Two polymethylmethacrylate functional nanosphere series, specifically designed for the reversible adsorption of oligonucleotides, were prepared by emulsion polymerization in the presence of two structurally different ionic comonomers, namely two quaternary ammonium salts of 2-(dimethylamino)ethyl methacrylate. The nanosphere size is substantially affected by the ionic comonomer structure and amount. The width of the size distribution tends to decrease with increasing the comonomer amount in solution, and monosized nanosphere samples are obtained at a high comonomer amount. The ionic comonomer weight percentage on the nanospheres increases monotonically in both sample series as the comonomer concentration increases. In contrast, the trend of the quaternary ammonium group surface density is different in the two sample series displaying a regular increase or a maximum value as the ionic comonomer concentration increases.