Photobleaching Process Research Articles

Rapid photo-bleaching gamma irradiated Yb-doped optical fibers by high-energy ns pulsed laser

A rapid and efficient photo-bleaching process was demonstrated with a high-energy nanosecond pulse to recover existing and/or revealed color centers on 10 kGy Gamma-irradiated Yb-doped optical fiber. Multi-mJ pulsed laser based on an optical parametric amplifier system operating at wavelengths of 532 nm, 680 nm and 793 nm was used. The photo-bleaching performance is investigated as a function of the wavelength and energy of the pulsed light source. It was observed that the photo-bleaching level of the Yb-doped optical fiber increased when the exposure time of the pulsed laser light and the photon energy was increased. The maximum PB occurred in the pulsed laser of 532 nm wavelength in the optical fiber. Also, a drastically increase in the PB was observed due to the increasing laser energy at the wavelength of 532 nm and 680 nm pulsed laser. The results show that the recovery levels of color centers in the Yb-doped optical fibers could be reached up to 96 % in a shorter time (h) by using the pulsed laser compared to that of the studies using continuous laser.

Photobleaching-induced changes in the optical and photochemical properties of algal organic matter.

Algal organic matter (AOM), a significant source of endogenous dissolved organic matter (DOM) is released in high concentrations during cyanobacterial blooms, along with cyanotoxins. Subsequent photobleaching of AOM is an important phenomenon to investigate. In this study, intracellular organic matter (IOM) and extracellular organic matter (EOM) were extracted from cultured cyanobacteria taken from Taihu Lake in China. The formation of photochemically produced reactive intermediates in different stages of IOM and EOM photobleaching was compared to Suwannee River DOM (SRDOM, reference standard DOM). Results revealed notable differences influenced by the pigment component among IOM, EOM, and SRDOM. The pigment in IOM contributed to a triplet state pool with strong energy-transfer but limited electron-transfer capabilities. Notably, IOM exhibited the highest triplets state quantum yield value in the visible region, suggesting its potential significance in pollutant degradation in deeper water layers. For EOM, one of the pools exhibits photolability and remarkable electron-transfer capability, indicating it as a high-energy triplet state component. Moreover, three cyanotoxins (MC-LR, ACA, and ATX-a) were detected in the extracted AOM, and their photodegradation was monitored during the AOM photobleaching process. This highlights the potential role of AOM as a photosensitizer in the natural self-cleaning mechanisms of water bodies, facilitating the degradation of organic pollutants through photochemical reactions. The findings of this study contribute to understanding the dynamic nature of AOM and its implications in environmental processes.

Reversible Photobleaching of Silver Clusters in Silica‐Based Glass under Ultraviolet Irradiation

AbstractInorganic glasses doped with luminescent silver clusters are promising materials for photonic applications as white light generation, optical data storage, and spectral conversion. This work reports the photostability study of luminescent silver clusters dispersed in silica‐based glass under continuous ultraviolet irradiation. The photobleaching process model is proposed and the quantum yield of photobleaching is derived from the experimental data. The proposed mechanism of photobleaching is photoionization of silver clusters. Degradation of cluster luminescence is reversible and restores after the heat treatment, indicating the possibility to release trapped electrons and return the initial charge state of clusters. The effect of heat treatment temperature on the luminescence restoration is studied, the amount of restored luminescent clusters depends linearly on the heat treatment temperature.

Structural basis of antibacterial photodynamic action of curcumin against S. aureus

Antimicrobial photodynamic therapy (aPDT) is an alternative tool to commercial antibiotics for the inactivation of pathogenic bacteria (e.g., S. aureus). However, there is still a lack of understanding of the molecular modeling of the photosensitizers and their mechanism of action through oxidative pathways. Herein, a combined experimental and computational evaluation of curcumin as a photosensitizer against S. aureus was performed. The radical forms of keto-enol tautomers and the energies of curcumin's frontier molecular orbitals were evaluated by density functional theory (DFT) to point out the photodynamic action as well as the photobleaching process. Furthermore, the electronic transitions of curcumin keto-enol tautomers were undertaken to predict the transitions as a photosensitizer during the antibacterial photodynamic process. Moreover, molecular docking was used to evaluate the binding affinity with the S. aureus tyrosyl-tRNA synthetase as the proposed a target for curcumin. In this regard, the molecular orbital energies show that the curcumin enol form has a character of 4.5% more basic than the keto form – the enol form is a more promising electron donor than its tautomer. Curcumin is a strong electrophile, with the enol form being 4.6% more electrophilic than its keto form. In addition, the regions susceptible to nucleophilic attack and photobleaching were evaluated by the Fukui function. Regarding the docking analysis, the model suggested that four hydrogen bonds contribute to the binding energy of curcumin's interaction with the ligand binding site of S. aureus tyrosyl-tRNA synthetase. Finally, residues Tyr36, Asp40, and Asp177 contact curcumin and may contribute to orienting the curcumin in the active area. Moreover, curcumin presented a photoinactivation of 4.5 log unit corroborating the necessity of the combined action of curcumin, light, and O2 to promote the photooxidation damage of S. aureus. These computational and experimental data suggest insights regarding the mechanism of action of curcumin as a photosensitizer to inactivate S. aureus bacteria.

