Functionalizing Nanochannels with Polyelectrolyte Polymer Brushes for Nanofluidic Applications

Nanochannels with responsive gating characteristics are attractive design elements in a variety of applications such as particle sorting, viral detection, and flow regulation. To achieve this, we employed selective functionalization of nanochannel sidewalls with poly(dimethylaminoethyl methacrylate) (PDMAEMA) as a pH-responsive polyelectrolyte polymer. We investigated the channel gating response to variations in solution pH and ionic strength by tracking conformational and structural changes of the PDMAEMA brush using specular and off-specular neutron reflectometry. Simultaneous fits of the specular and off-specular signals to a dynamical theory model showed that the polymer brush assumes a collapsed state under basic solution conditions – equivalent to an open gate. In contrast, measurements under acidic conditions revealed an expanded brush state, representing a partially closed gate. Additional variations in salt concentration resulted in further modifications to the brush conformation and channel gate width. These findings open new possibilities in polyelectrolyte polymer applications in tunable nanofluidics and lab-on-chips devices with advanced designs and improved functionality.