Embodiments herein relate to implantable chemical sensors for detecting a physiological analyte and medical devices including the same. In an embodiment, an implantable medical device is included. The implantable medical device can include a chemical sensor configured to detect an ion concentration in a bodily fluid. The chemical sensor can include a sensing element. The sensing element can include an outer barrier layer forming a top, a bottom, and opposed sides of the sensing element and a structural reinforcing element contacting the outer barrier layer. The top of the outer barrier layer of the sensing element can include a polymeric matrix permeable to analytes.