Synthesis of poly[(ar-vinylbenzyl)trimethylammonium chloride] brush covalently attached to silicon disc surface by reversible addition-fragmentation chain transfer polymerization and its use for dna immobilization

In this study, cationic poly[(ar-vinylbenzyl)trimethylammonium chloride] (PVBTAC) brushes covalently attached to silicon wafer surface were synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization technique and used for DNA immobilization. (4-cyanopentanoic acid)-4-dithiobenzoate was synthesized as RAFT agent and characterized by 1H Nuclear magnetic resonance and Fourier transform infrared spectroscopy (FT-IR). Bromine and amine terminated silicon surfaces were prepared by using 3-bromopropyltrimethoxysilane and allylamine precursors, respectively. Then, RAFT agent or initiator was immobilized on these organic overlayers. Finally, cationic PVBTAC brushes were synthesized by RAFT polymerization. The chemical composition and other properties of the brushes were characterized by X-ray photoelectron spectroscopy (XPS), FT-IR, atomic force microscopy (AFM), ellipsometry and water contact-angle measurements. The surface morphologies observed by AFM indicated that the surfaces were extremely homogeneous. Hysteresis values of the surfaces determined by dynamic water contact angle measurements decreased with increasing polymerization time. The water contact angle titration of the surfaces indicated that cationic state of the surfaces did not change with increasing pH. The number average molecular weight of the free polymers formed in the solution was determined by gel permeation chromatography. Grafting parameters such as grafting density and surface coverage etc. values were calculated from the ellipsometric thickness and the number average molecular weight values. These cationic brushes were used for DNA immobilization. Effects of DNA concentration and incubation time on the DNA immobilization were investigated. The results of these studies showed that the cationic PVBTAC brushes can be potentially used in DNA immobilization.