Degradation-as-ignal: a digital-twin framework for disposable optical glucose sensing with lead-free...

Metal-halide perovskites are often regarded as unstable materials whose rapid breakdown under moisture and oxidative stress limits deployment. Here, we invert this paradigm and propose a degradation-driven sensing concept in which controlled chemical decomposition serves as the transduction mechanism for optical glucose detection. We develop a minimal, mechanistically informed, design-oriented digital-twin model for a lead-free halide perovskite-like thin film functionalised with glucose oxidase (GOx). Enzymatic oxidation of glucose produces hydrogen peroxide, which accelerates oxidative degradation of the sensing layer and yields a glucose-dependent loss of optical signal. The framework combines an analytic 0D constant-rate baseline with a GOx-driven transient rate model and a compact power-law optical readout, enabling efficient parameter sweeps over representative glucose ranges (70-300 mg dL^-1). Simulations predict well-separated decay trajectories and monotonic single-time readouts within practical windows (typically ∼30-45 min). Design optimisation within the explored parameter space identifies an operating point (basal half-life 480 min; accelerated half-life 30 min at 200 mg dL^-1; β = 1.5) yielding a mean classification error ≈1.4% (≈98.6% mean accuracy) across representative clinical pairs and >rbin99.9% accuracy for higher-contrast pairs (e.g., 100 vs. 200 mg dL^-1) 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.