Ls. Shlyakhtenko et al., Atomic force microscopy imaging of DNA covalently immobilized on a functionalized mica substrate, BIOPHYS J, 77(1), 1999, pp. 568-576
A procedure for covalent binding of DNA to a functionalized mica substrate
is described. The approach is based on photochemical cross-linking of DNA t
o immobilized psoralen derivatives. A tetrafluorphenyl (TFP) ester of trime
thyl psoralen (trioxalen) was synthesized, and the procedure to immobilize
it onto a functionalized aminopropyl mica surface (AP-mica) was developed.
DNA molecules were cross-linked to trioxalen moieties by UV irradiation of
complexes. The steps of the sample preparation procedure were analyzed with
x-ray photoelectron spectroscopy (XPS). Results from XPS show that an AP-m
ica surface can be formed by vapor phase deposition of silane and that this
surface can be derivatized with trioxalen. The derivatized surface is capa
ble of binding of DNA molecules such that, after UV cross-linking, they wit
hstand a thorough rinsing with SDS. Observations with atomic force microsco
py showed that derivatized surfaces remain smooth, so DNA molecules are eas
ily visualized. Linear and circular DNA molecules were photochemically immo
bilized on the surface. The molecules are distributed over the surface unif
ormly, indicating rather even modification of AP-mica with trioxalen. Gener
ally, the shapes of supercoiled molecules electrostatically immobilized on
AP-mica and those photocross-linked on trioxalen-functionalized surfaces re
main quite similar. This suggests that UV cross-linking does not induce for
mation of a noticeable number of single-stranded breaks in DNA molecules.