Colorimetric Detection of Potassium Ions by Electrochromic Thin Film Devices

Potassium ion (K + ) detection technology based on electrochemical sensing has proven to be feasible and widely used in physiological real‐time monitoring and pathological prediction. Nevertheless, chip integration, wireless communication needs, and specific detection limits present challenges. In this study, high‐performance electrochromic materials (W 18 O 49 nanowires) and ion‐selective thin films are introduced to present a highly selective, colorimetric K + biosensor, which demonstrates excellent selectivity in complex ionic environments. The thin film electrochromic electrode offers both colorimetric and electrochemical K + detection simultaneously from 1 m m to 1000 m m concentration range, achieving up to ≈48% optical transmittance modulation, with a coloration time of 15 s. At the clinically relevant K + concentration range of 1–10 m m , the electrode displays a linear transmittance modulation sensitivity of ≈0.6% per m m concentration change. Stability tests demonstrate that the colorimetric detection maintains 96% of its efficiency after 100 full concentration change cycles. A compact solid‐state sensing device incorporating the electrochromic thin films has also been fabricated, and optically quantified K + concentration in real‐life sweat samples.