Photobleaching Efficiency Research Articles

Optimization of energy parameters for laser-induced photodynamic therapy of cervical tissues using numerical simulation and fluorescent navigation

SignificanceThe main problem in the photodynamic therapy of tumors is insufficient light exposure to tissue depth or the appearance of undesirable surface effects. It is required to investigate the influence of energy density and radiation spot diameter on the photosensitizer photobleaching efficiency by depth. ApproachOptimization of energy parameters for laser-induced photodynamic therapy of cervical tissues was conducted using numerical simulation and fluorescent navigation. ResultsThe laser radiation fluence rate in the near-surface layer of cervical tissue increases relative to the incident radiation fluence rate with increasing spot diameter in the range from 0.2 to 15 mm. The photosensitizer photobleaching increases with an increase in the spot diameter from 5 to 15 mm. ConclusionsThe developed method will improve the efficiency of photodynamic therapy by providing a therapeutic effect throughout the entire depth of tumor invasion without superficial thermal damage.

Anion effect on crystal structure of Zn-complexes of spironaphthopyran and their chromogenic properties in solution

Effect of the anion nature on crystal structure of Zn-complexes of spironaphthopyran and their chromogenic properties in solution were studied. Complexes with zinc chloride and zinc picrate exhibited tertahedral and octahedral coordination environment of the metal ion respectively. The structure of the complex with zinc picrate demonstrates a rare example of the co-crystallization of two types of complexes differing in the number of coordinated picrate anions. The composition, stability, and absorption properties of zinc complexes in acetone essentially depend on the counter anion nature. When the coordinating ability of the counter ion increases in the range BF4−, ClO4−, NO3–, Pic−, I−, Cl−, CH3COO–, (CH3)3CCOO– the complex stability is reduced from logK = 8.7 to 2.96. This is accompanied by the chromogenic effect which is related to the decrease in the spectral shift of the long-wavelength absorption band of the complex relative to the merocyanine ligand from 846 up to 168 cm−1. The complex photo-initiated processes include fluorescence and thermally reversible dissociation. Fluorescence is characterized by band maxima in the 622–637 nm region and normal Stokes shifts of 1087–1454 cm−1 with an efficiency being weakly dependent on the anion nature. In contrast, the negative photochromism of the complexes demonstrates a significant dependence of the photo-bleaching efficiency on the anion nature in the range 0.012–0.17. The presence of a chromogenic photochromic effect along with fluorescence makes it possible to consider the complex as fluorescent switch.

In-situ regeneration of P-doped optical fiber dosimeter

We demonstrate the feasibility of resetting and reusing dosimeters exploiting the measurement of the infrared radiation-induced attenuation (IR-RIA) in phosphosilicate optical fibers (OFs) to provide point or distributed dose measurements in radiation environments. To bleach the room temperature stable IR-RIA, we used the photobleaching (PB) phenomenon. The PB efficiency was evaluated for different wavelengths in the [400-1100] nm range. The best identified PB resetting condition consists in using a continuous-wave Argon-ion laser at 514 nm. This treatment successfully bleached ∼97% of the IR-RIA at 1550 nm of a 30 m-long P-doped single mode optical fiber X-ray irradiated at a dose of 100 Gy. Successive re-irradiations of the same OF sample, regenerated after each run, confirm that the dosimeter keeps the same calibration curve during the whole process.

Investigation of cerium influence on photo-darkening and photo-bleaching in Yb-doped fibers

Photo-bleaching (PB) is considered as a convenient way to mitigate the photo-darkening (PD) in Yb-doped fibers. In this work, Ce doping into the fiber was proposed to improve the PD resistance and the efficiency of PB. Compared to Yb/Al-co-doped fiber, the PD-induced excess loss in Yb/Al/Ce-co-doped fiber was more than 50 % suppressed. The measurements also showed that more than 30 % PD loss in Yb/Al/Ce-co-doped fiber was bleached after 180-min pumping of 793-nm LD, while the percentage in Yb/Al-co-doped fiber was less than 20 %. Besides, a self-bleaching phenomenon was observed in Yb/Al/Ce-co-doped fiber. The PD was effectively relaxed after the 915-nm pump power was turned off for 16 h. This work shows a capable and convenient approach for maintenance of fiber lasers and amplifiers.

