EFFECT OF HYDROPHOBICITY AND ELECTROSTATICS ON ADSORPTION AND SURFACE-DIFFUSION OF DNA OLIGONUCLEOTIDES AT LIQUID SOLID INTERFACES/

It is generally known that both electrostatic and hydrophobic interact ions are major driving forces for protein adsorption at solid/liquid i nterfaces, but relatively little is known about how these interactions affect the interfacial behavior of single-stranded DNA molecules. Thi s information is important for the design of DNA hybridization sensors . In this study, total internal reflectance microscopy/fluorescence re covery after photobleaching (TIR/FRAP) was applied to measure the deso rption rate constants and the surface diffusion coefficients of a 21-b ase oligonucleotide on four different surfaces including two cationic amino-silanized and two hydrophobic-silanized surfaces. Adsorption iso therms of the oligonucleotide were determined by using porous glass be ads that were identically silanized. The results indicate that the oli gonucleotide adsorbs reversibly and interacts strongly with the four s urfaces studied. Approximately 50% less oligonucleotide adsorbed on th e hydrophobic substrates than on cationic amino-silanized glasses. The desorption rate constant decreases as the density of the hydrophobic silane surface layer increases and it depends on the chemical properti es of the substrate. The surface diffusion coefficients depend on the density of the adsorbed oligonucleotides on the hydrophobic surfaces i n phosphate-buffered saline (pH 7.4) solution (PBS). When ethanol was added to the adsorption buffer, the initial slopes of the adsorption i sotherms for hydrophobic dimethyldichlorosilane-treated (DMS) surface as well as the two secondary amino-silanized glasses were lowered. On the other hand, the kinetics of adsorption and surface diffusion of ol igonucleotides in the presence of ethanol on all substrates was indepe ndent of the substrate properties and the equilibrium adsorption affin ity. DNA oligonucleotides have both ionic and hydrophobic characterist ics which result in complex adsorption and surface diffusion behavior on glass silanized with a range of ionic and hydrophobic silanes. The orientation of the oligonucleotide lying on the surface and the quanti ty adsorbed appear to be influenced by whether the surface is cationic or hydrophobic. (C) 1998 Academic Press.