G-quadruplex based impedimetric 2-hydroxyfluorene biosensor using hemin as a peroxidase enzyme mimic

We describe a sensitive and selective biosensor for the environmental metabolite 2-hydroxyfluorene (2-HOFlu). It is based on electrochemical impedance spectroscopy and was obtained by assembling a thiolated single-stranded DNA on a gold electrode via S-Au covalent bonding. It is then transformed to a K⁺-stabilized G-quadruplex-hemin complex which exhibits peroxidase-like activity to catalyze the oxidation of 2-HOFlu by H₂O₂. This results in the formation of insoluble products that are precipitated on the gold electrode. As a result, the charge transfer resistance (R _CT) between the solution and the electrode surface is strongly increased within 10 min as demonstrated by using the ferro/ferricyanide system as a redox probe. The difference in the charge transfer resistances (ΔR _CT) before and after incubation of the DNA film with 2-HOFlu and H₂O₂ serves as the signal for the quantitation of 2-HOFlu with a 1.2. nM detection limit in water of pH 7.4. The assay is highly selective over other selected fluorene derivatives. It was exploited to determine 2-HOFlu in spiked lake water samples where it displayed a detection limit of 3.6 nM. Conceivably, this method has a wide scope in that it may be applied to other analytes for which respective G-quadruplexes are available.

A G-quadruplex DNAzyme based impedimetric biosensor for sensitive detection of 2-hydroxyfluorene using hemin as a peroxidase enzyme mimic was constructed with a detection limit of 1.2 nM in water and 3.6 nM in spiked lake water samples.