Colorimetric determination of uranyl (UO22+) in seawater via DNAzyme-modulated photosensitization

Various DNA-modulated photosensitization schemes have been reported for various applications, but DNAzyme has not yet been included. Here, we found the DNAzyme with metal ion as cofactor could also be efficient in modulation of photosensitization process. The UO22+-specific DNAzyme can switch between double strand DNA (dsDNA) and single strand DNA (ssDNA) upon UO22+ cleavage, which can regulate the photosensitization process of SYBR Green I. Coupling with photosensitization-induced chromogenic reaction (TMB oxidation), a simple colorimetric sensor for UO22+ was developed accordingly. To increase the visual resolution of the proposed assay, a background color was supplied. Compared with the previous DNAzyme-based UO22+ sensors, the proposed assay featured label-free and simple. Besides, the tolerance for high salinity of this assay is appealing. The proposed assay offered a detection limit of 0.08 mu g/L with UV - vis detection and 0.5 mu g/L with the naked eye. With the proposed colorimetric assay, UO22+ levels in the range of 0.7-1.2 mu g/L (2.9-5.0 nM) were identified in high salinity seawater samples, with spike-recoveries ranging from 93% to 104%.