Luminescence versatility

Several instmmental methods are available for quantitative estimation of from moderate to trace amounts of cerium in other materials. X-ray fluorescence is widely available, versatile, and suitable for deterrninations of Ce, and any other Ln, at percent levels and lower in minerals and purer materials. The uv-excited visible luminescence of cerium is characteristic and can be used to estimate Ce content, at ppm levels, in a nonluminescing host. X-ray excited optical luminescence (15), a technique especially appropriate for Ln elements including cerium, rehes on emissions in the visible, and also measures ppm values. Atomic emission spectrometry is appHcable to most lanthanides, including Ce (16). The precise lines used for quantitative measurement must be chosen with care, but once set-up the technique is suitable for routine analyses. 

An historical outline has been presented of some of the important developments in the study of luminescence, which reveals that most of the theory and practise used today were already in place by 1930. This is followed by a selection of recent developments in applications of luminescence intended to suggest to the reader possible uses of this versatile research tool in his own research. 

A very versatile piece of equipment that is affordable for individual laboratories is the microplate reader. This allows multiple samples to be analyzed at once, commonly in a 96-well format, although 384- and 1536-well formats are available. Typical measurements that can be performed include UV-Vis absorbance, fluorescence, or luminescence, allowing a range of assays to be performed, such as cell growth, enzyme kinetics, enzyme stability, or enzyme-linked immunosorbent assay [60-62]. Functionality can be increased by the use of liquid dispensing systems or automatic plate handling. 

The versatility of luminescence goes beyond intensity-, wavelength- and kinetic-based measurements. Fluorescence polarization (or anisotropy) is an additional parameter still largely unexplored for optical sensing yet widely used in Biochemistry to study the interaction of proteins, the microfluidity of cell membranes and in fluorescence immunoassays. Although only a few optosensors based on luminescence polarization measurements can be found in the literature, elegant devices have recently been reported to measure chemical parameters such as pFI or O2 even with the bare eye41. 

The variety of assays reported here displays the great versatility of luminescent detection systems. As already described, in all luminescent systems the main advantages are the high sensitivity and specificity, which reduce to the minimum the sample treatment, and the ease of use of the reagents and the luminometer. Immobilized systems greatly reduce the cost per assay on the other hand, their preparation requires expertise, especially in the surface activation step on nylon tubes. 

Mayr T, Borisov SM, Abel T, Enko B, Waich K, Mistlberger G, Klimant I (2009) Light harvesting as a simple and versatile way to enhance brightness of luminescent sensors. Anal Chem 81 6541-6545... 

The versatility of the quinolyl derivative (295) is exemplified in the complex [Ru(295-A,A )(295-A,A, A")C1]. The coordination behavior of (295) has been compared with those of (296) and (297) and factors influencing didentate vs. tridentate preferences have been examined. Perchlorate salts of [Ru(tpy)L)] " and [RUL2] where L = (298)-(300) have been synthesized and characterized, and their properties compared with those of [Ru(tpy)2] ". Complexation of Ru with 2,6-bis(4 -phenyl-2 -quinolyl)pyridine (L) affords [RUL2] , spectrosccmic properties of which have been discussed. " The bis(7 -methyl)-derivative of this ligand, L, has also been prepared and incorporated into the complexes [M(L )2f, [ (L CIs] (M = Ru, Os), and [Ru(L )(tppz)] + where tppz = 2,3,5,6-tetra(2 -pyridyl)pyrazine. Related cyclometallated complexes have also been studied. All the complexes luminesce at 77 K and [M(L )2] (M = Ru or Os), [Ru(L )(L )] , and two of the cyclometallated species are luminescent at room... 

The building block [Au(CN)2] has been revealed as a versatile unit in the formation of heteronuclear arrays which, in some cases, display unusual and interesting luminescent properties, such as vapochromic behavior. In many of these complexes the cyanide group uses the carbon and nitrogen ends as Lewis bases able to coordinate two different metal cations (i.e., Au-CN-M) [82-86]. These ideas may be illustrated by the reaction of K[Au(CN)2] with MX2 salts (M = Cu, Ni, Co, Mn ... 

The use of europium chelates, with their unusually long fluorescence decay times, as labels for proteins and antibodies has provided techniques that are referred to as time-resolved fluoroimmunoassays (TRFIA). Fluorophores as labels for biomolecules will be the topic of Sect. 3. Nevertheless, TRFIAs always have to compete with ELISA (enzyme-linked immunosorbent assays) techniques, which are characterized by their great versatility and sensitivity through an enzyme-driven signal amplification. Numerous studies have been published over the past two decades which compare both analytical methods, e.g., with respect to the detection of influenza viruses or HIV-1 specific IgA antibodies [117,118]. Lanthanide luminescence detection is another new development, and Tb(III) complexes have been applied, for instance, as indicators for peroxidase-catalyzed dimerization products in ELISAs [119]. 

Due to the versatility of QDs and sol-gel processes, it can be envisaged that such concepts hold a great potential to develop new active phases for luminescence-based (bio)sensors. 

Most impressive from the photophysical evaluation of the combinatorial libraries, a remarkable luminescent color versatility, spanning from blue to orange-red emission, can be observed. Furthermore, this set of data was well suited for correlations with static DFT calculations to establish whether it is feasible to predict the luminescent behavior of novel materials. 

Luminescence has proven a useful probe of structure and dynamics in a broad range of heterogeneous media, from zeolites to micelles to biomaterials. The sensitivity of this process to its environment, and its ease of detection, make it a highly versatile analytical tool. To date, luminescence as a probe of solid-liquid interfacial processes in SAMs is still relatively limited. However, with the development of fluorescence-based analytical methods of increasing spatial and temporal resolution, it is likely to be used increasingly in answering fundamental questions regarding monolayer behavior. 

Luciferase-based ATP detection (Promega kinase Glo, Perkin-Elmer Easylite Kinase) ATP-dependent luminescent signal from ludferase conversion of luminal kinase-dependent depletion of ATP is measured Versatile and non-radioactive Signal decrease assay susceptible to luciferase inhibitors Koresawa (2004)... 

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