pH-Driven Actuation of Unmodified DNA Origami Rectangles.

DNA origami is a versatile method for constructing molecular machinery, yet many designs rely on responsive motifs or added components to achieve dynamic behavior. Here, we show that unmodified DNA origami rectangles-one of the most widely used DNA origami structures-exhibit a reversible transition between planar and tubular states upon pH modulation. We propose that this transformation occurs due to the cooperative mechanical coupling of crossover junctions in overwound DNA: no DNA modification, special sequences, or extra motifs are needed. The curling/uncurling response extends to connected rectangles: dimers and nanoribbons curl reversibly below pH 7 to form nanotube architectures. This unexpected conformational flexibility of monolayer DNA with pH provides a simple framework for engineering responsive nanostructures that can be transformed without chemical modification or specific sequence motifs.