Fluorescence resonance energy transfer-based ratiometric fluorescent probe for detection of Zn(2+) using a dual-emission silica-coated quantum dots mixture.

In this work, we report the design and application of a new ratiometric fluorescent probe, which contains different-colored quantum dots (QDs) as dual fluorophores, ultrathin silica shell as spacer, and meso-tetra(4-sulfonatophenyl)porphine dihydrochloride (TSPP) as receptor, for Zn(2+) detection in aqueous solution and living cells. In the architecture of our designed probe, the silica shell plays the key roles in controlling the locations of QDs, TSPP, and Zn(2+), preventing the direct contact between QDs and Zn(2+) but affording fluorescence resonance energy transfer (FRET) from dual-color QDs to TSPP. In the presence of Zn(2+), the analyte-receptor reaction changes the absorption in the range of the Q-band of TSPP and accordingly the efficiencies of two independent FRET processes from the dual-colored QDs to the acceptor, respectively, leading to fluorescence enhancement of green-emission QDs whereas fluorescence quenching of yellow-emission QDs. Benefiting from the well-resolved dual emissions from different-colored QDs and the large range of emission ratios, the probe solution displays continuous color changes from yellow to green, which can be clearly observed by the naked eye. Under physiological conditions, the probe exhibits a stable response for Zn(2+) from 0.3 to 6 μM, with a detection limit of 60 nM in aqueous solutions. With respect to single-emission probes, this ratiometric probe has demonstrated to feature excellent selectivity for Zn(2+) over other physiologically important cations such as Fe(3+) and Cu(2+). It has been preliminarily used for ratiometric imaging of Zn(2+) in living cells with satisfying resolution.