Caltech Scientists Invent Polymer For Detecting Blood Glucose

PASADENA— Scientists have designed a polymer that could vastly improve the way diabetics measure their blood glucose levels. The polymer is described in the current issue of Nature Biotechnology.

According to Dr. Frances Arnold, a professor of chemical engineering at the California Institute of Technology, the polymer is superior to the current enzyme-based glucose detectors because it is not of biological origin. The polymer will be easier to make and thus lead to cheaper and more reliable glucose sensors.

"This has the potential to help a lot of people, and that's what I find exciting," says Arnold. "A 1993 clinical study showed that if you monitor glucose carefully, the serious complications of diabetes such as gangrene and retinal damage could be reduced by 65 percent."

Arnold believes that her invention will improve the monitoring of glucose, especially for patients in developing countries of the world. Depending on the mechanisms devised for patient use, the polymer will likely be easy and cheap to manufacture and use, which could simplify and widen the practice of frequent testing of blood glucose throughout the day—a practice that many experts say is important to minimizing the complications of diabetes.

Also, the polymer will be more chemically stable and possibly less immunogenic in the human body than the enzymes currently available for glucose monitoring. This could make it more reliable for use in biosensors that remain in the body for extended periods.

At the heart of the polymer is a copper metal complex. The metal is held by a chelating agent that occupies three out of five or six possible "slots" for binding. The other two or three slots, however, can be used to indirectly measure glucose by examining the manner in which hydroxyl groups from the glucose bind.

"The net reaction with glucose is the release of a proton," Arnold explains. Ultimately, the polymer works with a pH meter because hydrogen ions are released from the polymer complex. More hydrogen ions means a more acidic solution (a lower pH), and an acidic response corresponds to high glucose levels in the blood.

And because the substance is nonbiological, it can bypass the blood's normal buffering capacity in order to work at optimal pH levels. This would allow for a simple and straightforward interaction with the blood that, coupled with the inexpensiveness of the materials, would allow for significant reductions in cost to the patient.

The cost reduction would be especially important in the Third World, where diabetes is on the rise.

Also involved in the research are Guohua Chen, a postdoctoral fellow at Caltech, and Vidyasankar Sundaresan, a Caltech graduate student. Former postdoctoral researchers on the project are Zhibin Guan and Chao-Tsen Chen.