Anna Bratek-Skicki oral presentation (OB4-Fri1-1-2)
Selective Protein Adsorption on Stimuli-Responsive Polymer Brushes Studied by ToF-SIMS and Gel Electrophoresis
1 Institute of Condensed Matter and Nanosciences, Université catholique de Louvain, Place Pasteur 1, 1348 Louvain-la-Neuve, Belgium
2 J. Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, Niezapominajek 8, 30-239 Cracow, Poland
Protein adsorption on solid surfaces provides either beneficial or adverse outcomes depending on the application. Therefore, the desire to predict, control, and manipulate protein adsorption on different surfaces has been the main driving force in this area.
In this work, the adsorption of human serum albumin (HSA - 66 kDa, iep at pH 4.7), human fibrinogen (Fb – 340 kDa, iep at pH 5.8), and Lysozyme (Lys – 14 kDa, iep at pH 10) was investigated on stimuli-responsive brushes composed of poly(ethylene oxide) (PEO), poly(acrylic acid) (PAA), and/or poly(2-(dimethylamine)ethyl methacrylate) (PDMAEMA) formed on a gold substrate. Polymer brushes were characterized by X-ray Photoelectron Spectroscopy (XPS), Atomic Force Microscopy (AFM), and water contact angle measurements. PEO inhibits protein adsorption. PAA and PDMAEMA are weak anionic and cationic polyelectrolytes, respectively, featuring a variable density of negative or positive charges depending on pH .
Polymer brush formation and protein adsorption/desorption were further studied by Quartz Crystal Microbalance (QCM). Protein adsorption was performed at pH 7.4-9.0 and ionic strength of 10-3-10-2M, while desorption was carried out by rinsing with a sodium chloride solution at pH 9.0 and ionic strength of 0.15 M. Firstly, protein adsorption was measured from single protein solutions. It was observed that at pH 9.0 and in the ionic strength range 10-3-10-2M, Fb and Lys adsorb on mixed PEO/PAA brushes, while the adsorption of HSA was not observed. Significant adsorption of HSA and Fb was observed on the mixed PEO/PDMAEMA brushes while the adsorption of lysozyme (Lys) was not observed.
Next, adsorption was performed from mixtures of two or three proteins. Time-of-flight ion mass spectrometry (TOF-SIMS) and gel electrophoresis coupled with silver staining were used to identify the adsorbed proteins. Principal Component Analysis (PCA) was used to obtained a more detailed interpretation of the ToF-SIMS spectra. It was proved that selective adsorption of Lys from the mixture of Lys/HSA/Fb on the PEO/PAA polymer brushes is possible at pH 9.0 and ionic strength 10-3M, while Lys and HSA, but not Fb, were adsorbed at ionic strength 10-2M and pH 9.0. Further work is now focused on the performances of PEO/PDMAEMA brushes.
This study shows that by controlling both pH and ionic strength, it is possible to tune protein adsorption/desorption on stimuli-responsive polymer brushes, and that selective adsorption can be achieved from protein mixtures.
This project has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No 659391.