Monolithic silica fiber laser operating at 585 nm.

We report, to the best of our knowledge, the first monolithic silica fiber laser operating in the visible. The laser cavity is based on a dysprosium-doped aluminosilicate fiber bounded by a pair of fiber Bragg gratings operating at 585 nm. The yellow laser signal reaches a record output power of 147 mW. Although the pump irradiation causes photodarkening, significant reduction of the photoinduced absorption losses is demonstrated via a photobleaching process with visible light.

Insight into the photoinduced phenomena in ternary Ge-Sb-Se sputtered thin films

The kinetics of photoinduced changes, namely, photobleaching and photodarkening in sputtered ternary Ge 29 Sb 8 Se 63 thin films, was studied. The study of time evolution of the absorption coefficient Δ α ( t ) upon room-temperature near-bandgap irradiation revealed several types of photoinduced effects. The as-deposited films exhibited a fast photodarkening followed by a dominative photobleaching process. Annealed thin films were found to undergo photodarkening only. The local structure studied by Raman scattering spectroscopy showed significant structural changes upon thermal annealing, which are presumably responsible for a transition from the photobleaching observed in as-deposited and reversible photodarkening in annealed thin films. Moreover, a transient photodarkening process was observed in both as-deposited and annealed thin films. The influence of the initial film thickness and laser optical intensity on the kinetics of photoinduced changes is discussed.

Deterioration of Bismuth-Doped fiber lasers performance induced by blue and green laser light launched into cladding

For the first time, we demonstrate the photobleaching process of bismuth-related active centers (BACs) induced by blue and green laser radiation launched into the cladding of an active fiber having the low-refractive index polymer coating. The changes in small-signal loss spectra of the exposed Bi-doped fibers are presented and analyzed. Temporal evolution of luminescence intensity of BACs is measured for different powers of bleaching light. The effect of bleaching on Bi-doped fiber laser characteristics was studied. It was found that time-to-destruction of Bi-doped fiber laser varies in dependence on the power and wavelength of the used bleaching light. In particular, the blue laser radiation launched into the active fiber cladding for a timespan of almost 10 sec can completely disable the operation of a bismuth laser at 1.71 µm. We estimated the efficiency of bleaching process in Bi-doped fiber under blue laser irradiation.

Numerical Simulation of the Photobleaching Process in Laser-Induced Fluorescence Photobleaching Anemometer

At present, a novel flow diagnostic technique for micro/nanofluidics velocity measurement—laser-induced fluorescence photobleaching anemometer (LIFPA)—has been developed and successfully applied in broad areas, e.g., electrokinetic turbulence in micromixers and AC electroosmotic flow. Nevertheless, in previous investigations, to qualitatively reveal the dynamics of the photobleaching process of LIFPA, an approximation of uniform laser distribution was applied. This is different from the actual condition where the laser power density distribution is normally Gaussian. In this investigation, we numerically studied the photobleaching process of fluorescent dye in the laser focus region, according to the convection–diffusion reaction equation. The profiles of effective dye concentration and fluorescence were elucidated. The relationship between the commonly used photobleaching time constant obtained by experiments and the photochemical reaction coefficient is revealed. With the established model, we further discuss the effective spatial resolution of LIFPA and study the influence of the detection region of fluorescence on the performance of the LIFPA system. It is found that at sufficiently high excitation laser power density, LIFPA can even achieve a super-resolution that breaks the limit of optical diffraction. We hope the current investigation can reveal the photobleaching process of fluorescent dye under high laser power density illumination, to enhance our understanding of fluorescent dynamics and photochemistry and develop more powerful photobleaching-related flow diagnostic techniques.