Improvement of Orange II Photobleaching by Moderate Ga3+ Doping of Titania and Detrimental Effect of Structural Disorder on Ga Overloading

Highly photoactive Ga3+‐doped anatase modification of titania was prepared by homogeneous hydrolysis of aqueous solutions mixture of titanium oxo‐sulphate TiOSO4 and gallium(III) nitrate with urea. Incorporation of Ga3+ into the anatase lattice has a clear positive effect on the photocatalytic activity under UV and Vis light irradiation up to a certain extent of Ga. Ga3+ doping decreased the size of the crystallites, increased surface area, and affected texture of the samples. Higher amount of gallium leads to the formation of a nondiffractive phase, probably photocatalytically inactive. The titania sample with 2.18 wt.% Ge3+ had the highest activity during the photocatalysed degradation in the UV and visible light regions; the total bleaching of dye Orange II was achieved within 29 minutes. Ga concentration larger than 5% (up to 15%) significantly inhibited the growth of the anatase crystal domains which formed the nondiffractive phase content and led to remarkable worsening of the photobleaching efficiency.

PH-sensitive photocatalytic activities of TiO2/poly(vinyl alcohol)/poly(acrylic acid) composite hydrogels

Abstract The pH-sensitive photocatalytic system was prepared by embedding TiO2 into poly(vinyl alcohol)/poly(acrylic acid) hydrogel. Two different type TiO2/hydrogel composites, such as matrix and nanofiber, were prepared to investigate the morphological effects on the photocatalytic activity. TiO2 was distributed uniformly in the composite hydrogel and kept the original anatase structure without any structural change. The photocatalytic activity of TiO2 was evaluated based on the efficiency of photobleaching of dye. The photobleaching of dye was improved greatly as the pH was changed into basic condition and the larger surface area of hydrogel was available for TiO2 by using nanofiber supports.

Inactivation of faecal bacteria in wastewater by methylene blue and visible light

The high inactivation of faecal indicators [faecal coliforms (FC), E. coli and faecal streptococci (FS)] using a combination of methylene blue (MB) with natural sunlight or artificial visible light determined on a small scale, was dependent mainly on the MB concentration, its application process and pH. In order to avoid primarily leaching of the compound into the environment and to further understand the MB photosensitization mechanisms, MB should be properly immobilized within resin. The FC and FS were found to be susceptible to the photodynamic action of MB fixed to the support. The mechanism of faecal bacteria inactivation by MB also seems to be a combination of Type I and Type II processes, and the relative efficiency of each of them depends notably on the experimental conditions. In parallel, the MB stability under light “photobleaching” has been studied by optical absorption spectroscopy. It has been shown that it was dependent essentially on pH, nature of the medium (distilled water and secondary wastewater effluent) and time exposure to light. Practically, all of the MB (10 μM) disappeared from effluent, exposed to sunlight, by the end of a 12 h experiment with a bleaching rate from 92 at neutral pH. Kinetic data indicate that the dye photobleaching efficiency can be approximated by pseudo-first-order reaction.

Photodynamic activity of pyropheophorbide methyl ester and pyropheophorbide a in dimethylformamide solution

Comparative spectroscopic study including the photosensitizers of pyropheophorbide methyl ester (PPME) and pyropheophorbide a (PPa) was performed to study their photodynamic activity. The investigated photosensitizers in a homogeneous system of dimethylformamide (DMF) are not photostable upon irradiation. The photobleaching efficiency of PPa is higher than that of PPME. Combining these results with the data obtained by measuring the singlet oxygen quantum yield and the hydroxyl group generation, it was revealed that the photobleaching efficiency could be correlated with the singlet oxygen quantum yield and the hydroxyl group production of the photosensitizer.

