An optical-based sensor for detecting the presence or amount of an 
analyte using both indicator and reference channels. The sensor has a sensor body with a source of 
radiation embedded therein. 
Radiation emitted by the source interacts with indicator membrane indicator molecules 
proximate the surface of the body. At least one optical characteristic of these indicator molecules varies with 
analyte concentration. For example, the level of 
fluorescence of fluorescent indicator molecules or the amount of light absorbed by light-absorbing indicator molecules can vary as a function of 
analyte concentration. In addition, 
radiation emitted by the source also interacts with reference membrane indicator molecules 
proximate the surface of the body. 
Radiation (e.g., light) emitted or reflected by these indicator molecules enters and is internally reflected in the sensor body. Photosensitive elements within the sensor body generate both indicator channel and reference channel signals to provide an accurate indication of the concentration of the analyte. Preferred embodiments are totally self-contained and are sized and shaped for use 
in vivo in a 
human being. Such embodiments preferably include a power source, e.g. an 
inductor, which powers the source of 
radiation using external means, as well as a 
transmitter, e.g. an 
inductor, to transmit to external 
pickup means the 
signal representing the level of analyte.