Carbon nanodots with a controlled N structure by a solvothermal method for generation of reactive oxygen species under visible light

Carbon nanodots can function as photosensitizers that have the ability to generate reactive oxygen species such as singlet oxygen, hydroxy (OH) radicals, and superoxide ions. However, most of these can only be generated upon ultraviolet light excitation. Additionally, the mechanism of reactive oxygen species generation by carbon nanodots remains unclear. The development of carbon nanodots that can photosensitize under visible light irradiation is desirable for applications such as photodynamic therapy and pollutant decomposition under visible light. Here, we report novel carbon nanodot-based photosensitizers that generate reactive oxygen species under visible light; they were synthesized using a solvothermal method with two solvents (formamide and water) and amidol as the carbon source. Carbon nanodots from the solvothermal synthesis in formamide showed blue fluorescence, while those obtained in water showed green fluorescence. The photo-excited blue-fluorescent carbon nanodots produced OH radicals, superoxide ions, and singlet oxygen, and therefore could function as both type I and type II photosensitizers. In addition, photo-excited green-fluorescent carbon nanodots generated only singlet oxygen, therefore functioning as type II photosensitizers. It is proposed that the two photosensitizers have different origins of reactive oxygen species generation: the enrichment of graphitic N for blue-fluorescent carbon nanodots and molecular fluorophores for green-fluorescent carbon nanodots.     

Effect of 2,3-butanedione on human myeloperoxidase

1. Myeloperoxidase is inhibited by various diketones that are recognized arginine reagents. 2. Although arginine residues in the enzyme were modified in both the light and the dark, enzyme inactivation occurred only in the presence of light. 3. Under conditions where diketones caused inactivation of myeloperoxidase, spectral studies indicated marked damage to the haem residues of the enzyme. 4. It was concluded that diketones serve simply as photosensitizers of visible light-induced inactivation of myeloperoxidase. 5. Studies on other haemoproteins indicated the great ease with which the presence of diketones sensitized haem residues for photodestruction.     

聚合物纳米粒在肿瘤光动力治疗中的研究进展

光动力治疗创伤小,在恶性肿瘤治疗方面的应用已经得到了临床认可。治疗过程中需要给予光敏剂,在光照下产生分子氧对肿瘤细胞产生杀伤作用。但是,大多数光敏剂缺乏对肿瘤细胞的特异性,其在肿瘤中的富集主要与细胞高代谢有关,并且在水相媒介中溶解度比较差。纳米技术应用于光动力治疗提供了一种有效地体内运输光敏剂的方式。目前,聚合物纳米粒与光动力药物传递的研究越来越多,光敏剂通过纳米粒的运输为弥补光动力治疗的不足提供了可能,这是因为纳米载体可以将治疗浓度的光敏剂运送到肿瘤细胞而不造成非靶向组织的副损伤。本文将介绍对肿瘤光动力治疗中具有特异性的聚合物纳米粒的种类及在临床中的应用情况,为肿瘤靶向治疗提供新思路。     

Triazinyl porphyrin-based photoactive cotton fabrics: preparation, characterization, and antibacterial activity

In the present work, we report on the synthesis of cellulose cotton fibers bearing different types of photosensitizers with the aim to prepare new efficient polymeric materials for antimicrobial applications. Anionic, neutral, and cationic amino porphyrins have been covalently grafted on cotton fabric, without previous chemical modification of the cellulosic support, using a 1,3,5-triazine derivative as the linker. The obtained porphyrin-grafted cotton fabrics were characterized by infrared (ATR-FTIR), diffuse reflectance UV-vis (DRUV) spectroscopies, and thermogravimetric analysis (TGA) to confirm the triazine linkage. Antimicrobial activity of porphyrin-cellulose materials was tested under visible light irradiation against Staphylococcus aureus and Escherichia coli . The results showed excellent activity on the Gram-positive bacterium, showing structure-activity relationship, although no photodamage of the Gram-negative microorganism was recorded. A mechanism of bacterial inactivation by photosensitive surfaces is proposed.     

