Biosensors: For Glucose, Cholesterol and …

Professor H. Allen O. Hill, Oxford Biosensors Ltd.

No-one could fail to be fasci­nated by electron transfer reactions in biological systems. All living systems depend on such processes: without ‘moving’ electrons, there is death. Of course, we must be clear: electrons, in living systems, are always associated with molecules and are trans­ferred when conditions are right and when the molecules meet.

At a seminar in the seventies, I asked the speaker whether or not the electrochemistry of such proteins involved in electron transfer have ever been studied. As far as he knew there had been no such reports. This I found to be very strange. I had come to regard highly electrochemistry as a technique when I used it in the sixties to fathom the chemistry of vitamin B12: it was neat, cheap and easy to interpret. I persuaded a young undergraduate student, Mark Eddowes to ‘have a go’. Initially, we had no success but we then realised that the protein we were investigating, cytochrome c, was highly charged, having not one, not two but seven positive charges and most likely it was stuck on the surface of the electrode. What we needed was a molecule that bound to the electrode surface and would interact with the positively-charged cytochrome c. We chose a simple compound, 4,4’-bipyridine and, amazingly, the electrochemistry in the first experiment was ‘perfect’. That led to much work all over the world and now any protein that takes part in an oxidation or reduction experiment can be so studied.

Even in these early days, I was concerned to extend the technique to the study of the electrochemistry of enzymes, i.e., those that have an electron transfer step in their sequence of reactions. We used small organic mediators to ‘shuttle the electrons’ between electrode and enzymes, which we studied in collaboration with a colleague from Kent University, Dr. John Higgins, but the reactions were very subject to interference from molecular oxygen, a somewhat ubiquitous material! It was then that ‘chance favoured the prepared mind’ because I knew of a compound – ferrocene – that would act as an ‘electron shuttle’ but was not particularly sensitive to molecular oxygen. On 28 June 1982, Dr. Tony Cass, Mr. Graham Davis and I found that it worked remarkably well in coupling the enzyme that handled glucose to the electrode. There was some consid­erable excitement and we fully expected someone would be interested. We approached organisations or companies with whom we had had some connections but all politely declined to offer any real money for support. We were about to submit the work for publication when we met a young man, Mr. Ron Zwanziger, who liked the work, had money enough for one year’s support and, provided we could show that the system worked in whole blood, said he would raise sufficient funds to engage in real research and development. We did and he did! We had shown a number of useful features: it did work in whole blood; it wasn’t too sensitive to interference; the results were obtained from a small drop of blood with no pre-treatment being necessary. We also showed, since, at the time we were interested in developing a device suitable for implantation that it worked well at body temperature. A company, eventually called MediSense, was formed in Abingdon in 1984, and an elegant device was launched towards the end of the decade.

What lessons could one learn from the experience of being associated with such a venture? It would have been so easy to have just simply published the work but, for familial reasons, we had a real interest in creating such a device. It was crucial to have sufficient funds to do the job properly both in the company, of course, but also in the University where research was carried out seeking other examples of the effectiveness of ferrocenes as mediators, e.g., as in a cholesterol sensor. Whilst we had estimated that it would cost ~$10m to take the device to market, it did eventually cost ~$40m: MediSense was sold to Abbott Laboratories in the mid-nineties for ~$800m. Whereas in the early eighties, there were essentially no electrochemical glucose sensors, now almost all of the devices are electrochemical.

The smaller one makes an electrode, the larger the sensi­tivity, as judged by the signal-to-noise value. Therefore, Dr. Nick Walton and I were investigating whether or not these would have any value for bioelectrochemical purposes. At the end of that decade, I attempted to persuade MediSense that one could make a device that contained separate electrodes that were sensitive – since each would have on it a different enzyme – to more that one substance. They were too preoccupied with the glucose market since, even then, the numbers of diabetics were growing – and still are growing – enormously. A colleague, Peter Dobson, experi­enced in semi-conductor devices, said it would be relatively straightforward to fashion multielectrode devices. We did, all the while expecting that Abbott Laboratories would be inter­ested. In the end, they gave us support to ‘go it alone’.

With the existence, now, of a revised Isis and the help of Tim Cook and Herb Askew, Oxford Biosensors, with the help of Peter Leigh and Luet Wong, eventually got off the ground. It had, unlike MediSense, to operate on a shoe string, at least until East Hill invested. We were concerned to create a platform technology, i.e., one that could be used for a variety of purposes. The device would, of course, have its specificity determined by enzymes, be made of carbon, the response would be rapid and capable of a simple interpre­tation. We have developed a cardiac risk sensor, i.e., one capable of detecting cholesterol, high and low density lipids and triglycerides and it is hoped to have the device ready for the market in 2007.

This article first appeared in Isis News Ediiton 47, Spring 2006