Mercury ion-mediated “molecular beacon” integrating with hybridization chain reaction: Application to fluorescence turn-on detection of glutathione by using quantum dots and Ru complex

A fluorescence turn-on strategy is described for the detection of glutathione (GSH) based on mercury ion (Hg2+)-mediated molecular beacons (MBs) integrating with hybridization chain reaction (HCR) coupled with quantum dots (QDs) and Ru complex. Specifically, the thymine-Hg2+-thymine (T-Hg2+-T) ligation facilitates the single-stranded oligonucleotide into MBs with a hairpin structure if GSH is absent. This prevents the occurrence of HCR on magnetic microparticles (MMPs), and thus allows the fluorescence quenching of Ru toward QDs in supernate. If, However, GSH is present, the competition binding between GSH and Hg2+ changes MBs strand into open form, resulting in the hybridization with another single-stranded DNA conjugated on MMPs with a sticky tail left. Hence, double-stranded (dsDNA) polymers on MMPs are formed through HCR. Obvious fluorescence increase of QDs is obtained due to the strong affinity of Ru complex to dsDNA on MMPs. The fluorescence intensity of QDs is directly related to GSH concentration. Under the optimal conditions, the approach exhibits high sensitivity to GSH with a detection limit of 8.2 nM. This method is further employed to evaluate cellular GSH levels by analyzing cell lysates, demonstrating good consistencies with fluorescence imaging and commercial GSH kit.