Characterization of the Interactions between Titanium Dioxide Nanoparticles and Polymethoxyflavones Using Surface-Enhanced Raman Spectroscopy

Nanosized titanium dioxide (TiO2) particles are commonly present in TiO2 food additives (E171) and have been associated with potential adverse effects on health. However, little knowledge is available regarding the interactions between TiO2 nanopartides (NPs) and other food components, such as flavonoids. In this study, we aim to study the molecular interactions between TiO2 anatase NPs and three structurally closely related polymethoxyflavones (PMFs, flavonoids found in citrus fruits), namely, 3',4'-didemethylnobiletin (DDN), 5-demethylnobiletin (5DN), and 5,3',4'-tridemethylnobiletin (TDN), using ultraviolet-visible (UV-vis) spectrometry and surface-enhanced Raman spectroscopy (SERS). In the UV-vis absorption spectra, bathochromic effects were observed after DDN and TDN conjugated with TiO2 NPs. The results from SERS analysis dearly demonstrated that DDN and TDN could bind TiO2 NPs with the functional groups 3'-OH and 4'-OH on ring B and formed charge-transfer complexes. However, 5DN with functional groups C = 0 on ring C and 5-OH on ring A could not bind TiO2 NPs. Knowledge on the molecular interactions between TiO2 NPs and food components, such as flavonoids, will facilitate the understanding of the fate of TiO2 NPs during food processing and in the gastrointestinal tract after oral consumption.