Terbium fluorescence lifetime

The fluorescence lifetime can be measured by time-resolved methods after excitation of the fluorophore with a light pulse of brief duration. The lifetime is then measured as the elapsed time for the fluorescence emission intensity to decay to 1/e of the initial intensity. Commonly used fluorophores have lifetimes of a few nanoseconds, whereas the longer-lived chelates of europium(III) and terbium(III) have lifetimes of about 10-1000 /tsec (Table 14.1). Chapter 10 (this volume) describes the advantages of phase-modulation fluorometers for sensing applications, as a method to measure the fluorescence lifetime. Phase-modulation immunoassays have been reported (see Section 14.5.4.3.), and they are in fact based on lifetime changes. 

Dieke and Hall (88) measured the fluorescent lifetimes of some rare-earth salts. Their data were collected by an electronic-switch technique. Their results of the 5D4 state of terbium at 77°K and 293°K are ... 

Studies of the fluorescent lifetime of terbium in the series Tbo.srare eartho.shexaantipyrene triiodide (50) give some indication of the distance... 

Rieke and Allison (97) studied the fluorescent lifetime of terbium in the chelate terbium trianthranilate (TbAn3). They concluded that the spectra and fluorescent lifetime of the chelate differ markedly from unchelated terbium compounds. Fluorescent-lifetime measurements were made at 25°C, 0°C, and 77°K using a stroboscopic light source with a decay time of 20 /xsec and a comparison was made with TbCl3 4H20. At all... 

The authors point out that the fluorescent lifetime of the terbium chelate at 25°C is more than twice that of the chloride and that measurements at 0°C and 77°K showed that the lifetime for TbAn3 increases slightly as the temperature decreases. They also measured the lifetimes of each of the individual 5Z)4->7/ transitions and found the same values, as expected. 

The temperature dependence of the fluorescent lifetime was also studied. The series of samples which used aluminum oxide as the backup material were selected for these experiments. Figure 24 shows the fluorescence lifetime of terbium as a function of concentration at IT and 4.2°K compared... 

He gives a fluorescent lifetime of about 700 jxscc for the terbium 5D4 state at 77°K. The fluorescence is quenched at room temperature. Unfortunately, the temperature dependence of the fluorescent lifetime was not measured. 

Liquids. Kondrat eva (101) made an extremely interesting and important observation concerning the fluorescent lifetime of terbium and gadolinium in the compounds Tb2(S04)3 and Gd2(S04)3. It was found that in certain solutions of sulfuric acid-water the lifetimes were approximately three times as long as in aqueous solutions of the same salts. 

In another study, Kondrat eva (103) made a determination of the luminescent quantum yield of the 5D4 state of the terbium ion in aqueous solution. The method used was based upon fluorescent-lifetime measurements and had previously been used by Rinck (96) and Geisler and Hellwege (96) to determine the quantum yield of rare earths in crystals. Kondrat eva made his studies on chloride and sulfate solutions, using the electronic shutter technique of Steinhaus et al. (66). 

The enhancement of the fluorescent yield of terbium, europium, and gadolinium in heavy-water solutions was studied by Kropp and Windsor (105). They observed substantial increases in emission intensities for both terbium and europium compounds when ordinary water was replaced by deuterated water. No appreciable increase was observed for gadolinium, however. For terbium they also obtained the fluorescent lifetimes of the 5D4 state. 

The radial dependence of the fluorescence-quenching interaction between terbium, holmium, and neodymium in aqueous chloride solution was examined by Holloway and Kestigian (108a). From the concentration dependencies of the fluorescence lifetimes, they concluded that the probability for quenching interaction falls off as 1/r6, where r is the average spacing between the ions. If the mechanism of resonance transfer is assumed, the observed radial dependence implies a dipole-dipole interaction. 

Kondrat eva and Lazeeva (108b) studied the temperature dependence of the fluorescent lifetime of the 5D4 state of terbium sulfate in H20 and... 

