pH-sensitive fluorescent dyes: are they really pH-sensitive in cells?

Chemically synthesized near-infrared aza-BODIPY dyes displayed off-on fluorescence at acidic pH (pKa = 6.2-6.6) through the suppression of the photoinduced electron transfer and/or internal charge transfer process. The apparent pKas of the dyes were shifted well above physiological pH in a hydrophobic microenvironment, which led to "turned-on" fluorescence in micelles and liposomes at neutral and basic pH. Bovine serum albumin also activated the fluorescence, though to a much lesser extent. When these small molecular dyes entered cells, instead of being fluorescent only in acidic organelles, the whole cytoplasm exhibited fluorescence, with a signal/background ratio as high as ∼10 in no-wash live-cell imaging. The dye 1-labeled cells remained highly fluorescent even after 3 days. Moreover, slight variations of the dye structure resulted in significantly different intracellular fluorescence behaviors, possibly because of their different cellular uptake and intracellular activation capabilities. After the separation of cellular components, the fraction of plasma membrane and endoplasmic reticulum showed the highest fluorescence, further confirming the fluorescence activation by membrane structures. The fluorescence intensity of these dyes at different intracellular pHs (6.80 and 8.00) did not differ significantly, indicating that intracellular pH did not play a critical role. Altogether, we showed here for the first time that the fluorescence of pH-sensitive aza-BODIPY dyes was switched intracellularly not by acidic pH, but by intracellular membranes (and proteins as well). The excellent membrane permeability, ultrahigh fluorescence contrast ratio, persistent fluorescent signal, and minimal biological interference of dye 1 make it an ideal choice for live-cell imaging and in vivo cell tracking. These findings also imply that the intracellular fluorescence properties of pH-sensitive dyes should be carefully examined before they are used as pH indicators.

[Effect of different coating materials on hygroscopicity of compound Luhui granules].

OBJECTIVE: To study the effect of different coating materials (hydroxy-propyl methylcellulose, ethylcellulose, polyacrylic resin) on hygroscopicity of granules of traditional Chinese medicine. METHODS: The methods coated with the single coating material, the complex membrane (coated with two or three kinds of coating materials in turn), the mixed membrane (coated with two or three kinds of coating materials mixed) and the combination of mixed membrane with complex membrane were used, respectively. Taking decreasing percentage of moisture absorption of coated granules as index, the optimum condition of coating technology (the optimum coating method, coating material and its dosage) was optimized by orthogonal test. RESULTS: The damp-proof effect of coated with the combination of mixed membrane with complex membrane (decreasing percentage of moisture absorption of coated granules: 35.39%) was better than that of coated with the single coating material (decreasing percentage of moisture absorptions < or = 21.82%), the complex membrane (decreasing percentage of moisture absorption: 30.28%), or the mixed membrane (decreasing percentage of moisture absorption: 31.37%) (P < 0.05). CONCLUSION: The method coated with the combination of mixed membrane (mixed coating materials composed of ethylcellulose and polyacrylic resin) and with complex membrane (coating material composed of HPMC; The granules were coated firstly with the mixed coating materials, followed by HPMC) , obviously reduces the hygroscopicty of compound Luhui granules, and raises the stability of compound Luhui capsules. It is advantageous to the preparation production, storage and application.