Layer-by-Layer Assembly of Polyelectrolytes in Nanofluidic Devices

Abstract

A hybrid micro-/nanofluidic device which contains an array of parallel nanochannels has been employed to study polyelectrolyte multilayer (PEM) deposition in confined geometries. Layer-by-layer (LbL) assembly of poly(allylamine hydrochloride) (PAH) and poly(styrenesulfonate) (PSS) at pH 4 and salt concentrations ranging from 0.1 to 1 M was used to conformally coat the nanochannel walls, systematically narrowing the channel width from 222 to 11 nm in the wet state. The thicknesses of confined multilayers were measured using SEM and these results were compared with those obtained on planar, unconfined surfaces. A procedure for direct measurement of the gap thickness using dc conductance was also developed. LbL assembly in the nanochannels resulted in lower bilayer thicknesses than those obtained on planar surfaces. This observation is attributed to the surface charge-induced depletion of unadsorbed polyelectrolytes within the channel. The ability to conformally coat the walls of the nanochannels with functional PEMs opens up new possibilities in the design of active nanochannel devices.