Structural Chirality Transfer from Agar Hydrogel to Chiral Luminescent Carbon Dots via Hydrothermal Carbonization

Chiral carbon dots are commonly constructed using chiral molecular precursors, heteroatom-associated asymmetric environments, or surface chiral ligands, but whether precursor-level hierarchical organization can be transformed into chiroptically active carbon nanostructures remains unclear. Here, we report chiroptically active fluorescent carbon dots derived from agar hydrogel. Under the present measurement conditions, the dispersed agar-chain control shows no detectable circular dichroism (CD), whereas the cooling-induced agar hydrogel exhibits a distinct CD response, indicating that gelation-induced supramolecular organization plays a critical role in the observed chiroptical activity. This hydrogel-derived organization leaves a measurable chiroptical imprint in the resulting agar-derived carbon dots. The CD response reaches a maximum after 12 h of treatment and becomes negligible upon prolonged carbonization for 24 h, while fluorescence continues to increase. This divergence suggests that chiroptical activity and fluorescence follow different formation pathways: the former is associated with a hydrogel-derived chiroptical imprint that is most effectively expressed at an intermediate carbonization stage, whereas the latter mainly arises from localized carbonized emissive domains, oxygen-rich surface states, and defect-related sites. The resulting Agar-CDs are stable in water and interact with bovine serum albumin, modulating protein fluorescence and amplifying its CD response at the bio-nano interface. This work establishes a structural-inheritance strategy for constructing chiral fluorescent carbon dots and demonstrates their potential for bionano interfacial chiral amplification.