Cyclometalated Iridium Complex-Based Label-Free Photoelectrochemical
Biosensor for DNA Detection
by Hybridization Chain Reaction Amplification
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Abstract
Photoactive
material is the most crucial factor which intimately
determines analytical performances of the photoelectrochemical sensor.
On the basis of the high affinity of dipyrido [3,2-a:2′,3′-c]
phenazine (dppz) with DNA helix, a novel photoactive intercalator,
[(ppy)<sub>2</sub>Ir(dppz)]<sup>+</sup>PF<sub>6</sub><sup>–</sup>(ppy = 2-phenylpyridine and dppz = dipyrido [3,2-a:2′,3′-c]
phenazine) was prepared and characterized by UV–vis absorption
spectroscopy, fluorescence spectroscopy, and cyclic voltammetry. The
photoelectrochemical properties of the as-prepared iridium(III) complex
immobilized on the ITO electrode was investigated. Either cathodic
or anodic photocurrent generation can be observed when triethanolamine
(TEOA) or dissolved O<sub>2</sub> is used as a sacrificial electron
donor/acceptor, respectively. The probable photocurrent-generation
mechanisms are speculated. A highly sensitive iridium(III) complex-based
photoelectrochemical sensor was proposed for DNA detection via hybridization
chain reaction (HCR) signal amplification. Under optimal conditions,
the biosensor was found to be linearly proportional to the logarithm
of target DNA concentration in the range from 0.025 to 100 pmol L<sup>–1</sup> with a detection limit of 9.0 fmol L<sup>–1</sup> (3σ). Moreover, the proposed sensor displayed high selectivity
and good reproducibility, demonstrating efficient and stable photoelectric
conversion ability of the Ir(III) complex