Methods for the accurate positioning of nanometric beads on a substrate have been developed over a number of years, and range from serial AFM techniques for single bead positioning, e.g., to parallel techniques for the positioning of large populations of beads in monolayer or multilayer architectures, typically from a liquid suspension. For example, topographic cues have been used for bead-based protein array production, although, in this case, there is a random distribution of beads within the topography. Bead patterning has also been achieved in capillaries using a Micromolding in Capillaries (MIMIC) technique. Submitted to 2 Line patterns with micrometer widths are possible with this technique achieving good multilayer organization. For monolayer bead patterning at micrometer dimensions, electrostatic forces and similar electrostatic assemblies using nano-xerography, as well as patterning by selective chemical functionalisation and by subtracting top-down processes are possible.

Recently, approaches to the micropatterning of nano-dimensioned beads based on contact printing have appeared. Single-particle resolution has been achieved by directed assembly of the nano-beads on structured poly dimethylsiloxane) (PDMS) templates. The beads are then transferred from the filled PDMS template to a substrate by micro-contact printing. The beads’ surface composition during assembly must be tuned to maximize the bead-surface interaction forces and to avoid strong adherence to the PDMS. Printing of dry nano-beads is however hard to realize. On the other hand, selective removal of beads from a surface, using PDMS structured moulds, has been achieved by lift-off and micro-contact stripping. While the former needs a 3 hour contact heat treatment to pattern close-packedsilica nano-beads, the latter reports on a resolution limitation due to the crystal packing of the beads. Normally, in the reported contact printing based methods, the beads have to be loosely attached so that bead transfer or removal will not be inhibited.

Advanced Materials DOI: 10.1002/adma