To the best of our knowledge, very few works have been done on the continuous real-time monitoring of proton exchange membrane fuel cells (PEMFCs) membrane degradation based on fluoride-specific electrochemical microsensors. PEMFCs are eco-smart energy sources for efficient transportation but experience variable degradation rates that wear the membrane electrode assembly (MEA), a critical component of the fuel cell's functionality. Current market options lack specific diagnostics and legitimate indication of when exactly the membrane must be replaced. As such, this work focused on manufacturing a sensor for measuring MEA degradation in real-time by selectively monitoring fluoride concentration in effluent water, a signature PEMFCs degradation status, through functionalized LaF3:(Au nanoparticle) thin films (~60 nm). The sensor’s exceptional specificity/sensitivity has been achieved in real-time at a sub 10 ppb level, optimized through spin-coating deposition and post-annealing process. Its multimodal readout has been achieved and studied through the characterizations of open circuit potential, cyclic voltammetry, chronoamperometry and differential pulse voltammetry, revealing a consistent linear decrease of 15.7 mA/cm2 at 0 ppb to 10.2 mA/cm2, while also maintaining its low-cost, small size, and robustness.