Self-Assembled Luminescent Droplets from Graphene Quantum Dots Induced by a Gemini Surfactant for Selective Detection of Mercury(II)

Herein, we report the fabrication of a new class of luminescent coacervate droplets from graphene quantum dots (GQDs) and a gemini surfactant in aqueous medium and utilized them toward detection of mercuric ions (Hg²⁺). The self-assembly of negatively charged GQDs and positively charged gemini surfactant exists mainly because of their electrostatic interaction, leading to coacervation. Confocal laser scanning microscopy (CLSM) and field-emission scanning electron microscopy (FESEM) were utilized to analyze the luminescent and morphological structures of the self-assembled droplets. CLSM images display droplets that are naturally luminescent. The droplets exhibit luminescence quenching in the presence of Hg²⁺ ions. Our study demonstrates that Hg²⁺ ions interact through electrostatic interactions with the free carboxylate groups on the surface of GQDs in the hollow structure of the droplets. For Hg²⁺ ion sensing, the limit of detection (LOD) using the present system is found to be 30.5 nM, which is substantially lower than that of many of the previously reported similar systems. The sensor demonstrated high sensitivity for Hg²⁺ ions and exhibited a strong linear correlation within the concentration range of 100-500 nM. The current results indicate that the flexibility of surface ligands and organic nanoparticles in hybrid droplets plays a crucial role in the development of multifunctional materials for diverse applications.