Full Spectrum Of Visible Light Research Articles

Synthesis of Fe2O3–NiO–Cr2O3 composites from NiFe-layered double hydroxide for degrading methylene blue under visible light

To develop a low-cost and highly efficient photocatalyst under the visible illumination, Ni3Fe–CO3–LDH (referred to hereafter as NiFe-layered double hydroxide or NiFe–LDH) was used as a precursor to synthesize Fe2O3–NiO–Cr2O3 composite. The NiFe–LDH was prepared by co-precipitation and then it was exchanged with dichromate. After calcining at 600°C, the Fe2O3–NiO–Cr2O3 composite was obtained. The composites' absorption edge intensely extended up to ca. 700nm covering the full visible light spectrum and showed high catalytic activity at natural pH under the visible light illumination. A very high methylene blue degradation of 91.2% was achieved with the aid of H2O2 in 120min with no detectable Cr in solution.

Triphenylphosphine modified graphene quantum dots: spectral modulation for full spectrum of visible light with high quantum yield

The spectral modulation for visible light with high quantum yield is developed based on triphenylphosphine modified graphene quantum dots.

Growth of bell pepper plants (Capsicum annuum) affected by coloured covers

While a plant utilizes the full spectrum of visible light, some colours of light have more important applications than others. The aim of this study was to evaluate the responses of bell pepper plants grown under coloured covers. Bell pepper plants (Capsicum annuum) were grown hydroponically in a greenhouse in Tunja, Colombia, under different light quality regimes that were obtained with polypropylene films (yellow, green, blue, transparent, red, and a control without a plastic film cover). Conventional growth indices were calculated or measured as response variables. All of the evaluated parameters were influenced in a different ways by the colour of the covers, e.g. the leaf area was higher under the green and blue covers. The highest water uptake was found in the plants grown under the blue film. Plants under the yellow cover presented higher water use efficiency than the other treatments. The chlorophyll content index was higher under the blue, green and transparent covers. Based on these results, a coloured cover that favors most of the growth indices of plants cannot be selected; however, according to the needs of growers, the supplemental light quality can be used to achieve a specific effect.

Stress induced acquisition of somatic embryogenesis in common bean Phaseolus vulgaris L.

Common bean Phaseolus vulgaris L. has been shown to be a recalcitrant plant to induce somatic embryogenesis (SE) under in vitro conditions. We used an alternative strategy to induce SE in common bean based upon the use of a cytokinin (BAP) coupled with osmotic stress adaptation instead of SE response that is induced by auxins. Explants derived from zygotic embryos of common bean were subjected to osmotic stress (sucrose 12 % w/v, 0.5 M) in the presence of BAP 10 mg/L and adenine free base 40 mg/L to induce somatic embryos from specific competent cells of the apical meristem and cotyledonary node. Somatic embryos were obtained from the competent cells in a direct response (direct SE). In a secondary response (secondary SE), those somatic embryos formed proembryogenic masses (PEM) that originated/developed into secondary somatic embryos and showed the SE ontogeny. Maturation of somatic embryos was achieved by using different osmolality media and converted to plants. Full-visible light spectrum was necessary to achieve efficient plant regeneration. Long-term recurrent SE was demonstrated by propagation of PEM at early stages of SE. This protocol is currently being applied for stable genetic transformation by means of Agrobacterium tumefaciens and bioballistics as well as for basic biochemical and molecular biology experiments.

Facile preparation of black Nb4+ self-doped K4Nb6O17 microspheres with high solar absorption and enhanced photocatalytic activity.

Black Nb(4+) self-doped K4Nb6O17 microspheres were prepared for the first time through a facile UV light photoreduction method. By the introduction of Nb(4+), the defective K4Nb6O17 can harvest the full spectrum of visible light as well as near-infrared light. The black K4Nb6O17 microspheres showed improved visible-light-driven photocatalytic H2 production activity. Importantly, the present synthetic approach is also applicable to the preparation of other Nb(4+) self-doped niobates.

