This study investigates the interaction between ascorbic acid-derived carbon dot nanoparticles (CD-NPs) and phospholipid bilayers, key components of cellular membranes. CD-NPs, synthesized via a hydrothermal method using ascorbic acid, exhibit biocompatibility, making them promising candidates for drug delivery applications. The interaction of CD-NPs with cell membranes is critical for effective drug delivery to target cells. It is influenced by the physicochemical properties of both CD-NPs and phospholipid bilayers.
CD-NPs were synthesized by heating a 114 mM aqueous ascorbic acid solution in an autoclave. By varying the temperature and heating time—180°C for 6 hours, 180°C for 11 hours, 180°C for 20 hours, 180°C for 24 hours, 200°C for 24 hours, and 220°C for 48 hours—the particle size decreased from 480 nm to 128 nm, 82 nm, 53 nm, 5 nm, and finally 3 nm, respectively. Heating the solution at 220°C for 48 hours resulted in stable nanoparticles with an average size of 3–5 nm.
This work examines the interactions of CD-NPs with phospholipid bilayers using Dynamic Light Scattering (DLS). The POPC phospholipid bilayers exhibited an average size of 360 nm, while the CD-NPs exhibited an average size of 5 nm, as determined by DLS. Upon mixing various concentrations of CD-NPs with the phospholipid bilayers, DLS data revealed significant size changes in the combined systems, depending on the phospholipid-to-CD-NP ratios (%v/v). At a 1:1 ratio, three peaks were observed at 17 nm, 53 nm, and 110 nm. However, at 1:5, 1:10, and 1:100 ratios, only one peak at 110 nm was observed. The peak intensity increased as the concentration ratio shifted from 1:5 to 1:10 and 1:100. This data supports the conclusion that CD-NPs interact with and penetrate the phospholipid bilayers, localizing within vesicles. Additionally, the phospholipid bilayers, after interaction with the CD-NPs, appeared to divide into smaller-sized vesicles.
Future work will further investigate these interactions using Transmission Electron Microscopy (TEM) imaging. In addition, 5-doxyl phosphocholine (5-DPC) and cholestane (CLS) spin labels are being incorporated into the model phospholipid bilayers and analyzed using Electron Paramagnetic Resonance (EPR) spectroscopy. Collectively, the results from DLS, EPR, and TEM techniques are expected to complement one another, demonstrating the integration of CD-NPs into phospholipid bilayers. These findings highlight the potential of CD-NPs as carriers in drug delivery systems, with their biocompatibility and ability to localize within lipid membranes further supporting their promise for developing novel therapeutic platforms.