Disposable Strip Biosensor for Visual Detection of Hg2+ Based on Hg2+-Triggered Toehold Binding and Exonuclease III-Assisted Signal Amplification

A disposable strip biosensor for the visual detection of Hg2+ in aqueous solution has been constructed on the basis of Hg2+-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 Hg2+. binding with the help of T-Hg2+-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 Hg2+ as low as I pM without instrumentation. This sensing system also displays remarkable specificity to Hg2+ against other possible competing ions. This sensor is robust and can be applied to the reliable monitoring of spiked Hg2+ 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 Hg2+ in environmental and biological samples.