A fluorescence sensing device for determining the presence or concentration of an analyte in a liquid or gaseous medium is constructed of a light-emitting diode having a hole generally perpendicular to the P-N junction, such that light is emitted from said junction into said hole. The hole is filled with a fluorescent matrix which is permeable to analyte and which contains fluorescent indicator molecules whose fluorescence is attenuated or enhanced by the presence of analyte. A photodetector is positioned at one end of the hole, such that fluorescent light received from the fluorescent indicator molecules if converted to an electrical signal that may be correlated to the presence or concentration of analyte in a gaseous or liquid medium in contact with the fluorescent matrix.