The illegal addition of melamine in dairy products and mercury (Hg2+) water contamination is a robust threat to human health. Hence, herein a highly sensitive colorimetric sensor for the visual...
Reliable, label-free,
and ultraselective detection of Pb2+ and Ag+ ions is of paramount importance for toxicology
assessment, human health, and environmental protection. Herein, we
present a novel recyclable fluorometric aptasensor based on the Pb2+ and Ag+-induced structural change of the GC-rich
ssDNA (guanine cytosine-rich single-strand DNA) and the differences
in the fluorescence emission of acridine orange (AO) from random coil
to highly stable G-quadruplex for the detection of Pb2+ and Ag+ ions. More interestingly, the construction and
principle of the aptasensor explore that the GC-rich ssDNA and AO
can be strongly adsorbed on the CaSnO3@PDANS surface through
the π–π stacking, hydrogen-bonding, and metal coordination
interactions, which exhibit high fluorescence quenching and robust
holding of the GC-rich ssDNA. However, in the presence of Pb2+, the specific G-rich ssDNA segment could form a stable G-quadruplex
via G4–Pb2+ coordination and capture of AO from
the CaSnO3@PDANS surface resulting in fluorescence recovery
(70% enhancement). The subsequent addition of Ag+ ion induces
coupled cytosine base pairs in another segment of ssDNA to get folded
into a duplex structure together with the G-quadruplex, which highly
stabilizes the G-quadruplex resulting in the maximum recovery of AO
emission (99% enhancement). When the Cys@Fe3O4Nps are added to the above solution, the sensing probe was restored
by complexation between the Cys in the Cys@Fe3O4Nps and target metal ions, resulting in the fabrication of a highly
sensitive recyclable Pb2+ and Ag+ assay with
detection limits of 0.4 and 0.1 nM, respectively. Remarkably, the
Cys@Fe3O4Nps can also be reused after washing
with EDTA. The utility of the proposed approach has great potential
for detecting the Pb2+ and Ag+ ions in environmental
samples with interfering contaminants.
In this study, we have designed a three-fluorophore-labeled Y-shaped DNAzyme with a high catalytic cleavage activity and a three-dimensional (3D) MOF-MoS 2 NB (metal−organic framework fused with molybdenum disulfide nanobox), which was synthesized as an efficient quencher of the fluorescent biosensor. The synthesized porous 3D MOF-MoS 2 NBs and Y-shaped DNAzyme exhibited a good analytical response toward the simultaneous multiple detections of Hg 2+ , Ni 2+ , and Ag + ions over the other coexisting metal ions. More specifically, the three kinds of enzyme aptamer and substrate aptamer (SA) were hybridized and annealed to form the Y-shaped DNAzyme structure and labeled with three different fluorophores such as FAM, TAMRA, and ROX over the 3′-end of SA. When the targets were induced, the DNAzyme was triggered to cleave the fluorophore-labeled SAs. Then, the cleaved SAs (FAM-SA, TAMRA-SA, and ROX-SA) were adsorbed on the 3D MOF-MoS 2 NB surface to quench the fluorescence signal due to a noncovalent interaction (van der Waals and π−π stacking interaction), which transmuted the fluorescence on-state to off-state. As a result, the fluorescence assay confiscated the high selectivity and sensitivity for the target analytes of Hg 2+ , Ni 2+ , and Ag + ions achieved for the detection limits of 0.11 nM, 7.8 μM, and 0.25 nM, respectively. Accordingly, the sensitivity of the developed sensor was explored with a better lower detection limit than the previously reported biosensors. The utility of the designed Y-shaped DNAzyme may find a broad field of application in real water sample analysis with interfering contaminants.
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