Biosensors in the Body. Continuous In Vivo Monitoring

Biosensors involve the integration of a biological recognition molecule with a physical or chemical transducer such that the biomolecule can be exploited for transduction purposes. This basic idea has seen myriad developments and a fast-expanding literature. Of all the niche areas, in vivo monitoring is one where few other technologies can compete. However, both for sensors and patients alike, there are dangers, and the issues merit detailed analysis. Yet there is no comprehensive text marking out the relevant scientific territory, so this multi-author, multidisciplinary volume is a valuable first which gives due cognizance to implant biology. The editor has put together a creditable list of practitioners with the requisite level of real experience to contribute new insights. That said, there is a certain abstraction to the choice of topics; rather predictably, glucose monitoring takes the lion's share, but an opportunity has been missed in not covering a large and important literature on sensors for ions and gases. These latter, not strictly biosensors, throw up all the issues relating to blood and tissue compatibility and safety, and yet have very limited coverage in the final chapter. Chapter one is a self-contained, well referenced review of many of the measurement opportunities, written by the editor, clearly an enthusiast for his subject. This chapter can serve as a stand-alone introductory text to those new to the field, and succeeds in giving the right balance of sensor chemistry and material science needed. For once, due emphasis is given to the latter, by contrast to quite weak descriptions in the literature hitherto. In chapter two, a review of glucose monitoring is provided, with a succinct comparative assessment of different electrochemical strategies. There is sufficient technical detail to allow the reader to reach an independent view. Chapter three gives the non-invasive counterweight to glucose monitoring using near infrared. The method is, of course, attractive, but the problems are many, and the goal elusive. If one accepts that such a technology has any place at all in a text on biosensors, then the theory, instrumentation and biological outcomes given here is a reasonable summary. Chapter four returns to glucose sensors, but now deals with the needs of long-term fully implanted telemetry-based devices. Practical design needs and quite respectable performance data are detailed in an animal model; certainly this lends some support to the proposition for long-term biochemical monitoring. The devil, however, is in the detail, extensive review of the host tissue response is an acute reminder of how little we really understand of either the markers or the effectors of the tissue rejection process. A concerted effort using mini- and micro-sensors for following stimulated brain metabolite and neurotransmitter changes has been made in recent years. Because of the relative low grade adverse response of brain tissue, meaningful data and some new insights have emerged. A full chapter (six) given over to this area does cover the literature well, though someone not familiar with the underlying electrochemistry may find it difficult to follow. Chapter seven gives a concise summary of microfabrication methods and structural outcomes for different transducer types. Though of practical interest, most of the sensors covered are unlikely to be used in vivo for reasons of innate chemistry. Chapter 8 is an overview of optical sensors, mainly for blood gas analysis, with yet more on near infrared, this time with suggested opportunities for imaging. Anyone in the business of developing medical sensors will find this a useful source book for well referenced, recent advances. The glucose sensor preoccupation certainly makes for some repetition, but enthusiastic coverage of topics by most of the contributors makes this a worthy statement about the field. If nothing else, the book will at least raise the `biomaterials' aspects of in vivo sensors.