Role of photobleaching process of indocyanine green for killing neuroblastoma cells

Indocyanine green (ICG) is an FDA-approved near infrared (NIR) imaging agent for diagnosis and imaging guided surgery. It also exhibits phototoxicity under high-dose NIR irradiation, expanding its application as a photo-therapeutic agent. Since ICG's efficiency as a type II photosensitizer has been controversial due to its low triplet state yield, other mechanisms have been explored. While claims of toxic decomposition products, accompanied by irreversible ICG photobleaching, were proposed as the main mechanism, evidences from systemic studies are lacking. In this work, we aimed to unravel the factors affecting ICG photobleaching and the associated photo-killing effect on neuroblastoma, one of the most common pediatric tumors but often escapes therapy. Specifically, we examined how albumin-induced ICG stabilization affects the ICG photobleaching process, and the effect of photobleached ICG on cell proliferation and viability of neuroblastoma cells. It was found that ICG photobleaching was significant only under aerobic conditions and was more efficient in solutions with higher concentration ICG monomers, which were stabilized from aggregates by the presence of BSA while increasing photobleaching and associated oxygen consumption. Photobleached ICG inhibited cell proliferation, indicating another effect of tumor treatment by ICG. Taken together, while enhanced photobleaching by BSA-bound ICG monomers may reduce the photodynamic effect targeting cellular components, the photoproducts directly contribute to tumor growth inhibition and assist in a secondary mechanism to stop tumor growth.

Photodynamic antimicrobial activity of magnesium(II) porphyrazine with bulky peripheral sulfanyl substituents

Magnesium(II) porphyrazine bearing bulky sulfanyl substituents was evaluated as a photosensitizer (PS) for photodynamic antimicrobial chemotherapy (PACT). In the photostability study, the studied porphyrazine under light irradiation decomposed via photobleaching process with quantum yields up to 1.05 ⋅ 10−5. Singlet oxygen quantum yields for the PS were determined by indirect method with chemical singlet oxygen trap (1,3-diphenylisobenzofuran, DPBF) and reference (unsubstituted zinc(II) phthalocyanine). Liposomes containing porphyrazine derivative were obtained with thin-film hydration method and their size was measured with NanoSight LM10 (Malvern). Biological activity evaluation was performed with the agar plate method. The photocytotoxicity of sulfanyl porphyrazine against various wound bacteria (Staphylococcus aureus, methicillin-resistant Staphylococcus aureus (MRSA), Staphylococcus epidermidis, and Streptococcus pyogenes) was studied. The highest reduction value in bacterial growth exceeding 4 log was observed for S. epidermidis. Equally high reduction values of 3.4 log and 4.2 log at 10 and 100 µM, respectively, were observed against S. pyogenes. The novel sulfanyl porphyrazine can be considered as a potential PS in further antimicrobial photodynamic therapy related studies.

Photobleaching and Recovery of Symbiodiniaceae Effrenium voratum SCS01 Reveals Life Form Transformation Under Thermal Stress

Dinoflagellates in the family Symbiodiniaceae contain a number of species and play an important role in the establishment of coral reef ecosystems in oligotrophic marine waters. Effrenium voratum is likely an exclusively free-living and heterotrophic species of Symbiodiniaceae. How this species responds and acclimates to warming is largely unknown. The present study experimentally established the phenotypic landscapes related to the photobleaching and recovery processes of Effrenium voratum SCS01 following thermal stress. We found that thermal stress bleached the plastids of E. voratum SCS01 and caused the cells to become lighter in color. Thereafter, the bleached cells recovered rapidly when they returned to the optimal temperature. The dominant life form of E. voratum SCS01 shifted from mastigote cells to coccoid cells then returned to mastigote cells. Transcriptome analysis revealed that the photobleaching of E. voratum SCS01 was due to increased degradation and decreased biosynthesis of photosynthetic pigments. The thermally induced life form changes were related to the downregulation of genes for cell motility. Our results revealed the mechanism of photobleaching in E. voratum SCS01 and indicated life form transformation as a newly identified survival strategy of Effrenium voratum SCS01 under thermal stress.

Non-symmetric porphyrins encapsulated in liposomes: Tumor cell destruction via non-photodynamic activity

Two non-symmetric free-base porphyrins, one with an electron density withdrawing group (–NO2), H2(NPTPP), and the other with an electron density donor group (–NH2), H2(APTPP), were synthesized, characterized and the photophysical properties reported. The compound H2(APTPP) showed a fluorescence quantum yield (ΦFl = 0.12) similar to that of H2(TPP), and this derivative showed the longer lifetime in the singlet state (τ1 = 1.51 ns and τ2 = 7.74 ns; bi-exponential process) and the ability to generate singlet oxygen. It also showed relative resistance to the photobleaching process. However, it presented a high degree of aggregation in a medium that mimicked the biological one. In cell viability tests against B16–F10 cells, H2(APTPP) did not show cytotoxic activity either in absence or presence of a light stimulus. H2(NPTPP) at 50 μM showed a reduction in cell viability (of up to 50%) under dark or light conditions. The liposomal formulation containing H2(APTPP) was stable for 2 h and caused the death of tumor cells (up to 95%) even in absence of light stimulus, showing that cell death is associated with non-photodynamic processes.

