Substantial Enhancement of the Antioxidant Capacity of an alpha-Linolenic Acid Loaded Microemulsion: Chemical Manipulation of the Oil-Water Interface by Carbon Dots and Its Potential Application

Various active ingredients play a crucial role in providing and supplementing the nutritional requirements of organisms. In this work, we attempted to chemically manipulate the interfacial microstructure of oil-water microemulsions (ME) with carbon dots (CDs), concentrating on substantially enhancing the antioxidant capacity of alpha-linolenic acid (ALA). To this end, CDs were synthesized and introduced into an ME. The molecular interaction of surfactant with CDs was investigated by Fourier-transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR). The microstructure of the ME was monitored by transmission electron microscopy (TEM) and cryo-electron microscopy (cryo-EM). The cryo-EM result showed the oil-water interface in the ME was better defined after the CDs were loaded, and H-1 NMR proved the CDs were distributed mainly at the interface. On the basis of these results, interfacial models were proposed. Final evaluation results demonstrated the stabilizing effect and oxidation-inhibition ability of the ALA-loaded ME was substantially enhanced after the introduction of the CDs, indicating a turn off effect of the interface. Interestingly, CDs do not affect the in vitro release of ALA, indicating a turn on effect of the interface. This work provided a successful interface manipulation with a nanocarrier that can be used for a large diversity of food nutraceuticals.