DNA origami structures have great potential as functional platforms in various biomedical applications. Many applications, however, are incompatible with the high Mg concentrations commonly believed to be a prerequisite for maintaining DNA origami integrity. Herein, we investigate DNA origami stability in low-Mg buffers. DNA origami stability is found to crucially depend on the availability of residual Mg ions for screening electrostatic repulsion. The presence of EDTA and phosphate ions may thus facilitate DNA origami denaturation by displacing Mg ions from the DNA backbone and reducing the strength of the Mg -DNA interaction, respectively. Most remarkably, these buffer dependencies are affected by DNA origami superstructure. However, by rationally selecting buffer components and considering superstructure-dependent effects, the structural integrity of a given DNA origami nanostructure can be maintained in conventional buffers even at Mg concentrations in the low-micromolar range.

The atomic structure of the polar ZnO(0001) surfaces in a dry and humid oxygen environment is studied combining diffraction experiments and density-functional theory. Our results indicate that for similar stoichiometries a large number of very different, but energetically almost degenerate reconstructions exist. Thus vibrational entropy, which could be safely neglected for most semiconductor surfaces becomes dominant, giving rise to a hitherto not reported strong dependence of surface phase diagrams on temperature. Based on this insight we are able to consistently describe and explain the experimentally observed surface structures on polar ZnO(0001) surfaces.

DNA origami represent powerful platforms for single-molecule investigations of biomolecular processes. The required structural integrity of the DNA origami may, however, pose significant limitations regarding their applicability, for instance in protein folding studies that require strongly denaturing conditions. Here, we therefore report a detailed study on the stability of 2D DNA origami triangles in the presence of the strong chaotropic denaturing agents urea and guanidinium chloride (GdmCl) and its dependence on concentration and temperature. At room temperature, the DNA origami triangles are stable up to at least 24 h in both denaturants at concentrations as high as 6 M. At elevated temperatures, however, structural stability is governed by variations in the melting temperature of the individual staple strands. Therefore, the global melting temperature of the DNA origami does not represent an accurate measure of their structural stability. Although GdmCl has a stronger effect on the global melting temperature, its attack results in less structural damage than observed for urea under equivalent conditions. This enhanced structural stability most likely originates from the ionic nature of GdmCl. By rational design of the arrangement and lengths of the individual staple strands used for the folding of a particular shape, however, the structural stability of DNA origami may be enhanced even further to meet individual experimental requirements. Overall, their high stability renders DNA origami promising platforms for biomolecular studies in the presence of chaotropic agents, including single-molecule protein folding or structural switching.

The adsorption of water monomers, small water clusters, and water thin films on ␣-Al 2 O 3 ͑0001͒ surfaces is studied by density-functional theory. For the metal-terminated surface, the calculations favor the dissociative adsorption for low coverages and the formation of hexagons of alternating dissociatively and molecularly adsorbed water monomers for water-rich conditions. The calculated adsorption energy per water molecule decreases from about 1.5 eV for single adsorbed molecules to about 1.2 eV for thin films in very good agreement with our temperature programmed desorption experiments. The fully hydroxylated ͑gibbsitelike͒ surface, however, represents the thermodynamic ground state of the ␣-Al 2 O 3 ͑0001͒ surface in the presence of water.

GuidoG rundmeier, [a] AdrianK eller,* [a] andV eikkoL inko* [a, b, c] DNA nanostructures have emerged as intriguing tools for numerous biomedical applications. However, in many of those applicationsa nd most notably in drug delivery,t heir stability and function may be compromised by the biological media. A particularly important issue for medicala pplications is their interaction with proteins such as endonucleases, which may degrade the well-defined nanoscale shapes.H erein, fundamental insights into this interaction are provided by monitoring DNase Id igestion of four structurally distinct DNA origami nanostructures (DONs) in real time and at as ingle-structure level by using high-speed atomic force microscopy.T he effect of the solid-liquidi nterface on DON digestioni sa lso assessed by comparison with experiments in bulk solution. It is shown that DON digestion is strongly dependentoni ts superstructure and flexibility and on the local topology of the individual structure.The rapidly evolvingf ield of DNA nanotechnology enables custom fabrication of various nanoscale shapes with unprecedented addressability; [1] these have found some fascinating implementations in materials science and especiallyi nm any biochemicala nd biophysical systems. [2][3][4][5] In recenty ears, programmable DNA origami nanostructures (DONs) [6][7][8][9][10] have been considered promising candidates for the development of tailored and multifunctional drug-delivery vehicles. [11][12][13][14] For therapeutic in vivo applications, the DON vehicles should preferably be compatible with the immunes ystem, resistant to nucleases, have as ufficiently long circulation half-life, and be able to maintain their shape at the ionic strengths of the biological fluids. [15] However,c oncerns have been raised regarding the stabilityo fD ONs and their performance in biological media. [16, 17] Although it has been shown that DONs can survive under low-cation conditions, [18,19] stability studies performedi n serum or cell culture media have yielded somewhat controversial and quite distinct results. [8,15,[19][20][21] Therefore, significant efforts have been madei nto coating ands tabilizing DONs under biologically relevant conditions. [17,[22][23][24][25] Herein, we study DON digestion by endonucleases (DNase I) in dependence of DON superstructure. DNase Ii sw idely present in serum and varioust issues,w hich makes it one of the most relevantt hreatst ot he stability of DONs in vivo. Previously,D ON cleavage by endonucleases was studied by employing ratherl ong timescales. [8,16] Therefore, thesea pproaches can only resolve the time points at which the whole or most of the nanostructure has been digested. Moreover,t hese experiments could neither reveals patial variations of DNase Is usceptibility within as ingle DON, nor facilitate parallel comparison of different structures under the same conditions. Herein, we thus employ high-speed atomicf orce microscopy (HS-AFM) [26] to study the degradation of four well-established and structurally disti...

