Detecting diseases such as HIV and malaria in third-world countries is often a costly process, but that might soon change because a team from the University of Texas at Austin has designed a three-dimensional sensor crafted from paper that could make diagnosis simple and cheap. Clearly using origami as an inspiration, the Paper Analytical Devices, or oPADs cost less than 10 cents each – and they stand to revolutionize how doctors work in labs where equipment is scarce. “This is about medicine for everybody,” says Richard Crooks, the Robert A. Welch Professor of Chemistry. “Anybody can fold them up. You don’t need a specialist, so you could easily imagine an NGO with some volunteers folding these things up and passing them out. They’re easy to produce, so the production could be shifted to the clientèle as well. They don’t need to be made in the developed world.”
Paper sensors are already commonly used for pregnancy tests, but they have limitations. However the oPAD is able to test for more substances on a smaller surface area and provide results for more complex tests.
The inspiration for the sensor came when doctoral student Hong Liu read a pioneering paper by Harvard University chemist George Whitesides. Whitesides was the first to build a three-dimensional “microfluidic” paper sensor that could test for biological targets, but his creation was expensive, time-consuming and limited.
“They had to pattern several pieces of paper using photolithography, cut them with lasers, and then tape them together with two-sided tape,” said Liu, a member of Crooks’ lab. “When I read the paper, I remembered when I was a child growing up in China, and our teacher taught us origami. I realized it didn’t have to be so difficult. It can be very easy. Just fold the paper, and then apply pressure.” After a few weeks of experiments, Liu had fabricated the sensor on one simple sheet using photolithography. Folding it over into multiple layers took less than a minute and required no tools or special alignment techniques.
The sensor works by embedding test reagents into the paper. If urine, blood, or saliva is placed on the paper, it reacts once it detects what it is designed to find. “Biomarkers for all kinds of diseases already exist,” says Crooks. “Basically you spot-test reagents for these markers on these paper fluidics. They’re entrapped there. Then you introduce your sample. At the end you unfold this piece of paper, and if it’s one color, you’ve got a problem, and if not, then you’re probably OK.”
Crooks and Liu have also engineered a way to add a simple battery to their sensor so that it can run tests that require power. Their prototype uses aluminum foil and looks for glucose in urine. The addition of a battery would only add only a few cents to the cost of producing the sensor.
“You just pee on it and it lights up,” says Crooks. “The urine has enough salt that it activates the battery. It acts as the electrolyte for the battery.”