Polyamidoamine-grafted silica nanoparticles were synthesized, characterized and investigated for the feasibility as pseudostationary phases in alkaline buffer for separation of cationic and anionic proteins, viz., lysozyme, cytochrome C, gamma globulin, and myoglobin. Neither bare silica nanoparticles nor polyamidoamines nor their mixtures as pseudostationary phases could lead to simultaneous separation of the four proteins. However, polyamidoamine-grafted silica nanoparticles not only suppressed the irreversible wall adsorption of the cationic lysozyme and cytochrome C, but also provided selectivity toward all the proteins. We found that polyamidoamine generation two-modified silica nanoparticles were the optimum pseudostationary phases with respect to detection sensitivity and separation efficiency; presence of the nanoparticles at 0.01% in the running buffer of 12.5 mM tetraborate/phosphate at pH 9.1 resulted in baseline resolution of the four proteins.

We studied the influences of imidazolium-based ionic liquids as additives in low ionic strength phosphate solution on releasing DNA from polyamidoamine dendrimer-grafted silica nanoparticle surfaces. The effects of the side-chain length of the imidazolium group, the anion and the concentration of the ionic liquid, the generation of the dendrimer, and the pH and the concentration of the release solution were investigated. It was found that addition of 4 mM 1-hexyl-3-methylimidazolium bromide to 5 mM phosphate at pH 11 could markedly promote the desorption of DNA fragments, with a desorption efficiency of 99.0%. Compared with the conventional strategies employing high-salt solutions or elevated temperature for acceptable recoveries, the method described here enabled quick release of DNA fragments that permitted direct, accurate analysis, and further treatment without desalting.

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