Photocatalytic Degradation of Methyl Orange: Influence of H2O2 in the TiO2-Based System

The purpose of this study was to investigate the photocatalytic oxidation of a reactive azo dye. The photocatalytic activity of the TiO2 was studied using a reactor equipped with UV-A sources, with maximum emission at 365 nm. The photocatalytic activity of the TiO2 powder (99.9% anatase) and thin films has been measured through the decomposition of methyl orange solutions. The thin film was prepared by doctor blade and spray pyrolysis deposition (SPD). The TiO2 suspensions were prepared at 1 g/L concentration, and the initial methyl orange concentration was fixed at 7.8125 mg/L. The influence of the TiO2 (powder or thin films) and/or O2 and H2O2 on the photobleaching rate, was tested under different experiments, at pH = 5. Thin films (doctor blade) of TiO2 formed of mezo-sized aggregates formed of nanosized anatase crystallites show better photobleaching efficiency than thin film (SPD) due to their large internal surface. The rate is even higher in H2O2 compared to oxygen environment.

Novel and efficient dye-linked radical generators for visible light photoinitiating polymerization

Dye-linked initiators consisting of a benzothiazolylidene-rhodanine merocyanine dye (M) and a substituted bis(trichloromethyl)-1,3,5-triazine initiator (T) linked by a different number of methylene units and at different positions were prepared in order to reveal the effect of the structure of linked systems on the efficiency of photopolymerization. The spectroscopic studies clearly showed that the dye-linked initiators exhibit a marked increase in the efficiency of photobleaching and fluorescence quenching compared to a simple mixture of the dye/initiator and that the efficiency among the linked systems is dependent on the number and position of methylene units. These results are reasonably explained in terms of the efficiency of electron transfer between the dye and the initiator, which eventually results in the formation of a radical. The relative photoinitiating efficiency of dye-linked initiators in photopolymerization of acrylates was also evaluated and the trends observed for polymerization are essentially the same as that observed spectroscopically.

Photobleaching of chlorins in homogeneous and heterogeneous media

Comparative spectroscopic studies and quantum chemical calculations involving sensitizers chlorin (C), meso-tetraphenyl chlorin (MTPC), octaethyl chlorin (OEC), pheophorbide a (PPa) and chlorin e6 (Ce6) have been performed. Upon irradiation, all except chlorin bleached detectably in a homogeneous system (DMF). The order of photobleaching efficiencies was Ce6>PPa>OEC>MTPC>C. Combining these results with data from quantum calculations suggest that the efficiency of photobleaching is determined by the substituent groups in the photosensitizer. In a heterogeneous system (DPPC liposomes), however, only Ce6 photobleached significantly. This might be caused by the change of polarity of the environment around sensitizer molecules. In addition, the effects of additives that enhance or decrease photobleaching rates have also been assessed. The results suggest that the mechanisms of sensitizer photodegradation are complex and media-dependent.

Optically Gated Capillary Electrophoresis of o-Phthalaldehyde/β-Mercaptoethanol Derivatives of Amino Acids for Chemical Monitoring

Optically gated capillary electrophoresis (CE) of amino acids derivatized with o-phthalaldehyde/β-mercaptoethanol (OPA/β-ME) was explored as a means to monitor amino acids with high temporal resolution. In agreement with a theoretical model described herein, 98% of a given concentration of OPA/β-ME derivatives can be photobleached by a few milliwatts of the 350-nm line of an argon ion laser with just 0.7-ms exposure times in 5-μm-i.d. capillaries. The low background from such high photobleaching efficiency allows detection limits in the low-nanomolar range for all amino acids tested. The short injection times possible with optical gating allow separation efficiencies of nearly 200 000 plates to be achieved in less than 1 s under ideal conditions. Under mock in vivo conditions, separations were slower and had lower efficiency due to reduced electroosmotic flow associated with the high salt content. To demonstrate chemical monitoring, the optically gated CE system was interfaced to two different sampling probes with on-line derivatization with OPA/β-ME. With microdialysis sampling, the optically gated CE system could assay the sample stream every 2 s but actual temporal resolution for monitoring was limited by band broadening in the dialysis probe to ∼12 s. Optically gated CE was also interfaced to a 10-μm-i.d. sampling capillary that continuously pulled samples into the separation capillary at 6.5 nL/min. This direct sampling probe allowed monitoring of multiple amino acids with 10-s temporal resolution with several advantages compared to microdialysis including improved detection limits and spatial resolution.

