An optical fiber senor with a semipermeable membrane is developed and described as a first step toward a continuous insulin sensor. A PEGDMA 2000 formulation was developed that allows insulin to diffuse through, but blocks larger proteins, in order to provide a physical immunoisolative barrier. Next, this material was incorporated into a semipermeable membrane and an optical fiber sensor was created. This sensor was validated with Twitch 2B, a protein with CFP and YFP fluorophores on either end. In the presence of calcium, Twitch 2B will FRET, and the CFP will transfer energy to YFP, causing YFP to emit light instead of CFP. This protein was used as a stand-in molecule for an insulin binding protein currently under development, and an optical fiber sensor was created that responded to increasing concentrations of calcium with increasing FRET. Diffusion tests were conducted on this sensor, to demonstrate that insulin can diffuse through but larger molecules are blocked. Finally, it was shown that changes in FRET from Twitch 2B caused by increasing calcium concentrations can be detected using a photodiode and emission filters, providing an avenue to transition into a circuit sensor design. It was also shown that the Twitch 2B protein can be incorporated into a composite material made up of PEGDMA formulations and PTFE sheets, to allow for a thinner design.