Orthogonal Adsorption of Carbon Dots and DNA on Nanoceria

Carbon dots (CDs) are highly fluorescent nanomaterials with surface carboxyl and amino groups. However, their exact structure remains under debate. In this work, we probed the surface properties of CDs by physically adsorbing them onto various nanomaterials. Three types of nanomaterials, including CeO₂ nanoparticles (nanoceria), gold nanoparticles, and graphene oxide were tested. Among them, nanoceria strongly adsorbed the CDs and quenched their fluorescence. For the tested anions to compete with the CDs for adsorption, only phosphate and F^- induced desorption of the CDs from nanoceria, and the phosphate-induced desorption was less compared to that by F^-. This was opposite to the desorption of DNA from nanoceria, where phosphate induced more DNA desorption. Furthermore, using calcein and fluorescein as representative dyes for comparison, we conclude that the CDs might use their carboxyl groups to adsorb on nanoceria, while DNA uses its phosphate backbone for adsorption. This difference may explain their occupying different surface sites on nanoceria and different displacement by phosphate and F^-. Using nanomaterials as probes to understand the surface properties of CDs is effective, and such understanding might in turn be used for building hybrid materials for applications.