Counting Molecules with Chemistry? There’s an App for That

SlipChip Counts Molecules with Chemistry and a Cell Phone

There’s limited access to expensive equipment and trained medical professionals in places like developing nations, rural areas, and even one’s own home. However,  California Institute of Technology (Caltech) have demonstrated a method for using a lab-on-a-chip device and a cell phone to determine a concentration of molecules, such as HIV RNA molecules, in a sample. This digital approach can consistently provide accurate quantitative information.

“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

The researchers place a SlipChip in a makeshift darkroom and then photograph its wells using a smartphone outfitted with a special filter attachment — the smartphone flash is then able to “excite” the fluorescent DNA dye, and the smartphone camera can capture an image of the fluorescence.

“We were surprised that this cell phone method worked, because both cell phone imaging and automated processing are error prone,” Rustem 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.”

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