Biosensors optical

The combination of selectivity of biochemical origin with the high intrinsic selectivity of optical spectroscopy makes the optical sensors potentially the most selective of all types of chemical sensors. It is not surprising, because most bioassays use optical detection. Moreover, the coupling requirements between the primary interactions in the selective layer and the transducer part of the sensor are relatively simple. The molecule that provides the signal (absorber) merely has to be present in the optical path in order to be counted. 

The detection and quantification of the presence of biomolecules at the surface is based on specific interactions taking place in the evanescent field, generated by the total internal reflectance or by the surface plasmon resonance. The latter is the key transduction principle in the optical bioanalysis and biosensing area (Narayanaswamy and Wolfbeis, 2004). Launched in the early 1980s in Sweden, 

Enzymatic reactions coupled to optical detection of the product of the enzymatic reaction have been developed and successfully used as reversible optical biosensors. By definition, these are again steady-state sensors in which the information about the concentration of the analyte is derived from the measurement of the steady-state value of a product or a substrate involved in highly selective enzymatic reaction. Unlike the amperometric counterpart, the sensor itself does not consume or produce any of the species involved in the enzymatic reaction it is a zero-flux boundary sensor. In other words, it operates as, and suffers from, the same problems as the potentiometric enzyme sensor (Section 6.2.1) or the enzyme thermistor (Section 3.1). It is governed by the same diffusion-reaction mechanism (Chapter 2) and suffers from similar limitations. 

In this section, only the important differences resulting from the optical detection are highlighted. The optimum conditions for the operation of optical enzyme sensors, particularly the thickness of the enzyme layer, could be found again by solving the set of diffusion-reaction equations for a given geometry. There is, however, an 

An example of an optical enzyme sensor (Arnold, 1985) in a bifurcated optical fiber is shown in Fig. 9.32. The bifurcated fiber delivers and collects light to and from the site of the enzymatic reaction. The enzyme, alkaline phosphatase (AP), catalyzes hydrolysis of p-nitrophenyl phosphate to p-nitrophenoxide ion which is being detected (A = 404 nm). 

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Later on, such S-layer-based sensing layers were also used in the development of optical biosensors (optodes), where the electrochemical transduction principle was replaced by an optical one [97] (Fig. 10c). In this approach an oxygen-sensitive fluorescent dye (ruthenium(II) complex) was immobilized on the S-layer in close proximity to the glucose oxidase-sensing layer [97]. The fluorescence of the Ru(II) complex is dynamically quenched by molecular oxygen. Thus, a decrease in the local oxygen pressure as a result of... 

A large number of possible applications of arrays of nanoparticles on solid surfaces is reviewed in Refs. [23,24]. They include, for example, development of new (elect-ro)catalytical systems for applications as chemical sensors, biosensors or (bio)fuel cells, preparation of optical biosensors exploiting localized plasmonic effect or surface enhanced Raman scattering, development of single electron devices and electroluminescent structures and many other applications. 

S. Sayler, Optical biosensor for environmental online monitoring of naphthalene and salicylate bioavailability with an immobilized biolumine.scent catabolic reporter bacterium. Appl. Environ. Microbiol. 60 1494 (1994). 

Fiber-optic biosensors based on luminescence and immobilized enzymes for the detection of NADH and ATP can be found in ref. (147-152). 

Schaffar B.P.H., Wolfbeis O.S., Chemically Mediated Fiber Optic Biosensors, chapter 8 in Biosensors Principles and Applications, L.J. Blum, P.R. Coulet (eds.), M. Dekker, New York, chapter 8, pp. 163-194 (1991). 

Marazuela M.D., Moreno-Bondi M.C., Fiber-optic biosensors - an overview, Anal. Bioanal. Chem. 2002 372 664. 

Freeman M.K., Bachas L., Fiber-optic biosensor with fluorescence detection based on immobilized alkaline phosphatase, Biosensors Bioelectron. 1992 7 49. 

Scheper T., Bueckmann A.F., A fiber optic biosensor based on fluorometric detection using confined macromolecular nicotinamide adenine dinucleotide derivatives, Biosens. Bioelectron. 1990 5 125. 

