Construction of multiple generation nitriloacetates from poly(PEGMA) brushes on planar silicon surface for enhancement of protein loading

We constructed multiple generation nitriloacetates from poly(poly(ethylene glycol)monomethacrylate) brushes on a planar silicon surface (Si-g-P(PEGMA)) to improve the capacity of binding proteins and the biofouling repellence. Firstly the freshly etched Si(111)-H reacted with 10-undecen-1-ol under an optimized microwave irradiation condition to produce hydroxyl-terminated substrates. Secondly surface initiators for atom transfer radical polymerization were introduced by means of esterification between 2-bromo-2-methylpropionyl bromide and surface hydroxyl groups. Thirdly polymer brushes of Si-g-P(PEGMA) were grown from surface initiators; then their side chain hydroxyls were carboxylated with succinic anhydride to become polymer brushes of Si-g-P(PEGMA-COOH). Finally multiple generation nitriloacetates were obtained by iterative esterification of carboxylic acids with N-hydroxysuccinimide (NHS)/N,N'-dicyclohexylcarbodiimide, yielding amino-reactive NHS esters, and successive amidation with aminobutyl nitrilotriacetic acid. After coordinated with Ni(II), the first to third generation nitriloacetates were applied to bind histidine-tagged thioredoxin-urodilatin. All stepwise conversions were monitored with multiple transmission-reflection infrared spectroscopy (MTR-IR). The highly sensitive MTR-IR spectra provide clear stretching bands of amide v(NH) at 3441 and 3345 cm(-1), whose integrated peak areas were used to estimate the enhancement ratios of protein loading by multiple generation nitriloacetates as first generation:second generation:third generation = 1:1.7:2.3. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim