In situ small-angle X-ray scattering reveals strong condensation of DNA origami during silicification

Abstract

The silicification of DNA origami structures increases their mechanical and thermal stability and provides chemical protection. So far, it is unclear how silicification affects the internal structure of the DNA origami and whether the whole DNA framework is embedded or if silica just forms an outer shell. By using in situ small-angle X-ray scattering (SAXS), we show that the net-cationic silica precursor TMAPS induces substantial condensation of the DNA origami, which is further enhanced by the addition of TEOS at early reaction times to an almost 10 % size reduction. We identify the SAXS Porod invariant as a reliable, model-free parameter for the evaluation of the amount of silica formation at a given time. Contrast matching of the DNA double helix Lorentzian peak reveals that silica growth also occurs on the inner surfaces of the origami. The less polar silica forming within the origami structure, replacing more than 40 % of the internal hydration water causes a hydrophobic effect: origami condensation. In the maximally condensed state, thermal stabilization of the origami up to 60 {\deg}C could be observed. If the reaction is driven beyond this point, the overall size of the silicified origami increases again due to more and more silica deposition on the DNA origami. DNA origami objects with flat surfaces show a strong tendency towards aggregation during silicification, presumably driven by the very same entropic forces causing condensation. Our studies provide novel insights into the silicification reaction and hints for the formulation of optimized reaction protocols.