Electrochemical sensors technology

Chapters 1 to 5 deal with ionophore-based potentiometric sensors or ion-selective electrodes (ISEs). Chapters 6 to 11 cover voltammetric sensors and biosensors and their various applications. The third section (Chapter 12) is dedicated to gas analysis. Chapters 13 to 17 deal with enzyme based sensors. Chapters 18 to 22 are dedicated to immuno-sensors and genosensors. Chapters 23 to 29 cover thick and thin film based sensors and the final section (Chapters 30 to 38) is focused on novel trends in electrochemical sensor technologies based on electronic tongues, micro and nanotechnologies, nanomaterials, etc. 

At present spectroscopy, in all its variations, appears the most widely accepted, among analytical techniques for PAT approach in the food industry. However, the main advantage of the electrochemical sensor technology over spectroscopy is that electronic-nose (e-nose) and electronic-tongue (e-tongue) can be tailored to the monitoring process in a way that complementary information nonobtainable with spectroscopy can be acquired. 

Recent advances in the rapidly developing field of electrochemical sensor technology using engineered materials such as functionalized carbon nanostructure have shown a great potential for VOC detection. However, in most cases the devised sensor was tested in a control environment to estimate its sensing potential. Hence, their effectiveness in real environment is questionable for real application. 

Microfabrication technology has made a considerable impact on the miniaturization of electrochemical sensors and systems. Such technology allows replacement of traditional bulky electrodes and beaker-type cells with mass-producible, easy-to-use sensor strips. These strips can be considered as disposable electrochemical cells onto which the sample droplet is placed. The development of microfabricated electrochemical systems has the potential to revolutionize the field of electroanaly-tical chemistry. 

Based on many of the advances described above in electrochemical approaches to immunoassay, it is tempting to conclude that commercialization of some of the approaches is imminent. This may be true, but the historical use of optical methods for many clinical chemistry tests coupled with their rapidly growing use in immunoassay is a difficult barrier for any radically different method to overcome, though electrochemical sensors have become more important in the clinical chemistry laboratory over the last decade. In any event, to be successful ECIA methods will have to demonstrate clear superiority over existing and emerging technologies in both cost and performance. Some of the more recently described approaches such as those using enzyme amplified amperometric detection and ecLIA appear... 

Ionic liquid advances in optical, electrochemical, and biochemical sensor technology... 

After reviewing the properties and structure of ionic liquids, leading specialists explore the role of these materials in optical, electrochemical, and biochemical sensor technology. The book then examines ionic liquids in gas, liquid, and countercurrent chromatography, along with their use as electrolyte additives in capillary electrophoresis. It also discusses gas solubilities and measurement techniques, liquid-liquid extraction, and the separation of metal ions. The final chapters cover molecular, Raman, nuclear magnetic resonance, and mass spectroscopies. 

Apart from the aforementioned most frequently used sensor technologies, also selective electrochemical sensor combinations have been commercialised for use in dedicated applications. The combination of electrochemical CO, H2S, SO2 and NH3 sensors was used for quality and freshness control of foods like fish [98] and meat [99]. Combinations of MOSs and MOSFETs supplemented with a selective IR absorption sensor for carbon dioxide and a humidity sensor for measuring relative humidity were also described [100]. 

Other Techniques - Other electrochemical techniques that could be employed in sensor technology would include potential-step methods (or chrono-amperometry, as current is recorded with time), current-step methods (or chronopotentiometry, as potential is recorded with time) and AC impedance. None of these techniques appear to have yet been applied to catalyst sensing in a systematic way. 

M.J. Schoening, Voltohmmetry —a new transducer principle for electrochemical sensors. In V.M. Mirsky (Ed.), Ultrathin Electrochemical Chemo- and Biosensors. Technology and Performance, Springer, Berlin, 2004. 

In aspect of chip-based technology, electrochemical genosensors based on different materials and transducers have been recently developed in response to clinical demand of giving promising results [18-25]. Different sensor technologies provide a unique platform in order to immobilize molecular receptors by adsorption, crosslinking or entrapment, complexation, covalent attachment, and other related methods on nanomaterials [5,7,26]. 

Electrochemical sensors and biosensors offer the achievable opportunity of simplifying the analyses of complex matrices, outside of the laboratory, by suitable modification of appropriate electrode materials [1-5]. One of the most attractive methods for the fabrication of such devices involves the use of screen-printing technology. This allows the (bio)sensors to be manufactured in a wide range of geometries at low cost, particularly when carbon is used therefore, this allows the devices to become disposable [1,2]. A typical screen-printed electrode design commonly used in our laboratories for prototype investigations is shown in Fig. 23.1. 

In the last 20 years, there has been a continuous increase in the use of nucleic acid combined with electrochemical transducers to produce a new kind of affinity biosensor. Among the different kind of electrochemical sensor formats available, SPE based on thick and thin film technology have played an important role. This is surely due to their recognized advantages in terms of cost that allow their disposable use. 

In this part we will describe recent achievements in the development of biosensors based on DNA/RNA aptamers. These biosensors are usually prepared by immobilization of aptamer onto a solid support by various methods using chemisorption (aptamer is modified by thiol group) or by avidin-biotin technology (aptamer is modified by biotin) or by covalent attachment of amino group-labeled aptamer to a surface of self-assembly monolayer of 11-mercaptoundecanoic acid (11-MUA). Apart from the method of aptamer immobilization, the biosensors differ in the signal generation. To date, most extensively studied were the biosensors based on optical methods (fluorescence, SPR) and acoustic sensors based mostly on thickness shear mode (TSM) method. However, recently several investigators reported electrochemical sensors based on enzyme-labeled aptamers, electrochemical indicators and impedance spectroscopy methods of detection. 

This chapter focuses on the approach we followed for developing a novel electrochemical sensor platform based on disposable polymer microchips with integrated microelectrodes for signal transduction. It presents the development of the so-called Immuspeed technology, which is dedicated to quantitative immunoassays with reduced time-to-results as well as sample and reagent volumes. Prior to presenting the specific characteristics of Immuspeed, the basic principles integrated in this platform are first presented and illustrated with reference to... 

R. Myrdal, K. Videm, 0. Vennesland and E. J. Sellevold, Sensor technology and electrochemical measurements. What has been learnt on the Gimspystraumen project , Proc. International Conference on Repair of Concrete Structures, Svolvasr, Norway, May 28-30,1997, Norwegian Road Research Laboratory (Ed. A. Blankvoll), pp 419 124. 

In order to maintain the advantage of the microfabrication approach which is intended for a reproducible production of multiple devices, parallel development of membrane deposition technology is of importance. Using modified on-wafer membrane deposition techniques and commercially available compounds an improvement of the membrane thickness control as well as the membrane adhesion can be achieved. This has been presented here for three electrochemical sensors - an enzymatic glucose electrode, an amperometric free chlorine sensor and a potentiometric Ca + sensitive device based on a membrane modified ISFET. Unfortunately, the on-wafer membrane deposition technique could not yet be applied in the preparation of the glucose sensors for in vivo applications, since this particular application requires relatively thick enzymatic membranes, whilst the lift-off technique is usable only for the patterning of relatively thin membranes. 

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