Electrostatic and hydrophobic interactions on the ODN adsorption process

M. L. CAROT; P. A. FIORITO; R. M. TORRESI; C. D. GARCÍA; C. E. GIACOMELLI

Congreso; 6th International Conference of Biological Physics (ICBP 2007). 5th Southern Cone Biophysics Congress.; 2007

Nucleic acid hybridization is widely used in the detection of the specific complementary strand in molecular biology and appliedfields, such as diagnostic in medicine. An ideal system for theses applications results when solid surfaces are combined with anoligodeoxyribonucleotide (ODN), a fragment of single strand DNA, to induce surface hybridization. Clearly, the capability ofhybridization in such a system is controlled by the orientation and conformation of the adsorbed ODN molecules, which mainlydepend on the surface properties and the solution conditions.The purpose of the present work is to study the adsorption behavior ofsynthetic oligo-ODN (20 bases) onto different solid surfaces. In view of the practical application, this study is especially focused onhow this process is affected by the interactions between ODN molecules and surfaces and on how these biomolecule-surfaceinteractions determine the adsorbed state of the ODN molecules.Information about the interactions involved was obtained bychanging the physico-chemical properties of the system. Hydrophobic interactions were studied by comparing the adsorption onhydrophilic (silica) and hydrophobic (silica + CNT) surfaces. The electrostatic interactions were modulated by performing theadsorption experiments at different ionic strength with and without divalent cations.The surfaces were characterized by tapping modeAFM. The kinetic aspects of the adsorption process were studied by C, an optical technique which enables a continuousmonitoring of the adsorbed amount in time, as a function of the ODN concentration. For an adequate analysis of the experimentalresults, an appropriate optical model considering the surface roughness and the adsorption mode was developed.The adsorption-desorption process of oligo-ODN is conditioned by the electrostatic ODN-surface interactions. On hydrophilic surfaces, adsorptiononly takes place under favorable electrostatic interactions. However, when the electrostatic repulsion is suppressed on thehydrophobic surface, ODN molecules adsorb with the bases (apolar region of the molecule) towards the surface. This orientation ofthe adsorbed ODN is unfavorable for the surface hybridization, indicating that to properly biofunctionalized the surface, hydrophobicinteractions need to be minimized.