A system including a sensor and a transceiver and configured to determine a concentration of an analyte in a medium of a living animal. The sensor may include first and second signal photodetectors and first and second reference photodetectors, which may each be covered by an associate filter. The first photodetector may receive light emitted from first and second grafts, respectively. The grafts may receive excitation light from one or more light sources. The transceiver may receive signals from the photodetectors of the sensor and may determine the analyte concentration based on the received signals.