Electrochromic titania nanotube arrays for the enhanced photocatalytic degradation of phenol and pharmaceutical compounds

Vertically aligned, electrochromic-coloured, amorphous titania nanotube arrays (TNAs) were fabricated using a facile room-temperature, solution-based electrochemical cathodisation method. Rapid cathodisation within 30 s converted pristine TNAs into their dark analogues. Compared to their untreated counterparts, the cathodised dark TNAs exhibited significantly enhanced optical absorbance, covering the full spectrum of visible light. Further annealing of the electrochromic coloured amorphous TNAs in a N2 atmosphere induced their transformation into dark crystalline TNAs, which directly harnessed simulated sunlight for the photocatalytic degradation of organic contaminants, including phenol, ibuprofen, carbamazepine and caffeine. Compared to the pristine crystalline TNAs (annealed in air), the dark crystalline TNAs showed higher optical absorbance, larger charge carrier density, lower electron transport resistance, and an enhancement of 107−131% in degradation kinetics for the target organic contaminants.

Porphyrin-silica microparticle conjugates as an efficient tool for the photosensitised disinfection of water contaminated by bacterial pathogens

A tetracationic meso-substituted amphiphilic porphyrin (abbreviated as C14) was encapsulated within silica microparticles to yield a conjugate with a mean particle diameter of ca. 0.9 μm. The conjugate displayed a complete stability for at least 3 months when suspended in a neutral aqueous medium. The encapsulated C14 underwent a limited photobleaching when the conjugate was exposed to full spectrum visible light. Illumination of the silica microparticle-bound C14 by visible light resulted in the generation of singlet oxygen and induced a decrease in the survival of 4 log for a 20 min irradiation of the Gram-positive bacterium meticillin-resistant Staphylococcus aureus (MRSA) and a 30 min irradiation of the Gram-negative bacterium Escherichia coli (E. coli). Under identical experimental conditions photoexcited free C14 caused a decrease in viability of 5 log for MRSA and 6 log for E. coli. When the conjugate loaded with 12 μM C14 was added to a water sample contaminated with MRSA (10(8) cells per ml) a tight association of the bacterial cells with the silica microparticle-porphyrin system was achieved. Subsequent illumination of the conjugate with visible light (30 min, 100 mW cm(-2)) caused a 3 log reduction in the population of MRSA cells in the water sample. Importantly, the conjugate was readily recovered by filtration of the aqueous suspension and shown to maintain a high antibacterial photoactivity when introduced into a new MRSA-contaminated medium and irradiated.

Photoelectrode Characteristics of Partially Hydrolyzed Aluminum Phthalocyanine Chloride/Fullerene C60 Composite Nanoparticles Working in a Water Phase

Photoelectrochemical measurements were used to study the photoelectrode characteristics of composite nanoparticles composed of fullerene C60 and partially hydrolyzed aluminum phthalocyanine chloride (AlPc). In cyclic voltammetry measurements, the electrodes coated with the composite nanoparticles were found to have photoanodic [electron donor: 2-mercaptoethanol (ME)] and photocathodic (electron acceptor: O2) characteristics similar to those of the vapor-deposited p/n junction electrode. Their photoanodic features were further investigated with respect to the transient photocurrent response to light irradiation and the dependence on ME concentration (under potentiostatic conditions), from which it was noted that there was a decrease in the initial spiky photocathodic current and saturation of the steady-state photoanodic current at a higher ME concentration. Thus, the reaction kinetics was probably dominated by charge transport process. Moreover, external and internal quantum efficiency spectrum measurements indicated that the composite nanoparticles responded to the full spectrum of visible light (<880 nm) for both the photoanodic and photocathodic current. The present research will assist comprehension of photocatalytic behavior of the composite nanoparticles.

Photocatalytic decomposition of N-methyl-2-pyrrolidone, aldehydes, and thiol by biphase and p/n junction-like organic semiconductor composite nanoparticles responsive to nearly full spectrum of visible light

Organic semiconductor nanoparticles composed of fullerene C60 and/or partially hydrolyzed aluminum phthalocyanine chloride (AlPc) were synthesized using a reprecipitation method. The composite's biphase structure was confirmed using scanning electron microscopy, scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy, zeta potential, and dynamic light scattering, and a possible formation mechanism for the biphase structure was also proposed. In the photodegradation experiments, the composite showed enhanced photocatalytic activity for the oxidation of various organic compounds (e.g. N-methyl-2-pyrrolidone, methanal, ethanal, and 2-mercaptoethanol (ME)) to CO2 as compared to the C60 or AlPc nanoparticles. Moreover, its action spectrum for the photocatalytic decomposition of ME to CO2 also covered almost the full spectrum of visible light (<700 nm). The present research demonstrated a novel organic photocatalyst featuring a biphase structure and p/n junction-like characteristics.

