Fluorescence-quenching effect

Fig. 4 Explanation of the fluorescence-quenching effect [2]. — (A) chromatograms of the same quantities of saccharin and dulcin observed under UV 254 light, (B) schematic representation of fluorescence quenching, (C) spectral reflectance curves of saccharin and dulcin.

The separation of uncolored samples is usually done on TLC plates containing a fluorescent dye so as to use the fluorescence-quenching effect for sample location. If such plates are not available or if samples show no quenching effect, two universal reagents can help. If the TLC plate is simply sprayed with water, sample spots are very often not translucent but white. Clearer zones can be obtained sometimes by first saturating... 

The apphcation of an optical transducer based on the fluorescence quenching effect of oxygen was described by Preininger et al. [3]. Another interesting technique is represented by the use of the luminous bacterium Photobacterium phos-phoreum [34]. This device is based on the correlation of the intensity of luminescence to the cellular assimilation of organic compounds from the wastewater. 

As an example, the assay commonly used to measure the direct generation of ROS by nanoparticles is based on the conversion by ROS of the 2,7-dichlorodihydrofluorescein dye into a fluorescent product, 2,7-dichlorofluorescein. There is also a range of fluorescent probes that measure NM-induced ROS production inside the cells, in different intracellular compartments (e.g., dihydrorhoda-mine-1,2,3 in the mitochondria, 2,7-dichlorodihyydrofluorescein diacetate in the cytoplasm, dihydroethidium bromide in the nucleus) [59]. They are all relatively easy to use for quantification in a fluorimeter, multiwall plate reader, or by flow cytometry, but a potential drawback of all these assays is the background caused by particles as well as the fluorescence quenching effects that need to be controlled and taken into account to reliably measure the free radical production [59, 60]. 

Table 1 summarizes the results of the competition studies for 12 of the 24 anthraquinones previously characterized [9]. The extent of competition for the Qb binding domain was determined through a consideration of the additivity of the fluorescence quenching effects of two individual quinones when simultaneously present in a chloroplast sample. Competition for the same or overlapping binding sites was indicated by a chlorophyll fluorescence level in the presence of both quinones that was not as low as that achieved in the presence of either one of the quinones individually. Non-competitive quinones with different binding sites quenched chlorophyll fluorescence to the level expected if the quenchir g effects of the individual quinones were additive. Partial competition was characterized by an extent of fluor-... 

The fluorescence quenching effect of mercury in algal cells in the presence of DCMU is presented in Fig. lA. The intensity of the quenching effect was dependent on the incubation time and on the mercury concentration. The shape of the curves for the different incubation... 

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