Other Collisional Quenchers

A wide variety of molecules can act as quenchers (Ch q ter 8), and they permit devdopment of sensors based on collisional quenching. Boizo[h]fluotoanthene was found to be highly sensitive to sulfur dioxide. Oxygen interfered with the measurements but was 26-fold less efficient as a quencher than SOz- Halogenated anesthetics ate known to quench protein fluraescence and can be detected by collisional quenching of anthracoie and petylene. Carbazole is quenched by a wide variety of chlorinated hydrocarbons. NO. which serves as a signal for blood vessel dilation, is also a collisional quencher.  

A wide variety of pH indicators are availaUe from analytical chonistry. Since indicators are intended for visual observation, they display pH-dependent absorption spectra, with absmption at visible wavdengths. These indicators have formed the basis for a number of RET pH/jpCOz sensors. One of the earliest reports used eosin as the donor and Phenol Red as the acceptor. Phenol Red was selected becauseit displays apiK. near 7, and the basic form absorbs at S46 nm, when eosin emits. Consequently, the eosin intensity decreased as the pH increased. In the case of this particular sensor, it was not certain whether the decreased intensity was due to RET or to an inno- filto- effect, but it is dear that RET is a usdiil mechanism as a basis for designing sensors. 

Acceptor displays chains in its absorption spectrum in response to analyte. 

Oind 2%. The plMse.aii iiiB siiiaiieiiU were mideiti light roodoh-liail fteqnengr of 138.14 MHz. Rnn Ref. S9. 

A critical point in sensor design is the support containing the probes. For the pCOj sensor, the support consisted of an yl cdlulose (EC) film coated on a glass slide. The EC contained tetraodylanunonium hydroxide (TOAH), which served as a phase-transfer agent for theCC 2. These 

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Dynamic quenching occurs within the fluorescence lifetime of the fluorophore, i.e., during the excited-state lifetime. This process is time-dependent. We have defined fluorescence lifetime as the time spent by the fluorophore in the excited state. Collisional quenching is a process that will depopulate the excited state in parallel to the other processes already described in the Jablonski diagram. Therefore, the excited-state fluorescence lifetime is lower in the presence of a collisional quencher than in its absence. 

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