Basic layout of an opto-chemical sensor: the layer with the analyte-sensitive
dye (e.g. for oxygen, orange layer) is excited by the LED (green), and emits light of
a longer wavelength (e.g. red). The intensity and decay time of the fluorescent light
depends on the analyte concentration, and is measured by the photodetector. (For
interpretation of the references to color in this figure legend, the reader is referred
to the web version of this article.)