Fluorescence response

On occasion it will be observed that the fluorescence response for substances in TLC will be far less than expected froa measurements made in solution, will occur at different excitation and emission wavelengths than in solution, and may diminish over time at varying rates [10,19,20,173,180]. Adsorption onto the sorbent layer provides additional nonradiatlve pathways for the. . 

To our benefit, fluorescence is a well-observed phenomenon characteristic for many materials. This allows providing broad selection of fluorescence reporters that have to be chosen according to different criteria high molar absorbance and fluorescence quantum yield, convenient wavelengths of excitation and emission, high chemical stability, and photostability. They are well-described in other chapters of this book and in other books of these series. As we will see subsequently, they should be adapted to particular technique of target detection and to particular method of observation of fluorescence response, which needs establishing additional criteria for their selection. 

Demchenko AP (2005) Optimization of fluorescence response in the design of molecular biosensors. Anal Biochem 343 1-22... 

Callis PR (2010) Electrochromism and solvatochromism in fluorescence response of organic dyes. A nanoscopic view. In Demchenko AP (ed) Advanced Fluorescence Reporters in Chemistry and Biology I. Springer Ser Fluoresc 8 309-330... 

Karpovich DS, Blanchard GJ (1995) Relating the polarity dependent fluorescence response of pyrene to vibronic coupling. Achieving a fundamental understanding of the py polarity scale. J Phys Chem 99 3951-3958... 

A Ca2+-specific fluorescent chemosensor 25 in aqueous buffer signals Ca2+ via a decrease in fluorescence intensity, whereas excess of Mg2+ ions has no effect on the emission [85]. This probe has limited solubility in aqueous solution after binding to Ca2+. A Zn2+ sensitive probe 26 showing different fluorescence responses depending on the complexation stoichiometry is described in [86],... 

Squaraine dyes 10b, 39a, 39b, 41a, 41c, 41d, and 41e were used to measure different proteins such as BSA, HSA, ovalbumin, avidin from hen egg white, lysozyme, and trypsin (Fig. 12) [58]. It is difficult to predict correlations between the dyes structures and the affinity or sensitivity of the dyes for different proteins. All squaraine probes exhibit considerable fluorescence increases in the presence of BSA. Dicyanomethylene-squaraine 41c is the brightest fluorescent probe and demonstrates the most pronounced intensity increase (up to 190 times) in presence of BSA. At the same time, the fluorescent response of the dyes 10b, 39a, 39b, 41a, 41c, 41d, and 41e in presence of other albumins (HSA and ovalbumin) is, in general, significantly lower (intensity increases up to 24 times). Dicyanomethylene-squaraine 41a and amino-squaraines 39a and 39b are the most sensitive probes for ovalbumin. Dyes 41d, 10b, and 41e containing an A-carboxyalky I -group demonstrate sufficient enhancement (up to 16 times) in the presence of avidin. Nevertheless, the presence of hydrolases like lysozyme or trypsin has only minor effects on the fluorescence intensity of squaraine dyes. 

Dilek G, Akkaya EU (2000) Novel squaraine signalling Zn(II) ions three-state fluorescence response to a single input. Tetrahedron Lett 41 3721-3724... 

Fig. 4 (a) Changes in the absorption spectra of Mcy-I upon titration by Hg2+ (b) absorption spectra changes of Mcy-1 upon addition of different cations (10 equiv) (c) fluorescence responses of Mcy-1 to various metal cations (d) bars represent the percentage of fluorescence quenched (reprint from ref. [53], Copyright 2008 American Chemical Society)... 

Electrochromism and Solvatochromism in Fluorescence Response of Organic Dyes A Nanoscopic View... 

The basis for the different response times of these probes is their response mechanism. In order to produce a change in fluorescence, a change in electric field must induce some movement either of the dye molecule as a whole or of its electrons. The degree of movement determines the speed of the fluorescence response. 

The ideal electric field sensitive dye would respond to changes in intramembrane field strength or transmembrane electrical potential within femtoseconds the magnitude of its absorbance or fluorescence response would be enormous it would... 

Oxoquinolizine-3-carboxylates (e.g., 466) are excellent fluorophores that show a strong fluorescent response to Mg2+ but not to Ca2+, avoiding the very frequent interference between both cations <2001BCC203>. The fluorescence of indolo[2,3-tf]quinolizines has also been used for the design of fluorescent histamine H2 receptor antagonists as probes of this receptor <2003BML1717>. 

An important demonstrated application of this artificial nose system is the high-speed detection of low levels of explosives and explosive-like vapors. Several sensors, based on Nile Red attached to silica microspheres, show high sensitivity to nitroaromatic compounds (NAC) within a mixture12. Different fluorescence response profiles were observed for several NAC s, such as 1,3,5-trinitrotoluene (TNT) and 1,3-dinitrobenzene (DNB), despite their similar structures. These responses were monitored at low concentrations of the NAC vapors (ca. 5 ppb) and at short vapor exposure... 

In addition, a linear dependence was found between the concentration of DNB and its fluorescence response profile. All these characteristics demonstrate that this sensor array is suitable for use in detecting explosive vapors. 

Figure 6.15 Left stress-induced response of native and recombinant bacteria. Right single E. coli cell fluorescent response after induction by mitomycin C. (Reproduced from ref. 16, with permission.)...

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