DEVELOPING DYE ASSAY TO QUANTIFY CHARGE DENSITY SURFACE-GRAFTED BY PYRIDINE-N-OXIDES

The formation of biofilm on surfaces is currently a problem in various fields, from industrial to medical settings. To prevent the attachment of biomolecules and microorganisms on surfaces, it has been demonstrated that surface modification with zwitterionic polymers is an efficient approach. Recently, polymeric N-oxides have emerged as promising candidates for such applications, exhibiting low-fouling properties and antibacterial activity. The quantification of the charge density provided by N-oxides is a critical parameter to determine, as it plays an important role in antifouling and antibacterial properties. The polymeric N-oxide used in this project is pyridine. Initially, 4-vinylpyridine is grafted onto the activated PE surface via plasma activation; subsequently, to obtain the oxidized form, a solution of hydrogen peroxide and glacial acetic acid (1:1) is used. The success of the grafting is confirmed by IR spectroscopy and contact angle measurements. To characterize the charge density of polymeric N-oxides, a three-step process using a dye solution has been developed: the staining step, where the dye interacts with the grafted surface; the washing step, to eliminate residual dye; and the desorption step, to release the molecule and then quantify the dye concentration via UV-vis spectroscopy. This process exploits the electrostatic interaction between the dye and the grafted surface. This occurs because, at a specific pH, the N-oxides present a positive charge on the nitrogen, while the dye, containing a sulfonic group, presents a negative charge. This indicates that pH also plays an important role in this research. The assay conditions determined in this investigation were effectively employed to determine the charge density grafted of Pyridine-N-oxides.