Scheme 1. Schematic Illustration of the Synthetic Protocol Used to Introduce the Biotin Functionality at the Reducing End of Tunicate Nanocrystals (Represented as Gray Rectangles), Involving a First Step of Oxidation of Carbonyl Groups and a Second Step of the Acid–Amine Coupling by N-Hydroxysuccinimide (NHS)–N-(3-Dimethylaminopropyl)-N-ethylcarbodiimide Hydrochloride (EDC) Chemistry.

The structures of the two biotin derivatives: (+)-biotinamidohexanoic acid hydrazide (HC-Biot) and biotin-dPEG7-NH₂ (PEG-Biot) (left bottom). Dimensions of t-CNC and biotin derivatives are not scaled.