Luminescent signalling

Several solid surfaces, such as filter paper, sodium acetate, and silica gel chromatoplates with a polyacrylate binder, have been used in solid-surface luminescence work (1,2). Experimentally it is relatively easy to prepare samples for analysis. With filter paper, for example, a small volume of sample solution is spotted onto the surface, the filter paper is dried, and then the measurement is made. In many cases, an inert gas is passed over the surface during the measurement step to enhance the RTF signal. For powdered samples, the sample preparation procedure is somewhat more involved. Commercial instruments can be readily used to measure the luminescence signals, and a variety of research instruments have been developed to obtain the solid-surface luminescence data (1,2). 

Interactions in Solid-Surface Luminescence Temperature Variation. Solid-surface luminescence analysis, especially solid-surface RTF, is being used more extensively in organic trace analysis than in the past because of its simplicity, selectivity, and sensitivity (,1,2). However, the interactions needed for strong luminescence signals are not well understood. In order to understand some of the interactions in solid-surface luminescence we recently developed a method for the determination of room-temperature fluorescence and phosphorescence quantum yields for compounds adsorbed on solid surfaces (27). In addition, we have been investigating the RTF and RTF properties of the anion of p-aminobenzoic acid adsorbed on sodium acetate as a model system. Sodium acetate and the anion of p-aminobenzoic acid have essentially no luminescence impurities. Also, the overall system is somewhat easier to study than compounds adsorbed on other surfaces, such as filter paper, because sodium acetate is more simple chemically. 

Recently, Gianotti et al. (96) reported photoluminescence and DRUV spectra of pure siliceous MCM-41 and Ti-MCM-41 containing Ti4+ species anchored to the inner walls of the siliceous MCM-41. They observed complex luminescence signals and concluded that these could be used for a clear distinction of the emission of tetrahedral Ti4+ ions from those of silica surface centers. 

Perhaps the most obvious strategy for a chemist is to use an actual chemical reaction involving covalent bond formation rather than the interplay of supramo-lecular forces. The following section thus illustrates the use of chemical reactions in the context of luminescence signaling, concentrating on two different phenomena (i) the production of a fluorophore in a chemical reaction, which still requires a conventional fluorescence measurement setup, and (ii) chemiluminescence (CL), where photons are produced by a chemical reaction, but which only needs a detector for registration of the emitted light. 

In the silica nanomatrix, the low diffusion was also reported in both liquid and gas phases. In the gas-phase reaction, it was found that the luminescence signal of Ru(bpy)32+ doped in DDSNs remained stable when the air pressure increased from 1 to 8 psi, showing no quenching by oxygen in the air. When the air pressure was further increased to above 8 psi, a decrease in fluorescence emission intensity was observed. The results suggested a slow diffusion of quencher oxygen in the silica nanomatrix. 

SPA (scintillation proximity assay) Amersham Biosciences (GE Healthcare) Binding of radiolabeled moiety to beads containing scintillant produces luminescent signal... 

Many scientists would argue that the flexibility and reliability of SPA more than offset these potential disadvantages, and SPA is still in wide use for HTS today. Nevertheless, methods that generate fluorescent and luminescent signals without radioisotopes have become favorites in some HTS laboratories. These fluorescence- and luminescence-based methods,... 

Comparing this value to the typical sensitivity provided by a spectrophotometer, (OT>)niin = 5 X 10 (see Section 1.4), we see that the luminescence technique is much more sensitive than the absorption technique (about 10 times for this experiment). Although this large sensitivity is an advantage of photoluminescence, care must be taken, as signals from undesired trace luminescent elements (not related to our luminescent center) can overlap with our luminescent signal. 

Kurkijarvi et al. were the first to demonstrate the feasibility of seg-mented-flow bioluminescence assays by use of a bioreactor packed with bacterial bioluminescent enzymes immobilized on Sepharose 4B [60]. The packed glass colunrn used was placed in front of the photomultiplier tube of a luminometer. The luminescence signal obtained was linearly related to the NADH concentration from 1 pmol to 10 nmol for sample volumes of 2-20 pL. In the region of 400 NADH assays could be performed with a single enzyme column, with no appreciable change in sensitivity or accuracy. However, problems arising from packing or disruption of the matrix were encountered after 4 days of intensive use. 

Although in this text they are not described as such, many of the applications described in section 3.5.6 fall into the category of luminescent signalling. For instance, the detection of in section 3.S.6.3, the measurement of pH in section 3.5.6.4, and the use of lanthanide chelates in DNA studies outlined in section 3.5.6.9 all use the change in fluorescence for both the signalling and quantification of the target. 

Luminescent signalling systems can be devised to show both molecule-molecule and molecule-atom interactions. The signalling principles of the most useful systems have been classified into the following main categories ... 

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