Label-Free Fluorescent Determination of Sunset Yellow in Soft Drinks Based on an Indicator-Displacement Assay

Abstract

This work reported a fluorescence sensing platform for Sunset Yellow (SY) determination based on competitive host-guest interaction between cucurbit[7]uril (CB7) and signal probe/target molecules. Luteolin/epigallocatechin gallate (EGCG) and SY were selected as the probe and target molecules, respectively. When luteolin or EGCG entered the CB7 host, its fluorescence significantly improved. However, upon the presence of SY in the performed luteolin·CB7 or EGCG·CB7 complex, this led to a remarkable decrease in fluorescence. This result was due to the fact that the binding constant of CB7/SY (4.9×104 M−1) was greater than that of CB7/luteolin (3.2×103 M−1) or CB7/EGCG (4.8×103 M−1). The fluorescence intensities of CB7/luteolin and CB7/EGCG complexes decreased linearly with increased SY concentration ranges of 0.5–50.0 and 2.0–50.0 μM. The proposed method had detection limits of 0.12 and 0.45 μM and was successfully used to determine SY samples with good recoveries ranging from 96.3% to 103.8%. This competitive mode provided a promising fluorescence assay strategy for potential applications in food safety.