Magneto‐Responsive Photonic Liquid Gate with Color‐Indicated Gas Transport Switching Threshold

Abstract Liquid gates, which combine the characteristics of both solid and liquid materials, possess unique advantages of reconfigurable interfaces, dynamic responsiveness, and adaptability, demonstrating great promise for various practical applications. Currently, a major challenge for liquid gates is the observation of their switching behavior in real‐time and in situ, which directly limits the applicability across various scenarios. Here, a magneto‐responsive photonic liquid gate is developed to enable instantaneous, in situ monitoring of gas transport switching threshold through dynamic structural color changes. By leveraging particle reconfiguration within confined magnetic colloidal suspensions, both the interfacial mechanical properties and diffracted light are simultaneously tuned by the magnetic field, creating a direct correspondence between the gas transport switching thresholds and the observable color state of liquid gates. This visual system features responsive changes in both appearance and functionality, enabling real‐time modulation of gas release to be perceived with the naked eye. Furthermore, this material strategy, characterized by direct recognition, rapid predictability, and straightforward manipulation, opens new opportunities for visual chemical detection, dynamic fluid control, and multifunctional integrated systems.