Ion‐Dependent Stability of DNA Origami Nanostructures in the Presence of Photo‐Generated Reactive Oxygen Species

<jats:p>DNA origami nanostructures are promising carries for drug delivery applications. However, their limited stability under relevant conditions often presents a challenge. Herein, the structural stability of DNA origami nanostructures is investigated in a setting compatible with their application in photodynamic therapy (PDT). To this end, DNA origami triangles and six‐helix bundles (6HBs) are loaded with the clinically tested photosensitizer methylene blue, which upon irradiation with red light generates reactive oxygen species (ROS) that attack the DNA origami nanostructures. ROS‐induced structural damage is observed to depend on the ionic composition of the surrounding medium and becomes more severe at low ionic strength. Mg<jats:sup>2+</jats:sup> ions can efficiently protect the DNA origami nanostructures from ROS‐induced damage and may even heal some of the damage obtained under Mg<jats:sup>2+</jats:sup>‐free conditions when added after irradiation. Finally, the employed DNA origami 6HBs are more resistant toward ROS‐induced structural damage than the triangles, which is attributed to their markedly different mechanical properties. These results thus provide some fundamental insights into the stabilizing role of DNA origami superstructure that may guide the selection or design of DNA origami nanocarriers with optimized stability for their application in PDT.</jats:p>