Electrochemiluminescence of Polymer Dots Featuring Thermally Activated Delayed Fluorescence for Sensitive DNA Methylation Detection

Polymer dots (Pdots) as electrochemiluminescence (ECL) emitters have drawn intensive attention for expanding the application of ECL analytical technology. Here we used a donor- acceptor polymer with thermally activated delayed fluorescence (TADF) property as a precursor to design and synthesize a kind of highly efficient Pdots with desirable annihilation and co-reactant ECL behaviors. The TADF Pdots possessed a highly stable negative-charged state in the ECL process, and their ECL emission followed the "S-route", thus achieving theoretically 100% excitons harvesting for radiative decay. With S2O82- or tripropylamine as the co-reactant, the TADF Pdots exhibited intensive bandgap ECL emission and possessed ultrahigh ECL efficiency, which were superior to conventional fluorescent Pdots due to the TADF property and the shielding of oxygen quenching effect toward triplet excitons. By combining the stable cathodic ECL property of TADF Pdots with rolling circle amplification reaction, a sensitive ECL biosensor was designed for DNA methylation detection with RASSF1A gene fragment as a target model, which showed detection limits down to the fM level and realized the localization of the methylation site on target DNA based on steric hindrance effect. This work revealed the great potential of TADF emitters in ECL efficiency elevation and offered a new idea for the development of detection kits to quantitatively detect gene methylation.