Fibre optic-based flow-through optical biosensors

1 Fibre optic-based flow-through optical biosensors The dramatic advances in fibre optic development in die last decade have promoted construction of sensors where radiation, whether emitted, transmitted or reflected, is conducted fi-om the sample to the detection system. The wide variety of available optical waveguide types (solid rods, hollow cylinders, micro-planar geometries) has been used with varying success in sensor development. 

Strongly enhanced capabilities of chemically modified IR fibre optics for use in miniature biosensors. 

There are several luminescence flow-through sensors based on both fluorescence quenching phenomena and biolimiinescent reactions. 

Schmid et al. used the same principle to develop sensors to be incorporated into FI systems for the determination of ascorbic acid in fruit juices [38] and that of lactic acid in dairy products [39]. The membrane used in both applications consisted of decacyclene dissolved in silicone rubber that was treated similarly as the membrane in glucose sensors (Fig. 3.4.B). The oxygen optrode was coated with a sheet of carbon black as optical insulation in order to protect it from ambient light or intrinsic sample fluorescence. Ascorbic acid oxidase or lactic acid oxidase was immobilized by adsorbing it onto carbon black and cross-linking it with glutaraldehyde. The FI system automatically buffered and diluted the food samples, thereby protecting the biosensor from a low pH and interferents. 

Light production in some biochemical reactions (bioluminescence) has been recognized as a powerful tool for biochemical and clinical analyses. Emitted light can be measured with a high sensitivity, so very low detection levels can indeed be achieved. 

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A DNA optical sensor system was proposed by Cass and co-workers [35] based on the combination of sandwich solution hybridization, magnetic bead capture, flow injection and chemiluminescence for the rapid detection of DNA hybridization. Sandwich solution hybridization uses two sets of DNA probes, one labelled with biotin, the other with an enzyme marker and hybridization is performed in solution where the mobility is greater and the hybridization process is faster, rather than on a surface. The hybrids were bound to the streptavidin-coated magnetic beads through biotin-streptavidin binding reaction. A chemiluminescence fibre-optic biosensor for the detection of hybridization of horseradish peroxidase-labelled complementary DNA to covalent immobilized DNA probes was developed by Zhou and co-workers [36]. 

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