Multivalent cations are known to condense DNA into higher ordered structures, including toroids and rods. Here we report that solid supports treated with monovalent or multivalent cationic silanes, followed by removal of soluble molecules, can condense DNA. The mechanism of this surface-directed condensation depends on surface-mobile silanes, which are apparently recruited to the condensation site. The yield and species of DNA aggregates can be controlled by selecting the type of functional groups on surfaces, DNA and salt concentrations. For plasmid DNA, the toroidal form can represent > 70% of adsorbed structures.
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