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

Abstract

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 nanoparticles (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 clearly 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═O 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.