TODAY PROGRESS OF SENSOR DEVELOPMENT

Jean-Michel Kauffmann
Laboratory of instrumental analysis and bioelectrochemistry ,Pharmaceutical Institue, FreeUniversity of Brussels, Brussels, Belgium. jmkauf@ulb.ac.beAnalytical sciences are facing considerable challenges due to the ever increasing demand for
instruments allowing highly selective and sensitive measurements of chemical and naturalcompounds of environmental, medical, agricultural, and military, etc. interests.
Today new equipements must preferably offer high throughput capabilities for rapid assays
e.g. in drug discovery and screening, antibody production and screening, DNA based
diagnostics, pollution control, food quality control etc. Also instruments for decentralized
testing, requiring minimum maintainance and operating skills, are highly demanded.
Classical analytical methods based on separations such as chromatography and capillaryelectrophoresis generally offer satisfaction in numerous applications. The detection systems
associated with those methods have been substantially improved in terms of sensitivity,
selectivity, reliability and robustness. Currently, mass spectrometric detectors coupled or notto separation methods, can be considered as a universal sensing system for many application
fields. Yet such instrumentation needs considerable skill, high power consumption andmaintainance facilities in addition to the high cost of the entire set up. Also such « heavy »equipements often do not satisfy the high throughput capabilities required as mentionedabove.
Downsizing chemistry in chip formats is a promising approach in modern instrumentation
development. Benefits are : high throughput capabilities, automation, reduced waste sreams,
increased precision and accuracy and disposability. Yet the requirement for sensitivity is amajor challenge for microchip designer. Mass spectromety is of course universal and highly
sensitive and selective but laser fluorescence and electrochemical detection modes offer,when applicable, equally high sensitivity. Electrochemistry is particularly advantageous in
microsensors since the electrodes may be readily shaped in miniaturized configurations andarranged in microarray formats.
In the general trend to improve the selectivity and sensitivity of sensors the modification of
conventional or microsized electrodes is currently under intensive investigation.Gold andcarbon based electrodes are especially attractive materials for sensor development. Gold canbe readily modified by thiol molecules for subsequent biocomponents attachment (enzyme,antibody, antigen, etc.)
With respect to selectivity, the modification of gold electrodes by a self assembled layer e.g.
of thiocholesterol offers substantial selectivity improvement in amperometric discriminationof signals between analyte and interferent [1,2]. Other application may require electrodemodification by electropolymerization for selectivity improvement [3].
With respect to signal amplification, carbon based composite electrochemical detectors (EC)with immobilized enzyme horseradish peroxidase (HRP) offer extremely high sensitivity forhydrogen peroxide. Amperometric monitoring of HRP in the presence of a suitable redox
mediator allows subnanomolar determination of hydrogen peroxide [4]. Such abioelectrocatalytic system may be advantageously exploited in enzyme (oxidase) based EC,in electrochemical immunoassays and in DNA biosensing.
Major demands for (bio)sensors are in applications where conventional instrumentation andmicrochips do not allow proper determination because of analyte instability, or because of
the need for remote or micro-positioning. Determination of analytes such as hydrogen
peroxide, nitric oxide, oxygen and reactive oxygen species (ROS), cyanide, sulfite,neurotransmittors etc. are challenging in applications where short time resolution, highselectivity and sensitivity are mandatory.
This presentation will illustrate some current trends in (bio)sensor development withparticular emphasis on recent authors results in this domain.

1.Z.Yang, I.Enquist, B.Liedberg, J-M Kauffmann, Electrochemical characterization of mixed
monolayer assemblies of thiol analogues of cholesterol and fatty acids on gold.
J.Electroanal.Chem., 430(1997)189

2.Z.Yang, J-M Kauffmann, M.I.Acedo Valenzuela, S.Ozkan, Electroanalytical behaviour ofnanoarray self-assembled thiocholesterol gold electrode. Microchim.Acta, 131(1999)85.

3.M.Pravda, J-M Kauffmann, Y.Michotte, Development of an on-line electrochemical
biosensor for glucose determination in rat brain using microdialysis sampling.
Electroanalysis, 12 (2000)912

4.S.Serradilla Razola, E.Aktas, J-C Viré, J-M Kauffmann, Reagentless enzyme electrodebased on phenothiazine mediation of horseradish peroxidase for subnanomolar hydrogenperoxide determination . The Analyst, 125 (2000)79.