Photographs by Ken Richardson
Diagnostics for All, a nonprofit in Cambridge, Massachusetts, is making a test for liver damage that could cost just pennies. It consists, remarkably, of a stamp-size square of paper with wells that change color when a drop of blood is applied.
The test could provide an enormous benefit in poor countries, where liver damage is widespread as a side effect of drugs administered to HIV and tuberculosis patients. (As many as one-fourth of people taking antiretroviral drugs in the poor world develop liver problems—five times the rate elsewhere.) The liver function tests administered regularly in the developed world require tubes of blood, lab equipment, and electricity. The paper chip from Diagnostics for All needs none of that.
The test uses patterned channels and wells to allow for filtering and multistep reactions; the technology originated in the lab of Harvard chemist George Whitesides, who pioneered this method, and was licensed from Harvard (see “Paper Diagnostics”). The paper absorbs sample fluids and uses capillary action to convey them to the test wells imprinted on it. These wells are spotted with chemicals that change color when they react with certain markers in a liquid.
The chip is meant to work simply with little additional equipment, making it suitable for the poorest regions. “This is a world in which there are very few resources—that is to say, almost no money, very few doctors, no electricity in many places, no refrigeration,” Whitesides says. “The conditions are such that it’s very difficult to imagine how you deliver even pretty straightforward health care.”
Five years after the company was formed, Diagnostics for All, which is led by biotech executive Una Ryan and sustained by grants from the Gates Foundation and others, is moving toward a viable product. The first trial of the liver test is in progress on HIV patients at a hospital in Vietnam. Funding, manufacturing, and distribution models are still being worked out, but the company can make between 500 and 1,000 tests per day at its Cambridge facility and hopes to obtain regulatory approvals so that the liver test can reach patients by 2014, says Jason Rolland, who leads engineering efforts as the company’s senior director of research.
DFA (as the company is known) is working on other paper-based diagnostics: an assay that detects antigens for multiple diseases, including malaria and dengue fever; a test for preëclampsia in pregnant women; and even nucleic-acid tests to detect pathogens in blood. The company is also developing tests that farmers could use to check for foodborne toxins. In all cases, results can be interpreted by a clinician or a smartphone app, after which test patches can be incinerated. They are, after all, just paper.
Paper is printed with wax to define zones for 55 tests. Each test measures two liver enzymes. Finished tests include a sandwich of two such sheets.
The sheets are baked for 30 seconds at 130 °C to allow the wax to melt completely through the paper’s 0.2-millimeter thickness.
The test wells are wax-free circles two millimeters across.
Measured amounts of the reactant chemicals are deposited on each of the two sheets. The first sheet gets reagents that react with enzymes. The second sheet (shown here) gets dyes that change color if exposed to products released by the first reactions.
The two sheets are fused together with adhesives in a press.
An adhesive sheet with circular blood filters is prepared. Later, this sheet is affixed to the fused paper sheets. Only plasma reaches the paper layers.
In a final step, a protective laminate is affixed to the top of the package.
The completed tests are cut into individual squares.
A drop of blood first encounters a plasma filter. The plasma then wicks through test wells on the two layers of paper.
Test results take about 15 minutes to appear. At left is the back of an unused test; at right, one activated with blood.
The results (right) show that the blood has normal enzyme levels, as indicated by the color in the top wells. The other four wells are controls that tell whether the test worked properly.
The scale in this guide offers a way to gauge the level of enzymes present. Clinicians could use this information to change a drug regimen or order additional tests.