Novel water-soluble photosensitizers from dextrans

Novel water-soluble polymeric photosensitizers based on the natural polymer dextran were synthesized and studied. The modified dextran contained photoactive anthracene (An) chromophores. They were soluble in water with the solubility decreasing with an increase in the number of An moieties bound to the polymeric chain. In aqueous solutions, the macromolecules adopted a compact conformation which resulted in the formation of hydrophobic microdomains. The properties of these domains were characterized with molecular probes such as perylene and pyrazolo-quinoline derivative. The polymer absorbed in the UV/vis region and photosensitized reactions mediated by energy and/or electron transfer from electronically excited An to the molecules of organic compounds solubilized in polymeric microdomains or resided in water.     

Immediate pigment darkening: its evolutionary roles may include protection against folate photosensitization

The evolution of dark human skin colors in tropical areas is possibly related to photoprotection of folates. However, natural folates absorb mainly UVB radiation, and too little UVB can penetrate down to folates in dermal vessels to cause serious damage. However, endogenous photosensitizers, like riboflavin and uroporphyrin, absorbing UVA and visible light, can cause photosensitization of folates. Immediate pigment darkening (IPD), generated by UVA, has an absorption spectrum covering those of the endogenous photosensitizers. IPD is most prominent for darker skin types, which were typical for populations living under tropical solar fluences. We here propose that the biological role of IPD is protection of folates against photodegradation, which would be of large evolutionary importance for early hominids.     

Oxidative damage to E. coli membranes caused by superoxide radicals]

The effects of bacterial membranes of active oxygen species photochemically generated by riboflavin-histidine systems were studied. According to SDS-PAAG data, the formation of high molecular weight protein aggregates and the appearance of fluorochromes whose fluorescence is seen in the longwave length region of the spectrum (lambda excit = 350 nm, lambda emis = 400-500 nm) and which are bound to the proteins, are suggestive of membrane oxidation consisting in the chemical modification of protein components. The presence in E. coli membranes of endogenous photosensitizers which upon illumination with visible light induce the oxidation of membrane proteins, was established.     

KillerOrange,a Genetically Encoded Photosensitizer Activated by Blue and Green Light

Genetically encoded photosensitizers, proteins that produce reactive oxygen species when illuminated with visible light, are increasingly used as optogenetic tools. Their applications range from ablation of specific cell populations to precise optical inactivation of cellular proteins. Here, we report an orange mutant of red fluorescent protein KillerRed that becomes toxic when illuminated with blue or green light. This new protein, KillerOrange, carries a tryptophan-based chromophore that is novel for photosensitizers. We show that KillerOrange can be used simultaneously and independently from KillerRed in both bacterial and mammalian cells offering chromatic orthogonality for light-activated toxicity.     

Inducing local DNA damage by visible light to study chromatin repair

Dynamics of DNA repair and recruitment of repair factors to damaged DNA can be studied by live cell microscopy. DNA damage is usually inflicted by a laser beam illuminating a DNA-interacting photosensitizer in a small area of the nucleus. We demonstrate that a focused beam of visible low intensity light alone can inflict local DNA damage and permit studies of DNA repair, thus avoiding potential artifacts caused by exogenous photosensitizers.     

Soybean oil as a possible solubilizing and vehicular medium for zinc phthalocyanine in photodynamic therapy.

Soybean oil (SBO) is used as a medium to solubilize zinc phthalocyanine (ZnPc), a known photosensitizer, which has been found to be of potential use in photodynamic therapy. It absorbs red light in this medium at 670 nm with good molar absorptivity comparable to its value in most organic solvents (2.45 x 10(5) M(-1) cm(-1)). The wavelength of the fluorescence emission band peaked at 700 nm when excited at 591 nm, and when excited at 560 nm, the emission band was observed at 680 nm. The characteristic emission band of ZnPc at the near end of the visible spectral region suggests that this compound exists in this medium in a monomeric form, a form most useful in photo therapeutic applications. Moreover, the excitation wavelength, observed in the far-red region, precludes minimal effect, if any, of skin photonecrosis if this medium is used in PDT. A fluorescence spectral analysis of the ZnPc-SBO solution carried out for thirty-eight days indicates that this solution is stable within this time frame. No toxicity was detected when this solution was seeded in human endothelial cells in a culture well for 36 hr and also when injected subcutaneously into the nude and Balb C mice. In both cases the ZnPc was observed to clear from the injected area in a reasonable time. This fact coupled with its good solubilizing property for ZnPc and its virtual nontoxicity may make soybean oil a possible vehicular medium for transporting useful photosensitizers to target cells in photodynamic therapy and related applications.     

