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. 2021 Jan 29;12:699. doi: 10.1038/s41467-021-20908-y

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© The Author(s) 2021

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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Fig. 4 — a A geminate label with two different messages of a green “2019” reflective pattern and a cyan “2020” fluorescent pattern. In program, the color of the rectangles represents the reflection colors of the microdroplets and the slashes in the rectangles represent the microdroplets with fluorescence. The scale bar is 1 cm. b–g Encryption and decryption of an enhanced-security-level geminate label created by eight kinds of microdroplets in a “pixelated” array (21 × 21). The fluorescent QR code of “LC” is concealed behind a colorful reflective “Christmas tree”, which can be decrypted by smartphones upon UV irradiation. Each pixel is 2.0 mm × 2.0 mm × 400 μm, and the distance between two pixels is 0.5 mm.