Abstract
Responsive optical materials offer real-time visual feedback to external stimuli by converting them into visible light signals, holding great promise in display, sensing, and information encryption. Typically, heterogeneous Janus droplets can exhibit vivid coloration induced by total internal reflection and interference (TIRI) at concave liquid–liquid interfaces. Yet, achieving stimuli-responsive TIRI-based structural colors remains a challenge due to the difficulty in controlling interface curvature and reflective behavior under external stimuli. Here, we report the fabrication of Janus droplets with tunable TIRI structural colors that respond to both surfactant composition and temperature. By tailoring surfactant formulation, the droplet morphology and interface curvature can be adjusted, enabling reversible modulation of structural color appearance, including both iridescent and non-iridescent modes depending on incident light conditions. Furthermore, the structural color can be reversibly or irreversibly switched on/off in response to temperature changes, due to phase transitions that alter light reflection at the concave interface. Owing to their temperature-dependent optical response and real-time visual signaling, these droplets can serve as single-use security labels for monitoring freeze history of freeze-sensitive pharmaceuticals, providing reliable indication of product integrity.
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The data that support the findings of this study are available from the corresponding authors upon request. Unprocessed raw data are provided as Supplementary Data 1. Source data are provided in this paper.
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Acknowledgements
This work was financially supported by the National Natural Science Foundation of China (52222304 and 52293474) and National Key R&D Program of China (2025YFE0100100). The authors gratefully acknowledge the Analytical & Testing Center (HUST) and the Research Core Facilities of Life Science (HUST) for their facility assistance.
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Y. X., M.T., J.X., and J.Z. conceived the idea and designed the experiments; Y.X. and M.T. prepared and characterized the optical behavior of Janus droplets; Y.X. and G.H. investigated the application of security labels in protecting freeze-sensitive pharmaceuticals; D.H. and M.Z. contributed to the analysis and discussion of the results; Y.X. and M.T. wrote the paper; J.X., S.-H.K., and J.Z. revised the manuscript; J.X. and J.Z. supervised the overall study.
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Xu, Y., Tian, M., Zhang, M. et al. Dual-responsive coloration of Janus droplets via total internal reflection and interference applied as single-use freezing indicators. Nat Commun (2026). https://doi.org/10.1038/s41467-026-70055-5
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DOI: https://doi.org/10.1038/s41467-026-70055-5
