Ultrasensitive colorimetric strategy for Hg2+ detection based on T-Hg2+-T configuration and target recycling amplification

A novelty aptasensor for ultrasensitive detection of Hg 2+ 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 2+ , a DNA duplex can be formed due to the strong coordination of Hg 2+ 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 2+ . Then, the released Hg 2+ binds with another ssDNA probe through T-Hg 2+ -T coordination. After Exo III-assisted Hg 2+ 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 2+ 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 2+ as low as 50 pM by the naked eye. More importantly, the assay can be applied to the reliable determination of spiked Hg 2+ in sea water samples with good recovery.