Polymer-induced perylene probe excimer formation and selective sensing of DNA methyltransferase activity through the...

A new label-free strategy for sensitive fluorometric biosensing based on perylene probe monomer-excimer transition has been developed. A negatively charged perylene probe (compound 1) was used. Compound 1 shows strong monomer fluorescence in an aqueous buffer solution. A cationic polymer could induce aggregation of compound 1 through noncovalent interactions. Compound 1 monomer emission was quenched, and meanwhile strong excimer emission was observed. Upon addition of a single-stranded DNA (an anionic polymer), strong electrostatic attractive interactions between the cationic polymer and the DNA weakened the binding of aggregates of compound 1 to the polycation. Compound 1 monomers were released, and excimer-monomer emission transition was detected. This observation formed the basis for DNA methyltransferase (MTase) activity detection. When the 3'-OH terminus of a duplex DNA was removed, the DNA strands could not be elongated by terminal deoxynucleotidyl transferase (TdT), and little restoration of compound 1 monomer emission was detected. However, in the presence of MTase and endonuclease, the DNA could be specifically methylated and then cleaved into single-stranded fragments. The DNA fragments contained newly generated 3'-OH termini, which could be elongated by TdT. An excimer-monomer transition signal could then be detected. Simple, sensitive, selective, and inexpensive sensing of DNA methylation was therefore established.