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 (W₁₈O₄₉ 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 mm to 1000 mm 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 mm, the electrode displays a linear transmittance modulation sensitivity of ≈0.6% per mm 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.