Fluorescent optical sensors

Offenbacher H., Wolfbeis O.S., Ftirlinger E., Fluorescence optical sensors for continuous determination of near-neutral pH values, Sensors Actuat. 1986 9 73. 

What is the advantage of a time-resolved fluorescence optical sensor ... 

Keywords. In-situ, Non-invasive monitoring. Fluorescence, Optical sensor, Bioprocess control... 

A fluorescence optical sensor for dansyl-L-phenylalanine has been reported [17]. In the optical sensor, the imprinted polymer was held in front of a fiber-optic device by a nylon net. Although the system worked well, there are some inherent problems that need to be addressed the... 

Opitz, N., Lubbers, D. W., Electrochromic Dyes, Enzyme Reactions and Hormone-Protein Interactions in Fluorescence Optic Sensor (Optode) Technology , Thlanta 35 (1988) 123-128. 

Werner T (1997) Fluorescence optical sensors for ion recognition. EPA Newsletter 60 19-29. 

Optomembranes for Ca measurements can be based on absorption or fluorescent reagents. Absorption indicators form stable complexes with the calcium ions at basic pH values. This obviously requires a preparation of the sample, which is not a common practice in measurements by sensors. On the other hand, fluorescent optical sensors utilize more complex measuring system. 

Liebsch G, Klimant I, Krause C, Wolfbeis OS (2001) Fluorescent imaging of pFl with optical sensors using time domain dual lifetime referencing. Anal Chem 73 4354 -363... 

Following the discovery that the fluorescence of metalloporphyrins is strongly quenched by oxygen57, optical sensor membranes were developed that are suitable for phosphorescent sensing of oxygen58. Table 1 summarizes fundamental articles on optical sensors for oxygen until the year 2000. 

As the potential of optical fiber probes for pH measurements was rapidly recognized, several other articles appeared within a few years75 83. Most were reflectance-based, and Seitz reported the first fluorescent pH sensors84, 78. The article by Janata85 on whether pH optical sensors can really measure pH is another "must" in the early literature since it points to aspects hardly addressed in pH sensor work. 

Later, it was discovered138 that the FAD coenzymes of certain oxidases display large changes in their fluorescence if exposed to their substrates. Thus, the fluorescence of the FAD unit of lactate mono-oxygenase changes substantially on loading with lactate, and this can serve as the analytical information in an optical sensor. 

A novel fiber optic sensor concept using antibody-antigen reactions at a glass-liquid interface was reported by Daehne146. The reaction of antibodies immobilized onto the surface of fused silica fiber optic or planar waveguides with antigens in solution was detected by interaction with the evanescent wave. By detecting in-line fluorescence, the measurement of human IgG is described. 

Other medical products based on optical sensor technology include those of Cardiomed (System 4000), Puritan-Bennett, and one of Radiometer (Copenhagen) which has been withdrawn meanwhile. Optical (but non-fiber) sensors for oxygen and for C02 also are widely used for the determination of bacteria in blood. In 1986, Gehrich et al.36 described an optical fluorescence... 

Zhujun Z., Mullin J.L., Seitz W.R., Optical sensor for sodium based on ion-pair extraction and fluorescence, Anal. Chim. Acta 1986 184 251. 

Wolfbeis O.S., From fluorescent probes to optical sensors, Anal. Proceed. 1991 28 357. 

Optical sensors rely on optical detection of a chemical species. Two basic operation principles are known for optically sensing chemical species intrinsic optical property of the analyte is utilized for its detection indicator lor label) based sensing is used when the analyte has no intrinsic optical property. For example, pH is measured optically by immobilizing a pH indicator on a solid support and observing changes in the absorption or fluorescence of the indicator as the pH of the sample varies with time1 20. 

Fluorescent chemical sensors occupy nowadays a prominent place among the optical devices due to its superb sensitivity (just a single photon sometimes suffices for quantifying luminescence compared to detecting the intensity difference between two beams of light in absorption techniques), combined with the required selectivity that photo- or chemi-luminescence impart to the electronic excitation. This is due to the fact that the excitation and emission wavelengths can be selected from those of the absorption and luminescence bands of the luminophore molecule in addition, the emission kinetics and anisotropy features of the latter add specificity to luminescent measurements8 10. 

Fluorescence resonance energy transfer (FRET) has also been used very often to design optical sensors. In this case, the sensitive layer contains the fluorophore and an analyte-sensitive dye, the absorption band of which overlaps significantly with the emission of the former. Reversible interaction of the absorber with the analyte species (e.g. the sample acidity, chloride, cations, anions,...) leads to a variation of the absorption band so that the efficiency of energy transfer from the fluorophore changes36 In this way, both emission intensity- and lifetime-based sensors may be fabricated. 

Sensitivity impacts upon the limit of detection and resolution of the device, making it a key performance parameter. Recently, several strategies have been developed in order to provide sensitivity enhancements for optical sensor platforms based on both optical absorption and fluorescence phenomena. These strategies are the result of rigorous theoretical analyses of the relevant systems and, combined with polymer processing technology and planar fabrication protocols, provide a viable route for the development of low-cost, efficient optical sensor platforms. 

Evanescent Wave Effects and Fluorescence-Based Optical Sensors... 

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. 

Huber C., Krause C., Werner T., Wolfbeis O.S., Serum chloride optical sensors based on dynamic quenching of the fluorescence of photo-immobilized lucigenin, Microchimica Acta 2003 142 245-253. 

Optical transduction modes applied in combination with enzyme based fiber-optic sensors include absorbance, reflectance, fluorescence,... 

An optical sensor for the measurement of carbon dioxide in modified atmosphere packaging (MAP) applications was developed89. It was based on the fluorescent pH indicator l-hydroxypyrene-3,6,8-trisulfonate (HPTS) immobilized in a hydrophobic organically modified (ormosil) matrix. The CO2 sensor was stable over a period of at least 7 months and its output was in excellent agreement with a standard reference method for carbon dioxide analysis. 

Optical sensors for oxygen measurement are attractive since they can be fast, do not consume oxygen and are not easily poisoned. The most common method adopted in construction is based on quenching of fluorescence from appropriate chemical species. The variation in fluorescence signal (I), or fluorescence decay time (x) with oxygen concentration [O2] is described by Stem-Volmer equation91 ... 

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. 

Wolfbeis O.S., Fluorescence-based optical sensors for biomedical applications, In Scheggi A.M.V., Martelluci, S., Chester, A.N., Pratesi, R. (Eds.), Biomedical Optical Instrumentation and laser-Assisted Biotechnology, Kluwer Academic Publishers, 1996, p.327-337. 

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