Biosensors conventional techniques

There are several different techniques employed for the detection of OPC, including conventional analytical methods enzyme, hnorescence, and radioimmunoassay techniques immunochemical methods some biosensor technology, which includes optical, piezoelectric, electrochemical, microhuidic, and array-based (Lab-on-a-chip) biosensors. These techniques are described later in this chapter. 

Biosensors ai e widely used to the detection of hazardous contaminants in foodstuffs, soil and fresh waters. Due to high sensitivity, simple design, low cost and real-time measurement mode biosensors ai e considered as an alternative to conventional analytical techniques, e.g. GC or HPLC. Although the sensitivity and selectivity of contaminant detection is mainly determined by a biological component, i.e. enzyme or antibodies, the biosensor performance can be efficiently controlled by the optimization of its assembly and working conditions. In this report, the prospects to the improvement of pesticide detection with cholinesterase sensors based on modified screen-printed electrodes are summarized. The following opportunities for the controlled improvement of analytical characteristics of anticholinesterase pesticides ai e discussed ... 

As opposed to conventional analytical techniques, optical sensors and biosensors, particularly those employing absorption and fluorescence-based sensing materials potentially allow for measurement through transparent or semi-transparent materials in a non-destructive fashion4, 5> 9 10. Chemical sensor technology has developed rapidly over the past years and a number of systems for food applications have been introduced and evaluated with foods. 

Semiconductor fabrication techniques have also been successfully applied to the construction of conventional transducers sensitive to hydrogen peroxide, oxygen, and carbon dioxide, A hydrogen peroxide-sensitive silicon chip was made by using metal deposition techniques (28,29). The combination of the hydrogen peroxide-sensitive transducer and enzyme-immobilized membranes gave a miniaturized and multifunctional biosensor. Similarly, an oxygen- and a carbon dioxide-sensitive device was made cmd applied to the construction of biosensors (25, 30, 31). 

Optical biosensors have had, and still are having, an increasing impact on analytical technology for the detection of biological and chemical species. Optical biosensing technology can be an alternative and/or a complement to conventional analytical techniques as it avoids expensive, complex and time-consuming detection procedures. For this reason it has been the subject of active research for many years [1-6]. 

Regarding biosensor production, its marketing is in competition with many chemical analytical systems as well as conventional laboratory techniques. Most of the patents are presented by scientific institutions as biosensor prototypes without a real potential for commercialisation. The insritutions should stricdy collaborate vwth industries to define the properties of a real marketable product. Econontical and technical problems should be overcome, together with the manufecture of the sensing and transductions components and their increased reliability and stability. 

Microdialysate samples have been analyzed using a variety of nonseparation-based analytical techniques including immunoassay, biosensors, and MS [1-4]. The main limitation to the use of these methods is that they are typically restricted to the measurement of a single analyte. For more complex samples, the detection of multiple substances is usually necessary. In this case, the dialysate sample is normally analyzed by conventional chromatographic or electrophoretic separation methods employing optical, electrochemical, or mass spectrometric modes of detection [5]. 

Conventional enzyme electrodes employ disorete-maorosoopio membranes to overcome problems associated with interferences, enzyme immobilization, and electrode fouling. While these types of enzyme electrodes have been commercially developed, there are some limitations with this approach. Some sensors use three relatively thick membranes, resulting in a slow smd complex diffusion path for reactants reaching the enzyme and hydrogen peroxide reaching the electrode. Slow diffusion in this type of system adversely affects the response and recovery time, decreasing sampling rate. Each sensor must be individually constructed, and this construction technique is limited to two-dimensional surfaces. In addition, for sensors that have complex and slow diffusion paths, rates of diffusion must remain constant, otherwise calibration of the biosensor, and more important the maintenance of calibration, are difficult. A variety of factors can influence rates of diffusion, and consequently the performance of the enzyme layer and the performance of the sensor. These complicated, and most often uncharacterizable, properties have made the development of roost biosensors difficult. 

For low-BOD samples, the kinetic mode has not been shown to be as sensitive as either of the conventional BOD methods or the steady-state biofilm method. Both biosensor techniques share with oxygen electrodes the danger of fouling of the biosensor membrane with oil. Because biofilm techniques allow rapid process control, they are most likely to find application in monitoring a consistent organic process waste. 

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