"In each well, you are performing a qualitative experiment; the result is like a pregnancy test: either yes or no, positive or negative, for the presence of an HIV RNA molecule," says David Selck, a graduate student in Ismagilov's lab and a first author on the study. "But by doing a couple of thousand qualitative experiments, you end up getting a numerical, quantitative result: the concentration of HIV RNA molecules in the sample. By calculating the concentration from the number of wells that contain fluorescenceand therefore HIVyou're leveraging the robustness of many qualitative 'yes or no' experiments to fulfill the need for a quantitative, numerical result," he says.
When the researchers compared quantification results from dRT-LAMP to those obtained by the real-time, kinetic version of this chemistry, RT-LAMP, they found that the digital format provided accurate results despite changes in temperature and time, while the kinetic format could not. This finding adds to a body of research that the laboratory has been developing on the robustness of converting analog signals (i.e., a readout reflecting a changing concentration over time) into a series of positive or negative digital signals. Another recent paper, published in the Journal of the American Chemical Society, explored a variation on this analog-to-digital conversion.
Ismagilov's group also tested a way to take an image of the fluorescence pattern in the wells of the SlipChip and, from that image, determine the viral loadwithout the use of expensive microscopes or trained staff. They turned to a nearly ubiquitous 21st-century tech
|Contact: Deborah Williams-Hedges|
California Institute of Technology