Magnetic beads-based DNAzyme recognition and AuNPs-based enzymatic catalysis amplification for visual detection of trace uranyl ion in aqueous environment

We herein developed a novel biosensor for the visual detection of trace uranyl ion (UO22+) in aqueous environment with high sensitivity and specificity by using DNAzyme-functionalized magnetic beads (MBs) for UO22+ recognition and gold nano-particles (AuNPs)-based enzymatic catalysis oxidation of TMB (3,3′,5,5′-tetramethylbenzidine sulfate) for signal generation. The utilization of MBs facilitates the magnetic separation and collection of sensing system from complex sample solution, which leads to more convenient experimental operation and more strong resistibility of the biosensor to the matrix of sample, and the utilization of AuNPs-based enzymatic catalysis amplification greatly improved the sensitivity of the biosensor. Compared with the previous DNAzyme-based UO22+ sensors, the proposed biosensor has outstanding advantages such as relative high sensitivity and specificity, operation convenience, low cost and more strong resistibility to the matrix of sample. It can be used to detect as low as 0.02 ppb (74 pM) of UO22+ in aqueous environment by only naked-eye observation and 1.89 ppt (7.0 pM) of UO22+ by UV-visible spectrophotometer with a recovery of 93-99% and a RSD≤5.0% (n=6) within 3 h. Especially, the visual detection limit of 0.02 ppb (74 pM) is much lower than the maximum allowable level of UO22+ (130 nM) in the drinking water defined by the U.S. Environmental Protection Agency (EPA), indicating that our method meets the requirement of rapid and on-site detection of UO22+ in the aqueous environment by only naked-eye observation.