Dependence upon ionic strength in the immobilization of probing oligonucleotides onto streptavidin-modified probe surfaces

For the production of reliable DNA chip systems, it is imperative that the probe DNA be properly immobilized upon the electrode surface. The ionic strength in solution is the one of the most important factors for the proper immobilization of DNA. We have observed the dependence upon ionic strength (I) in buffer solution by quartz crystal microbalance (QCM) when probe ssDNA molecules were immobilized upon gold electrode surfaces by utilizing the characteristics of streptavidin–biotin interaction. When utilizing a Tris–HCl buffer solution with I = 0.01, biotinylated probe ssDNA was not successfully immobilized upon the streptavidin-modified gold surface. Conversely, when a combination of Tris–HCl and TBS buffer with I = 0.16 was utilized; we were successful in immobilizing biotinylated probe ssDNA upon the streptavidin-modified surface. This is a strong indication that ionic strength in buffer solution is an important factor in the stability of the immobilization process of biomolecular reagents onto the gold electrode surface.