An optical sensor for implantation within a living animal and measurement of a concentration of an analyte in a medium within the living animal, the optical sensor comprising: indicator molecules having an optical characteristic responsive to the concentration of the analyte, the indicator molecules being configured to interact with the analyte in the medium within the living animal when the optical sensor is implanted within the living animal; a semiconductor substrate; a photodiode fabricated in the semiconductor substrate and configured to output an analog light measurement signal indicative of the amount of light received by the photodiode, wherein the light received by the photodiode includes light emitted by the indicator molecules; a light source configured to emit excitation light to the indicator molecules; an analog to digital converter fabricated in the semiconductor substrate and configured to convert the analog light measurement signal to a digital light measurement signal; an inductive element; an input/output circuit fabricated in the semiconductor substrate and configured to wirelessly transmit via the inductive element measurement information and wirelessly receive via the inductive element a measurement command and power; and a measurement controller fabricated in the semiconductor substrate and configured to: (i) in accordance with the measurement command, control the light source; (ii) generate the measurement information in accordance with the digital light measurement signal; and (iii) control the input/output circuit to wirelessly transmit the measurement information. indicator molecules having an optical characteristic responsive to the concentration of the analyte, the indicator molecules being configured to interact with the analyte in the medium within the living animal when the optical sensor is implanted within the living animal; a semiconductor substrate; a photodiode fabricated in the semiconductor substrate and configured to output an analog light measurement signal indicative of the amount of light received by the photodiode, wherein the light received by the photodiode includes light emitted by the indicator molecules; a light source configured to emit excitation light to the indicator molecules; an analog to digital converter fabricated in the semiconductor substrate and configured to convert the analog light measurement signal to a digital light measurement signal; an inductive element; an input/output circuit fabricated in the semiconductor substrate and configured to wirelessly transmit via the inductive element measurement information and wirelessly receive via the inductive element a measurement command and power; and a measurement controller fabricated in the semiconductor substrate and configured to: (i) in accordance with the measurement command, control the light source; (ii) generate the measurement information in accordance with the digital light measurement signal; and (iii) control the input/output circuit to wirelessly transmit the measurement information. (i) in accordance with the measurement command, control the light source; (ii) generate the measurement information in accordance with the digital light measurement signal; and (iii) control the input/output circuit to wirelessly transmit the measurement information.