Cassette series designed for live‐cell imaging of proteins and high‐resolution techniques in yeast

During the past decade, it has become clear that protein function and regulation are highly dependent upon intracellular localization. Although fluorescent protein variants are ubiquitously used to monitor protein dynamics, localization and abundance; fluorescent light microscopy techniques often lack the resolution to explore protein heterogeneity and cellular ultrastructure. Several approaches have been developed to identify, characterize and monitor the spatial localization of proteins and complexes at the suborganelle level, yet many of these techniques have not been applied to yeast. Thus, we have constructed a series of cassettes containing codon-optimized epitope tags, fluorescent protein variants that cover the full spectrum of visible light, a TetCys motif used for fluorescein arsenical hairpin (FlAsH)-based localization, and the first evaluation in yeast of a photoswitchable variant, mEos2, to monitor discrete subpopulations of proteins via confocal microscopy. This series of modules, complete with six different selection markers, provides the optimal flexibility during live-cell imaging and multicolour labelling in vivo. Furthermore, high-resolution imaging techniques include the yeast-enhanced TetCys motif, which is compatible with diaminobenzidine photo-oxidation used for protein localization by electron microscopy, and mEos2, which is ideal for super-resolution microscopy. We have examined the utility of our cassettes by analysing all probes fused to the C-terminus of Sec61, a polytopic membrane protein of the endoplasmic reticulum of moderate protein concentration, in order to directly compare fluorescent probes, their utility and technical applications. Our series of cassettes expand the repertoire of molecular tools available to advance targeted spatiotemporal investigations using multiple live-cell, super-resolution or electron microscopy imaging techniques.

A red anatase TiO2 photocatalyst for solar energy conversion

Narrowing the bandgap of wide-bandgap semiconductor photocatalysts (for instance, anatase TiO2) by introducing suitable heteroatoms has been actively pursued for increasing solar absorption, but usually suffers from a limited thermodynamic/kinetic solubility of substitutional dopants in bulk and/or dopant-induced recombination centres. Here we report a red anatase TiO2 microsphere with a bandgap gradient varying from 1.94 eV on its surface to 3.22 eV in its core by a conceptually different doping approach for harvesting the full spectrum of visible light. This approach uses a pre-doped interstitial boron gradient to weaken nearby Ti-O bonds for the easy substitution of oxygen by nitrogen, and consequently it substantially improves the nitrogen solubility. Furthermore, no nitrogen-related Ti3+ was formed in the red TiO2 due to a charge compensation effect by boron, which inevitably occurs in common nitrogen doped TiO2. The red anatase TiO2 exhibits photoelectrochemical water splitting activity under visible light irradiation. The results obtained may shed light on how to increase high visible light absorbance of wide-bandgap photocatalysts.

Photocatalytic Activity and Characterization of Carbon-Modified Titania for Visible-Light-Active Photodegradation of Nitrogen Oxides

A variety of carbon-modified titania powders were prepared by impregnation method using a commercial available titania powder, Hombikat UV100, as matrix material while a range of alcohols from propanol to hexanol were used as precursors of carbon sources. Rising the carbon number of alcoholic precursor molecule, the modified titania showed increasing visible activities ofNOxphotodegradation. The catalyst modified with cyclohexanol exhibited the best activities of 62%, 62%, 59%, and 54% for the totalNOxremoval under UV, blue, green, and red light irradiation, respectively. The high activity with long wavelength irradiation suggested a good capability of photocatalysis in full visible light spectrum. Analysis of UV-visible spectrum indicated that carbon modification promoted visible light absorption and red shift in band gap. XPS spectroscopic analysis identified the existence of carbonate species (C=O), which increased with the increasing carbon number of precursor molecule. Photoluminescence spectra demonstrated that the carbonate species suppressed the recombination rate of electron-hole pair. As a result, a mechanism of visible-light-active photocatalyst was proposed according to the formation of carbonate species on carbon-modified TiO2.

Non‐invasive diagnostic evaluation of phototherapeutic effects of red light phototherapy of acne vulgaris

During the past few years, various phototherapeutic protocols with full-spectrum visible light or selected wavebands have been investigated in the treatment of acne vulgaris with variable results. Fifteen women suffering from moderate acne vulgaris of the face were exposed to 20 J/cm(2) of broad-band red (lambda: 600-750 nm) light twice weekly for 4 weeks. In addition, with the aim to improve the present knowledge of the mechanisms of action of phototherapy, we measured skin sebum, pH, hydration and trans-epidermal water loss (TEWL). Lesions of the trunk were not irradiated and served as controls. A significant improvement of acne lesions and a significant decrease of skin sebum excretion and TEWL of the face were registered at the end of the therapy and at the 3-month follow-up visit. The results could be related to a reduced follicular colonization of Propionibacterium acnes, in that it was lethally damaged by photoactivated endogenous porphyrins. The present findings seem to indicate that red light phototherapy may represent an effective, well-tolerated, safe, simple and inexpensive treatment option for moderate acne vulgaris.

