Use of Single-Molecule Plasmon-Enhanced Fluorescence to Investigate Ligand Binding to G-Quadruplex DNA

Single-molecule measurements are crucial for studyingthe interactionsbetween G-quadruplex (GQ) DNA and ligands, as they provide higherresolution and sensitivity compared to those of bulk measurements.In this study, we employed plasmon-enhanced fluorescence to investigatethe real-time interaction between the cationic porphyrin ligand TmPyP4and different topologies of telomeric GQ DNA at the single-moleculelevel. By analyzing the time traces of the fluorescence bursts, weextracted dwell times for the ligand. For parallel telomeric GQ DNA,the dwell time distribution followed a biexponential fit, yieldingmean dwell times of 5.6 and 18.6 ms. For the antiparallel topologyof human telomeric GQ DNA, plasmon-enhanced fluorescence of TmPyP4was observed, with dwell time distributions following a single-exponentialfit and a mean dwell time of 5.9 ms. Our approach allows the nuancesof GQ-ligand interactions to be captured and holds promisefor studying weakly emitting GQ ligands at the single-molecule level.