Electrochemical enzyme biosensors: from fundamental studies of the reactivity of enzymes immobilized on electrode surfaces to the elaboration of highly sensitive analytical devices
Université Paris Diderot (LEM), 15, rue Jean-Antoine de Baif, Paris 75205, France
The possibility to convert the catalytic activity of an enzyme immobilized on an electrode surface into an electric current has lead to the development of a wide range of electrochemical biosensors in various fields of analytical applications ranging from health to environment or food. It is possible to distinguished two main categories of electrochemical enzyme biosensors. The first one takes advantage of the electronic transduction of the catalytic and molecular recognition properties of an enzyme towards its substrate to provide an analytical means to detect the respective substrate. The most common approach used redox enzyme wherein the electron transfer between the electrode and the enzyme can be achieved with a small redox mediator that shuttles between the enzyme and the electrode or, less commonly, by direct electron transfer between the enzyme redox site and the electrode. A widespread example of such device is the commercialized blood glucose biosensor used by diabetes patients for monitoring their level of glucose in blood. The second type of electrochemical enzyme-based biosensors is related to the detection of the enzyme itself. This is typically the case in enzyme-amplified bioaffinity electrodes (as, for example, in electrochemical enzyme-amplified immuno- or DNA-sensors) that use the enzyme as an amplifying reporter label to achieve the electrochemical transduction of a biomolecular recognition event occurring between a target analyte molecule in solution and a receptor immobilized on the surface of an electrode. In this framework, enzyme labeling is thus a powerful manner of amplifying the electrochemical response. Coupling of several enzymes is also a promising way of boosting amplification. So far, most of electrochemical enzyme biosensors were however developed on an empirical base, where everyone offers his recipe for immobilizing the enzyme on the surface of an electrode, the final plots of the calibration curve serving to judge of the analytical performance of the device. The problem with this empirical approach is that it does not allow discerning the key factors that limit and govern the analytical performances of the biosensor, making it difficult to rationalize and optimize these devices. This is for this reason that, during the last years, our efforts have been directed towards the development of theoretical tools with the aim to predict the electrochemical current response (in particular, cyclic voltammetric responses) of the analytical device as a function of the mechanism and kinetics of the immobilized enzyme and the concentrations of species involved into the process, and with the aim to discern the key factors that limit and govern the analytical performances of the biosensor (1, 2). To achieve these goals, different enzymatic systems assembled as a mono-layer or multilayers on an electrode surface (using for example the avidin-biotin binding system) have been thoroughly investigated by cyclic voltammetry and analyzed with our theoretical kinetic models. Several of them will be presented with a particular attention to the specific case of enzyme-amplified bioaffinity electrodes (3).
(1) B. Limoges, D. Marchal, F. Mavré, J-M. Savéant J. Am. Chem. Soc., 2006, 128, 2084-2092.
(2) B. Limoges, F. Mavré, D. Marchal, J-M. Savéant J. Am. Chem. Soc., 2006, 128, 6014-6015.
(3) B. Limoges, D. Marchal, F. Mavré, J-M. Savéant, B. Schöllhorn J. Am. Chem. Soc., 2008, 130, 7259-7275.
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Presentation: Tutorial lecture at SMCBS'2009 International Workshop, by Benoit Limoges
See On-line Journal of SMCBS'2009 International Workshop
Submitted: 2009-10-06 11:00 Revised: 2009-10-06 11:16