Advances in Endoscopic Imaging of Barrett’s Esophagus

o B b t a l a t w F r c i l r creening and surveillance of Barrett’s esophagus may prevent esophageal adenocarcinoma by detecting precursor esions. In most cases, however, dysplasia is invisible to the eye f the endoscopist. Therefore, surveillance requires extensive andom biopsies and histologic examination of the excised issue for dysplasia. This biopsy strategy has several limitations, ncluding sampling errors, increased time and cost of endosopy, and limited reliability of histologic interpretation of dyslasia. Over the past 10, years there have been major advances n optical methods for detection of dysplasia and early carcioma. These methods include imaging methods focused on oth anatomic and functional changes of dysplasia, as well as ther non–image-based optical methods such as spectroscopy. lthough many of the imaging methods remain experimental, 005 and 2006 saw the introduction of advanced imaging ethods into mainstream endoscopic systems such as narrow and imaging (Olympus Corp, Melville, NY), intelligent chrooendoscopy (Fujinon, Wayne, NJ), and integrated optical coerence tomography systems (Pentax, Golden, CO). The value f these systems has not yet been established; however, they are eing rapidly adopted into practice. In this review, I discuss the echnological basis of these systems and speculate on their pplications. The currently available advanced endoscopic imaging sysems all rely on anatomic imaging, seeing the actual tissue or ven cells, but using methods to increase magnification and ontrast, and focus on regions relevant to distinguishing nonysplastic from dysplastic Barrett’s epithelium. At a fundamenal level, dysplasia is classified based on both cytologic (inreased nuclear size, density, irregularity) and histologic distortion of the single-layer epithelium and uniform crypt attern). In addition, there are vascular changes that mirror hese, such as increased vascularity and increasing irregularity f capillary arcades. Each imaging method aims at identifying ne or more of these pathologic changes. Imaging of cytologic changes is largely restricted to optical oherence tomography and confocal endomicroscopy and is the ubject of previous reviews.1 Macroscopic anatomic imaging nd functional imaging are now the most common methods of etection of dysplastic changes in Barrett’s esophagus. The two urrently available methods—narrow band imaging and intellient chromoendoscopy— both rely on similar methods. Narrow and imaging uses 2 characteristics of light to enhance surface ontracts and highly vascular changes. The first of these is the se of short wavelength light in the visible spectrum (blue light) o illuminate the tissue. Because light of shorter wavelength is ighly scattered by dense cell nuclei and collagen, only light rom the most superficial layers of the mucosal and submucosa re visualized. Although not often recognized, standard white ight endoscopy visualizes a thick slab of tissue at least 5–10 m thick as evidenced by the routine appearance of deep ubmucosal vessels on routine endoscopy. The surface characeristics of the mucosa are often lost because of the diffusion of he light from multiple layers at the same time. Using narrow ands of blue light overcomes this problem by allowing more solated imaging of the thin slab of tissue at the mucosal urface (Figure 1). The second method is aimed at increasing the visualization f small blood vessels by increasing the contrast and resolution. lood typically appears red owing the absorption of blue light y hemoglobin. When tissue is illuminated with the full specrum of visible light, the blue light is absorbed and the red light, mong other colors is reflected. Connective tissues and epitheial cells typically reflect the full spectrum of light and thus ppear white. The contrast between vasculature and connective issue/epithelium can be increase by selectively illuminating ith blue light so that the vessels appear black and the sur-

Tuning the emitting wavelength of InGaN/GaN superlattices from blue, green to yellow by controlling the size of InGaN quasi-quantum dot

High quality blue, green and yellow LEDs comprised of stable indium-rich clusters in InGaN/GaN multiple quantum wells (MQWs) have been successfully grown by metal-organic chemical vapor deposition. We show that the common degradation phenomenon on crystallinity can be avoided by these quasi-quantum dots as obtained from the integrated results of high resolution transmission electron microscopy (HRTEM), rocking curve and ω-scan analysis. Ultra-small sized indium clusters of 2 nm, 2.5 nm and 3 nm in diameter have been observed in the quantum wells from HRTEM analysis. We also show that by well controlling the dot size in the active layers, emitting wavelength in full visible light spectrum is achieved. In addition, several interesting observations were also found during analysis. First, the propagation of threading dislocations would be efficiently stopped by the quasi-dots, which behave as real quantum dots. Secondly, the thickness dependence of phase separation has also been demonstrated in the sample emitting blue light where the quantum well thickness ranges in 1.7∼2 nm and nominal In content is in 8∼10% regime. Thirdly, the phase separation is independent of film polarity (Ga-polarity or N-polarity).

