Enrichment and sensitive detection of polyphenolic compounds via β-cyclodextrin functionalized fluorescent gold nanorods

We report on a simple and rapid method for the enrichment of polyphenolic compounds (pPhCs) by means of gold nanorods whose surface was functionalized with a monolayer of beta-cyclodextrin (beta-CD-AuNRs) via thiol chemistry. Enrichment is based on the formation of inclusion complexes between pPhCs and beta-cyclodextrin through hydrophobic interactions and hydrogen bonding. Fourier transform infrared spectroscopy, mass spectrometry, and transmission electron microscopy were applied to confirm the inclusion of the pPhCs. Moreover, binding leads to a quenching of the red fluorescence of the AuNRs. This effect can be applied to quantify the polyphenols mangiferin, chrysin, and daphnetin with detection limits at 5 nM, 15 nM, and 20 nM concentrations, respectively. Water samples were spiked with pPhCs, and their extraction by using beta-CD-AuNRs gave recoveries ranging from 97.6 to 110.2 %.