Biorecognition optical biosensor elements

The main advantages of immobilizing whole cells over the isolated enzymes are (i) cells are more resistant to changes in pH or temperature and (ii) a single cell can contain all the enzymes and cofactors needed for bioconversion of the analyte [82], Most of the whole cell-based optical biosensors used in toxicity or bioremediation studies [83,84] employ microorganisms [85— 87], animal [88], plant tissues [89,90] or cell receptors [91] as biorecognition elements. 

Chemical sensors and biosensors for environmental monitoring present an interesting alternative to these conventional methods and offer numerous attractive features such as ease of use, low cost, portability, and the abihty to perform detection in the field [12-16]. Optical biosensors based on surface plasmon resonance (SPR) show potential for rapid and sensitive detection of chemical and biological contaminants in the environment. SPR sensors provide a generic platform which, in conjunction with appropriate biorecognition elements, can be tailored for detection of numerous compounds related to environmental protection [17-19]. 

In recent years many efforts have been made to develop immunochemical techniques integrating the recognition elements and the detection components, in order to obtain small devices with the ability to carry out direct, selective, and continuous measurements of one or several analytes present in the sample. In this context biosensors can fulfill these requirements. Biosensors are analytical devices consisting of a biological component (enzyme, receptor, DNA, cell, Ab, etc.) in intimate contact with a physical transducer that converts the biorecognition process into a measurable signal (electrical or optical) (see Fig. 4). In... 

SPR sensors directly measure refractive index. In conjunction with appropriate biorecognition elements, they can be used as affinity biosensors allowing detection of the capture of analyte molecules by biorecognition elements immobibzed on the sensor surface. The abihty of SPR sensors to perform measurements is described by the performance characteristics, of which the most important are the sensitivity, resolution, accuracy, reproducibihty, and hmit of detection. The sensitivity and resolution are primarily determined by the properties of the optical system of the SPR sensor and can be linked to specific design parameters. 

The SPR biosensor systems for analysis of complex samples in the field have to integrate several key elements. These include, in particular, a sample preparation unit, a fluidic system, a biorecognition element, and an SPR optical platform (Fig. 1). 

In this biosensor system, a sample is pretreated in the sample preparation unit and dehvered by the fluidic system into contact with the biorecognition element immobihzed on the sensor surface. The SPR optical platform converts its specific interaction with the analyte into the sensor output. 

The range of biosensors for the analysis of vitamins that use enzymes as the biorecognition elements is rather restricted. However, affinity biosensors have opened a new horizon in the field of vitamin analysis with surface plasmon resonance (SPR) biosensors at the forefront. Commercialization of optical SPR... 

Enzymes have been widely used as biorecognition elements in biosensors as they are able to catalyze reactions that produce electrochemical, optical, and thermal sig-nals." " Most popularly, glucose oxidase is widely used in electrochemical glucose biosensors that have found wide usage in clinical and medical settings. Enzymes offer ease of immobilization on transducers by physical adsorption, covalent linkage, and... 

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