Embodiments of the invention are related to electro-optical implantable sensors, amongst other things. In an embodiment, the invention includes an implantable medical device including a housing defining an interior volume, the housing comprising a housing wall and defining an aperture. The implantable medical device can include an optical sensor assembly coupled to the housing wall. The optical sensor assembly can occlude the aperture in the housing wall. The optical sensor assembly can include an electro-optical module including an optical excitation assembly and an optical detection assembly. The optical sensor assembly can also include a chemical sensing element configured to detect a physiological analyte by exhibiting a change in optical properties. An optical window can be disposed between the electro-optical module and the chemical sensing element. The optical window can be configured to allow the transmission of light between the electro-optical module and the chemical sensing element. Other embodiments are also included herein.