Nanopatterns of polymer brushes for understanding protein adsorption on the nanoscale

We present fabrication of patterned poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) brushes with sub-100 nm features over large areas. The patterned polymer brushes are fabricated by a combination of block copolymer micelle lithography and surface-initiated atom transfer radical polymerization. The PDMAEMA brushes are neutralized and collapsed at pH 9, and positively charged and swollen at pH 4. The protein adsorption and desorption on the patterned PDMAEMA brushes are studied by laser scanning confocal microscopy, atomic force microscopy (AFM), and quartz crystal microbalance with dissipation (QCM-D). In 1 mM NaCl solution at pH 5.8, the patterned brushes take up bovine serum albumin (BSA, isoelectric point similar to 4.8) via electrostatic interactions. BSA adsorbs both inside the brushes and at the outer edge of the brushes. BSA at the outer edge of the brushes is released by rinsing the brushes with 1 M NaCl solutions at pH 4 and 9. Part of the absorbed BSA remains trapped inside the brushes, resulting in an increase of their volume. The regular sub-100 nm features of the patterned PDMAEMA brushes allowed us to directly visualize protein adsorption/desorption by AFM on a nanoscale. The large area of the patterned brushes allowed us to collect statistical results of the nanostructures by QCM-D.