Blum L.J., Gautier S.M., Coulet P.R., Luminescence fiber-optic biosensor, Anal. Lett. 1988 21 717. 

Zhou X., Arnold M.A., Internal enzyme fiber-optic biosensors for hydrogen peroxide and glucose, Anal. Chim. Acta 1995 304 147-156. 

Blum L.J., Chemiluminescent flow injection analysis of glucose in drinks with a bienzyme fiber optic biosensor, Enzyme Microb. Technol. 1993 15 407-411. 

Hlavay J., Haemmerli S.D., Guilbault G.G., Fibre-optic biosensor for hypoxanthine and xanthine based on a chemiluminescence reaction, Biosens. Bioelectron 1994 9 189-195. 

Hlavay J., Guilbault G.G., Determination of sulphite hy use of a fiber-optic biosensor based on a chemiluminescent reaction, Anal. Chim. Acta 1994 299 91-96. 

Marquette C.A., Blum L.J., Luminol electrochemiluminescence-based fibre optic biosensors for flow injection analysis of glucose and lactate in natural samples, Anal. 

Tsafack V. C., Marquette C. A., Leca B., Blum L. J., An electrochemiluminescence-based fibre optic biosensor for choline flow injection analysis, Analyst 2000 125 151-155. 

Cush R., Cronin J.M., Stewart W.J., Maule C.H., Molloy J., Goddard N. J., The resonant mirror a novel optical biosensor for direct sensing of biomolecular interactions, Part I Principle of operation and associated instrumentation, Biosensors and Bioelectronics 1993 8 347-353. 

Homola J., Yee S.S., Myszka D., Surface plasmon biosensors, in F. S. Ligler and C. R. Taitt (editors), Optical Biosensors Present and Future, Elsevier, 2002. 

Perhaps the most effective demonstration of the advantages of evanescent wave interrogation is provided by the optical biosensor platform depicted in Figure 5. The platform consists of a multimode slab waveguide on the upper surface of which antibodies have been immobilised. 

Figures 13(a) and 13(b) illustrate the intensity distributions for two environment/substrate combinations, namely air/glass and water/glass. It can be concluded that the dipole located at a dielectric surface preferably radiates into the higher refractive index substrate at angles close to the critical angle. The intensity radiated into the environment is, on the other hand, relatively small. Yet it is this fraction of the fluorescence intensity that forms the basis of the sensor signal in conventional systems such as the optical biosensor...

While planar optical sensors exist in various forms, the focus of this chapter has been on planar waveguide-based platforms that employ evanescent wave effects as the basis for sensing. The advantages of evanescent wave interrogation of thin film optical sensors have been discussed for both optical absorption and fluorescence-based sensors. These include the ability to increase device sensitivity without adversely affecting response time in the case of absorption-based platforms and the surface-specific excitation of fluorescence for optical biosensors, the latter being made possible by the tuneable nature of the evanescent field penetration depth. 

Ligler F.S., Rowe Tait C.A., Optical biosensors present and future, Elsevier, Amsterdam, 2002. 

Table 1 summarizes the international classification of enzymes. Classes EC1 and EC3 are the most widely used for the development of optical biosensors. Sometimes different enzymes and transducing schemes can be applied to the analysis of a single analyte and the best combination should be selected depending on the application. 

Enzyme-based optical sensor applications will be further described in this book. They are still the most widespread optical biosensors but work is needed to overcome limitations such as shelf life, long term stability, in situ measurements, miniaturization, and the marketing of competitive devices. 

Zang W., Chang H., Rechnitz A., Dual enzyme fiber-optic biosensor for pyruvate, Anal. Chim. Acta. 1997 350 59-65. 

Walters B.S., Nielsen T.J., Arnold M.A., Fiber-optic biosensor for ethanol based on an internal enzyme concept, Talanta 1988 35 151-155. 

Construction of the optode for optical biosensor requires immobilization of sensitive compounds in the host matrix. There are several methods enabling molecules entrapment. One can use gels, polymers, saccharose, various meshes and membranes78. In case of fiberoptic indirect sensors optode must be attached to the fiber tip. Nowadays, there are two commonly used optode host materials sol-gel materials and polymers. 

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