Liquid‐in‐Liquid Prints: High‐Density Biochemically Encoded Information Preserved in Microdroplet Arrays

Abstract Liquids are dense repositories of information, challenged only by how well their compositions are defined, preserved, accessed, or measured. The precise spatial patterning of solutes within a bulk liquid is challenging since diffusion disperses local concentrations and thereby attenuates functionality. Herein, a new concept is introduced for writing and preserving information in the liquid state through liquid‐in‐liquid microdroplet array printing. This technology produces fine resolution, 2D liquid structures, composite of indexed water‐in‐oil droplet pixels each with a precise composition, a high spatial resolution and a tight inter‐pixel pitch. With extreme control over droplet composition and by applying standard and custom encoding schemes, various forms of information are written biochemically such as images, QR codes, text characters and words. As a composite material, reversible phase transitions between dissolved liquid and crystallized solid states control information encryption and decryption. Compared to current liquid printing and chemical encoding paradigms, ours introduces a fundamentally new precedent for deterministically programming information release, exchange or decay without stimuli or physical processing. Further computational principles such as error correction and information storage are demonstrated. These micro‐liquid patterns are relevant to any application based on precise liquid handling such as information theory, materials design and biological assays.