Phototransformations of sensitizers 1. Significance of the nature of the sensitizer in the photobleaching process and photoproduct formation in aqueous solution

Comparative spectroscopic studies of haematoporphyrin, haematoporphyrin derivative, dimethoxyhaematoporphyrin, Photofrin II, Photosan-3, meso-tetraphenylporphine tetrasulphonate, chlorin e 6 and aluminium phthalocyanine tetrasulphonate have been performed. The photosensitizers studied are not photostable and are bleached during illumination. The rate constants of absorption bleaching, measured in pH 7.2 phosphate buffer, indicate that, of the investigated sensitizers, chlorin e 6 is the least photostable and aluminium phthalocyanine tetrasulphonate is the most photostable. Simultaneous with photobleaching, the formation of red-absorbing photoproducts is observed for haematoporphyrin-like sensitizers. The efficiency of photobleaching and the formation of photoproducts in aqueous solution seems to be conditioned by the aggregation state and chemical structure of the photosensitizer. Spectroscopic changes induced during illumination have important consequences for the dosimetry of photosensitized tumour therapy.

Photobleaching recovery and anisotropy decay of green fluorescent protein GFP-S65T in solution and cells: cytoplasmic viscosity probed by green fluorescent protein translational and rotational diffusion

The green fluorescent protein (GFP) was used as a noninvasive probe to quantify the rheological properties of cell cytoplasm. GFP mutant S65T was purified from recombinant bacteria for solution studies, and expressed in CHO cell cytoplasm. GFP-S65T was brightly fluorescent in solution (lambda ex 492 nm, lambda em 509 nm) with a lifetime of 2.9 ns and a rotational correlation time (tc) of 20 ns. Recovery of GFP fluorescence after photobleaching was complete with a half-time (t1/2) in aqueous saline of 30 +/- 2 ms (5-micron diameter spot), giving a diffusion coefficient of 8.7 x 10(-7) cm2/s. The t1/2 was proportional to solution viscosity and was dependent on spot diameter. In contrast to fluorescein. GFP photobleaching efficiency was not affected by solution O2 content, triplet state quenchers, singlet oxygen scavengers, and general radical quenchers. In solutions of higher viscosity, an additional, rapid GFP recovery process was detected and ascribed to reversible photobleaching. The t1/2 for reversible photobleaching was 1.5-5.5 ms (relative viscosity 5-250), was independent of spot diameter, and was unaffected by O2 or quenchers. In cell cytoplasm, time-resolved microfluorimetry indicated a GFP lifetime of 2.6 ns and a tc of 36 +/- 3 ns, giving a relative viscosity (cytoplasm versus water) of 1.5. Photobleaching recovery of GFP in cytoplasm was 82 +/- 2% complete with a t1/2 of 83 +/- 6 ms, giving a relative viscosity of 3.2. GFP translational diffusion increased 4.7-fold as cells swelled from a relative volume of 0.5 to 2. Taken together with measurements of GFP translation and rotation in aqueous dextran solutions, the data in cytoplasm support the view that the primary barrier to GFP diffusion is collisional interactions between GFP and macromolecular solutes.

Characterization of Photophysics and Mobility of Single Molecules in a Fluid Lipid Membrane

Properties of single fluorescence-labeled lipids in a fluid phospholipid membrane were analyzed using sensitive fluorescence microscopy. The high signal-to-noise ratio for detection of individual fluorescence-labeled molecules of 5-70 permitted detailed study of their photophysical parameters. From single fluorophores a signal of 49 counts/ms was detected when excited above their saturation intensity of 7.6 kW/cm2. These data, obtained at the level of individual fluorophores, are found to agree quantitatively with predictions from a conventional three-level model using known ensemble-averaged rate constants. Light-induced photochemistry of single fluorophores was found to occur as a sudden disappearance of their fluorescence characterized by a photobleaching efficiency of 9 x These photophysical properties of the fluorescence label permitted analysis of the motion of individual lipid molecules. Lipid motion was tracked at a rate of up to 66 images per second. The high fluorescence image-contrast allowed for determination of lipid positions with a precision of 30 nm. For short length-scales the observed trajectories were described by a random two-dimensional motion with a lateral diffusion constant of 1.42 x cm2/s. Free diffusion was found to be restricted to length-scales of 100 nm, attributed to membrane defects.

