Construction of an off-on fluorescence sensing platform for FRET-based detection of coumarin in cosmetic samples

2-Hydroxypropyl-beta-cyclodextrin (2-Hp-beta-CD)-functionalized CdTe quantum dots (QDs) were used for coumarin-sensing with high sensitivity and selectivity. This fluorescence resonance energy transfer (FRET)-based sensor was established by attaching rhodamine 6G (Rh6G) to the QDs via a 2-Hp-beta-CD linker. Rh6G could get into the cavity of 2-Hp-beta-CD, and then trigger the FRET between the QDs and Rh6G, providing an "off" state of the QDs. However, the effect of FRET was weakened by the coumarin, because of its larger hydrophobic association constant with 2-Hp-beta-CD, resulting in the dissociation of Rh6G. In the presence of additive coumarin, the fluorescence intensity of QDs@2-Hp-beta-CD@Rh6G increases (an "on" state). The FRET-based off-on nanoprobe shows a good linear relationship in the range of 0-25 mu M with a good correlation coefficient (R2 = 0.9986). We also obtained an excellent result using this spectrophotometric method for coumarin sensing in cosmetics, which has potential for application in the biomedical area. We expect this sensing platform could be useful in other analogous nanoprobes in relevant fields. An off-on nanoprobe was constructed by attaching Rh6G to QDs via a linker. The UV-Vis absorption spectrum of Rh6G overlaps with the fluorescence emission spectrum of the QDs, causing FRET-based coumarin-sensing with high sensitivity and selectivity.