Many slender and flexible medical devices are designed to be inserted through the skin. For example, sensors facilitate the sensing of certain conditions within a patient. Electrochemical sensors are commonly used to monitor blood glucose levels in the management of diabetes. In one scheme, an electrochemical sensor incorporating an enzyme is fabricated onto a small diameter wire. A second reference electrode is also fabricated around the wire near the sensing electrode. The sensor assembly is inserted through the skin so that it is surrounded by interstitial fluid. A portion of the sensor remains outside the body, where electrical connections to the sensing electrode and reference electrode may be made. A suitable electronic measuring device outside the body may be used to measure electrical current from the sensor for recording and display of a glucose value, or other measurement. These types of devices are described, for example, in U.S. Pat. No. 5,965,380 to Heller et al. and U.S. Pat. No. 5,165,407 to Wilson et al.
In addition to electrochemical glucose sensors, a number of other electrochemical sensors measure the chemistry of blood or other body fluids or materials. Electrochemical sensors generally make use of one or more electrochemical processes and electrical signals to measure a parameter. Other sensors use optical techniques to perform a measurement.
Biosensors are sometimes housed in an apparatus that sits on the skin during operation. To prevent infection and for other reasons, the apparatus may be discarded after each use.