Self-Destructive Structural Color Liquids for Time–Temperature Indicating

Vaccines are undoubtedly a powerful weapon in our fight against global pandemics, as demonstrated in the recent COVID-19 case, yet they often face significant challenges in reliable cold chain transport. Despite extensive efforts to monitor their time-temperature history, current time-temperature indicators (TTIs) suffer from limited reliability and stability, such as difficulty in avoiding human intervention, inapplicable to subzero temperatures, narrow tracking temperature ranges, or susceptibility to photobleaching. Herein, we develop a class of structural color materials that harnesses dual merits of fluidic nature and structural color, enabling thermal-triggered visible color destruction based on triggering agent-diffusion-induced irreversible disassembly of liquid colloidal photonic crystals for indicating the time-temperature history of the cold chain transport. These self-destructive structural color liquids (SCLs) exhibit inherent irreversibility, superior sensitivity, tunable self-destructive time (minutes to days), and a wide tracking temperature range (-70 to +37 °C). Such self-destructive SCLs can be conveniently packaged into flexible TTIs for monitoring the storage and exposure status of diverse vaccines via naked-eye inspection or mobile phone scanning. By overcoming the shortcomings inherent in conventional TTIs and responsive photonic crystals, these self-destructive SCLs can increase their compatibility with cold chain transport and hold promise for the development and application of the next-generation intelligent TTIs and photonic crystals.