Degradation-as-signal: a digital-twin framework for disposable optical glucose sensing with lead-free perovskite-inspired films

) under 2% additive signal noise. A one-dimensional reaction-diffusion extension for thin films (∼100-500 nm) reveals surface-initiated degradation gradients while preserving a monotonic thickness-averaged signal suitable for macroscopic optical readout. Monte Carlo simulations indicate robust discrimination (≈97-100% accuracy across glucose pairs) under realistic noise. The half-life values explored here should be interpreted as experimentally informed design targets spanning plausible degradation windows, rather than as direct fitted kinetic constants for a single validated glucose-responsive composition. Altogether, the model maps sensitivity, half-life contrast targets, and readout windows, providing quantitative design rules that narrow the experimental search space for lead-free optical biosensors where instability is intentionally harnessed as a functional asset.