What type of bond forms between DNA and positively charged nylon membrane?
Positively charged nylon membranes contain quaternary ammonium groups that initially attract negatively charged phosphate backbone of DNA through electrostatic interaction during Southern or Northern transfer. For permanent immobilization, membrane is exposed to ultraviolet irradiation at 254 nm. Photochemical reaction creates covalent bonds between thymine residues of DNA and amine groups of nylon matrix. This covalent fixation withstands high stringency hybridization, high temperature washing, and repeated stripping cycles. By contrast, nitrocellulose relies solely on hydrophobic interaction
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.
