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We herein present a simple, low-cost, and ultrasensitive colorimetric sensing strategy for the detection of mercury ions (Hg2+) that takes advantage of the natural pore structure in rose petals to encapsulate gold nanoparticles (AuNPs). AuNPs easily aggregate in high salt concentrations, which restrict their application, for example, as a catalyst in real sample analysis. Rose petals offer a three-dimensional (3D) space for more efficient dispersability of AuNPs in their extensive network of channels, which will increase the specific surface area, thereby enhancing the catalytic capability of AuNPs. The presence of Hg2+ triggers the formation of gold amalgam, which results in remarkable enhancement of the catalytic ability of citrate-capped AuNPs. On the basis of this effect, a colorimetric signal amplification is achieved via the use of gold amalgam to catalyze the reaction of methylene blue (MB) and sodium borohydride. A limit of detection (LOD) as low as 10 fM can be obtained by naked eye observation. Our sensor has promising potential for detection and quantitation of Hg2+ in environmental samples. [ABSTRACT FROM AUTHOR]

Robust but ultrasensitive aptasensors with an ability to detect lower concentrations of heavy metal ions enable the detection of serious environmental and health issues. We herein develop a label-free aptasensor for ultrasensitive detection of the silver ion (Ag + ) utilizing gold nanoparticle (AuNP) intensity measurement methodology by dark-field microscopy, which is based on target Ag + and exonuclease III (Exo III)-dependent DNA cleavage recycling amplification. In the presence of target Ag + , thymine (T) bases at two termini of hairpin DNA bind with Ag + through C-Ag + -C coordination to form a DNA duplex, Exo III can recognize the blunt 3' end of the DNA duplex and digest it from the 3' end to the 5' direction. The released target Ag + then binds with another hairpin DNA via C-Ag + -C pairs. After many cycles of the digestion of the DNA duplex by Exo III, numerous remaining single-stranded DNA (ssDNA) are generated. These ssDNA are absorbed on the surface of AuNPs, enhancing the repulsion force between AuNPs, which further promotes the dispersion of AuNPs, leading to a significantly decreased intensity of yellow and red dots (aggregated AuNPs) under dark-field microscopy observation, in contrast to that of the blank solution (without target Ag + ). On this basis, the detection limits of 41 and 39 fM were achieved for Ag + in Tris-HCl buffer and river water, respectively.