A tiny chip to indicate infection
by: Mara Grunbaum

Wielding only two pieces of glass no bigger than a stick of chewing gum, Feng Shen and Wenbin Du want to battle disease. The University of Chicago chemists recently developed a method for simply and quickly identifying pathogens on a handheld chip, and they hope it will eventually help improve medicine in developing countries.

More than 14 million people die yearly of infectious diseases like HIV, malaria and tuberculosis, according to the World Health Organization. Properly diagnosing those diseases, identifying mutated strains and doling out treatments accordingly could prevent many deaths. But doing so often requires modern equipment, clinical labs, and skilled technicians, which are rare in the developing world. Doctors and health organizations have put out the call for diagnostic tools that are as cheap, portable and simple to use as a home pregnancy test.

Shen and Du’s attempt to answer is a device called the SlipChip. It performs the polymerase chain reaction (PCR), which can identify bacterial or viral strains by latching onto unique sequences in their genetic codes.

“It’s really easy,” Shen says. “Easy to use and easy to fabricate, and it’s low-cost, and it can perform all the standard molecular diagnostics that currently are used by a clinical lab.”

The chip consists of two small plastic or glass plates embossed with microscopic wells and channels. When the plates are stacked together, the channels connect, forming a pathway for the test sample to fill many wells at once. After the sample is injected, sliding the sides of the chip works like flipping a railroad switch—it breaks the pathways and creates hundreds of isolated reaction compartments. Each one can be pre-loaded with the necessary PCR ingredients to test for a different strain of bacteria or virus. Fluorescent markers signal positive tests.

In lab experiments, published in June in the journal Analytical Chemistry, Shen and Du found that the chip correctly identified five different infectious agents. It also recognized antibiotic resistance in a strain of Staphylococcus bacteria. Since the compartments are never open to air, they found, there was no significant cross-contamination, which can be a problem with traditional PCR. The SlipChip also needs less external equipment and requires a much smaller test sample—only 10 microliters total, or less than one drop of blood.

“It’s a neat technology,” says Luc Bissonnette, a biochemist who has researched molecular diagnostics for a decade at the Centre de Recherche du CHUQ in Quebec. “It’s very simple... I think it has some future.” But he cautions that the more tests a single device performs, the more complicated the FDA approval process—so the chip may have a long way to go before on-the-spot diagnostic use.

Shen and Du plan to have the chip manufactured as soon as possible. They say it will have many applications in hospitals and research labs, though they’re most hopeful about its potential for the developing world.

“[If] we can produce it and give it to people who really need it, we can change people’s lives,” said Shen, who himself grew up in a poor family in China with limited health care access. “Usually the rich portion get most of the resources, but the poor portion don’t,” he added. “But they also deserve a good life.”