“Turn-On” Fluorescent Sensor for Hg²⁺ Based on Single-Stranded DNA Functionalized Mn:CdS/ZnS Quantum Dots and Gold Nanoparticles by Time-Gated Mode

Abstract

An ultrasensitive "turn-on" fluorescent sensor was presented for determination of Hg(2+). This method is mainly based on Hg(2+)-induced conformational change of a thymine-rich single-stranded DNA. The water-soluble long-lifetime fluorescence quantum dot (Mn:CdS/ZnS) acted as the fluorophore, which was labeled on a 33-mer thymine-rich single-stranded DNA (strand A). The gold nanoparticles (GNPs) functionalized 10-mer single-stranded DNA (strand B) is selected as the quencher to quench the fluorescence of Mn:CdS/ZnS. Without Hg(2+) in the sample solution, strands A and B could form hybrid structures, resulting in the fluorescence of Mn:CdS/ZnS being decreased sharply. When Hg(2+) is present in the sample solution, Hg(2+)-mediated base pairs induced the folding of strand A into a hairpin structure, leading to the release of GNPs-tagged strand B from the hybrid structures. The fluorescence signal is then increased obviously compared with that without Hg(2+). The sensor exhibits two linear response ranges between fluorescence intensity and Hg(2+) concentration. Meanwhile, a detection limit of 0.18 nM is estimated based on 3α/slope. Selectivity experiments reveal that the fluorescent sensor is specific for Hg(2+) even with interference by high concentrations of other metal ions. This sensor is successfully applied to determination of Hg(2+) in tap water and lake water samples. This sensor offers additional advantage to efficiently reduce background noise using long-lifetime fluorescence quantum dots by a time-gated mode. With excellent sensitivity and selectivity, this sensor is potentially suitable for monitoring of Hg(2+) in environmental applications.

Recent developments on nanomaterials-based optical sensors for Hg2+ detection

“…For instance, Zhu et al [82] reported an Hg 2+ sensor in the near-infrared region based on MAA-capped InP QDs, in which the fluorescence intensity was enhanced in the presence of Hg 2+ because of the formation of HgS nanoparticles, which acted as electron-hole recombination centers. Huang et al [83] presented a "turn-on" fluorescent sensor for Hg 2+ based on single-stranded DNA functionalized Mn:CdS/ZnS QDs and Au NPs. As shown in Fig.…”

Surface Decoration of Organic Ligands on Quantum Dots: Fine Tuning of Photophysical Properties

“…The electron transfer also leads to quenching of PL of QDs by the ions bound to T-basis. Huang et al developed a "TURN-ON" fluorescent sensor with high sensitivity and selectivity for the determination of mercuric ions (Hg 2+ ) in the aqueous solution on a single-stranded DNA functionalized Mn:CdS/ZnS quantum dots and gold nanoparticles [34]. The water-soluble Mn:CdS/ZnS QD acting as a flourophore was labeled on thymine (T)-rich ssDNA (strand A) and strand B was functionalized with gold nanoparticles (GNPs) which is being used as a quencher to quench the fluorescence of Mn:CdS/ZnSQD.…”

An electrochemical aptamer biosensor based on “gate-controlled” effect using β-cyclodextrin for ultra-sensitive detection of trace mercury

“…Aptamers are antibody-like nucleic acids (Tang et al, 2011) and synthetic nucleic acid ligands; they are of particular importance in analytical chemistry because of their excellent efficiency and selectivity (Huang et al, 2013;Bini et al, 2007;McCauley et al, 2003). Aptamer-based sensors can be used not only to detect biological macromolecules but also detect metal ions.…”