DNA origami has become a widely used method for synthesizing well-defined nanostructures with promising applications in various areas of nanotechnology, biophysics, and medicine. Recently, the possibility to transfer the shape of single DNA origami nanostructures into different materials via molecular lithography approaches has received growing interest due to the great structural control provided by the DNA origami technique. Here, we use ordered monolayers of DNA origami nanostructures with internal cavities on mica surfaces as molecular lithography masks for the fabrication of regular protein patterns over large surface areas. Exposure of the masked sample surface to negatively charged proteins results in the directed adsorption of the proteins onto the exposed surface areas in the holes of the mask. By controlling the buffer and adsorption conditions, the protein coverage of the exposed areas can be varied from single proteins to densely packed monolayers. To demonstrate the versatility of this approach, regular nanopatterns of four different proteins are fabricated: the single-strand annealing proteins Redβ and Sak, the iron-storage protein ferritin, and the blood protein bovine serum albumin (BSA). We furthermore demonstrate the desorption of the DNA origami mask after directed protein adsorption, which may enable the fabrication of hierarchical patterns composed of different protein species. Because selectivity in adsorption is achieved by electrostatic interactions between the proteins and the exposed surface areas, this approach may enable also the large-scale patterning of other charged molecular species or even nanoparticles.

Aggregation and fibrillization of human islet amyloid polypeptide (hIAPP) plays an important role in the development of type 2 diabetes mellitus. Understanding the interaction of hIAPP with interfaces such as cell membranes at a molecular level therefore represents an important step toward new therapies. Here, we investigate the fibrillization of hIAPP at different self-assembled alkanethiol monolayers (SAMs) by quartz crystal microbalance with dissipation monitoring (QCM-D), atomic force microscopy (AFM), and polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS). We find that hydrophobic interactions with the CH-terminated SAM tend to retard hIAPP fibrillization compared to the carboxylic acid-terminated SAM where attractive electrostatic interactions lead to the formation of a three-dimensional network of interwoven fibrils. At the hydroxyl- and amino-terminated SAMs, fibrillization appears to be governed by hydrogen bonding between the peptide and the terminating groups which may even overcome electrostatic repulsion. These results thus provide fundamental insights into the molecular mechanisms governing amyloid assembly at interfaces.

DNAo rigami structures have great potential as functional platforms in various biomedical applications.Many applications,h owever,a re incompatible with the high Mg 2+ concentrations commonly believed to be ap rerequisite for maintaining DNAo rigami integrity.H erein, we investigate DNAo rigami stability in low-Mg 2+ buffers.D NA origami stability is found to crucially depend on the availability of residual Mg 2+ ions for screening electrostatic repulsion. The presence of EDTAa nd phosphate ions may thus facilitate DNAo rigami denaturation by displacing Mg 2+ ions from the DNAb ackbone and reducing the strength of the Mg 2+ -DNA interaction, respectively.M ost remarkably,t hese buffer dependencies are affected by DNAo rigami superstructure. However,b yr ationally selecting buffer components and considering superstructure-dependent effects,t he structural integrity of ag iven DNAo rigami nanostructure can be maintained in conventional buffers even at Mg 2+ concentrations in the low-micromolar range.DNA origami [1,2] has become awidely used method for the fabrication of complex, yet well-defined nanostructures [3] with applications in biophysics, [4] molecular biology, [5] and drug and enzyme delivery. [6] Since many of these applications rely on intact DNAn anostructures,t he investigation of DNA origami stability under application-specific conditions has become am ajor research focus. [7][8][9][10][11] Biomedical applications in particular are often incompatible with the comparatively high (10-20 mm)M g 2+ concentrations required for DNA origami assembly.Onthe other hand, low-Mg 2+ concentration ( 1mm)h as been identified as one of the two most critical parameters that reduce DNAorigami stability in cell culture media. [8] Consequently,many approaches have been reported for protecting DNAo rigami nanostructures against destabilizing conditions and in particular low-Mg 2+ concentrations. [12][13][14] All the more surprising was the discovery that DNAorigami are stable in water for several weeks. [10] In these experiments,t he Mg 2+ -containing assembly buffer was exchanged for water through spin filtering,r esulting in Mg 2+ concentrations of afew micromolar.Although not completely Mg 2+ -free,m any applications may benefit from intact DNA origami nanostructures under such low-Mg 2+ conditions. However,other studies observed DNAorigami denaturation in buffers containing low-Mg 2+ concentrations. [7,8,11,12,14] These discrepancies could have various origins,s uch as differences in the buffer-exchange methods,buffer conditions, and DNAo rigami designs.I nt his work, we therefore investigate the stability of three DNAorigami nanostructures in as election of low-Mg 2+ buffers using the spin filteringbased buffer-exchange approach established by Linko et al. [10] We find that the composition of the buffer plays acritical role in DNAo rigami stability,w hile different DNAo rigami nanostructures show different buffer dependencies.First, we set out to reproduce the results of Linko et al. for the three DNAo rigami nanost...