Inhibition of DNA dependent RNA synthesis by porphyrin photosensitizers

Select porphyrin photosensitizers were studied to determine their effects on DNA-dependent RNA synthesis in the presence and absence of visible light. All of the porphyrins were found to inhibit wheat germ polymerase II to some degree in the dark. In the presence of light, the inhibitory effects of the porphyrins was found to result from both inactivation of the enzyme and impairment of the ability of DNA to serve as a template.     

Sunlight-activated insecticides: historical background and mechanisms of phototoxic activity

Several photosensitizing agents, which are activated by illumination with sunlight or artificial light sources, have been shown to be accumulated in significant amounts by a variety of insects when they are administered in association with suitable baits. The subsequent exposure of such insects to UV/visible light leads to a significant drop in survival. Of the photosensitizers tested so far, xanthenes (e.g. phloxin B) and porphyrins (e.g. haematoporphyrin) appear to be endowed with the highest photoinsecticidal activity. In particular, porphyrins absorb essentially all the UV/visible light wavelengths in the emission spectrum of the sun; hence they are active at very low doses. Thus, 1 h irradiation of Ceratitis capitata, Bactrocera oleae (also known as Dacus oleae) or Stomoxys calcitrans which ingested a few nanomoles of porphyrin per fly with light intensities of the order of 1000 microE s(-1) m(-2) causes about 100% death in laboratory tests. Present evidence suggests that such photosensitizers act on the membranes of the midgut with consequent feeding inhibition, as well as on the neuromuscular sheath. No apparent onset of photoresistance has been observed. The rapid photobleaching of xanthenes and porphyrins when illuminated by visible light, as well as the lack of significant toxicity of such compounds in the dark, minimizes the risk of an important environmental impact of such photoinsecticidal agents.     

Fast and Effective Photodynamic Inactivation of Multiresistant Bacteria by Cationic Riboflavin Derivatives

Photodynamic inactivation of bacteria (PIB) proves to be an additional method to kill pathogenic bacteria. PIB requires photosensitizer molecules that effectively generate reactive oxygen species like singlet oxygen when exposed to visible light. To allow a broad application in medicine, photosensitizers should be safe when applied in humans. Substances like vitamin B2, which are most likely safe, are known to produce singlet oxygen upon irradiation. In the present study, we added positive charges to flavin derivatives to enable attachment of these molecules to the negatively charged surface of bacteria. Two of the synthesized flavin derivatives showed a high quantum yield of singlet oxygen of approximately 75%. Multidrug resistant bacteria like MRSA (Methicillin resistant Staphylococcus aureus), EHEC (enterohemorrhagic Escherichia coli), Pseudomonas aeruginosa, and Acinetobacter baumannii were incubated with these flavin derivatives in vitro and were subsequently irradiated with visible light for seconds only. Singlet oxygen production in bacteria was proved by detecting its luminescence at 1270 nm. After irradiation, the number of viable bacteria decreased up to 6 log₁₀ steps depending on the concentration of the flavin derivatives and the light dosimetry. The bactericidal effect of PIB was independent of the bacterial type and the corresponding antibiotic resistance pattern. In contrast, the photosensitizer concentration and light parameters used for bacteria killing did not affect cell viability of human keratinocytes (therapeutic window). Multiresistant bacteria can be safely and effectively killed by a combination of modified vitamin B2 molecules, oxygen and visible light, whereas normal skin cells survive. Further work will include these new photosensitizers for topical application to decolonize bacteria from skin and mucosa.     

