1. SCANNING PROBE MICROSCOPY
Developments of the technique have meant that good representations of biological materials are now obtainable. Most importantly, the equipment is now available whereby both Atomic Force Microscopy and Scanning Tunnelling Microscopy can be conducted on aqueous solutions of proteins and more elaborate biological structures. We, (Dr. Jason J. Davis and I) have been successful in obtaining STM images of proteins, including metallothionein, azurin (A), rubredoxin (B) and cytochrome P450 (C). AFM images have been obtained of amyloid fibrils (D) (in collaboration with Professor C. M. Dobson) and striking images of cardiac cells (E) have been derived (in collaboration with Professor T. Powell, Physiology).
Shown below is a movie generated from the raw tunnelling imaging data of glucose oxidase molecules adsorbed on a graphite electrode surface (under ambient conditions). The electrode is a single crystalline (HOPG) model of a real surface and was initially (mildly) pre-oxidised (by anodising) prior to enzyme deposition. This process generates hydrophilic surface oxygen-based moieties which serve to anchor the enzyme molecules to the (otherwise hydrophilic) surface. Striking is the fact that the butterfly shape of the structure can be resolved by the tunnelling tip; each molecule is approximately 6nm across. The molecules immobilised in an active state; on the addition of substrate and a ferrocene mediator (FMCA) a characteristic catalytic electrochemical response is observed.
2. THE DESIGN OF ULTRAMICROELECTRODES
We, in collaboration with Prof. P. J. Dobson, (Dept. Engineering Science) have been successful in making electrodes as small as 200nm in diameter. However, 1-2mm-diameter electrodes are sufficient for sensors. Most interest concerns their elaboration into microarray electrodes (F) that should permit the simultaneous determination of a variety of substances. We have started a company, Oxford Biosensors, to exploit this methodology.
3. THE DIRECT ELECTROCHEMISTRY OF PROTEINS AND ENZYMES
The direct electrochemistry of enzymes can now be readily obtained (studied by Dr. E. N. K. Wallace and colleagues). We are directing this work towards those enzymes that might be of use in biosensors. Thus we are studying various monooxygenases including cytochrome P450, the latter in collaboration with Dr. L-L. Wong.
All the above topics are relevant to the design of sensors. Like the glucose sensor, which was developed eighteen years ago, we believe that novel sensors will result from the synthesis of the physics, chemistry and biochemistry and that is the main purpose of the company referred to above. We (Professor Peter Dobson, Dr. Peter Leigh, Dr. Luet Wong and I) are concerned with sensors that may find medical and environmental applications: a company, Oxford Biosensors Ltd., started in August 2000 and is well on the way to achieving this aim.