In First World countries' medical systems, the standard way of checking a patient's body fluid samples is to send them off to a lab. In developing nations, however, such labs often don't exist, nor does the infrastructure for transporting biological samples. Fortunately, a number of groups have been developing simple, inexpensive testing devices that could be used by clinicians in these countries. One of the latest gadgets is the very simple origami Paper Analytical Device, or oPAD - it's made out of paper, could be purchased for under 10 cents, and is folded together by the user.

The device was invented by Hong Liu and Richard Crooks, chemists at the University of Texas at Austin. Liu got the idea after reading a paper by Harvard chemist George Whitesides, who had created a three-dimensional microfluidic paper-bodied biosensor. Whitesides' device, however, required multiple pieces of paper to be patterned using photolithography, cut with lasers, then stuck together with two-sided tape. This somewhat complex production process would presumably be reflected in its price, and would require that it be assembled by trained personnel.

Liu remembered being taught origami as a child in China, and wondered if a similar sensor could be created from a single sheet of paper, shipped flat, then folded into shape on-site. After a few weeks of experiments, he discovered that it indeed could.

Sheets of paper being run off for use in oPADs, on an office printer

The principle is relatively straightforward. Using photolithography or even an office printer, a hydrophobic material such as wax or photoresist is deposited into miniature canyons on chromatography paper. When a liquid sample is introduced, those canyons guide it to areas on the paper treated with reagents. Should the sample contain the targeted substance, then the reagent will visibly react by changing color, or fluorescing under ultraviolet light. Different reagents can be used, depending on what's being tested for.

Many people, of course, are already familiar with paper sensors such as those used for pregnancy tests. The oPAD, however, is able to test for more substances using a smaller surface area, and is able to perform more involved tests.

In its current form, the paper must be unfolded at the end of the process, to reveal the color of the reagent. The scientists, however, have already developed a method of equipping the oPAD with a small battery, that could do things such as lighting up a small bulb if a given substance was present. They estimate that it would only add a few cents to the cost of the device.

A paper on the research was published last week in the journal Analytical Chemistry.

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