(color online) AFM images of DNA with spermine and spermidine in 1-mM TRIS. The inset bar are . (a) 0.1-mM spermidine at pH = 8.9 (b) 0.1-mM spermidine, at pH = 7.8; (c) 0.1-mM spermidine pH = 5.5, (d) 0.1-mM spermidine, at pH = 3.0; (e) 0.1-mM spermine at pH = 9.5. (f) 0.1-mM spermine, at pH = 7.8; (g) 0.1-mM spermine, at pH = 5.5; (h) spermine, at pH = 3.5.