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A novelty aptasensor for ultrasensitive detection of Hg2+ is developed, exploiting the combination of plasmonic properties of gold nanoparticles (AuNPs) and exonuclease III (Exo III)-assisted target recycling for signal amplification. In the presence of Hg2+, a DNA duplex can be formed due to the strong coordination of Hg2+ and T bases of single-stranded DNA (ssDNA) probe. Exo III digests the DNA duplex from the 3′ to 5′ direction, resulting in the releasing of Hg2+. Then, the released Hg2+ binds with another ssDNA probe through T-Hg2+-T coordination. After Exo III-assisted Hg2+ cycles, numerous ssDNA probes are exhausted, which promotes poly(diallyldimethylammonium chloride) (PDDA)-induced AuNP aggregation, leading to an obvious color change and aggregation-induced plasmon red shift of AuNPs (from 520 to 610 nm). Therefore, this biosensor is ultrasensitive, which is applicable to the detection of trace level of Hg2+ with a linear range from 5 pM to 0.6 nM and an ultralow detection limit of 0.2 pM. Furthermore, it enables visual detection of Hg2+ as low as 50 pM by the naked eye. More importantly, the assay can be applied to the reliable determination of spiked Hg2+ in sea water samples with good recovery. [ABSTRACT FROM AUTHOR]

A facile plasmonic nanoplatform was developed for rapid and sensitive determination of nucleic acid. Hg2+-regulated molecular beacon (MB, hairpin) containing rich thymine (T) bases at both ends is used as the probe. A hairpin structure can be formed in the MB probe due to the strong binding of Hg2+ to T. However, in the presence of target DNA, the hairpin structure is opened owing to target DNA-specific hybridization with the aptamer. Simultaneously, the opened MB interacts with poly(diallyldimethylammonium chloride) (PDDA) and hinders PDDA-induced aggregation of AuNPs, accompanied by a color change from blue to red and a decrease in absorption ratio (A620/A520). Hence, a good linear relationship was observed between the decreased absorption ratio (A620/A520) and DNA concentration ranging from 0.02 to 2 nmol/L with a low detection limit of 4.42 pmol/L. Moreover, this nanoplatform has been successfully utilized to discriminate between perfect target and mismatch sequences. More importantly, the bioassay is simple, versatile, rapid, and cost-effective compared with other common methods, which holds great promise for clinical diagnosis and biomedical application. [ABSTRACT FROM AUTHOR]

Activation mechanism of the nanoplatform AuNCs@MnO 2 nanosheets for GSH detection and intracellular imaging. [Display omitted] • A novel GSH-switched fluorescence nanoprobe has been constructed based on the integration between the inner filter effect of MnO 2 nanosheets and GSH-induced enhanced fluorescence of AuNCs. • The nanoplatform exhibits a high sensitivity for the detection of GSH with a low limit detection of 68 nM. • The nanoplatform achieves outstanding selectivity towards intracellular GSH over cysteine, homocysteine and ascorbic acid. • And that, it can selectively monitoring the GSH in human serum and the fluorescence imaging of endogenous GSH in living cell. Glutathione (GSH) plays a critical role in biological defense system and is associated with numerous human pathologies. However, it still remains a challenge for fluorescent detection of GSH over cysteine (Cys) and homocysteine (Hcy) because of their similar structures. In this work, MnO 2 nanosheets can efficiently quench the fluorescence of gold nanoclusters (Met-AuNCs) prepared by blending methionine and HAuCl 4 owing to their superior absorption capability. However, GSH can reduce MnO 2 nanosheets into Mn2+ which leads to the fluorescence recovery of Met-AuNCs. More intriguingly, GSH can dramatically and selectively enhance the fluorescence intensity of Met-AuNCs. Hence, a low background, ultrasensitive fluorescent detection of GSH was obtained with a detection limit of 68 nM. Moreover, the assay has been successfully used for GSH detection in human serum samples and cellular imaging with high selectivity over Cys and Hcy. [ABSTRACT FROM AUTHOR]