PCR temperature zones on their device in field tests in Ithaca, both outdoors and indoors, and showed that by reducing the incident intensity as external temperature increases, the temperature zones could be maintained within about a 5° C range over an ambient change of about 30° C.
Further, in lthaca, where sunlight is frequently limited, they were able to sufficiently heat their device even at an ambient temperature of -6° C. "In warmer climates, less solar intensity would be needed," the researchers wrote. "These results suggest that the device should function over a range of ambient temperatures and potentially under cloudy conditions as long as the solar intensity is sufficiently high."
Erickson said that the system is currently only capable of endpoint PCR detection, but it could be rejiggered for real-time PCR. However, "as soon as you start doing multiple measurements over a certain number of cycles, it just takes more power," he said. "It's a tradeoff [between] the number of tests you want to perform [and] quantification, or what have you."
Cornell has filed for a patent covering the invention on behalf of the inventors. Erickson's group currently has funding from the National Institutes of Health to support certain aspects of the system's development, and has NIH funding pending to support the entire project.
In the meantime, Cornell has made the technology available for licensing, and Erickson and colleagues are seeking industry partners to help productize the system and develop it for other diseases and diagnostic targets.