Fabrication of Functional 3D Nanoarchitectures via Atomic Layer Deposition on DNA Origami Crystals

Abstract

While DNA origami is a powerful bottom-up fabrication technique, the physical and chemical stability of DNA nanostructures is generally limited to aqueous buffer conditions. Wet chemical silicification can stabilize these structures but does not add further functionality. Here, we demonstrate a versatile three-dimensional (3D) nanofabrication technique to conformally coat micrometer-sized DNA origami crystals with functional metal oxides via atomic layer deposition (ALD). In addition to depositing homogeneous and conformal nanometer-thin ZnO, TiO₂, and IrO₂ (multi)layers inside SiO₂-stabilized crystals, we establish a method to directly coat bare DNA crystals with ALD layers while maintaining the crystal integrity, enabled by critical point drying and low ALD process temperatures. As a proof-of-concept application, we demonstrate electrocatalytic water oxidation using ALD IrO₂-coated DNA origami crystals, resulting in improved performance relative to that of planar films. Overall, our coating strategy establishes a tool set for designing custom-made 3D nanomaterials with precisely defined topologies and material compositions, combining the unique advantages of DNA origami and atomically controlled deposition of functional inorganic materials.

Figure 1

Overview of sample preparation. Folding of DNA origami monomers, crystal annealing, and silica growth are performed in an aqueous 1× Tris-EDTA buffer solution comprising a scaffold strand (gray), staple strands (green), and magnesium ions (not shown). The silicified and bare crystals are then transferred to surfaces (glass or silicon) in liquid and dried in air (following silicification) or via CPD (bare structures without silicification). Finally, various functional metal oxide coatings are grown via ALD.

Figure 2

SEM images of DNA origami crystals coated with metal oxides. (a) Top view of an air-dried, silicified crystal after conformal coating with 10 nm of TiO₂ using ALD, scale bar 2 μm. (b) Higher-magnification image of the {111} surface of the crystal shown in panel (a), scale bar 200 nm. (c) Image of the inner region of a crystal obtained by FIB milling of the crystal, scale bar 500 nm. (d–f) Image and composition maps obtained following FIB milling of a silicified crystal coated with two consecutive shells of 5 nm TiO₂ (TTIP process) and 5 nm ZnO; (d) SEM image and corresponding EDX signals for (e) Zn and (f) Ti; all scale bars are 1 μm.

Figure 3

SEM images of CPD-dried crystals. (a) Top view of a DNA origami crystal dried using CPD and subsequently coated with 10 nm of TiO₂ using ALD (TDMAT process, scale bar 2.5 μm). (b) Close-up view of the crystal shown in panel (a) (scale bar 100 nm). (c) Cross-sectional FIB cut of a CPD-dried crystal (scale bar 1 μm). (d) Zoomed-out cross-sectional view of a FIB cut crystal, with the Ti EDX signal overlaid in orange (scale bar 2.5 μm).

Figure 4

Experimental setup for electrocatalytic water oxidation using functionalized DNA origami crystals. (a) Sample preparation: Silicified DNA origami crystals were deposited and air-dried on an FTO-coated glass substrate. A thin layer of IrO₂ was subsequently grown via ALD, resulting in conformal deposition on both the exposed FTO substrate and on the SiO₂-coated DNA crystals. The substrate was then masked with PTFE, leaving an exposed 5 mm diameter circular area containing all of the DNA crystals. A separate exposed region on the edge of the sample was also defined, on which a Ag contact was placed. (b) Experimental three-electrode setup for electrocatalytic water oxidation with IrO₂-coated DNA origami crystals. (c–f) Exemplary SEM images of a 3× concentrated DNA origami crystal sample supported on FTO and coated with IrO₂ via ALD at different magnifications ((c) scale bar 500 μm, (d) scale bar 100 μm, (e) scale bar 10 μm, and (f) scale bar 2 μm).

Figure 5

Electrolysis of water with IrO₂-coated DNA origami crystals. The specific color shade of each curve and point represents an individual sample. The reference (“ref”) data (green shades) refer to FTO-covered glass substrates with 5.1 nm of IrO₂, without any DNA origami crystals. “1× DNA” (blue shades) denotes 0.28 pmol of crystal monomers deposited on the FTO-glass surface, and ″3× DNA” (red shades) denotes samples produced with three times as much material, as described in the text. (a, b) Current density as a function of applied electrochemical potential measured in (a) cycle 2 and (b) cycle 20. Insets show zoomed-in regions near the onset potential. (c) Statistical analysis of current density at 1.8 V vs RHE. (d) Statistical analysis of the electrochemical potential required to reach a current density of 1 mA/cm².