Abstract

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.