Fig 2.

PLL/oligonucleotide multilayer growth. (a) Thickness of PLL/oligonucleotide multilayer from ellipsometry measurements on silicon substrates that were prepared identically to the field-effect sensor surfaces. The thickness increases linearly. (b) Surface potential signal of multilayer growth in solution measured with a field-effect sensor. The signal alternates according to the charge of the adsorbed layer (positive for PLL and negative for oligonucleotides). The same PLL and oligonucleotide concentrations as described for a were used. Each solution was injected twice and followed by an injection of buffer before the next layer was adsorbed. Blue arrows indicate PLL injections, and red arrows indicate oligonucleotide injections.