Self-assembly or bottom-up assembly has been discussed as an alternative, apparently preferred by nature, to currently dominant top-to-bottom approach to fabrication of micro- and nanosystems. However, whereas the top-to-bottom approach offers a great deal of flexibility in terms of geometrical patterns and material selection, most of the recently developed methods of self-assembly are applicable to fabrication of highly periodic structures with building blocks made of the same material. While this limitation may be acceptable in some applications, such as photonic crystals, it is certainly unacceptable in many other important applications such as biosensors, chips for genetic discovery, and future electronic systems.

Can the advantages of self-assembly be combined with the flexibility of top-to-bottom fabrication methods? Magnetically programmable self-assembly will be discussed as one approach permitting such flexibility. In this approach, assembly of magnetic colloidal particles is guided by information magnetically recorded on a substrate. The colloidal particles may either carry different materials themselves, or be used to mask the substrate during self-assembly of different materials. Examples of structures fabricated by this technique will be shown and future challenges will be discussed.