Sensors luminescence-based

J. N. Demas and B. A. DeGraff, Luminescence based sensors microheterogeneity and temperature... 

The interaction phenomenon of the analyte with radiation is governed or modifies the principle on which light is transmitted through the waveguide. Depending on that interaction, we can differentiate three basic types of intrinsic optical sensors [82] refractive-index-type sensors, luminescence-based sensors and absorption-type sensors. 

The presence of inorganic particles in the sensitive layer complicates the quenching processes of luminescence-based sensors and provokes departure from the simple Stern-Volmer kinetics observed for homogeneous solutions of a luminophore (Eq. 1) [43] ... 

Aslan K, Holley P, Geddes CD (2006) Microwave-accelerated metal-enhanced fluorescence (MAMEF) with silver colloids in 96-well plates Application to ultra fast and sensitive immunoassays, high throughput screening and dmg discovery. J Immunol Methods 312 137-147 Matveeva E, Gryczynski Z, Malicka J et al (2004) Metal-enhanced fluorescence immunoassays using total internal reflection and silver-coated surfaces. Anal Biochem 334 303-311 Blue R, Kent N, Polerecky L (2005) Platform for enhanced detection efficiency in luminescent-based sensors. Electron Lett 41 682-684... 

The combinatorial possibility to synthesize a large number of different receptors based on DNA structure has been exploited for the development of luminescent-based sensor arrays [21]. In this case DNA is particularly attractive, because it offers the stability and the versatility as a biopolymer to allow the preparation of a wide range of different structures, which can also be tailored to the particular application. The DNA structure should be functionalized with a fluorescent dye, which acts as the unit signalling the interaction with the analyte. Initially both single and double stranded DNAs have been tested for sensing application, but only the single-stranded DNAs showed different responses to the VOCs tested, which can be related to the DNA sequences exploited. In these preliminary studies DNA oligomers were first stained in solution with two different dyes, both of them... 

An optical sensor platform consists of (1) an excitation source (2) the sensor layer and (3) a detector (Fig. 12.6). For luminescence-based sensors, the light source is usually tuned to the excitation wavelength that gives best probe selectivity. The sensor layer typically consists of a probe immobilised in an optically transparent, inert host matrix, which must be permeable to the analyte of interest. 

The luminescence-based sensors prepared from MOFs are just one group of sensors, the second group is based on semiconducting MOFs, which exploit the semiconducting properties of Zn, In, W, Sn, and Ti oxides, with electroresistivity or electroconductivity being the detection parameter. Unfortunately, in spite of a number of publications related to such sensors based on bulk oxides (ZnO, SnO, In Oj) [243,244], there is only one paper by Corma et al. [245] describing the semiconductor properties of the conventional Zn-MOF-5 (terephthalate). 

The commercialization of inexpensive robust LED and laser diode sources down to the uv region (370 nm) and cheaper fast electronics has boosted the application of luminescence lifetime-based sensors, using both the pump-and-probe and phase-sensitive techniques. The latter has found wider application in marketed optosensors since cheaper and more simple acquisition and data processing electronics are required due to the limited bandwidth of the sinusoidal tone(s) used for the luminophore excitation. Advantages of luminescence lifetime sensing also include the linearity of the Stem-Volmer plot, regardless the static or dynamic nature of the quenching mechanism (equation 10) ... 

Demas J.N., DeGraff B.A., Xu W., Modeling of Luminescence Quenching-Based Sensors Comparison of Multisite And Nonlinear Gas Solubility Models, Anal. Chem. 1995 67 1377-1380. 

Another approach, developed in our laboratory, consists of the compartmentalization of the sensing layer25"27. This concept, only applicable for multi-enzyme based sensors, consist in immobilizing the luminescence enzymes and the auxiliary enzymes on different membranes and then in stacking these membranes at the sensing tip of the optical fibre sensor. This configuration results in an enhancement of the sensor response, compared with the case where all the enzymes are co-immobilized on the same membrane. This was due to an hyperconcentration of the common intermediate, i.e. the final product of the auxiliary enzymatic system, which is also the substrate of the luminescence reaction, in the microcompartment existing between the two stacked membranes. 

The main performances of batchwise and flow luminescence-based optical fibre sensors are summarized in Tables 2 and 3. As it can be shown... 

Gautier S.M., Blum L.J., Coulet P.R., Dehydrogenase activity monitoring by flow injection analysis combined with luminescence based fibre-optic sensors, Anal. Chim. Acta 1992 266 331-338. 

Hartmann P., Trettnak W., Effects of polymer matrices on calibration functions of luminescent oxygen sensors based on porphyrin ketone complexes, Anal. Chem. 1996 68(15) 2615-2620. 

Lifetime [3,9-11] based sensors rely on the determination of decay time of the fluorescence or phosphorescence. Typically, the fluorescence lifetime is 2-20 ps and phosphorescence lifetime is 1 ps to 10 s. Lifetime-based sensors utilize the fact that analytes influence the lifetime of the fluorophore. Thus all dynamic quenchers of luminescence or suitable quenchers can be assayed this way. The relationship between lifetimes in the absence (t0) and presence (t) of a quencher is given by Stern and Volmer ... 

Even when the d-d state is at much higher energy than the emitting level, it can still be of paramount importance in the photophysics and photochemistry of the system. Indeed, a major contributor to the temperature-dependent loss of emission intensity in luminescent metal complex based sensor materials is nonradiative decay via high-energy d-d excited states.(15) The model for this is shown in Figure 4.4A. The excited state lifetime is given by... 

There are possible advantages of the temperature dependence of excited state lifetimes. The dependence can be used for luminescence-based temperature sensors, which is an area of considerable interest. Clearly, with a suitable AE, complexes that give significant lifetime changes in a wide range of possible temperatures can be designed. We discuss this issue elsewhere.(16)... 

We focus on luminescence quenching based sensors, but many of the principles are generic. Quenching-based oxygen detectors are probably the most mature. In homogeneous media with only a single component exponential decay the intensity and lifetime forms of the Stern-Volmer equations are ... 

R. Grigg and W. D. J. A. Norbert, Luminescent pH sensors based on di(2,2-bipyridyl) (5,5-diami-nomethyl-2,2 -bipyridyl)ruthenium (II) complexes, J. Chem. Soc. Chem. Commun. 1300-1302... 

In order to implement frequency domain based sensing systems capable of monitoring the temporal luminescence of sensors, in few seconds, data must be collected at multiple frequencies simultaneously. Single-frequency techniques have been used to make frequency domain measurements of luminescent decays. 14, 23 28) This approach is unsuitable for real-time applications since data must be acquired at several frequencies in order to precisely and accurately determine the temporal variables of luminescent systems. 1 Each frequency requires a separate measurement, which makes the single frequency approach too slow to monitor the evolution... 

Luminescent evanescent wave-based sensors use optical fibers and planar waveguides [105,106] as fight-guiding structures, and they are more complex than the absorbance ones. However, such optodes have been satisfactorily applied to measure fluorescence of indicators or labels for the measurement of gas molecules, proteins or labeled antigen-antibody interactions as well as directly in solution [24,107] when immobilized in matrices [23,109]. 

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