The researchers placed the SlipChip in a makeshift darkroom (a shoebox with a hole in the top) and then photographed its wells using a smartphone outfitted with a special filter attachmentso that the smartphone flash would be able to "excite" the fluorescent DNA dye, and the smartphone camera could capture an image of the fluorescence. The resulting images were uploaded to Microsoft SkyDrive, a cloud-based server, where custom softwaredesigned by the researchersdetermined the viral load concentration and sent the results back in an email. These capabilities allow the digital approach to perform reliably with automated processing, regardless of how poor the imaging conditions may be. As an example of its simplicity, a 5-year-old child was able to use this cell phone imaging method to obtain quantitative results using strands of RNA extracted from a noninfectious virus (a video of this demonstration is available on the Ismagilov lab's YouTube channel).
"We were surprised that this cell phone method worked, because both cell phone imaging and automated processing are error prone," Ismagilov says. "Because digital assays involve simply distinguishing positives from negatives, we found that even these error-prone approaches can be used to count single molecules reliably."
The fact that this method is robust not only to changes in time and temperature but also is amenable to cell phone imaging and automated processing makes it a promising technology for limited-resource settings. "We believe that our findings of the robustness of digital amplification could signal a major paradigm shift in how quantitative measurements are obtained at home, in the field, and in developing countries," Ismagilov says.
The researchers stress that there is still room for improvement, however. "While in this study we were examining robustness and used purified RNA, the next generation of devices will isolate HIV RNA molecules directl
|Contact: Deborah Williams-Hedges|
California Institute of Technology