Molecular Self-Assembly on Gold and Metal-Oxide Surfaces

Material Matters Volume 3 Article 2

Molecular Self-Assembly1 is the assembly of molecules without guidance or management from an outside source. Self-assembly can occur spontaneously in nature, for example the self-assembly of the lipid bi-layer membrane, surrounding cells.

An approach to Molecular Self-Assembly that is efficient and that has received ample attention during the last decade is the creation of Self-Assembled Monolayers (or SAMs) using relatively weak intermolecular interactions between certain types of organic molecules, such as thiols or phosphonic acids, and a gold or oxidic surface.

Molecular Self-Assembly on Gold

Several forces are driving assembly of alkyl thiols on a gold surface. First, the sulfur-gold interactions are quite strong, ~45 kcal/mol, which allow for a relatively strong bonding of the film-forming molecules to the surface.

Figure 1 Schematic overview of a thiol molecule on a gold surface

Furthermore, hydrophobic interactions between carbon and hydrogen atoms in the alkyl thiol molecules can significantly lower the overall surface energy thus promoting the formation of a self-assembled monolayer, especially if the alkyl chains contain at least 10 carbon atoms.2,3

Molecular Self-Assembly on Metal-Oxide Surfaces

Recent advances in the area of micro and nano electronic materials have extended SAMs beyond conventional gold/ thiol systems. To expand the choice of the substrates used for the preparation of SAMs, the chemical functionalities in film-forming molecules can be altered by introducing phosphate or phosphonate-groups. Such polar acidic molecules are capable of interacting with diverse metaloxide surfaces (e.g. Al2O3, Ta2O5, Nb2O5, ZrO2 and Ti2) and form films with a similar degree of ordering as for alkyl thiol SAMs on gold.4

Applications of SAMs comprise materials for semiconductor electronics industry such as nano-wires, nano-transistors, and nanosensors in large numbers. A few more examples of SAMs applications include surface wetting, non-fouling property, electrochemistry, surface passivation, protein binding, DNA assembly, corrosion resistance, biological arrays and cell interactions.5-7

Figure 2 Some applications of self-assembled monolayers.

  1. Non-fouling surfaces
  2. SAMs with specific binding receptors
  3. Cell supports for native cell growth and studies
  4. Molecular electronics
  5. Microarrays
  6. Separations

back to top Back to Top


  1. Material Matters™, 2006, Vol.1, No. 2.
  2. M.D. Porter et al. J. Am. Chem. Soc. 1987, 109, 3559.
  3. C.D. Bain et al. J. Am. Chem. Soc. 1989, 7155.
  4. G. Hahner et al. 17(22):7047–7052, 2001.
  5. J.C. Love et al. Chem. Rev. 2005, 105, 1103.
  6. N.K. Chaki et al. Biosensors & Bioelectronics 2002, 17, 1
  7. A. Ulman, Chem. Rev. 1996, 96, 1533.

back to top Back to Top

Related Links