Fluorescent reporter, competition with

Weller [21-23] has pointed out the competition between the rates of proton transfer and the deactivation in the excited state. In fact, it has been shown that proton-induced fluorescence quenching competitive with the proton-transfer reaction is present in the excited state of naphthylamines, that is, simple acid-base equilibrium cannot be accomplished in the excited state of aromatic amines, and that a dynamic analysis containing the quenching process is, therefore, needed in order to obtain the correct values [32,33]. The dynamic analyses by means of nanosecond time-resolved spectroscopy with fluorimetry have been applied to 1-aminopyrene [34,35], 1-aminoanthracene [36], phenanthrylamine [37,38], and naphthols [39]. This method to determine the values of naphthylamines has been used by Hafner et al. [40], and similar experiments for excited naphthols have been carried out by Harris and Selinger [41]. On the other hand, establishment of prototropic equilibrium has been reported in the case of 2-hydroxynaphthalene-6,8-disulfonate [42]. 

As far as we know, this is the first molecular probe that includes two different types of reporter units activated upon on a specific stimulus. The other option to achieve dual detection would be to use two separate probes. However, in this case there could be a problem of competitive catalysis (circumstances in which the Km of the two substrate is not identical). In our probe, 6-aminoquinoline and 4-nitrophenol, detected by fluorescence and absorbance spectroscopy, respectively, were used as reporter units. Due to the synthetic flexibility of our approach, other reporter molecules with different types of functional groups, like amine or hydroxyl, can be linked to our molecular probe. The two assays must be orthogonal to each other, in order to prevent disturbances in the detection measurement. Another advantage of the probe is the aqueous solubility... 

The (1,4) substituted naphthalenophanes undergo [4 + 4] photocycloaddition when irradiated at X > 280 nm, in addition to fluorescence. This photoreaction is competitive with fluorescence, and requires a conformational change that can be suppressed at low temperature 93). The few reports of the lifetime or quantum yield of naphthalenophane fluorescence indicate the effects of photocycloaddition. For the anti-[2.2](1,4) isomer, kpu/ku = 0.021 in cyclohexane 93) the lifetime of syn-[3.3](l,4) naphthalenophane fluorescence was given as 15.3 ns107). Both values are low relative to the naphthalene solution excimer (kpu/kjj 0.2 xD 80 ns 71)), and this may be due in part to the photoreaction of the (1,4) naphthalenophanes. 

An unusual example of delayed fluorescence exemplifying El Sayed s rules (Section 2.1.6) was recently reported for the triplet sensitizer xanthone,127 which undergoes ultrafast ISC within 1 ps. Delayed fluorescence with a lifetime of 700 ps was observed in aqueous solution. Temperature-dependent steady-state and time-resolved fluorescence experiments indicate that the T2(n,it ) state, which is primarily accessed by ISC from Si(ji,ji ), is nearly isoenergetic with the Sj state. The delayed fluorescence is attributed to reverse ISC from T2(n,it ), in competition with internal conversion to Tl(7I,7l ). 

A significant advantage of graphical methods of encoding compared with the spectroscopic methods is that the codes are binary, allowing for error correction. Furthermore, the capacity of these encoding methods is not restricted by competition with bandwidth from the fluorescent assay binding reporters. 

A fiber optic immunosensor (FOI) has also been reported for detection of PCBs in Aroclors [204]. The quartz fiber surface is coated with PAbs against PCBs and the competitive assay takes place using as fluorescent tracer, an analog of the analyte coupled to 2,4,5-trichlorophenoxybutyrate (TCPB) on the Ab-coated fiber. The LOD achieved is around 10 pg L L... 

An immunosensor based on a competitive fluorescence energy-transfer immunoassay was reported by Anderson 105) for the measurement of phenytoin. Texas red-labeled antibody was incubated with a phenytoin derivative. On displacement of the derivative by the antigen, the change in the fluorescence signal was recorded. Detection limits approached 5 /iM with response times ranging from 5 to 30 min. 

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