(color online) AFM observation of DNA complexes. Panel (a) λ-DNA in 5-mM Mg²⁺ solution; Panels (b)–(f) DNA conformations at different concentrations (0.01, 0.05, 0.1, 0.5, and 1 mM, respectively) of As⁺ in 5-mM Mg²⁺ buffer.