Wei Tao Huang

Label-free colorimetric detection of Hg2+ based on Hg2+-triggered exonuclease III-assisted target recycling and DNAzyme amplification

This work reported a label-free colorimetric assay for sensitive detection of Hg(2+) based on Hg(2+)-triggered hairpin DNA probe (H-DNA) termini-binding and exonuclease Ш (Exo Ш)-assisted target recycling, as well as hemin/G-quadruplex (DNAzyme) signal amplification. The specific binding of free Hg(2+) with the thymine-thymine (T-T) mismatches termini of H-DNA could immediately trigger the Exo Ш digestion, and then set free G-quadruplex segments and Hg(2+). The Exo Ш impellent recycling of ultratrace Hg(2+) produced numerous G-quadruplexes. The corresponding DNAzymes catalyzed efficiently the H2O2-mediated oxidation of the ABTS(2-) to the colored product in the presence of hemin. Using the color change as the output signal, and the Exo Ш-aided Hg(2+) recycling and DNAzyme as the signal amplifier, the ultrasensitive assay system successfully achieved visual detection of Hg(2+) as low as 1.0 nM by the naked eye, and was suitable for field monitoring. The calibration curve was linear in the range of 50.0 pM to 20.0 nM for Hg(2+) (R=0.9962) with a detection limit of 10.0 pM. Moreover, this proposed strategy showed excellent selectivity, portability and low-cost, and was successfully applied to colorimetric detection of Hg(2+) in laboratory tap water and Jialing river water samples.

A simple and facile strategy based on Fenton-induced DNA cleavage for fluorescent turn-on detection of hydroxyl radicals and Fe2+

We provide a novel, simple, and general strategy based on a DNA–graphene oxide (GO)–Fenton hybrid system for fluorescence turn-on detection of hydroxyl radicals (HO˙) and Fe2+, in which GO as a nanoquencher is utilized for reducing the background signal and simplifying procedures. Fluorescence resonance energy transfer (FRET) between GO and dye units incorporated into DNA is switched off as a result of HO˙-induced strand breakage in the single-stranded DNAs, restoring the fluorescence of the quenched fluorophores. In our assay, HO˙ is generated by Fe2+ catalyzing decomposition of hydrogen peroxide through the Fenton reaction. Therefore, switching off FRET depends on the amounts of Fe2+ and HO˙. In vitro assays with Fe2+ and HO˙ demonstrated increases in fluorescence intensity with a linear range from 10 nM to1 μM and a detection limit as low as 2.4 nM.

A triple-channel optical signal probe for Hg2+ detection based on acridine orange and aptamer-wrapped gold nanoparticles

A triple-channel optical signal probe has been designed for the detection of Hg2+ ions. In the absence of Hg2+, the thymine-rich ssDNA wrapped AuNPs were well dispersed. Thus, the colour of the solution is pink-red; the resonance light scattering (RLS) signal is low; the fluorescence of acridine orange (AO) is powerfully quenched. In the presence of Hg2+, the ssDNA formed a T–Hg2+–T configuration, which produces a colour change, RLS signal enhancement, and fluorescence of AO restoration. Under the optimum conditions, the system exhibits a dynamic response range for Hg2+ from 50 nM to 5 μM with a detection limit of 30 nM.

Silver(I) ions and cysteine detection based on photoinduced electron transfer mediated by cytosine-Ag(+)-cytosine base pairs.

Upon formation of cytosine-Ag(+)-cytosine base pairs as a mediator for the photoinduced electron transfer, the fluorescence of FAM-labeled DNA was quenched and the fluorescence emission wavelength exhibited a red shift. Based on these phenomena a novel dual-output fluorescent DNA sensor for Ag(+) ions and cysteine detection was developed.

Fuzzy logic sensing of G-quadruplex DNA and its cleavage reagents based on reduced graphene oxide.

Herein, by combining the merits of nanotechnology and fuzzy logic theory, we develop a simple, label-free, and general strategy based on an organic dye-graphene hybrid system for fluorescence intelligent sensing of G-quadruplexes (G4) formation, hydroxyl radical (HO∙), and Fe(2+) in vitro. By exploiting acridine orange (AO) dyes-graphene as a nanofilter and nanoswitch and the ability of graphene to interact with DNA with different structures, our approach can efficiently distinguish, quantitatively detect target analytes. In vitro assays with G4DNA demonstrated increases in fluorescence intensity of the AO-rGO system with a linear range of 16-338 nM and a detection limit as low as 2.0 nM. The requenched fluorescence of the G4TBA-AO-rGO system has a non-linear response to Fenton reagent. But this requenching reduces the fluorescence intensity in a manner proportional to the logarithm to the base 10 of the concentration of Fenton reagent in the range of 0.1-100 μM and 100-2000 μM, respectively. Furthermore, we develop a novel and intelligent sensing method based on fuzzy logic which mimics human reasoning, solves complex and non-linear problems, and transforms the numerical output into the language description output for potential application in biochemical systems, environmental monitoring systems, and molecular-level fuzzy logic computing system.