Invited Paper TF-WeM9
Size-Selected Clusters: From 3D Atomic Structure to Applications in Biochips

Wednesday, October 17, 2007, 10:40 am, Room 613/614

In this talk I will address both atomic-scale characterisation and biological applications of size-selected atomic clusters. Today’s advancements in nanotechnology present new challenges for the quality, speed and precision of nanostructure characterization. Here we show that the new generation of aberration-corrected scanning transmission electron microscopes (STEM), coupled with simple imaging simulation, is capable of providing three-dimensional structural information¹ with atomic resolution in a single shot, revealing not only the size but also the shape, orientation and atomic arrangement, for size-selected gold nanoclusters that are preformed in the gas phase and soft-landed on an amorphous carbon substrate. The structures of gold nanoclusters containing 309 (@+=@5%) atoms can be identified with either decahedral, cuboctahedral or icosahedral geometries. The work illustrates a new and efficient means to study the atomic structure and the stability of supported, ultra-small metal clusters in the nanometre range, e.g. catalyst and extracellular particles, with single atom sensitivity. The controlled deposition of such size-selected Au clusters, of size 1-10nm, also provides a route to the fabrication of novel surface binding sites for individual biological molecules, notably proteins. We report the pinning^2,3 of size-selected Au_N clusters (N = 1-100) to the (hydrophobic) graphite surface to create films of arbitrary, sub-monolayer density. Gold presents an attractive binding site for sulphur and thus for cysteine residues in protein molecules. AFM measurements in buffer solution^4,5 show that GroEL chaperonin molecules (15 nm rings), which contain free cysteines, bind to the clusters and are immobilised.⁵. Peroxidase⁶ and oncostatin molecules behave similarly. By contrast, green fluorescent protein (GFP) does not bind, consistent with detailed analysis of the protein surface; the cysteine residues lie in the interior of the folded protein. The results provide "ground rules" for residue-specific protein immobilisation by clusters. The extension of the approach to optical surfaces is enabling the production of prototype biochips (microrarrays) for protein analysis, e.g., early stage cancer-marker detection.

¹Z.Y. Li, J. Yuan, Y. Chen, R.E. Palmer and J.P. Wilcoxon, Adv. Mater. 17 2885 (2005).
²S. Pratontep, P. Preece, C. Xirouchaki, R.E. Palmer, C.F. Sanz-Navarro, S.D. Kenny and R. Smith, Phys. Rev. Lett. 90 055503 (2003).
³S.J. Carroll, S. Pratontep, M. Streun, R.E. Palmer, S. Hobday and R. Smith, J. Chem. Phys. (Comms) 113 7723 (2000); M. Helmer, Nature (News & Views) 408 531 (2000).
⁴R.E. Palmer, S. Pratontep and H.-G. Boyen, Nature Materials 2 443 (2003).
⁵C. Leung, C. Xirouchaki, N. Berovic and R.E. Palmer, Adv. Materials 16 223 (2004).