Colorimetric sensing of trace UO2(2+) by using nanogold-seeded nucleation amplification and label-free DNAzyme cleavage reaction.

In pH 4.4 HAC-NaAC buffer solution at 80 °C, nanogold particles (NG) strongly enhanced the slow, colored reaction of Ag(i)-gallic acid to form nanosilver particles, which exhibited a strong surface plasmon resonance (SPR) absorption peak at 460 nm, but the aggregated nanogold particles (ANG) exhibited a weak enhancement. The increased absorption value at 460 nm was linear to the NG concentration in the range of 3.6-72.5 ng mL(-1) Au. In pH 5.5 MES buffer solution at 80 °C, single-stranded substrate DNA and DNAzyme hybridize to form double-stranded DNA (dsDNA). The presence of uranyl (UO(2)(2+)) resulted in cleavage of the substrate DNA of dsDNA, releasing a short, single-stranded DNA that can be adsorbed onto the NG and protect them from aggregation; those un-adsorbed NG were aggregated to ANG. As the UO(2)(2+) concentration increased, more short, single-stranded DNA were released, and more NG were protected by the cleavage of substrate single-strand DNA, so the colored particle reaction and the absorption value at 460 nm enhanced linearly. On those grounds, 0.083-0.67 nmol L(-1) UO(2)(2+) can be detected rapidly by this colorimetric sensing assay, with a detection limit of 0.04 nmol L(-1).