Improving Disease Detection With A Little Heat

In many parts of the world where tuberculosis is endemic, medical resources, such as laboratory equipment, are sometimes scarce. So analytical chemists want to develop simple, low-cost diagnostic tests for the disease. To help detect dilute biomarkers for tuberculosis in urine, researchers now report an inexpensive method that increases a biomarker’s concentration on a strip of paper (Anal. Chem. 2014, DOI: 10.1021/ac503751a).

Doctors typically test for tuberculosis by examining a patient’s chest X-ray or by culturing their sputum. These methods require expensive, immobile equipment or lengthy bacterial growth periods, neither of which is practical in remote, low-resource regions. Sharon Yan Wong, a postdoc in the laboratory of Catherine M. Klapperich at Boston University, envisioned replacing those standard techniques with one that was as simple and fast as a home pregnancy test.

To do so, Wong and her colleagues wanted to look for lipoarabinomannan (LAM), a glycolipid found in the cell wall of the tuberculosis bacterium. LAM is shed into the urine of people with infectious tuberculosis. An existing paper-based urine test detects LAM, but there’s a problem: “It’s only useful for those who are coinfected with HIV,” Wong says. Scientists speculate that more of the biomarker ends up in a person’s urine if they have a compromised immune system. This suggests, Wong says, that a LAM urine test could work in the general population if researchers found a simple way to concentrate the urine.

The research team decided to test whether gentle heating could quickly concentrate a urinary biomarker by increasing the rate of evaporation. In a proof-of-principle test, they placed one end of a strip of chromatography paper, which is often used in paper analytical devices, against an electric heater and dipped the other end into a urinelike solution spiked with LAM. Through capillary action, the solution moved up the paper strip until it reached the heater, which evaporated off the water, allowing more solution—and more biomarker—to flow up the paper. Heating the paper to 220 ºC for 20 minutes removed approximately 600 µL of water. The researchers then checked the concentration of LAM at both ends of the strip using an antibody that binds to LAM. The glycolipid was nearly 20-fold more concentrated at the heater end of the strip than at the end submerged in the solution.

Wong is encouraged by these results, especially since the team hasn’t yet optimized the conditions. Next, the researchers plan to vary the dimensions of the strip, the temperature, and other factors to increase the concentration of LAM, as well as test the approach on clinical samples.

Charles S. Henry of Colorado State University says the method addresses a continuing challenge in developing low-cost diagnostics for resource-limited settings: concentrating dilute samples. “This is a simple and elegant way of improving sensitivity in those environments,” Henry says. The approach may have applications beyond tuberculosis, he says, though it’s unclear whether heating some biomarkers, such as proteins, would affect their detectability. To address that issue, Wong and her colleagues intend to test additional biomarkers.