Adsorption of DNA to octadecylamine monolayers at the air–water interface

In this work, surface properties of octadecylamine (ODA) monolayers in the presence of different concentrations of calf thymus DNA in the aqueous subphase covering a range of 2–8 μM have been investigated. The increase of DNA concentration is accompanied by a marked increment in the expansion of the corresponding isotherms. In addition, there is a change in the profile of the isotherms ranging from an abrupt liquid–solid transition for the lipid monolayer on pure water to a slow condensation of the monolayer in a liquid state when DNA is added to the subphase, demonstrating the effective adsorption of the polynucleotide to the long chain amine monolayer. Additional phase transitions appear in the isotherms upon addition of sufficient amount of DNA, revealing the existence of specific processes such as folding or squeezing out of the DNA. This system is, however, highly reversible during compression-expansion cycles due to the strong interaction between the two components. These results are also supported by Brewster Angle Microscopy (BAM) images showing significant changes in the morphology of the film. Integral reflectivity of the BAM microscope has been used to study both isotherms themselves and the kinetic process of DNA inclusion into the lipid-like ODA monolayer. This parameter has been proven to be very effective for quantification of the monolayer processes showing high consistency with the compressibility and kinetics results.

DNA interaction with octadecylamine monolayers on water is clearly visualized by Brewster Angle Microscopy (BAM). Interesting phase transitions and quantitative BAM reflectivity measurements are also shown in this work.Figure optionsDownload high-quality image (42 K)Download as PowerPoint slideResearch highlights
► Octadecylamine (ODA) monolayers on water are a suitable matrix for polynucleotide immobilization.
► The increase of DNA concentration leads to an expansion and a change in the profile of the ODA isotherm.
► New reversible phase transitions appear in the isotherms upon addition of sufficient amount of DNA.
► BAM reflectivity allows the quantification of monolayer compressibility and adsorption kinetics.