Rapid photoactuation of a DNA nanostructure using an internal photocaged trigger strand*

DNA nanotechnology is one of the most powerful methods for constructing nano-mechanical devices. The ability to actuate these devices on-demand would provide a powerful method for creating dynamic nanomachines that can reconfigure nanostructures, apply precisely defined forces, or spatiotemporally control self-assembly. Typically, DNA nanostructures have been temporally modulated by either 1) introducing external toehold-mediated displacement strands, or 2) incorporating photoswitchable azobenzene nucleotides that can reversibly break hybridization. However, these approaches suffer from drawbacks like 1) the need to introduce an exogenous strand (which is not feasible for many applications, especially in biology), and 2) slow kinetics or undesired reversibility. To circumvent these limitations, we have photo-caged the displacement strands within an existing nanostructure, preventing their action until illuminated. These “spring-loaded” nanostructures are in a metastable state until activated by light, whereupon the high local concentration of the displacement strand will drive irreversible nanostructure reconfiguration. To demonstrate this concept, we designed a nano-mechanical tweezer that switches between the closed and open state with UV light. In effect, this device can apply a nano-mechanical force within a few seconds of illumination, paving the way for dynamic nanomachines that can exert controlled motion. The tweezer was analyzed using AFM, FRET, and computational simulations. Our results demonstrate that the photocaged mechanism is efficient and fast, surpassing externally added strand displacement by almost two orders of magnitude. We envision that this approach will allow for light-activated nanomachines in the future for biophysical studies with cells.