Plasmonic Broadband Perfect Absorber for Visible Light Solar Cells Application

Plasmonics - Solar radiation is mainly concentrated in visible light region (50%), to achieve the perfect absorption of this spectral band is significant for many energy-related fields include...     

Keeping the spotlight on cytochrome P450

This review describes the recent advances utilizing photosensitizers and visible light to harness the synthetic potential of P450 enzymes. The structures of the photosensitizers investigated to date are first presented along with their photophysical and redox properties. Functional photosensitizers range from organic and inorganic complexes to nanomaterials as well as the biological photosystem I complex. The focus is then on the three distinct approaches that have emerged for the activation of P450 enzymes. The first approach utilizes the in situ generation of reactive oxygen species entering the P450 mechanism via the peroxide shunt pathway. The other two approaches are sustained by electron injections into catalytically competent heme domains either facilitated by redox partners or through direct heme domain reduction. Achievements as well as pitfalls of each approach are briefly summarized. This article is part of a Special Issue entitled: Cytochrome P450 biodiversity and biotechnology, edited by Erika Plettner, Gianfranco Gilardi, Luet Wong, Vlada Urlacher, Jared Goldstone.     

Analysis of beta-carotene absorbance for studying structural properties of human plasma low-density lipoproteins

A novel spectrophotometric assay for monitoring structural rearrangements of native low-density lipoproteins (LDL) is proposed. The approach is based on the analysis of the visible light absorbance maximum of lipoproteins at approximately 461 nm assigned to beta-carotene situated in the hydrophobic parts of LDL. It offers a direct method to study the surface-interior coupling of the lipoprotein particle under physiological conditions. The detected signal is intrinsic to LDL and responsible for the most of the beta-carotene signal from the whole plasma. The negligible interference of beta-carotene absorbance due to the high-density lipoproteins is experimentally verified. Since beta-carotene absorbance belongs to the visible spectral region, no spectral overlapping/artifacts in plasma are expected. The signal sensitivity has been studied through conformational changes of LDL induced by ionic strength, by temperature, and by ligand binding. The results of caffeine binding to LDL indicate that there could be only one dominant type of binding site for caffeine on LDL particles. It can be concluded that visible spectrum characteristics of beta-carotene molecules offer advantages in LDL ligand binding studies which can possibly be extended to monitor the interactions of LDL directly in plasma.     

The photodynamic effect: the comparison of chemiexcitation by luminol and phthalhydrazide

The presence of light, oxygen and photosensitizer (organic dye) is required for the photodynamic effect. Light and photosensitizer are harmless by themselves, but when combined with oxygen, reactive oxygen species (ROS) can be produced. This photodynamic effect is used in photodynamic therapy (PDT); the production of ROS as lethal cytotoxic agents can inactivate tumor cells. However, during PDT, there are many difficulties, so it is not possible to excite the photosensitizer using a laser, a source of light at the wavelengths specific to the photosensitizer (in visible region of the spectrum). Chemiluminescence is the light emission as a result of a chemical reaction. It is possible to use a chemiluminescent mixture to excite the photosensitizer even if the light emission does not conform to the absorption maximum of the photosensitizer. Luciferin and luminol have been used as chemiluminescent compounds (energizers) for the excitation of the photosensitizers. The aim of this work was to compare the chemiexcitation of some selected photosensitizers (e.g. fluorescein, eosin, methylene blue, hypericin and phthalocyanines) by chemiluminescent mixtures containing luminol (high chemiluminescent quantum yield) or phthalhydrazide (low chemiluminescent quantum yield) on some Gram‐positive (Enterococcus faecalis, Staphylococcus aureus) and Gram‐negative (Pseudomonas aeruginosa, E. coli) bacteria and some cell lines (NIH3T3 and MCF7). The efficiency of the chemiexcitation was dependent on the kind of the photosensitizer and on the type of the bacterial strain or cell line and was independent of the energizers. Copyright © 2010 John Wiley & Sons, Ltd.     

