Patterned Multilayer Systems and Directed Self‐Assembly of Functional Nano‐Bio Materials

Abstract

Patterned and controlled layer-by-layer (LbL) films on surfaces can serve as excellent molecular templates for applications in optoelectronic display materials, biosensor arrays, and drug screening devices. The ionic LbL assembly technique, introduced by Decher in 1991 [1, 2], is among the most exciting developments in this area. Films formed by electrostatic interactions between oppositely charged poly-ion species to create alternating layers of sequentially adsorbed poly-ions are called “polyelectrolyte multilayers” (PEMs). One of the soft lithographic methods, microcontact printing (mCP), has been used in physics, chemistry, materials science, and biology to transfer patterned thin organic films to surfaces with sub-micron resolution [3, 4]. Unlike other fabrication methods that merely provide topographic contrast between the feature and the background, mCP also allows chemical contrast to be achieved by selection of an appropriate ink. Microcontact printing offers advantages over conventional photolithographic techniques because it is simple to perform and is not diffraction limited. Lee and coworkers at the Michigan State University have challenged new patterning approaches for the last several years. For the first time, they have demonstrated self-assembled monolayer (SAM) patterning on PEMs, as opposed to on gold or silicon substrates [5]. In the work, the process of creating chemically patterned and physically structured surfaces was described by stamping polyethylene acid molecules on PEM coated surfaces, as illustrated in Figure 41.1. The activated carboxylate functional group binds ionically to the topmost positive surface of the PEM surfaces, and the other end (PEG units) resists the deposition of subsequent polymer (polyelectrolyte) layers. To deposit thin uniform PEG SAMs on PEMs, ionic interactions were capitalized. The deposited PEG patterns acted like an efficient resisting area which resists non-specific adsorption of polyelectrolytes, charged particles, and biomolecules and cells. The exposed PEM regions served as active surfaces attracting a variety of functional species (Figure 41.2) [5].