Modest in vivo exposure to solar wavelengths induces a visible absorbing chromophore in Skh-1 mouse epidermis.

In the previous work, we correlated epidermal hyperplasia with increased epidermal absorption in the 250-400 nm region. During a recent review of that work, the apparent formation of a chromophore, with absorption slightly longer than 400 nm, in the epidermis of irradiated animals was noted. In this study, we have extended the transmission measurement to include the 250-800 nm region. Age-matched Skh-1 hairless mice were separated into three groups. One group was irradiated with 6.3 J/cm(2) (0.9 minimal erythemal dose; MED) of solar simulating ultraviolet radiation (SSUVR) five times/week for 2 weeks, then increased to 1.1 MED (7.1 J/cm(2)) for two additional weeks (20-day group). A second 10-day group, added halfway through the protocol, was irradiated with 0.9 MED five times/week for 2 weeks. The control group received no UV irradiation. Routine H&E staining and epidermal absorption spectral analysis were carried out on biopsy specimens from each animal. This work confirms the development or enhancement of a visible chromophore with a maximum absorption at ca 412 nm. This peak appears to be radiation dose dependent. It can be discerned in both the groups, albeit more prominently in the 20-day animals. The absorption is sufficiently strong to impart a yellow to reddish appearance to skin viewed in full spectrum visible light. Accumulation of such a chromophore in humans may contribute to the coloration of chronically exposed skin. The absorption strength and wavelength location of the peak is strongly suggestive of a heme-like compound. We are currently conducting experiments to further characterize this chromophore.

Long-term Follow-up and Histological Changes of Superficial Nonmelanoma Skin Cancers Treated With Topical δ-Aminolevulinic Acid Photodynamic Therapy

To investigate the immediate and long-term effects of photodynamic therapy with delta-aminolevulinic acid (ALA-PDT) on superficial basal cell carcinomas (BCC) and superficial squamous cell carcinomas (SCC). Retrospective study with 60 months of maximal follow-up. University-based hospital in Graz, Austria. Forty-seven subjects with a total of 95 superficial BCC and 35 superficial SCC. A compound of 20% delta-aminolevulinic acid was topically applied under an occlusive and light-shielding dressing before exposure to either UV-A or different wave bands of polychromatic visible light (full-spectrum visible light, >515, >570, or >610 nm). Primary tumor responses and recurrence rates in the long-term follow-up, as well as histological changes associated with ALA-PDT, were studied. The complete primary response rate for all wave bands of light was 86% (82/95) for superficial BCC and 54% (19/35) for superficial SCC. There was no statistically significant difference among the response rates to the different wave bands of light. After a median follow-up of 19 months (range, 3-60 months) for BCC and 8 months (range, 3-47 months) for SCC, the overall recurrence rate was 44% (36/81) and 69% (11/16), respectively. At 36 months after therapy, the projected disease-free rate was 50% (95% confidence interval, 43%-57%) for BCC vs 8% (95% confidence interval, 7%-9%) for SCC (P<.001, log-rank test). Histopathologic studies revealed a significant increase of fibrosis in the dermis after ALA-PDT and appearance of a sharp border between fibrotic and nonfibrotic tissue. In 15 of 16 BCC examined, the border between fibrotic and nonfibrotic tissue was deeper in the dermis than the maximum tumor thickness before therapy (P<.001, Wilcoxon signed rank test). Similar histopathologic observations were made in SCC. Our study revealed poor long-term cure rates for superficial BCC and SCC treated with topical ALA-PDT and visible light. The histopathologic observations showing remarkable fibrosis in the dermis indicated that the effect of ALA-PDT reached deeper than the initial depth of invasiveness of the neoplastic tissue, suggesting in turn that the poor long-term results of ALA-PDT cannot be explained by insufficient penetration of the therapy effect.

