SERS-Based Flavonoid Detection Using Ethylenediamine-β-Cyclodextrin as a Capturing Ligand

Ethylenediamine-modified β-cyclodextrin (Et-β-CD) was immobilized on aggregated silver nanoparticle (NP)-embedded silica NPs (SiO₂@Ag@Et-β-CD NPs) for the effective detection of flavonoids. Silica NPs were used as the template for embedding silver NPs to create hot spots and enhance surface-enhanced Raman scattering (SERS) signals. Et-β-CD was immobilized on Ag NPs to capture flavonoids via host-guest inclusion complex formation, as indicated by enhanced ultraviolet absorption spectra. The resulting SiO₂@Ag@Et-β-CD NPs were used as the SERS substrate for detecting flavonoids, such as hesperetin, naringenin, quercetin, and luteolin. In particular, luteolin was detected more strongly in the linear range 10-7 to 10-3 M than various organic molecules, namely ethylene glycol, β-estradiol, isopropyl alcohol, naphthalene, and toluene. In addition, the SERS signal for luteolin captured by the SiO₂@Ag@Et-β-CD NPs remained even after repeated washing. These results indicated that the SiO₂@Ag@Et-β-CD NPs can be used as a rapid, sensitive, and selective sensor for flavonoids.