An implantable medical device comprising: a housing defining a recessed pan; and a first chemical sensor comprising an optical excitation assembly (312, 313, 611, 613, 615, 812, 813, 815, 822, 823, 825, 1212, 1213) comprising a first visible spectrum emitter; a second visible spectrum emitter; and at least one of a near-infrared emitter and an ultraviolet emitter; an optical detection assembly (314, 616, 617, 814, 816, 1214) comprising a colorimetric response detector; and a photoluminescent response detector; and a multimode sensing element (302, 304, 602, 704) disposed within the recessed pan comprising: an outer barrier layer comprising an ion permeable material and defining an interior volume a colorimetric response element (622, 624) specific for a first chemical analyte disposed on or in a first set of beads; a photoluminescent response element (622, 624) specific for a second chemical analyte disposed on or in a second set of beads; wherein both the first set of beads and the second set of beads are dispersed throughout the interior volume; wherein the optical excitation assembly emits at least one of visible spectrum light, near-infrared light, or ultraviolet light onto the multimode sensing element and the optical detection assembly receives an optical signal from the multimode sensing element, wherein the top of the outer barrier layer comprises an analyte diffusion window comprising an ion permeable material, wherein a membrane is disposed over the analyte window, wherein the membrane is opaque to the passage of light in the visible, UV, or NIR frequency spectrums. a housing defining a recessed pan; and a first chemical sensor comprising an optical excitation assembly (312, 313, 611, 613, 615, 812, 813, 815, 822, 823, 825, 1212, 1213) comprising a first visible spectrum emitter; a second visible spectrum emitter; and at least one of a near-infrared emitter and an ultraviolet emitter; an optical detection assembly (314, 616, 617, 814, 816, 1214) comprising a colorimetric response detector; and a photoluminescent response detector; and a multimode sensing element (302, 304, 602, 704) disposed within the recessed pan comprising: an outer barrier layer comprising an ion permeable material and defining an interior volume a colorimetric response element (622, 624) specific for a first chemical analyte disposed on or in a first set of beads; a photoluminescent response element (622, 624) specific for a second chemical analyte disposed on or in a second set of beads; wherein both the first set of beads and the second set of beads are dispersed throughout the interior volume; wherein the optical excitation assembly emits at least one of visible spectrum light, near-infrared light, or ultraviolet light onto the multimode sensing element and the optical detection assembly receives an optical signal from the multimode sensing element, wherein the top of the outer barrier layer comprises an analyte diffusion window comprising an ion permeable material, wherein a membrane is disposed over the analyte window, wherein the membrane is opaque to the passage of light in the visible, UV, or NIR frequency spectrums. an outer barrier layer comprising an ion permeable material and defining an interior volume a colorimetric response element (622, 624) specific for a first chemical analyte disposed on or in a first set of beads; a photoluminescent response element (622, 624) specific for a second chemical analyte disposed on or in a second set of beads; wherein both the first set of beads and the second set of beads are dispersed throughout the interior volume; wherein the optical excitation assembly emits at least one of visible spectrum light, near-infrared light, or ultraviolet light onto the multimode sensing element and the optical detection assembly receives an optical signal from the multimode sensing element, wherein the top of the outer barrier layer comprises an analyte diffusion window comprising an ion permeable material, wherein a membrane is disposed over the analyte window, wherein the membrane is opaque to the passage of light in the visible, UV, or NIR frequency spectrums.