Responsive structural colors as interfacial sensors: Mechanism of mass transport and interfacial phenomena

Responsive structural color materials emerge from the physical interaction of light with nanoscale architectures rather than from molecular absorption. Moving beyond phenomenological descriptions of color change, this review points out responsive dynamic materials as functional porous media. Analyte transports thermodynamically modulate optical properties through the nanoconfined pore network, and interfacial interactions at pore walls. This framework reveals key design parameters linking structure to performance. Pore tortuosity governs response time, while analyte adsorption capacity determines sensitivity. These mass transport and interfacial processes collectively alter key structural parameters including effective refractive index and lattice spacing, which are then transduced into visible optical shifts via Bragg diffraction, plasmonic resonance, or other structural coloration mechanisms. We systematically analyze how pore architecture influences analyte transport kinetics, and how interfacial thermodynamics from adsorption isotherms to polymer swelling equilibria control response sensitivity and selectivity. We also summarized emerging industrial applications of structural color sensors, particularly in intelligent packaging for real-time freshness monitoring, pathogen detection, and gas sensing. We critically discuss practical challenges, including nonspecific adsorption, fouling, limited selectivity, and long-term stability, and present interfacial engineering strategies to overcome these barriers. For the first time, this review establishes a quantitative cascade from analyte concentration to optical readout, thereby providing a rational design pathway for next-generation structural color sensors in food safety, environmental monitoring, and beyond.