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

Nanosized titanium dioxide (TiO 2 ) particles are commonly present in TiO 2 food additives (E171) and have been associated with potential adverse effects on health. However, little knowledge is available regarding the interactions between TiO 2 nanoparticles (NPs) and other food components, such as flavonoids. In this study, we aim to study the molecular interactions between TiO 2 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 TiO 2 NPs. The results from SERS analysis clearly demonstrated that DDN and TDN could bind TiO 2 NPs with the functional groups 3′-OH and 4′-OH on ring B and formed charge-transfer complexes. However, 5DN with functional groups C═O on ring C and 5-OH on ring A could not bind TiO 2 NPs. Knowledge on the molecular interactions between TiO 2 NPs and food components, such as flavonoids, will facilitate the understanding of the fate of TiO 2 NPs during food processing and in the gastrointestinal tract after oral consumption.