Failure mechanisms in electrochemical point-of-care sensors: biofouling, interfacial degradation, and signal drift.

Electrochemical point-of-care (POC) sensors are fundamental to decentralised diagnostics, yet a profound reliability gap persists between idealised laboratory prototypes and authentic clinical deployment. Despite advances in catalytic nanomaterials and flexible architectures, many devices succumb to catastrophic failure in complex matrices. This critical review systematically dissects the physicochemical origins of these failures, establishing a rigorous electrochemistry-centred framework for sensor demise. The analysis navigates from fundamental thermodynamic instabilities-including disrupted heterogeneous electron transfer, double-layer perturbation, and uncompensated ohmic drop-to macroscopic degradation. Biofouling is interrogated as a dynamic, matrix-dependent thermodynamic process governed by competitive protein displacement. Concurrent intrinsic vulnerabilities, encompassing galvanic corrosion, catalyst poisoning, polymer embrittlement, and potential-dependent passivation, are critically evaluated alongside mechanical breakdowns such as fatigue microcracking and swelling-induced interfacial delamination. Crucially, the review demonstrates that these pathways rarely operate in isolation; rather, they converge into self-reinforcing failure cascades that ultimately manifest as irreversible signal drift, hysteresis, and reference electrode collapse. To bridge this translational chasm, system-level mitigation architectures are evaluated, advocating for upstream microfluidic conditioning, multimodal redundancy, and algorithmic drift compensation. Confronting the reproducibility crisis pervasive in contemporary literature, a mandatory minimum reporting framework is proposed alongside the imperative for operando self-diagnostics. The central thesis is unequivocal: the future of decentralised electroanalysis depends no longer upon achieving marginal gains in nominal sensitivity, but entirely upon engineering highly resilient interfaces capable of preserving absolute analytical fidelity under severe, real-world operating conditions.