Intrinsic optical biosensors

In the light of promising applications offered by these supramolecular glycoconju-gate structures, notably for the intrinsic optical and electrochemical properties of metal complexes, this underexploited research area is undoubtedly in its infancy and holds promise for such systems as biomarkers or sensitive biosensors. 

Optical biosensors based on the use of fiber optics can be classified into two categories intrinsic sensors where interaction with the analyte occurs within an element of the optical fiber, and extrinsic sensors in which the optical fiber is used to couple light, usually to and fi om the region where the light beam is influenced by the measurand. Moreover, biosensors become attractive because they can be easily used by non-specialist personnel and they allow accurate determination with either none or little sample treatment. Therefore, fiber-optic biosensors may be especially useful in... 

The field of applications for optical biosensors is wide, covering clinical, industrial control processes, veterinary, food, environmental monitoring, among others [1]. For all these applications, it is desirable to have a compact sensor of high sensitivity, fast response time and which is able to perform real-time measurements. These requirements can be achieved mainly with optical sensors, due to the intrinsic nature of optical measurements that accommodate a great number of different techniques based on emission, absorption, fluorescence, refractometry or polarimetry. 

FIGURE 16 Schematic principles of bioaffinity fiber-optic biosensors. (a) Detection of intrinsically fluorescent molecule using immobilized antibody, (b) Competition assay using a fluorescent-labeled antigen, (c) Sandwich immunoassay using an immobilized antibody and a fluorescent-labeled antibody. 

Trettnak W., Wolfbeis O.S., A fully reversible fibre optic glucose biosensor based on the intrinsic fluorescence of glucose oxidase, Anal. Chim. Acta 1989 221 195. 

W. Trettnak, O.S. Wolfbeis, A fully reversible fiber optic lactate biosensor based on the intrinsic fluorescence of lactate monooxygenase, Fresenius Z. Anal. Chem. 1989, 334, 427. 

Fig. 20a.2. Optical sensor configurations (a) intrinsic sensors, (b) mediator assistant chemical sensor, and (c) chemical sensor-based biosensor.

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. 

Fig. 5.4. Optical Fiber biosensor, (a) Extrinsic optical fiber is used for the guiding the light to and from the sensor area, (b) Intrinsic the receptor molecules are immobilized on the fiber core after decladding of the fiber. The detection is based on fluorescence labels.

Keywords Fiber optic sensors Chemical sensors Biosensors Evanescent field sensor Intrinsic fiber optic sensors Multimode fibers Modal power analysis Modal power distribution Spatial intensity modulation Optical far-held pattern... 

It was mentioned before that fiber-optic chemical and biosensors are broadly classified into two categories extrinsic- and intrinsic-type sensors. In the extrinsic-type sensors, the fiber is acting as a link connecting optical signals to (and from) the active material (medium) positioned at the end of the fiber, such as the Optode case. In the intrinsic-type sensors, the fiber is modified in different ways, through construction of the sensing component, which will be explained next. 

Trettnak, W., Wolfbeis, O. S., Fully Reversible Fibre-Optic Glucose Biosensor Based on the Intrinsic Fluorescence of Glucose Oxidase , AnaL Chim. Acta 221 (1989) 195-203. 

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