Colorimetric Chemosensor and Turn on Fluorescence Probe for pH Monitoring Based on Xanthene Dye Derivatives and its Bioimaging of Living Escherichia coli Bacteria

A new turn on fluorescence probe based on 3',6'-dihydroxy-6-methyl-2-((pyridin-2-ylmethylene)amino)-4-(p-tolyl)spiro[benzo[f]isoindole-1,9'-xanthen]-3(2H)-one (BFFPH) derived from benzo[f]fluorescein was prepared. Full characterization of the prepared probe using spectroscopic analysis was described such as IR, NMR and MS spectra. The sensitivity of BFFPH for monitoring of pH change in alkaline medium was studied. BFFPH exhibited a high sensitivity to alkaline pH by two pKa values at 8.82 and 10.66 in UV/vis spectroscopy titration. The pH monitoring was studied in broad range of pH values (2.5-12.2) at two pKa values at 8.72 and 10.73 by recording the effect of pH on the fluorescence intensity of BFFPH. The acid-base reversibility character of the probe was investigated as well as the effect of the pH change on the fluorescence quantum yield. The application of the prepared BFFPH probe for detection of living Escherichia coli (E. coli) bacteria using confocal fluorescence microscope was investigated.

"Biotin-targeted mixed liposomes: A smart strategy for selective release of a photosensitizer agent in cancer cells"

The high incidence of cancer, necessity of treatment, and prognosis times are urgent issues that need to be addressed. In this work, we present DPPC liposomes coated with F127 triblock copolymers as a promising alternative in drug delivery systems for cancer therapy. The proposed mixed liposomes exhibit adequate size, high stability, and passive targeting that result from the EPR effect. An interesting strategy to obtain both passive and active targeting is the vectorization with a covalent bond between F127 and Biotin (a vitamin). Cancer cells can overexpress Biotin receptors, such as Avidin. Here, we evaluate the cytotoxic effects of the erythrosine-decyl ester (ERYDEC). This is a photosensitizer that can be utilized in photodynamic therapy (PDT) and incorporated in DPPC liposomes coated with F127 (F127/DPPC) and the biotinylated-F127 (F127-B/DPPC). The results showed that DPPC liposomes were efficiently mixed with common F127 or F127B, exhibiting adequate physical properties with simple and low-cost preparation. An HABA/Avidin assay showed the amount of Biotin available at the liposome surface. In addition, ERYDEC interaction with lipid vesicles showed high encapsulating efficiency and slow release kinetics. The ERYDEC monomeric species are represented by high light absorption and high singlet oxygen generation (1O₂), which confirm the presence of the drug in its monomeric state, as required for PDT. The ERYDEC/liposome system showed high stability and absence of significant cytotoxic effects (absence of light) in fibroblasts of the Mus musculus cell line. In addition, phototoxicity studies showed that ERYDEC/liposomes were able to inhibit cancer cells. However, in the biotinylated system, the effect was much greater than the common F127 coating. This dramatically decreased the inhibitory concentration of CC₅₀ and CC₉₀. In addition, cellular uptake studies based on fluorescence properties of ERYDEC showed that a two-hour incubation period was enough for the uptake by the cell. Therefore, the new vectorized-coated liposome is a potential system for use in cancer treatments, considering that it is a theranostic platform.

Two-photon imaging of 1,4-dithiothreitol (DTT) by a red-emissive fluorescent probe in living cells, tissues and animals

1,4-Dithiothreitol (DTT) is an important small-molecular reducing agent and has extensive applications in biochemistry, peptide/protein chemistry and clinical medicine. The development of effective methods for monitoring DTT is of great importance for its safe use and studying its toxicity to human. In this work, we present a two-photon red-emissive probe for the imaging of DTT in living cells, tissues and animals. The probe employed a two-photon red-emissive xanthene dye as the fluorophore and selected 2,4-dinitrophenylate as the novel recognition site for DTT. In response to DTT, the probe displayed excellent sensitivity and selectivity. The probe was successfully applied to the two-photon imaging of DTT in living cells, and the imaging of DTT in living tissues and animals.

Interaction between triethanolamine and singlet or triplet excited state of xanthene dyes in aqueous solution

Triethanolamine (TEOA) has been often used as a hole-scavenger in dye-sensitized semiconductor photocatalytic systems. However, the femtosecond time-resolved kinetics of the interaction between a sensitized dye and TEOA has not been reported in literatures. Herein, we selected four commonly used xanthene dyes, such as fluorescein, dibromofluorescein, eosin Y, and erythrosine B, and studied their ultrafast fluorescence quenching dynamics in the presence of TEOA in aqueous solution, respectively, by using both femtosecond transient absorption and time-resolved fluorescence measurements. We obtained the electron transfer rate from TEOA to each photoexcited xanthene dye in 2.0 M TEOA solution. We also obtained the intersystem crossing rate of each xanthene dye in aqueous solution with fluorescence quantum yield and lifetime measurements. Finally we found that TEOA mainly interacts with the singlet excited-state of fluorescein, dibromofluorescein, and eosin Y, and that TEOA can interact with both the singlet and triplet excited-states of erythrosine B in high concentration of TEOA aqueous solution.