Axe and Weller (52) studied fluorescence and energy transfer of europium in yttrium oxide. In an experiment somewhat similar to that of Peterson and Bridenbaugh (54) on terbium, Axe and Weller were able to obtain experimental evidence for nonradiative-energy transfer between europium and other trivalent rare earth ions. Their study included both intensity and fluorescent-lifetime measurements. 

From these excitation spectra and also from the fact that the fluorescent lifetime of the europium 5D0 state is unaffected by the presence of terbium leads one to conclude that little if any energy is lost from europium to terbium. 

An examination of the temperature dependence of the fluorescent lifetime of both terbium nitrate and europium nitrate in methanol and deuterated methanol was made. There was little change with temperature for either. 

A wide variety of fluorescent molecular probes have been demonstrated to be suitable for excitation by the He-Cd laser 4-bromomethyl-7-methoxycoumarln has been employed for the detection of carboxylic and phosphoric acids (44,55), 7-chlorocarbonyl-methoxy-4-methylcoumarln for hydroxyl compounds (42), 7-lsothlocya-nato-4-methylcoumarln for amines and amino acids (55), 7-dlazo-4-methyl-coumarln for a variety of aromatic compounds (55), and terbium chelate molecules with long fluorescence lifetimes ( 1 ms) for protein analysis (56). In this study, we examined the utility of l-dlmethylamlnonaphthalene-5-sulfonyl chloride (dansyl chloride) as a sensitive and selective reagent for the determination of biogenic amines and amino acids. 

The recognition of the limitations of short radiative fluorescence lifetime of some covalently bound labels used in studies of nucleic acids prompted Saavedra and Picozza to bind terbium to DNA via inunobilized DTPA [47]. Instead of the nanosecond lifetimes achieved with stains such as ethidium bromide, a radiative lifetime of 1.5 msec was obtained for terbium-labeled DNA. In addition, this material is stable under the conditions frequently encountered in polyacrylamide gel electrophoresis. This labeling technique could also be used for RNA. There can be no doubt that the requirements of genetic manipulation will bring about many similar procedures for analyzing nucleic acids. 

In n-butanol as solvent at 293 K Tb(acac)3-3H20 undergoes intermolecular energy transfer to the complexes R(acac)3-3H20 (R = Pr, Nd, Sm, Eu, Dy, Ho, or Er) (Napier et al., 1975). Measurement of the decay time of the D4 level of the terbium(III) ion indicates that transfer takes place from that level to the excited levels of the other rare earths with bimolecular rate constants of 0.5-4.9x lO dm mol s. The fluorescence lifetime for the D4 state of terbium in gaseous Tb(DPM)3 has also been determined. These measurements have been made by Jacobs et al. (1975) as a function of temperature and pressure and the results demonstrate that intermolecular collisional deactivation is not important. Rather, the non-radiative deactivation is an intramolecular process and occurs by means of a transfer to low-lying excited states of the chelate. The fluorescence decay time is 1 s at 200°C which is very much shorter than those observed in 95% ethanol ( 600 /ts) and in the solid state (—500 fis) at room temperature. 

Kropp and Windsor (105,107) studied extensively the effects of deutera-tion on the luminescence characteristics of some rare-earth complexes. Solutions of europium and terbium salts in heavy water give fluorescence intensities and lifetimes many times greater than the corresponding solutions in ordinary water. Table X gives the results of their studies on europium... 

Metal complexes like lanthanide chelates (mainly europium or terbium), ruthenium phenanthrolines or bipyridyls, and platinum porphyrins can be used as fluorescent labels for biomolecules. Their long decay times are perfectly suited for a detection by time-resolved imaging, and the labeled target molecules can be used for the determination of intracellular recognition processes or for the screening of DNA and protein arrays. Ratiometric lifetime-based imaging methods in combination with sophisticated data acquisition and evaluation tools can substantially contribute to the development... 

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