The effect of visible radiations on the germination and outgrowth of Bacillus spores

The effect of visible radiations on the germination and outgrowth of spores of Bacillus subtilis MD2 and Bacillus subtilis var. niger was determined by direct observation of populations irradiated on the surface of nutrient agar. Little effect on germination (phase darkening) was found but white light prevented outgrowth of some and retarded it for all spores. Different wavebands in the visible spectrum differed in their effect on outgrowth, the greatest retardation being found for the shorter wavelengths, 410–570 nm. Outgrowth in dark controls was always greater both in number of spores outgrown and rate of outgrowth. The results are consistent with others, suggesting an effect of singlet oxygen generated from endogenous photosensitizers by visible radiation.     

Design,synthesis and photocytotoxicity of upconversion nanoparticles: Potential applications for near‐infrared photodynamic and photothermal therapy

Photodynamic therapy (PDT) and photothermal therapy (PTT) are emerging modalities for the treatment of tumors and nonmalignant conditions, based on the use of photosensitizers to generate singlet oxygen or heat, respectively, upon light (laser) irradiation. They have potential advantages over conventional treatments, being minimally invasive with precise spatial‐temporal selectivity and reduced side effects. However, most clinically employed PDT agents are activated at visible (vis) wavelengths for which the tissue penetration and, hence, effective treatment depth are compromised. In addition, the lipophilicity of near‐infrared (NIR) photothermal agents limits their use and efficiency. To achieve combined PDT/PTT effects, both excitation wavelengths need to be tuned into the NIR spectral window of biological tissues. This paper reports the synthesis of neodymium‐doped upconversion nanoparticles (NaYF₄:Yb,Er,Nd@NaYF₄:Nd) that convert 800 nm light into vis wavelengths, which can then activate conventional photosensitizers on the nanoparticle surface for PDT. Covalently bonded IR‐780 dyes can readily be activated by 800 nm laser irradiation. The PEGylated nanoplatform exhibited a narrow size distribution, good stability and efficient generation of singlet oxygen under laser irradiation. The in vitro photocytotoxicity of this engineered nanoplatform as either a PDT or PTT agent in HeLa cells is demonstrated, while fluorescence microscopy in nanoplatform‐incubated cells highlights its potential for bioimaging.     

Discovery of signaling effect of UV-B/C light in the extended UV-A/blue-type action spectra for step-down and step-up photophobic responses in the unicellular flagellate algaEuglena gracilis

Summary Cultures of unicellular algal flagellateEuglena gracilis grown in different conditions were subjected to action spectroscopy for step-down and step-up photophobic responses, respectively. The spectral region was extended into the UV-B/C as well as in the UV-A and visible regions with the Okazaki Large Spectrograph as the monochromatic light source. The photophobic responses of the cells were measured with an individual-cell assay method with the aid of a computerized video motion analyzer. In the UV-A and visible regions, the shapes of the action spectra were the so-called UV-A/blue type. In the newly studied UV-B/C region, new action peaks were found at 270 nm for the step-down response and at 280 nm for the step-up one. The absorption spectrum of flavin adenine dinucleotide (FAD) appeared to fit the action spectrum for the step-up response, whereas the shape of the step-down action spectrum, which has a UV-A peak (at 370 nm) higher than the blue peak (at 450 nm), appeared to be mimicked by the absorption spectrum of a mixed solution of 6-biopterin and FAD. These observations might also account for the fact that the UV-B/C peak wavelength at 270 nm of the action spectrum for the step-down response is shorter by 10 nm than the action spectrum for the step-up response at 280 nm.Abbreviations FAD flavin adenine dinucleotide - FWHM spectral full width at half maximum - NIBB National Institute for Basic Biology - OLS Okazaki Large Spectrograph - PFB paraflagellar body - UV-A ultraviolet light of spectral region between 320 and 400 nm - UV-B/C ultraviolet light of spectral region between 190 and 320 nm