Unraveling the Fluidity-Dependent Interactions of Isomeric Reduced Carbon Dots with Lipid Membranes for Bioimaging: A Multifaceted Spectroscopic and Microscopic Investigation

Carbon dots (CDs) are cutting-edge fluorescent nanomaterials renowned for their remarkable optical properties, outstanding biocompatibility, and efficient electron transfer dynamics. Among them, reduced-state carbon dots (r-CDs) have recently emerged as a novel subclass offering unique physicochemical characteristics. However, recent research has focused on developing enhanced bioimaging tools, highlighting reduced carbon dots for their exceptional properties and potential in advanced biomedical applications. Herein, we investigate the phase-dependent interactions of lipid membranes with different transition temperatures using r-CDs synthesized from biologically relevant three positional aminophenol derivatives (oAMP, mAMP, and pAMP). The r-CDs demonstrate different interactions with the DPPC membrane while showing similar interactions with the DOPC membrane, highlighting the crucial role of membrane fluidity in governing these interactions. These interactions are driven by the inherent hydrophobicity and hydrogen bonding ability of r-CDs. The spectroscopic and imaging techniques further support these findings through nanoscale topographical mapping. The results highlight the specific interactions of r-CDs with phase-dependent lipid membranes, enabling structure-dependent applications in bioimaging and drug delivery through complete insertion and membrane fusion, while noninteracting variants contribute to extracellular activities. This study establishes r-CDs as next-generation membrane probes, paving the way for precision-controlled bioimaging and molecular transport applications.