Ultrasensitive colorimetric strategy for Hg detection based on T-Hg-T configuration and target recycling amplification.

A novelty aptasensor for ultrasensitive detection of Hg is developed, exploiting the combination of plasmonic properties of gold nanoparticles (AuNPs) and exonuclease III (Exo III)-assisted target recycling for signal amplification. In the presence of Hg, a DNA duplex can be formed due to the strong coordination of Hg and T bases of single-stranded DNA (ssDNA) probe. Exo III digests the DNA duplex from the 3' to 5' direction, resulting in the releasing of Hg. Then, the released Hg binds with another ssDNA probe through T-Hg-T coordination. After Exo III-assisted Hg cycles, numerous ssDNA probes are exhausted, which promotes poly(diallyldimethylammonium chloride) (PDDA)-induced AuNP aggregation, leading to an obvious color change and aggregation-induced plasmon red shift of AuNPs (from 520 to 610 nm). Therefore, this biosensor is ultrasensitive, which is applicable to the detection of trace level of Hg with a linear range from 5 pM to 0.6 nM and an ultralow detection limit of 0.2 pM. Furthermore, it enables visual detection of Hg as low as 50 pM by the naked eye. More importantly, the assay can be applied to the reliable determination of spiked Hg in sea water samples with good recovery.