Photodynamic Therapy of Superficial Basal Cell Carcinoma by Instillation of Aminolevulinic Acid and Irradiation With Visible Light

REPORT OF A CASE A 63-year-old man presented with a large, 4-cm, superficial basal cell carcinoma (BCC) on the right side of the lower part of his back that had been present for 5 years ( Figure , A). He refused surgical intervention. THERAPEUTIC CHALLENGE We needed an effective nonsurgical treatment modality for this large BCC. SOLUTION After giving his signed consent, the patient was treated with intralesional δ-aminolevulinic acid (ALA) photodynamic therapy (PDT). Two milliliters of 10% ALA in a 0.9% sodium chloride solution was injected intralesionally with a syringe. After light-shielding occlusion for 4 hours, visual evaluation of the treated lesion under Wood light in a darkened room revealed the typical red fluorescence of porphyrin limited to the tumor (Figure B). The lesion was then exposed to 180-J/cm 2 fullspectrum visible light produced by a slide projector (Leica P-2000, Leica, Leitz Wetzlar, Germany) equipped with a 250-W lamp. There was

Primary clinical response and long-term follow-up of solar keratoses treated with topically applied 5-aminolevulinic acid and irradiation by different wave bands of light

Photodynamic therapy with 5-aminolevulinic acid (ALA-PDT) is based on photosensitization by endogenous synthesis of protoporphyrin IX and its transient accumulation especially in malignant epithelially derived tissues. Recent studies have indicated that ALA-PDT is effective for the treatment of solar keratoses (SK), but there has been a lack of long-term clinical follow-up. The goal of the present study was to investigate the immediate and long-term effect of ALA-PDT on SK. Twenty-eight patients with a total of 251 SK were enrolled in the study. Standard treatment involved the topical application of 20% ALA, under occlusive and light-shielding dressing for 4 hours before exposure to UVA and/or different wave bands or wave band combinations of polychromatic visible light (full-spectrum visible light, and/or different wave bands of filtered visible light >515, >530, >570, or >610 nm) in one or two treatment sessions. The primary complete response rate of SK to ALA-PDT was 64% after one treatment, but 85% when the responses to a second treatment were included. Taken all treatments together, the complete response rate for lesions on face, scalp and neck was 93% for full-spectrum visible light, 96% for the combination of full-spectrum visible light and filtered light, 91% for different wave bands of filtered visible light, and 100% for the combination of long wave UVA and full-spectrum visible light, respectively. The complete response rate for lesions on forearms and hands was 51% for full-spectrum visible light and 33% for the combination of full-spectrum visible light and filtered light. The greater response rate for SK on the face, scalp, and neck was associated with a higher surface fluorescence and immediate response rate after ALA photosensitization at these sites ( X 2: p = 0.0001). However, due to the treatment protocol the mean light dose applied to lesions on the face, scalp and neck (50 J cm −2) was substantially higher than that for lesions on forearms and hands (35 J cm −2). In the long term follow-up of SK on face scalp and neck, the projected disease-free rate at 36 months after therapy was 71% for lesions treated with full-spectrum visible light versus 23% for lesions treated with different wave bands of filtered light (Log rank - Mantel Cox; p = 0.0001). These results indicate that treatment with full-spectrum visible light at higher light doses may be the most effective and promising form of light exposure in ALA-PDT of SK.

Dose-response relationships for photodynamic injury to murine skin.

Oedema and necrosis of murine tail skin have been measured after intravenous injection of haematoporphyrin derivative ("Photofrin", or PhI) followed 24 h later by graded exposures of the tail to full-spectrum visible light from a quartz-halogen lamp. End-points were degree of oedema and the proportion of mice in a dose-group that developed skin necrosis and tail atrophy. Oedema developed within 24 h of illumination and was a function of PhI dose and duration of light exposure. Onset of necrosis occurred after a minimum of 5 days and onset time was an inverse function of exposure time. Probit plots of proportion of necroses versus light exposure yielded values for ND50 (exposure corresponding to 50% incidence of necrosis) and l/slope. At the high but non-toxic dose of 2 mg PhI/mouse, ND50 was 18 min, l/slope 4 min, for pigmented BDF1 mice. Halving the PhI dose increased ND50 by a factor of 1.9. Albino BALB/c mice were markedly more sensitive to 2 mg PhI plus light than BDF1 mice: the ND50 was 7 min. Temporary occlusion of the blood supply to the tail (10 min before and during illumination) abrogated totally the oedematous and necrotic reactions to photodynamic therapy.