Singlet Oxygen-Based Photoelectrochemical DNA Sensing
Karolien De Wael,
Professor,
University of Antwerp
To avoid the main drawback of semiconductor-based photoelectrochemical
(PEC) systems, i.e. the uncontrollable nature of photo-induced charge or
electron transfer processes, a novel and innovative PEC sensing
paradigm has been introduced. The sensing paradigm is based on the
unique feature of type II molecular photosensitizers to transfer the
excitation energy to oxygen generating 1O2.
Indeed, the action is initiated by the absorption of a photon to yield
an excited sensitizer. Reactions of the excited sensitizer can involve
Type I or Type II reactions via intersystem crossing. The latter
involves an energy transfer from the excited photosensitizer to O2 to yield 1O2
and is of particular interest for our paradigm. It will be a matter of
minimizing or controlling the contribution of Type I reactions in the
mechanism through the selection of the photosensitizer or the use of
quenchers. The Type II photosensitizers can also be used as molecular
labels coupled to specific DNA sequences for highly sensitive and
cost-efficient photoelectrochemical DNA sensing applications. In this
lecture, the sensing mechanism will be explained together with the
photoelectrochemical properties of molecular photosensitizers used as
labels for biomolecules. The photocatalytic activity of different
photosensitizers in solution and attached to ssDNA have been evaluated
in the absence and presence of a redox reporter (hydroquinone). Both
type I and type II photosentiziers were studied. In particular, a
porphyrin chlorin e6 was found to give a well-detectable photocurrent
response in solution or as a label attached to ssDNA. With an intrinsic
background elimination by switching the light ON/OFF, this
photoelectrochemical strategy provides enhanced sensitivity. The
quantification of prostate cancer related miRNAs in human serum will be
discussed, and positioned towards electrochemiluminescent assays.
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