New glucose test on the way for diabetes.

California researchers have designed a glucose-sensing polymer to measure a diabetic's blood-sugar concentrations-inside or outside the body.

Because it does not trigger an allergic response, this new sensor holds out the prospect of implants for long-term glucose monitoring. It would prove especially valuable if teamed with automatic systems for insulin delivery. The sensor could also make glucose monitoring through finger-prick blood tests affordable throughout the nonindustrialized world, says Frances H. Arnold of the California Institute of Technology in Pasadena.

To limit complications that can result in blindness, amputation, and kidney failure, people with diabetes must carefully monitor concentrations of glucose in their blood and then fine-tune their diet or insulin administration to ensure that blood sugar does not become elevated for long periods.

Most glucose monitors rely on bacterial enzymes, which can break down in hot environments. They also vary in sensitivity from batch to batch, which necessitates expensive calibrations by manufacturers. These factors have put regular glucose monitoring beyond the economic reach of the millions of diabetics in developing countries, Arnold observes. In the April Nature Biotechnology, her team describes what it hopes will prove a better alternative.

The group has engineered a stable, porous polymer and impregnated it with copper. The metal binds glucose when exposed to a blood sample modified to have a high, or strongly alkaline, pH. Each glucose molecule that binds to this material gives up a proton, lowering the pH of the blood sample. If glucose concentrations in the blood fall, so will the number of glucose molecules bound to the sensor; each released molecule grabs a proton, raising the blood's pH. Thus, monitoring blood sugar becomes as simple as assaying pH, says Arnold.

The idea of measuring glucose via pH is not new, observes George S. Wilson of the University of Kansas in Lawrence in an accompanying commentary. Earlier attempts at harnessing pH were thwarted by the blood's capacity for neutralizing acids. He notes that the new polymer avoids this problem by operating at an unnaturally alkaline pH.

Though raising blood to this pH poses a challenge for implanted systems, Arnold says "it's definitely doable" and something her team is actively pursuing. Wilson suggests, for example, that a semipermeable membrane could keep the blood molecules that neutralize acid away from the glucose being sampled.

Arnold anticipates that products based on the new technology may reach the market "within a couple of years."