DNA Origami-Templated Individual Gold Nanocluster: Probing The Photophysical Dynamics Using Single Molecule Fluorescence Spectroscopy

Abstract

Single-molecule fluorescence microscopy demands ultrahigh stability of single fluorophore with less photobleaching and essentially no intensity fluctuations on experimentally relevant time scales. In this respect, there is a need to design fluorescent probes with excellent photostability and long-lived dark transient states. Herein, we report the site-specific synthesis of gold nanocluster (Au NC) on DNA origami. Rectangular DNA origami bearing poly-cytosine sequence in the centre was used as a template to guide the in situ synthesis of Au NC. The photophysical properties of DNA-templated AuNCs were extensively studied using single-molecule confocal fluorescence microscopy, which revealed the average on-time and off-time of 0.08 seconds and 0.05 seconds, respectively. The photon antibunching measurements confirmed the existence of single Au NC in the confocal volume and fluorescence transient studies revealed excellent brightness and remarkable photostability with long survival times and less blinking. Such DNA-templated Au NCs with ultrahigh photostability, intense brightness, and low toxicity has tremendous potential to be used as probes in single-molecule dynamics measurements in biologically relevant timescales. The precise addressability of DNA origami nanostructures provides the controlled attachment of various biomolecules specifically at a predesigned location on the origami template, allowing such platforms to be used as single nanocatalysis as well as performing imaging and sensing studies on single molecule level.