Photochemical fabrication of nonlinear optical polymer waveguides

Waveguides based on methacrylate polymers containing active dinitrostilbene chromophores have been fabricated by photobleaching using a xenon lamp. The efficiency of photobleaching, as well as the effective refractive index changes obtainable, represent a singnificant improvement over currently used materials, single‐mode waveguides being formed with a optical loss of less than 1 dB cm−1.

Photobleaching of the F? centre in KCl

Photobleaching of F– centres in KCl has been studied between 100 and 200 K. Under conditions of constant incident light intensity the photobleaching efficiency was constant and independent of temperature, indicating that the quantum yield for photodestruction of F– is constant, and probably equal to unity at all temperatures.Previous studies of F– photolysis have shown that at low temperatures (⩽ 80 K) the process F–→ 2F occurs. The quantum yield for F centre formation falls with increasing temperature, to become virtually zero at 200 K; it has been suggested that the reformation of F–(F–→ F–) is a competing process at higher temperatures.The present results are inconsistent with the above mechanism; it is necessary to postulate a high temperature process that involves neither F– nor F centres as an end product. This high temperature process is probably formation of F2 aggregate centres, since F2 centres also result from the thermal decay of F– centres at temperatures above 240 K.

Excitation of electrons trapped in glassy ethylene glycol+water mixtures

The mechanisms of excitation of electrons trapped in glassy ethylene glycol+water (1 : 1) have been studied by thermoluminescence and E.S.R. experiments. A steep increase of the quantum efficiency of photobleaching is observed above 2·3 eV, corresponding to a strong decrease in the intensity of thermoluminescence; this is attributed to photo-induced recombination of electrons with positive ions. The fact that excitation of the electrons with an energy of 2·1 eV or less cannot transfer the electrons to new traps shows that their lowest excited states are bound ones. From the E.S.R. spectra of samples containing small amounts of an electron scavenger, it is concluded that the reaction paths of excited trapped electrons depend strongly on the excitation energy: at low excitation energies reaction with this solvent dominates; at higher excitation energies reaction with other radicals, scavenger molecules or retrapping in new traps become important. The effects of bleaching on the thermoluminescence glow curve suggest that the positive ions modify the trapping condition for electrons trapped in their close vicinity and reduce the trap depth.

Photochemical Electron Transport in Photosynthetic Reaction Centers: IV. Observations Related to the Reduced Photoproducts

The formation and dissipation of reduced photoproducts in photochemical reaction centers from Rhodopseudomonas spheroides has been studied in three independent ways: by direct chemical reduction, by photochemical reduction (illuminating reaction centers in the presence of weak reductants), and by adding electron acceptors to illuminated reaction centers to reverse the reduction. In every case the reduction is attended by the appearance of an absorption band at 450 nm and the bathochromic shift of a band centered at 305 nm. Both reduction and oxidation of reaction centers, and also photochemical oxidoreduction, cause bathochromic shifts of absorption bands identified with bacteriopheophytin (BPh), and hypsochromic shifts of bands of bacteriochlorophyll (BChl) (P-800 and, in the case of reduction, P-870). Reduction causes relatively large shifts of BPh and small shifts of BChl; the reverse is seen with oxidation and oxidoreduction. Addition of sodium dodecyl sulfate (SDS) to reaction centers suppresses the 450 nm absorption change but not the band shifts associated with BPh and BChl. Under some conditions the 450 nm change and the band shifts show different kinetics, with the kinetics of the band shifts matching those of a transient change in the yield of P-870 fluorescence. New data, on the efficiency of photo-bleaching of P-870 in reaction centers in which part of the P-870 has already been oxidized with ferricyanide, militate against the idea that part of the photochemical bleaching of P-870 is due to reduction of that pigment.