Leland Clark invents the electronic biosensor.

The ARM that Dick Bernstein bought to measure his blood glucose levels was not that different from the glucose blood tests that Charles Best performed back in 192?.  The ARM was more convenient.  The chemicals are immobilized on a piece of paper.  So, you just have to add a drop of blood and wait for a minute, rather than preparing and mixing chemicals.  Charles Best interpreted the results of his blood glucose test by comparing the color of his solution to a standard color.  The ARM quantified the color by measuring the amount of light reflected from it.

In 1962, Leland Clark envisioned a different type of sensor.  He was working at the Medical College of Alabama on the problem of continuous monitoring of blood gases for patients hooked up to heart lung machines.   The problem is straightforward: if you have a machine breathing for you, how fast should it inhale and exhale.  If you set the machine to breathe too quickly, the patient will be hyperventilating.  If you set it too slowly, the patient will be hypoxic, not getting enough oxygen.  In order to know the ideal breathing rate (which might change), you need to know the concentration of relevant gases in the blood.

Clark had an electrode system for continuous monitoring of blood [http://www.ncbi.nlm.nih.gov/pubmed/14021529].  Using this system, they could make immediate measurements on how much oxygen was in the blood and adjust the artificial ventilator to either increase or decrease the oxygen in the blood.  They considered expanding their technique to measure other key analytes in the blood.

He had the insight to use glucose oxidase in his oxygen sensor.  The glucose oxidase converts glucose in solution to hydrogen peroxide. The hydroxen peroxide, in turn, gets separated into hydrogen, oxygen, and electrons.  The electrons are measured by the electrode.  The result of this invention is that the amount of glucose can be converted to an electrical current.

Many innovations have occurred since Leland Clark first built his glucose sensor.  Today, small battery operated devices smaller than a cell phone communicate wirelessly with a tiny glucose sensor that is embedded into your skin.  These devices, known as continuous glucose monitors, provide