Structural aspects of rod opsin and their implication in genetic diseases.

Vision in dim-light conditions is triggered by photoactivation of rhodopsin, the visual pigment of rod photoreceptor cells. Rhodopsin is made of a protein, the G protein coupled receptor (GPCR) opsin, and the chromophore 11-cis-retinal. Vertebrate rod opsin is the GPCR best characterized at the atomic level of detail. Since the release of the first crystal structure 20 years ago, a huge number of structures have been released that, in combination with valuable spectroscopic determinations, unveiled most aspects of the photobleaching process. A number of spontaneous mutations of rod opsin have been found linked to vision-impairing diseases like autosomal dominant or autosomal recessive retinitis pigmentosa (adRP or arRP, respectively) and autosomal congenital stationary night blindness (adCSNB). While adCSNB is mainly caused by constitutive activation of rod opsin, RP shows more variegate determinants affecting different aspects of rod opsin function. The vast majority of missense rod opsin mutations affects folding and trafficking and is linked to adRP, an incurable disease that awaits light on its molecular structure determinants. This review article summarizes all major structural information available on vertebrate rod opsin conformational states and the insights gained so far into the structural determinants of adCSNB and adRP linked to rod opsin mutations. Strategies to design small chaperones with therapeutic potential for selected adRP rod opsin mutants will be discussed as well.

Electrochemiluminescence Loss in Photobleaching.

The effects of photobleaching on electrochemiluminescence (ECL) was investigated for the first time. The plasma membrane of Chinese Hamster Ovary (CHO) cells was labeled with a [Ru(bpy)3 ]2+ derivative. Selected regions of the fixed cells were photobleached using the confocal mode with sequential stepwise illumination or cumulatively and they were imaged by both ECL and photoluminescence (PL). ECL was generated with a model sacrificial coreactant, tri-n-propylamine. ECL microscopy of the photobleached regions shows lower ECL emission. We demonstrate a linear correlation between the ECL decrease and the PL loss due to the photobleaching of the labels immobilized on the CHO membranes. The presented strategy provides valuable information on the fundamentals of the ECL excited state and opens new opportunities for exploring cellular membranes by combining ECL microscopy with photobleaching techniques such as fluorescence recovery after photobleaching (FRAP) or fluorescence loss in photobleaching (FLIP) methods.

Impact of Thermal Quenching on Bi Active Center Photostability in Bi/Er Co-Doped Fiber

The impact of thermal quenching on the photostability of bismuth active center (BAC) is investigated through measuring the photo-bleaching process under 830 nm irradiation in quenched Bi/Er co-doped fiber (BEDF). By fitting with the stretched-exponential model, the emission intensity ascribed to the photostable BAC associated with silica (BAC-Si) at 1400 nm (I(∞)), unbleachable ratio (γUB) and bleaching time (τB) are obtained. Compared to the untreated sample, the I(∞) increases with higher temperature or a longer dwell time, while both the γUB and τB decrease. The results show that BAC-Si could be bleached faster, while additional amount of BAC-Si could be retained in thermally quenched samples. Besides, the lower photostability of the newly quenching activated BAC, impacted by different quenching conditions, is estimated.

Photochemical properties and photocytotoxicities against wound bacteria of sulfanyl porphyrazines with bulky peripheral substituents

Porphyrazine macrocycles with bulky peripheral phenylalkylsulfanyl substituents were subjected to photochemical studies. The singlet oxygen generation potential of these macrocycles was assessed using an indirect method with DPBF and all molecules revealed low singlet oxygen generation with quantum yields up to 0.03. In the photostability study, porphyrazine derivatives underwent photobleaching processes under light irradiation with quantum yields up to 2.45 ∙ 10−5. The photocytotoxicities of sulfanyl porphyrazine derivatives were researched in liposomal nanoparticles against wound bacteria, such as Staphylococcus aureus, methicillin-resistant Staphylococcus aureus (MRSA), Staphylococcus epidermidis, and Streptococcus pyogenes. The most active macrocycles appeared magnesium(II) porphyrazines with 5-(3,5-dibutoxycarbonylphenoxy)pentylthio- and 2-[2-(3,5-dibutoxycarbonylphenoxy)ethoxy]ethylthio-substitents. According to calculated photokilling rates obtained in the photoinactivation study, the greatest reduction of bacterial growth up to 4.7 log was noted for S. pyogenes, whereas moderate activity 2.5–2.6 log was observed against S. aureus. Low or no photocytotoxicity of studied macrocycles was noted against MRSA and S. epidermidis.

