With a couple of million people in the U. S. with diabetes, it is necessary to have a simple, specific test for the concentration of glucose in the blood. A rapid test is needed to manage the levels of insulin in diabetes mellitus. If not enough insulin is present, the blood glucose may be very elevated. On the other hand if too much insulin is present, the glucose levels are too low.
Oxidation of Glucose
Blood glucose levels are now measured by a procedure based upon the enzyme glucose oxidase. Since an enzyme is used, it is very specific for only D-glucose, and will not be subject to interferences from other molecules in the blood.
Glucose is a reducing sugar, which means that it can be oxidized. The enzyme glucose oxidase catalyzes the oxidation of beta-D-glucose to D-gluconic acid. The alpha-D-glucose is rapidly converted to the beta form so that all of the glucose is measured at one time.
Diatomic oxygen from the air is the oxidizing agent acting upon the glucose reducing agent. During the reaction the ring opens and the aldehyde on carbon # 1 is converted to the acid, D-gluconic acid. At the same time the oxygen in the presence of water is converted to hydrogen peroxide. So far all of the chemicals are colorless, so you would not be able to see the reaction taking place. Therefore another step is needed to produce a color.
Color Producing Reaction
Several methods of detection are possible, but in most cases, the hydrogen peroxide reacts with a second color producing chemical. An example is something called o-Toluidine or 2-methylaniline which reacts with the hydrogen peroxide using an enzyme called peroxidase to produce a color forming chemical.
The concentration of the glucose can be related to the intensity of color produced. The more the intensity, the higher the concentration of glucose. A simple color chart can be used to "read" the concentration of the glucose.
- Charles Ophardt, Professor Emeritus, Elmhurst College; Virtual Chembook