Quantum dots (QDs)-based fluoresecnce resonance energy transfer (FRET) processes are implemented to develop a variety of optical sensors. Herein we report the construction of dual-colored QDs-based binary FRET (BiFRET) systems and demonstrate their feasibility for ratiometric detection of Zn2+. The QD-FRET system was constructed by first coating of spacer on the QD donor, followed by loading of multiple acceptors, meso-tetra(4-sulfonatophenyl)porphine dihydrochloride (TSPP), on the spacer. The spacer thickness controlled the QD-TSPP FRET distance, determining the FRET efficiency. Silica, DNA and poly(dA) were used, respectively, to control the QD-TSPP FRET distance and demonstrated different FRET efficiencies. The biocopolymer poly(dA) had the minimal space thickness of 1.7 nm, achieving the highest QD-TSPP FRET efficency of 70%. By mixing two QD-FRET systems, a QD-BiFRET system (FRET-1 for 517QD-TSPP, FRET-2 for 560QD-TSPP) was facilely prepared, which could be used for Zn2+ detection. In the absence of Zn2+, FRET-1 is efficient while FRET-2 is inefficient. In the presence of Zn2+, the chelation of Zn2+ changed the TSPP absorption at 515 nm and 555 nm in an oposite manner. Accordingly, FRET-1 became inefficient and FRET-2 became efficient. As a result, the QD-BiFRET system realized ratiometric detection of Zn2+. The system with the poly(dA) spacer had obtained the detection limit of 1 nM, which is sixtieth part of that of the system with the silica spacer.
This work is financially supported by NSFC (Grant: 21775021).