Measurement of the interaction forces at various pH levels by using AFM for the interpretation of DNA adsorption on silanized surfaces

Various surfaces have been used for deoxyribonucleic acid (DNA) immobilization, one example being a silanized surface. This is useful for determining DNA lengths and, thus, locating specific gene sequences in DNA by using fluorescence microscopy and scanning probe microscopy. In this study, we deposited DNA by using the molecular combing method and, we used fluorescence microscopy to study how the chain lengths of n-alkylsilanes affected the surface density of DNA deposited on the silanized surfaces in a tris-ethylenediaminetetraacetic acid (TE) buffer. The forces between a cleaned silicon-nitride (Si₃N₄) tip and each substrate surface in aqueous buffers at various pH levels (1.0 ~ 9.0) were also studied by using atomic force microscopy to measure the force-distance curves. We explain why the density of lambda bacteriophage DNA (λ-DNA) deposited by using the molecular combing method at pH 8 was lower on the silanized surface with the shorter alkyl chain than it was on the silanized surface with the longer alkyl chain in terms of the electrical double layer (EDL) and the adhesive force.