Validation of specific cation partitioning to molecular surfaces using fluorescent carbon quantum dots

Abstract

Specific salt effects are significantly involved in the aqueous colloidal solutions of proteins, nucleic acids, surfactants and nanomaterials. The mechanism of such effects has been systematically investigated here with a simple nanomaterial-based model system. Water-soluble fluorescent carbon quantum dots were synthesized for this purpose. This research work highlights the unique advantage offered by fluorescent carbon quantum dots to be utilized as a sensing probe for the detection of selective ion interactions based on their fluorescence turn-on response. Synthesized carbon quantum dots exhibited surface potential dependent strong fluorescence emission. It was further found that the functional group chemistry on the carbon quantum dot surface plays a crucial role in the ion partitioning. A remarkable enhancement of emission intensity observed in the presence of metal cations can be attributed to their relative tendency to form ion-pairs with the nanomaterial surface functionalities. Carbon quantum dots with deprotonated carboxylic groups on their surface showed a stronger affinity for strongly hydrated cations as compared to weakly hydrated cations. Uncharged yet polar nanomaterial surface, however, showed no selectivity towards different ions.