title: Robust deposition of lambda DNA on mica for imaging by AFM in air.
abstract: Long DNA molecules remain difficult to image by atomic force microscopy (AFM) because of their tendency to entanglement and spontaneous formation of networks. We present a comparison of two different DNA deposition methods operating at room temperature and humidity conditions, aimed at reproducible imaging of isolated and relaxed λ DNA conformations by AFM in air. We first demonstrate that a standard deposition procedure, consisting in adsorption of DNA in the presence of divalent cations followed by washing and air-drying steps, yields a coexistence of different types of λ DNA networks with a only a few isolated DNA chains. In contrast, deposition using a spin-coating-based technique results in reproducible coverage of a significant fraction of the substrate area by isolated and relaxed λ DNA molecules, with the added benefit of a reduction in the effect of a residual layer that normally embeds DNA strands and leads to an apparent DNA height closer to the expected value. Furthermore, we show that deposition by spin-coating is also well-suited to visualize DNA-protein complexes. These results indicate that spin-coating is a simple, powerful alternative for reproducible sample preparation for AFM imaging.
authors.affiliation: Advanced Materials Division, Instituto Potosino de Investigación Científica y Tecnológica, San Luis Potosí, Mexico.
authors.forename: Nancy Anabel Gerling
authors.initials: NA
authors.lastname: Cervantes
authors.forename: Braulio
authors.initials: B
authors.lastname: Gutiérrez-Medina
mesh_terms: D000327:Adsorption; D000538:Aluminum Silicates / Q000737:chemistry*; D010582:Bacteriophage lambda / Q000235:genetics* / Q000648:ultrastructure*; D004279:DNA, Viral / Q000737:chemistry* / Q000648:ultrastructure*; D018625:Microscopy, Atomic Force / Q000379:methods*
chemical_list: D000538:Aluminum Silicates; D004279:DNA, Viral; C011934:mica
keywords: AFM; DNA-protein; mica; spin-coating, lambda DNA