Disposable strip biosensor for visual detection of Hg(2+) based on Hg(2+)-triggered toehold binding and exonuclease III-assisted signal amplification.

A disposable strip biosensor for the visual detection of Hg(2+) in aqueous solution has been constructed on the basis of Hg(2+)-triggered toehold binding and exonuclease III (Exo III)-assisted signal amplification. Thymine-thymine (T-T) mismatches in the toehold domains can serve as specific recognition elements for Hg(2+) binding with the help of T-Hg(2+)-T base pairs to initiate toehold-mediated strand displacement reaction. Exo III-catalyzed target recycling strategy is introduced to improve the sensitivity. Using gold nanoparticles as a tracer, the output signals can be directly observed by the naked eye. The assay is ultrasensitive, enabling the visual detection of trace amounts of Hg(2+) as low as 1 pM without instrumentation. This sensing system also displays remarkable specificity to Hg(2+) against other possible competing ions. This sensor is robust and can be applied to the reliable monitoring of spiked Hg(2+) in environmental water samples with good recovery and accuracy. With the advantages of cost-effectiveness, simplicity, portability, and convenience, the disposable strip biosensor will be a promising candidate for point-of-use monitoring of Hg(2+) in environmental and biological samples.