Dynamic light scattering for probing metal ion induced aggregation of carbon dots

Abstract

Aggregate behaviour of carbon dots (СDs) in aqueous solutions in the presence of various metal ions was studied by means of dynamic light scattering (DLS). Colloidal CDs with different surface chemistries were exposed to Cu²⁺, Pb²⁺, Fe³⁺, Gd³⁺, and Ag⁺ ions at micromolar concentrations. The DLS measurements revealed a pronounced increase in hydrodynamic size upon metal ion addition, indicating the formation of metal-mediated CDs agglomerates. A distinct saturation of aggregate size values is observed, suggesting a finite number of accessible coordination sites on the CDs surface.To quantitatively compare ion-specific effects, an empirical aggregation ion efficiency parameter (IAE), defined as the ratio of the saturation aggregate size to the corresponding saturation ion concentration, is introduced. IAE parameter strongly depends on the nature of the metal ion and does not correlate directly with its charge state. The presented experimental approach demonstrates that the DLS-based aggregation analysis provides valuable structural information on metal-CDs interactions and can efficiently complement optical sensing techniques, contributing to the development of advanced nanoanalytical strategies for heavy metal detection.