Gold nanoparticles are among the best-studied materials in the context of the current nanotechnology adventure. The reasons for this are their chemical stability, interesting size and shape dependent properties and ease of preparation and handling. In particular, so called monolayer protected clusters (MPCs), which are particles protected by a self-assembled layer of organic thiols, have received much attention since their initial development over ten years ago.¹ They are distinguished from other preparations by their superior stability, which has facilitated previously impossible studies and applications in electrochemistry, nano-electronics, molecular recogniton, catalysis, sensing, materials science, bionanotechnology and other areas.²

After reviewing briefly the field, I will focus on recent developments in the preparation and properties of MPCs in aqueous systems. These materials are important for realizing the potential of gold (and silver) nanoparticles in advanced bio-analytical and biomedical applications. MPCs are easy to detect by a variety of methods, and their sizes range from protein molecules to cell organelles, which makes them ideal candidates for intracellular probes or delivery devices. From a chemist’s point of view the challenge is to design and prepare MPCs, which fulfill the stringent requirements of functioning in biological environments. The materials have to be soluble in water, stable against aggregation and non-specific binding over a range of pH and ionic strength in the presence of biomolecules, and the incorporation of a controlled number of moieties with specific functionality has to be possible.

I will discuss recent examples from our work in Liverpool on the use of short peptides as stabilizing ligands,³ the introduction of calixarenes as non-biological recognition groups in aqueous systems⁴ and the use of DNA and other biomolecular functionalities to control the binding properties of MPCs in solutions and on bio-analytical microarrays.⁵

1.         M. Brust, M. Walker, D. Bethell. D. J. Schiffrin, R. Whyman, J. Chem. Soc., Chem. Commun. 1994, 801.

2.         M. Brust, C. J. Kiely, Colloids and Surfaces A 2002, 202, 175.

3.         R. Levy, N. T. K. Thanh, R. C. Doty, I. Hussain, R. J. Nichols, D. J. Schiffrin, M. Brust, D.G. Fernig. J. Am. Chem. Soc. 2004, 126, 10076.

4.         T. R. Tshikhudo, D. Demuru, Z. Wang, M. Brust, A. Secchi, A. Arduini, A. Pochini, Angew. Chem. Int. Ed. 2005, 44, 2913.

5.         Z. Wang, R. Levy, D.G. Fernig, M. Brust, Bioconjugate Chem. 2005, in press.