ANALYTICAL PROCEEDINGS, JANUARY 1993, VOL 30 55 Biological Applications of Scanning Tunnelling Microscopy Some time ago a meeting on this topic was held in the University of Nottingham, convened on behalf of the Biological Methods Group by Dr. S. Tendler. At the time it proved impossible to secure extended summaries of the papers for Analytical Proceedings but because of considerable interest in the technique it has been decided to publish very brief abstracts of the papers as a report. STM of Biopolymers: How Does it Work, and What do the Images Mean? Professor S. M. Lindsay (Department of Physics, Arizona State University, Tempe, A 2 85287, USA) opening by stating that scanning tunnelling microscope (STMs) (and more recently atomic force microscopes, AFMs) have produced some impressive pictures of uncoated biomolecules.However, the STM (and AFM) tips interact strongly with substrates, producing artifacts and sweeping away loosely absorbed molecules. Electrochemical methods can be used to bind molecules reliably, and to control the environment of the adsorbate during imaging. The STM can image large ‘insulating’ molecules. While the contrast mechanism is not understood generally, theoretical and experimental studies indicate that resonant tunnelling plays a role, illustrating the potential of STM for probing electronic properties of individual adsorbed molecules. The complexity of the contrast mechanism can make interpretation of STM images very difficult, although chemical identification appears to be possible in certain instances. However, both the STM and AFM show promise of yielding important biological information on a nanometer scale.One example is the sequence directed kinking and bending of nucleic acid polymers. STM Analysis of Polysaccharides and Peptides - Molecu- lar Conformation, Packing and Surface Ordering of Biomolecules Drs. T . J. McMaster and V. J . Morris (Institute of Food Research, Norwich Laboratory, Colney Lane, Norwich NR4 7UA) pointed out that scanning tunnelling microscopy (STM) is of great potential for the direct imaging of biological and biomedical molecular systems to angstrom resolution, without the necessary recourse to the coating and in vacuo operation normally associated with other high resolution microscopical techniques. This will be demonstrated by reference to the results of STM studies on a range of biomolecules.Polysaccharide, peptide and protein molecules displaying a variety of structural forms have been imaged. Linear molecules of poly(y-benzyl-L-glutamate) (PBLG) have been induced to form two-dimensional periodic arrays on a flat surface, and the internal secondary structure has observed. Isolated molecules of the small cyclic polypeptide, valinomycin, have been imaged and the internal cavity has been resolved. Images of less ordered structures such as the zein protein from maize and immunoglobulin molecules have been obtained. These pro- teins are not crystallizable, and no complete X-ray structure is known for them. Hence, STM provides three-dimensional structural information not available from other biophysical techniques.Scanning Tunnelling Microscopy of Proteins Dr. M. Steadman (National Physical Laboratory, Teddington, Middlesex T W l l 0LW) discussed aspects of her work on the STM analysis of proteins which includes immunoglobulins. In addition, the need for accurate calibration of STM systems was highlighted. Calibration methods were discussed. Scanning Probe Microscopy Professor Andreas Engel (M. E. Muller Institute for High- Resolution Electron Microscopy at the Biocenter University of Basel, CH-4056 Basel, Switzerland) pointed out that scanning tunnelling microscopy exploits the tunnel effect to guide a tip at atomic distances over a conductor using a sensitive servo system. Notoriously low conductance of biomacromolecules requires a conducting metal coat for reproducible measure- ments of the surface topography.Alternatively, minute forces as well as temperature changes can be used to probe the surfaces of insulators. Such sensors can be used in aqueous media and may ultimately become tools to measure structure and function of biological systems in situ. Application of Atomic Force Microscopy to Biology Hans-Jurgen Butt (Max-Planck-Institut fur Biophysik, Kenne- dyallee 70, 6000 Frankfurt 70, Germany) said that the atomic force microscopy (AFM) is a scanning probe microscope capable of resolving atoms on hard materials. As the AFM does not require a conductive sample, it was soon applied to biological materials. A lysine crystal was resolved with molecular resolution and the clotting of fibrinogen was imaged in water in real time. Two important fields of investigation are sequencing DNA and-even more important -imaging of membrane structures.Although encouraging progress has been made, sequencing DNA with the AFM is not yet reliable. The main problem is that on flat surfaces like mica the DNA is pushed around by the tip. However, samples of membrane structures, organic monolayers and bilayers, proteins embed- ded in a lipid layer, and membrane proteins, have been imaged with molecular resolution. In addition, the surfaces of bacteria, plants, and red and white blood cells were imaged in air and water. A problem in atomic force microscopy is the force applied by the tip to the sample. Are these forces strong enough to deform or even destroy biological materials? This question will be addressed and perspectives of atomic force microscopy in biology will be discussed.Biological Applications of Scanning Tunnelling Micro- scopy: Integration with Computational Chemistry Drs. D. E. Jackson, M. C. Davies, C. D. Melia, S. J . B. Tendler and P. M. Williams (VG STM Laboratory for Biological Applications, Department of Pharmaceutical Sciences, University of Nottingham, Nottingham NG7 2RD)56 ANALYTICAL PROCEEDINGS, JANUARY 1993, VOL 30 produced the final paper. Dr. Tendler stated that the ability of scanning tunnelling microscopy to provide fundamental infor- mation on biological molecules was now being realized, with several studies reporting good image data on a range of molecule types. The potential for topographic information at near-atomic resolution on single surface-adsorbed biomol- ecules indicated that STM was emerging as a new and very important complementary biophysical technique for the struc- tural analysis of biomolecules.However, in order to establish STM in this biophysical role, initial data sets needed to be interpreted in the light of structural parameters derived by other techniques (e.g., X-ray crystallography, high-field NMR computational chemistry). His group believed that the cost effective way to integrate such complementary 3-dimensional data sets was through the development of appropriate software tools for use on high-performance computer graphics systems. The presentation described the ongoing programme of work in their laboratories to establish STM as a valuable tool for the structural elucidation of biomolecules.Initial results for the analysis of several biological samples including DNA and proteins were presented. New software algorithms were described for the manipulation, interrogation and display of STM data sets. In addition, image analysis techniques utilizing Fast Fourier Transforms convolutions were presented. JAASbase A unique database of atomic spectrometry reference information for the practising analyst JAASbase is a new PC-based product from the The database consists of listings of published Royal Society of Chemistry designed to meet every atomic spectrometry papers and conference atomic spectroscopist’s need for a comprehensive, papers , and includes tabulated information relating yet inexpensive source of current analytical atomic to the application of relevant techniques.The spectrometry information. It contains over 20,000 references are easily searched with the database regularly updated references compiled from the manager Idealist which also enables the addition of atomic spectrometry literature. personal data to the database. Subscription Details JAASbase 1993 Updates f99.00/$218.00 JAASbase Backfile (1987-1992) f230.00/$506.00 Idealist Software f 2 10.00/$462 .OO Six updates will be issued at regular intervals through 1993. Special Introductory Offer Take out a subscription to JAASbase Updates, buy the JAASbase Backfile and receive Idealist absolutely free! Offer available only until July 1993. ROYAL SOCIETY O F C H E M I S T R Y JAASbase is an invaluable tool for all practising analysts - order your copy today! @- To order JAASbase and for further information please contact: Sales and Promotion Department, Royal Society of Chemistry, Thomas Graham House, Tel: +44 (0)223 420066. Fax: +44 (0)223 423623. Telex: 818293 ROYAL. Science Park, Milton Road, Cambridge CB4 4WF, United Kingdom. && Intormation Services