Oligonucleotide-modulated photocurrent enhancement of a tetracationic porphyrin for label-free homogeneous photoelectrochemical biosensing.

This work reports the first demonstration of an oligonucleotide-modulated label-free homogeneous photoelectrochemical (PEC) biosensing platform based on the adsorption of tetracationic porphyrin (denoted as TMPyP here) onto 1-naphthalenesulfonate anion (NS-)-grafted indium tin oxide electrode (denoted as TMPyP-NS--ITO), which generates a stable and rapid photocurrent response. We found that when NS--ITO electrode was subjected to single-stranded oligonucleotide (ssON) before TMPyP adsorption, a remarkable enhancement of photocurrent intensity was observed from the resulted TMPyP-ssON-NS--ITO electrode with high specificity towards oligonucleotide. A series of investigations were carried out to understand the mechanism of this oligonucleotide-modulated photocurrent enhancement phenomenon. Moreover, the studies of this robust photocurrent enhancement mechanism was successfully extended to develop a signal-on homogeneous PEC biosensing platform for, as a proof-of-concept, label-free M.SssI methyltransferase activity analysis through a judiciously and compatibly engineered signal transduction strategy consisted of hairpin-shaped oligonucleotide probe, restriction endonuclease HpaII, and Exonuclease I. The rationally designed homogeneous PEC biosensor exhibit sensitive PEC response toward M.SssI methyltransferase with a low detection limit of 3.5 mU/mL and a wide linear range from 0.01 to 120 U/mL. Additionally, we show that our homogeneous PEC biosensing platform can be also utilized to screen methyltransferase inhibitors. Therefore, this work will provide a distinctive paradigm for versatile homogeneous PEC biosensing platform that can be used as potential powerful tool toward innovative label-free bioanalytical purposes.