Scanasyst air silicon tip on nitride lever

A 100 µL dA₃₀‐dsDNA₁₃ 700 µm in CA 20 mm Mag buffer was prepared. It was frozen with liquid nitrogen then dried in freeze‐drier overnight. The dried sample was placed on carbon tape and imaged by Hitachi SU3500 scanning electron microscope equipped with ultravariable pressure detector operating at 10 kV accelerating voltage under 30 Pa pressure.
A hydrogel with the same composition was broken down by adding 3 mL of Mag buffer and strongly mixing with the pipette, then 5 µL of the sample was dropped onto a freshly cleaved mica surface for 30 s, followed by wicking off most of the liquid from the mica surface using a filter paper. The mica surface was then further dried under a stream of compressed air for 30 s before it was put under vacuum for at least 2 h prior to imaging. AFM images were acquired in ScanAsyst mode under air conditions on a Multimode 8 Scanning Probe Microscope from Bruker with a Nanoscope V controller equipped with a ScanAsyst‐Air silicon tip on nitride lever (tip radius = 2 nm, k = 0.4 N m⁻¹, f_o = 70 kHz; Bruker).

TEM characterization was carried out using a Thermo Fisher FEI Tecnai Spirit Transmission Electron Microscopy operating at 120 kV. For QDs with organic ligands, 10 μl of QDs (50 μg/ml) was drop casted on 400-mesh carbon film square grids (Thermo Fisher Scientific, catalog number: 5024891). For DNA origami and QD/QR-origami assemblies, 10 μl of wireframe DNA origami objects with or without attached QDs/QRs (5 nM) was adsorbed on glow-discharged 400-mesh carbon film square grids and stained by 2% aqueous uranyl formate solution containing 25 mM NaOH.
AFM measurements were performed under air condition in either on an Icon Atomic Force Microscope (Bruker) in ScanAsyst mode using a ScanAsyst-Air silicon tip on nitride lever (tip radius = 2 nm, k = 0.4 N/m, f_o = 70 kHz; Bruker) or on an Asylum Research Jupiter XR AFM (Oxford Instruments) in tapping mode using an ARROW-UHF ultrahigh-frequency probe (tip radius < 10 nm, f_o = 2000 kHz; NanoWord).
Absorbance spectra were measured using an Evolution 260 Bio UV-vis spectrophotometer (Thermo Fisher Scientific), and steady-state emission spectra (λ_ex = 450 nm) were measured using a multimode microplate reader (Tecan Spark). Quantum yields of QDs/QRs were determined using the relative quantum yield determination method with rhodamine 101 in spectroscopic-grade ethanol as standard (λ_ex = 480 nm, Φ_s = 0.92) (79 (link)).