In the article "Scenes From a Marriage--Of Optics and Electronics" by Robert F. Service in Science, Vol. 268, Jun. 23, 1995, a method is described which is called fluidic self-assembly. Therein small optical components, such as lasers are mixed with a fluid, such as ethanol and are poured over a silicon wafer which comprises holes matching the shape of the lasers. Bit by bit the lasers settle into the holes under the influence of gravity. When a laser goes in a hole properly it stays there because it is effectively removed from the shear forces associated with the movement of the liquid that otherwise would carry the lasers away. By this method no alignment is needed to help the lasers go where they shall be located. However, no additional specific force guides the lasers to their destination.
The article "Direct Measurement of the Forces Between Complementary Strands of DNA" by Lee, Chrisey and Colton in Science, Vol. 266, Nov. 4, 1994, is related to interaction forces between single strands of DNA. Therefor, two surfaces covered with DNA strands are brought in near vicinity until the attractive forces of the strands effect a chemical binding such that the surfaces are held together by a specific force.
In "Immobilization of Antibodies on a Photoactive Self-Assembled Monolayer on Gold" by Delamarche et al. in Langmuir, Vol. 12, Nr. 8, pp. 1997-2006, Jan. 4, 1996 a strategy for immobilizing biomolecules on a photoactivable surface is discussed. Therefor, a gold substrate is functionalized with a dialkyl disulfide which forms a self-assembled monolayer (SAM). Afterwards the reactive ester groups at the termini of the SAM are converted into photoactivable groups based on benzophenone. This photoactivable group acts as a crosslinking agent that is inert under ambient light and is activated by near-UV light. UV irradiation causes biradical formation at the ketyl center of the benzophenone. Thereby, a molecule or macromolecule such as a protein undergoes covalent attachment to the substrate via the SAM. Proteins deposited on a solid substrate find applications e.g. in enzyme-based biosensors and in forming biocompatible surfaces.
Microcontact printing is the subject of the article "Patterning Self-Assembled Monolayers: Applications in Materials Science" by Kumar, Biebuyck and Whitesides in Langmuir, Vol. 10, Nr. Feb. 5, 1994, pp. 1498-1511. Polydimethylsiloxane (PDMS) is used as material of a stamp which is patterned by using a lithographic process. The stamp is then provided with alkanethiol serving as "ink" for the following stamping process. By touching a gold substrate surface the protrusions of the pattern transfer thiol onto the substrate where it forms a patterned SAM. The molecules in these SAMs are arranged in ordered crystalline domains on the surface of the substrate having one of their ends attached covalently to this surface and the other end extending upright, away from the substrate. Thus, the new surface of a substrate printed upon with thiol has interfacial properties characteristic of one end of the molecules of the SAM. This SAM can be used in a following step as a mask for an etching step such that the pattern is transferred into the surface of the substrate. The alkanethiol molecules are not oriented on the stamp with this procedure.
Further known is a method called the Langmuir-Blodgett process. Information about this process may be derived from A. Ulman's "An Introduction to Ultrathin Films", Academic Press, San Diego, Calif., 1991. This method of thin-film formation organizes molecules at an air-water interface (Langmuir film). Organization results from progressively greater lateral confinement of the molecules at the air-water interface by use of a moveable mechanical barrier to sweep them together. The molecules undergo a disorder-order transition at sufficiently high confinement that affects the organization of the molecules in two-dimensional crystals with a homogeneous in-plane composition and an asymmetric out-of-plane distribution having one end of the molecule rigorously disposed at the air interface and the other remaining immersed in the water. Moving a substrate through such an air-water interface having a Langmuir film transfers it to the substrate (Langmuir-Blodgett process). Although the molecules in the Langmuir-Blodgett film remain organized they are not covalently attached to the substrate a priori as is the case for the formation of SAMs. Because of this lack of covalent linkage Langmuir-Blodgett films are fragile. No method is known which may be used to pattern such a film while preserving its viability.
In "Light-directed, spatially addressable parallel chemical synthesis" by Foder et al. in Science, Vol 251, p. 767, Feb. 15, 1991, solid phase chemistry, photolabile protecting groups and photolithography have been combined to achieve light-directed spatially addressable parallel chemical synthesis to yield a highly diverse set of chemical products.
In "Guide to protein purification", by Murray P. Deutscher, Academic Press, Vol. 182 is given an introduction into affinity chromatography. Affinity chromatography is a technique by which ligands or receptors are purified. Typically, a solid substrate having a high surface area is derivatized on its surface with either the ligand or the receptor. A mobile phase, usually liquid, is moved over the solid substrate. This liquid contains the complement of the liquid or receptor, often in a matrix comprising many other types that do not form the complementary ligand-receptor complex. Thus, as the flow occurs, those molecules undergoing ligand-receptor complexation proceed slower than other molecules that have not such binding possibility. As a consequence of this retardation in the movement of molecules forming complexes, a separation is affected that concentrates increasingly those molecules forming the complexes. These methods are general and used extensively in the purification of small and large molecules known in the chemical and biochemical fields.
Providing colloidal particles of gold with DNA strands and their assembling via linking duplexes is reported on in "A DNA-based method for rationally assembling nanoparticles into macroscopic materials" by Chad et al in Nature, Vol 382, Aug. 15, 1996, pages 607-609. However, no ordered assembly is achieved. On pages 609-611 of the same journal the article "Organisation of `nanocrystal molecules` using DNA" deals with the use of long DNA linking duplexes for an ordered assembly of nanocrystal molecules.