Protein-rich marine Spirulina for synthesizing biocompatible carbon dots with high quantum yield for fluorescent yarns

Abstract

Carbon dots (CDs) are fluorescent carbon nanomaterials that can be widely used in multiple areas as an optical functional material. Compared to commercial chemicals used to synthesize CDs, biomass offers environmental friendliness and biocompatibility, especially for biomedical or human-contact applications. However, biomass-derived CDs often suffer from low quantum yields (QYs) and inconsistent quality due to compositional complexity. In this study, we demonstrate a new strategy utilizing Spirulina, a marine microalga that has high phycocyanin content, as the sustainable nitrogen-rich precursor for high-performance CD production. By refining Spirulina to extract high-purity phycocyanin and incorporating urea doping, we achieved nitrogen-enriched CDs (PU-CDs) with a QY of 20.4%, which was 1.3-fold and 2.4-fold higher than those from purified phycocyanin and raw Spirulina, respectively; the QY remained stable when the experiments were replicated 6 times with a standard deviation value of 1.14. Meanwhile, the PU-CDs show excellent biocompatibility and low cytotoxicity (93% cell viability at 500 µg mL⁻¹), which make them suitable for bioapplications. As a proof of concept, the as-prepared PU-CDs were successfully integrated into nylon fibers via a dyeing or electrospinning approach. PU-CDs in yarns demonstrate strong fluorescence under UV light and exceptional photostability (retaining 92.4% intensity after 20 h). This work highlights a reproducible and eco-friendly approach to synthesize biomass-based CDs for promising anti-counterfeiting textiles, improving consistency in precursor purity and performance.