Sea-buckthorn-seed composition inspired synthesis of carbon dots as robust fluorescent dyes

Fluorescent dyes have been widely used for textile, which are required to have brightness, processability, durability and safety. Organic fluorophores, inorganic phosphors and semiconductor quantum dots have been used as fluorescent dyes, while, they may suffer from photobleaching, migration, poor water processability or heavy-metal concerns. Biomass-derived carbon dots (CDs) are therefore emerging as a new class of fluorescent dyes because of their unique properties, such as biocompatibility, tunable fluorescent colors, metal-free-composition and excellent water-solubility. However, they are often limited by their low photoluminescence quantum yield (PLQY), unclear formation pathways and poor batch-to-batch reproducibility, due to the uncontrolled complexity of natural feedstocks. Here, sea buckthorn seed fractions were used as a compositionally differentiated platform to develop component-analysis-guided CDs synthesis. High-performance liquid chromatography (HPLC) was used to quantify soluble sugars, sugar alcohols, glucan-derived fragments and organic acids before and after hydrothermal treatment of the sea buckthorn seed, thereby identifying the reactive components involved in carbonization. Based on the HPLC result, a twelve-formulation precursor matrix is established via twelve sets of reactions using high-purity precursors to identify individual precursor effects, multicomponent synergy and nitrogen surface-state passivation. The HPLC-mimicking Mix-6 reproduced the main biomass-derived emission, whereas urea-enriched Mix7-CDs increased the PLQY to 23.8% by creating N-containing emissive and suppressing non-radiative traps, which is significantly higher than that of the P-CDs (5.8%) or F-CDs (6.2%). As a proof-of-concept, the as-prepared Mix7-CDs were used as fluorescent dyes for polyamide yarns, which enabled UV-readable nylon yarn/fabric labels with good photostability, washing retention and preliminary cytocompatibility, providing a precursor-to-dye design route for sustainable fluorescent polyamide textiles.