Visible Light–Induced Degradation of Inverted Polymer:Nonfullerene Acceptor Solar Cells: Initiated by the Light Absorption of ZnO Layer

Power conversion efficiencies (PCEs) of polymer solar cells (PSCs) have exceeded 18% in the last few years. Stability has therefore become the next most important issue before commercialization. Herein, the degradation behaviors of the inverted PM6:IT‐4F (PBDB‐T‐2F:3,9‐bis(2‐methylene‐((3‐(1,1‐dicyanomethylene)‐6,7‐difluoro)‐indanone))‐5,5,11,11‐tetrakis(4‐hexylphenyl)‐dithieno[2,3‐d:2′,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene) solar cells with different ZnO layers are systematically investigated. The PCE decay rates of the cells and the photobleaching process of the IT‐4F containing organic films on ZnO surface are directly correlated with the light‐absorption ability of the ZnO layer in the visible light range, indicating that photochemical decomposition of IT‐4F is initiated by the light absorption of ZnO layer. By analyzing the products of the aged ZnO/IT‐4F films with matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry (MALDI‐TOF‐MS), it is confirmed that photochemical reactions at the IT‐4F/ZnO interface include de‐electron‐withdrawing units and dealkylation on the side‐phenyl ring. Hydroxyl radicals generated by the photo‐oxidation of dangling hydroxide by ZnO are confirmed by electron spin resonance (ESR) spectroscopy measurements, which is attributed as the main reason causing the decomposition of IT‐4F. Surface treatment of ZnO with hydroxide and/or hydroxyl radical scavenger is found to be able to improve the stability of the PSCs, which further supports the proposed degradation mechanism.

Photo-induced bleaching and thermally stimulated recovery of BAC-P in Bi-doped phosphosilicate fibers.

The first results of the study on photobleaching and thermally induced recovery in Bi-doped phosphosilicate fiber have been presented. It was revealed that the rate of bleaching of phosphor-related Bi active center (BAC-P) becomes slower with the decrease of photon energy. The quadratic dependence of the bleaching rate of BAC-P on laser power is obtained under 532 nm laser irradiation. The effect of temperature on the bleaching dynamics of BAC-P is also investigated under 532 nm radiation, suggesting a thermally aggravated bleaching process upon heating at certain temperatures (≥300∘C). Furthermore, the thermal recovery of bleached Bi-doped silica-based fiber (BDF) is investigated and a 13% increase of luminescence is achieved upon thermal quenching for 5 min at 400ºC. The underlying mechanism of photobleaching and thermo-stimulated recovery process of BAC-P is also discussed.

Photoswitchable Photon Upconversion from Turn-on Mode Fluorescent Diarylethenes

Photon upconversion (UC) is one kind of anti-Stokes shift process, which generally requires a combination of two or more low-energy photons to produce one high-energy photon. However, another inter...

Online fluorescence imaging method by reducing the inequivalent photobleaching for quantitative capillary electrophoresis

In traditional capillary electrophoresis (CE) with fluorescence detection, the difference of the migration time of analytes leads to the inequivalent photobleaching, therefore the quantitative determination of the analytes is usually difficult. Especially, when an internal standard (IS) is used, the fluorescent intensities of analytes are hardly comparable to that of the IS if the inequivalent photobleaching is not restricted. We propose a practical approach to reduce the effect of inequivalent photobleaching via an online fluorescence imaging system coupled with the IS method. The detection was operated by the acquisitions of the fluorescent intensities from the divided small section array in the detection window and the electropherograms were obtained from the integrated each acquisition. Compared with the traditional CE detection method, the proposed method demonstrates a real-time detection to collect the fluorescence signals of different analytes under the definite exposure time, rather than the same traversing length. Experimental demonstration for the proposed method was carried out by using DNA-dye conjugations. As a result, our method provided a lower relative error of the peak area ratio of 0.3–3.2 % and a more practical operation because the efforts to restrict the photobleaching are exempted. Revealed in this paper also includes the fact that the photobleaching process manipulated the determination of the peak width and separation resolution.