Concentration problem

Abstract

Insulin, the hormone that enables glucose to be taken up by cells for conversion to energy, is present in nanomolar levels in the blood. Glucose levels, however, reach millimolar concentrations in the blood. In diabetes, the imbalance in the glucose:insulin ratio causes glucose to accumulate in the bloodstream to deleterious levels, resulting in cellular starvation. The difficulty in simultaneously measuring two interdependent substances whose concentrations differ by five-fold, has been one of the problems involved in developing an effective implantable sensor to monitor glucose and insulin levels. Researchers have now designed the first implantable device of its kind, which combines both sensors in an electronic needle-shaped framework [Anal. Chem. (in press)]. The glucose probe is based on the biocatalytic action of glucose oxidase and the insulin probe on the electrocatalytic activity of ruthenium oxidase. ‘The nice thing is that this is two different concepts,’ said Joseph Wang, from New Mexico State University in Las Cruces. ‘Despite the fact that they are completely different principles, we have found that they can be integrated and work independently.’ The researchers hope to streamline the sensor, reducing it to the thickness of 26-gauge wire (approximately the size of a hypodermic needle) before testing the device in animals. The sensor would provide an early warning signal of changing glucose levels. This would enable tighter control of blood sugar levels, lowering the incidence of diabetic complications such as hypoglycaemic attacks, renal disease, blindness, nerve degeneration and stroke. S. de B.