A gold nanoparticle-based colorimetric mercury(II) biosensor using a DNA probe with phosphorothioate RNA modification and exonuclease III-assisted signal amplification

Herein, we report a rapid and sensitive colorimetric detection of Hg²⁺ by designing a specific DNA probe with phosphorothioate RNA modification (PS-probe) for Hg²⁺ recognition and utilizing DNA-modified gold nanoparticles (DNA-AuNPs) as the transducer. The distance between two DNA-AuNPs is controlled by a linker DNA, providing the linker DNA-regulated aggregation or dispersion status of AuNPs in solution. Exonuclease III (Exo III) can trigger the recycled digestion of linker DNA strands, inhibiting the reformation of aggregated nanoparticles and hence leading to a color shift from purple to red. However, the Hg²⁺-induced cleavage of the PS-probe can efficiently prevent the digestion of linker DNA strands by Exo III and hence reassemble the modified AuNPs to form aggregates in purple color. Thus, a positive correlation between the linker DNA strands left and the addition of Hg²⁺ provides a quantitative basis for Hg²⁺ sensing. A linear range of A₅₂₀/A₇₀₀ versus Hg²⁺ concentration is achieved in the range 2–100 nM associated with a detection limit as low as 1.30 ± 0.04 nM. Moreover, the biosensor exhibits excellent selectivity for Hg²⁺. The strong selectivity behavior was confirmed by recoveries ranging from 96 to 114% in real water samples.