Surface‐Directed Colloid Patterning: Selective Deposition via Electrostatic and Secondary Interactions

Abstract

A great deal of excitement has been generated around the idea of controlled and ordered arrays of micron-to nanometer-scale particles arranged on surfaces. The ability to direct the positions of such small ªobjectsº onto a substrate provides a large advantage in the creation of molecular-to nanometer-scale devices, biological sensors, combinatorial arrays, and electronic and photonic devices. For these reasons, a number of approaches have been investigated which involve the manipulation of colloidal systems using electrostatics [1±6], lithography, dip-coating, physical confinement in etched or molded grooves [7], sedimentation [8±13], capillary forces [14], flow fields [15, 16], electrophoretics [17], and microfluidics to guide specific systems to different regions of a surface. An especially compelling approach to directing deposition is to use secondary interactions such as coulombic interactions, hydrogen bonding, hydrophobic interactions, and biospecific interactions, as a means of guiding different elements to a surface. This form of self-assembly provides the basis for positioning a broad range of elements based on the presence of complementary functional groups on planar and nonplanar surfaces; this concept of ªsurface sortingº has been explored in our group with polyelectrolytes [18±21], and more recently, colloidal particles [22±25], as a potential tool in microfabrication. The chemical basis of this approach is the use of surface functionality for templating and directing the assembly of nanometer to micron-sized materials systems.The concept of surface sorting is illustrated schematically in Fig. 10.1. A chemically patterned surface containing different regions of charged, hydrogen bonding, hydrophobic, or biospecific ligand groups, acts as a template to which materials species of complementary functionality deposit onto their corresponding sites. This process can take place through a series of sequential adsorption steps, or, under highly controlled conditions with more specific interactions, it may be possible to achieve the desired effect in a single step. This concept is universal, and can be extended to a broad range of systems, including polyelectrolytes, colloidal particles, proteins, DNA, nanotubes, etc. Nonlithographic patterning methods, particularly contact printing techniques [26], allow us to create such systems on a

Programmable patterning of polymeric microparticles by floating electrodes-assisted electrospray

“…Current approaches utilize electrostatic force [6], physical confinement [7], capillary force [8] or dielectrophoresis [9] for positioning colloidal microparticles at desired spatial sites. Among these methods, electrostatic manipulation of particles is attractive due to the enhanced surface-to-volume ratio at the small scales [10][11][12]. For example, aerosol droplets were sprayed to deposit small particles on a surface with prepatterned electrodes [13,14], where the patterning resolution can be enhanced by introducing ions to form the 'electrostatic lens' [15].…”

Nano-porous electrode systems by colloidal lithography for sensitive electrochemical detection: fabrication technology and properties

“…Following this strategy it is possible to generate extended arrays of nanopores by the evaporation of a metal layer on the top of the surface and the removal of the colloidal spheres. Surface directed deposition of colloidal particles is achieved by introducing a surface charge at specific regions on the sample employing self-assembled monolayers or physisorbed polyelectrolytes [22]. Adsorption phenomena may be described by the random sequential adsorption-(RSA) model [23].…”