Determination of the main forces driving DNA oligonucleotide adsorption onto aminated silica wafers

The adsorption of a 20-base long 5'-amino-linked oligodeoxyribonucleotide (ODN) onto aminopropylsilane-modified silica wafers has been investigated. At first, silanized surfaces were characterized by contact angle measurements, X-ray photoelectron spectroscopy (XPS), ellipsometry, and atomic force microscopy (AFM). Adsorbed amount of oligonucleotides was estimated by radioactive counting or colorimetric hybridization reaction. The first technique was useful for direct counting, while colorimetric detection, implying an hybridization reaction between adsorbed ODN and its complementary sequence, provided information about its accessibility on the wafer. With the purpose of determining the driving forces of the ODN adsorption onto these surfaces, conditions such as initial ODN concentration, pH, and ionic strength have been examined. The adsorption process could be described as a Langmuir reversible adsorption type. Surface charge contribution has been investigated by raising pH values from 4 to 10.8. Electrostatic interactions between the negatively charged ODN and the aminated groups on the silica wafers were found to play a major role in the adsorption process. Moreover, a drastic influence of the ionic strength on the ODN adsorbed amount was evidenced. (C) 1997 Academic Press.