To self-diagnose, spit on an iPhone

HANDHELD gadgets could one day diagnose infections at the push of a button by using the supersensitive touchscreens in today's smartphones.

Many believe that in the future collecting samples of saliva, urine or blood could be performed using a cheap, USB-stick-sized throwaway device called a lab-on-a-chip. The user would inject a droplet of the fluid in the chip, and micropumps inside it would send the fluid to internal vessels containing reagents that extract target disease biomarker molecules. The whole device would then be sent to a lab for analysis.

But Hyun Gyu Park and Byoung Yeon Won at the Korea Advanced Institute for Science and Technology in Daejeon think touchscreens could improve the process by letting your phone replace the lab work. Park suggests the lab-on-a-chip could present a tiny droplet of the sample to be pressed against a phone's touchscreen for analysis, where an app would work out whether you have food poisoning, strep throat or flu, for example.

The idea depends on a method the pair have devised to harness the way a touchscreen senses a fingertip's ability to store electric charge - known as its capacitance. The capacitive sensitivity of touchscreens is far higher than what is needed to sense our fingers as we play games or tap out tweets. "Since these touchscreens can detect very small capacitance changes we thought they could serve as highly sensitive detection platforms for disease biomarkers," says Park.

So the pair began proof-of-concept tests to see if the touchscreens in our pockets could play a role in diagnosing our ailments. First they took three solutions containing differing concentrations of DNA from the bacteria that causes chlamydia and applied droplets from each to an iPhone-sized multitouch display. They found that the output from the screen's array of crisscrossed touch-sensing electrodes could distinguish between the capacitances caused by each concentration using droplets of only 10 microlitres (Angewandte Chemie International Edition, DOI: 10.1002/anie201105986).

The technology is not yet able to identify individual pathogens but Park sees the display's ability to differentiate between concentrations as a first step towards this.