Poly(adenine)-mediated DNA-functionalized gold nanoparticles for sensitive detection of mercury ions in aqueous media

In this work, a facile and sensitive colorimetric sensor for Hg²⁺ ions based on poly (adenine)-mediated DNA-functionalized gold nanoparticles (Au NPs) is reported. One DNA sequence consisting of poly-A and T-rich DNA was designed rationally. Poly-A was used as an anchoring block to bind tightly to Au NPs, and T-rich DNA was utilized for specific recognition of Hg²⁺ ions. With the assistance of poly-A, T-rich DNA was easily introduced onto the surface of Au NPs and kept an upright orientation. In the presence of Hg²⁺ ions, T base binding with Hg²⁺ ions results in the formation of "T-Hg²⁺-T" among the Au NPs, which caused aggregation of the Au NPs and a subsequent change in the color of the solution, from wine red to grayish blue. On this occasion, the limit of detection (LOD) was 3.75 nM Hg²⁺ ions with a linear range from 5 nM to 200 nM, as measured by UV-Vis spectroscopy. Moreover, successful application of this method for the detection of Hg²⁺ ions in real samples was demonstrated.