8-Hydroxypyrene-l,3,6-trisulfonic acid

Fig. 1.5. Examples of hydrophobic, hydrophilic and amphiphilic probes. 1 pyrene. 2 8-hydroxypyrene-l,3,6-trisulfonic acid, trisodium salt (pyranine). 3 8-alkoxypyrene-l,3,6-trisulfonic acid, trisodium salt. 4 1-...

Pyranine, 8-hydroxypyrene-l,3,6-trisulfonic acid 8-Hydroxypyrene-1,3,6-trisulfonic acid (HPTS, also known as pyranine) can be used as a pH indicator. At low pH, HPTS fluorescence is greater with 405 nm excitation, whereas at neutral pH, fluorescence at 440 nm excitation is greater than at 405 nm excitation. Therefore, a strong fluorescence signal at 405 nm excitation indicates HPTS in acidic compartments (endosomes and lysosomes) a strong signal at 440 nm indicates HPTS in neutral compartments (cytosol) (126 128). 

Ertekin and coworkers developed an additional optical COj sensor based on the fluorescence signal intensity changes of the pH-sensitive fluorescent dye 8-hydroxypyrene-l,3,6-trisulfonic acid trisodium salt (HPTS) dissolved in ILs [18]. When HCO3 was added to HPTS solution, the fluorescence intensity of the peak centered around 520 nm decreased by 90% in [C4Qlm] [BF4] and by 75% in [C4Cilm]Br. The reported detection limit for CO2 (g) was 1.4% while the detection limit for dissolved COj was 10 M HCO3. The sensor exhibited excellent stability and repeatability over a time period >7 months. 

Ruthenium complexes with mixed bipyridyl ligands, immobilized inside a Nation film, may also be used as pH-sensitive sensor layers [90]. A completely different approach for a ratiometric imaging of pH sensor foils was developed for diagenetic studies of marine sediments, using the dual fluorescence excitation ratio of the pH-sensitive fluorophore 8-hydroxypyrene-l,3,6-trisulfonic acid (HPTS) [91]. Commonly used dual fluorophors with different absorption and emission maxima in the protonated and basic form for ratiometric measurements are the naphthofluorescein and seminaphthofluorescein derivates (SNARF and SNAFL) [92], It should be noted that ammonia or carbon dioxide can also be detected by some of these pH-sensitive materials [55,93]. 

The samples used were 10 M aqueous solutions of 8-hydroxypyrene-l,3,6-trisulfonic acid trisodium salt (HPTS or 3sPyOH) (Sigma-Aldrich) in buffers of pH 6 and pH 10. UV-Vis absorption spectra of the dye solutions at different pH environments were obtained with a Hitachi U-4001 uv-vis spectrophotometer. 

Near-neutral pH fluorescein diacetate, carboxyfluorescein and Its esters, 5-sulfofluorescein diacetate, BCECF Acidic pH di- and trifluorofluoresceins (Oregon Green) and dichlorofluores-cein, 9-amino-6-chloro-2-methoxyacri-dine, 8-hydroxypyrene-l,3,6-trisulfonic acid (HPTS)... 

Fig. 12 The distribution of the symplasmic tracer (HPTS -8-hydroxypyrene-l,3,6-trisulfonic acid) within the protodermal cells ol Arabidopsis explants. A - stomata as an example of the permanent symplasmic domain. B-C examples of the temp)oral symplasmic domains composed of a few cells (C) or in a single cell (D as to B, note the imequal distribution of fluorochromes in the daughter cells after a division - arrow bar = 10 pm).

Figure 5.22 Six carbohydrate receptors consisting of cationic bis-boronic acid appended benzyl viologens [3,3 -olm-, 4,3 -olm-, and 4,4 -o/m-BBV) and the anionic fluorescent dye 8-hydroxypyrene-l,3,6-trisulfonic acid trisodium salt (HPTS). Three corresponding benzyl viologens (3,3 -, 4,3 -, and 4,4 -BV) were used as controls.

HYDROXYPYRENE-l,3,6-TRISULFONIC ACID TRISODIUM SALT (HPTS) (PYRANINE)... 

Hydroxypyrene-l, 3,6-trisulfonic acid trisodium salt (HPTS) (Pyranine)... 

Even cationic species such as the (hydrated) hydrogen ion (H ) can be lured into the hydrophobic silicone films from water medium as long as they contain appropriate additives to allow penetration of the analyte. For instance, Nivens et al. [140,141] have reported fabrication of silicone/ sol-gel films using a hydroxy-terminated poly(dimethyl siloxane (PDMS-OH), tetraethoxysilane (TEOS) and 3-ami-nopropyltriethoxysilane (APTES) mixture in ethanol-water. Tetramethylammonium hydroxide (TMAOH) is added to the mixture to entrap the fluorescent pH indicator dye 8-hydroxypyrene-l,3,6-trisulfonic acid trisodium salt (HPTS) [102], after base-catalyzed polycondensation of the silanes and the PDMS-OH. Silica optical fibers are stripped from their jacket at the distal end and dip-coated with the indicator gel before the end of gelation (24 h). The optical fluorosensor is able to measure between pH 6.0 and 8.5 for 6 months if stored in buffer medium. 

Indirect LIF detection (8-hydroxypyrene-l,3)6-trisulfonic acid as the indirect probe)... 

The first example employed an immobilization of GOx and a pH-sensitive dye (l-hydroxypyrene-3,6,8-trisulfonate, HPTS) on the tip of an optical fiber.44 As the local pH was reduced by gluconic acid production, measurable changes in fluorescence were observed. Using flow-through measurements with buffer solutions of various strengths, the optrode response time was determined to be 8-12 min, with a detection limit of 1.8-36 mg/dL glucose and response saturation at 36-54 mg/dL. 

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