Oxidation causes melanin fluorescence. Invest Ophthamol Vis Sci

Department of Vitreoretinal Surgery, Division of Ophthalmology, University of Cologne, Germany.
Investigative Ophthalmology &amp Visual Science (Impact Factor: 3.4). 02/2001; 42(1):241-6.
Source: PubMed


The goal of this study is the characterization of the strong yellow fluorescence of oxidized melanin in the retinal pigment epithelium (RPE) and the choroid.
Naturally occurring melanin in the human retina and choroid was oxidized by exposing fixed and plastic-embedded sections of a human eye to light and hydrogen peroxide. Synthetic melanin was also oxidized in vitro by exposure to light and hydrogen peroxide. The fluorescence of oxidized melanin was examined by absorption spectroscopy, fluorescence spectroscopy, and fluorescence microscopy.
Naturally occurring melanin oxidized in situ exhibited a lipofuscin-like yellow fluorescence. Oxidation of melanin in vitro degraded the melanin polymer, resulting in a fluorescent solution. Fluorescence spectroscopy gave an excitation maximum at approximately 470 nm and an emission maximum at approximately 540 nm for both natural and synthetic melanin. Increasing the time of exposure to light or hydrogen peroxide increased melanin fluorescence.
The results indicate that the strong yellow fluorescence of melanin in the RPE and choroid in situ is a property of oxidized melanin and is not due to contamination of the melanin by proteinaceous or lipid materials. The data presented allow a reinterpretation of the results obtained from fluorescence investigations of melanin-containing tissue and suggest a link between melanin degradation and lipofuscin formation.

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Available from: Peter Kayatz, Feb 07, 2014
    • "[7] Melanin is known to exhibit autofluorescence, which is difficult to detect, [8] because it is a weak emitter with a very low quantum yield of fluorescence, [9] but under oxidative conditions fluorescence increases considerably. [10] The aim of the present study was to develop a simple, fast, and economic method to assess whether hair was oxidatively treated or not. It is based on the hypothesis that oxidative hair treatment should be detectable by a marked increase in fluorescence. "
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    ABSTRACT: In assessing abstinence from drug or alcohol abuse, hair analysis plays an important role. Cosmetic hair treatment influences the content of deposited drugs which is not always detectable during analysis. Since oxidation of melanin leads to an increase in fluorescence, a microscopic method was developed to distinguish natural from cosmetically treated hair. For validation, natural hair samples were treated with different types of cosmetics and inspected by fluorescence microscopy. Hair samples from 20 volunteers with documented cosmetic treatment and as a proof of concept 100 hair samples from forensic cases were analyzed by this method. Apart from autofluorescence with excitation at 365 nm, no obvious fluorescence was observed in untreated hair samples. Tinting and a natural plant product had no influence on fluorescence, but dyeing procedures including oxidation led to a marked increase in fluorescence. Proof of cosmetic treatment was achieved in hair samples from the 20 volunteers. In 100 forensic cases, 13 samples were characterized as oxidatively treated, which was in accordance with the respective disclosure except for one case where treatment was not admitted. This fluorescence microscopic procedure proved to be fast, easy, and reliable to identify oxidatively treated hair samples, which must be considered especially in evaluating cases of negative drug results. Copyright © 2015 John Wiley & Sons, Ltd.
    No preview · Article · Sep 2015 · Drug Testing and Analysis
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    • "Triplet excited carbonyls 350–550 nm [36] [75] Singlet excited pigments 360–560 nm melanin [76] [77] 680–740 nm chlorophyll [78] Triplet excited pigments 870–1000 nm chlorophyll + Dimolar singlet oxygen 634 nm, 703 nm [22] [23] [37] Monomolar singlet oxygen 1270 nm * + expected based on the singlet excited pigment emission but not yet directly confirmed as a contribution to ultra-weak photon emission. Emission wavelength from triplet excited chlorophyll is known from phosphorescence measurement [79]. "
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    ABSTRACT: This review attempts to summarize molecular mechanisms, spectral and intensity properties, detection techniques and applications of ultra-weak photon emission. Ultra-weak photon emission is the chemiluminescence from biological systems where electronically excited species are formed during oxidative metabolic or oxidative stress processes. It is generally accepted that photons are emitted (1) at near UVA, visible, and near IR spectral ranges from 350 to 1300nm and (2) at the intensity of photon emission in the range of several units to several hundreds (oxidative metabolic process) and several hundreds to several thousands (oxidative stress process) photons s(-1)cm(-2). Current development in detection using low-noise photomultiplier tubes and imaging using highly sensitive charge coupled device cameras allows temporal and spatial visualization of oxidative metabolic or oxidative stress processes, respectively. As the phenomenon of ultra-weak photon emission reflects oxidative metabolic or oxidative stress processes, it can be widely used as a non-invasive tool for monitoring of the physiological state of biological systems.
    Full-text · Article · Feb 2014 · Journal of photochemistry and photobiology. B, Biology
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    • "They are ubiquitous in nature and occur in various organisms, particularly fungi and bacteria have been found to show a high melanin content which is associated with microbial pathogenesis (Gomez and Nosanchuk, 2003; Nosanchuk and Casadevall, 2003). Compared to the other age-related pigments, melanin is regarded to show only a relatively weak fluorescence, but it has been shown that oxidation significantly increases fluorescence with a emission maximum at ∼540 nm when excited at ∼470 nm (Kayatz et al., 2001). Fluorescent light emission from tetrapyrrolic compounds (i.e. "
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    ABSTRACT: Primary biological aerosol particles (PBAP) are an important subset of air particulate matter with a substantial contribution to the organic aerosol fraction and potentially strong effects on public health and climate. Recent progress has been made in PBAP quantification by utilizing real-time bioaerosol detectors based on the principle that specific organic molecules of biological origin such as proteins, coenzymes, cell wall compounds and pigments exhibit intrinsic fluorescence. The properties of many fluorophores have been well documented, but it is unclear which are most relevant for detection of atmospheric PBAP. The present study provides a systematic synthesis of literature data on potentially relevant biological fluorophores. We analyze and discuss their relative importance for the detection of fluorescent biological aerosol particles (FBAP) by online instrumentation for atmospheric measurements such as the ultraviolet aerodynamic particle sizer (UV-APS) or the wide issue bioaerosol sensor (WIBS). In addition, we provide new laboratory measurement data for selected compounds using bench-top fluorescence spectroscopy. Relevant biological materials were chosen for comparison with existing literature data and to fill in gaps of understanding. The excitation-emission matrices (EEM) exhibit pronounced peaks at excitation wavelengths of ~280 nm and ~360 nm, confirming the suitability of light sources used for online detection of FBAP. They also show, however, that valuable information is missed by instruments that do not record full emission spectra at multiple wavelengths of excitation, and co-occurrence of multiple fluorophores within a detected sample will likely confound detailed molecular analysis. Selected non-biological materials were also analyzed to assess their possible influence on FBAP detection and generally exhibit only low levels of background-corrected fluorescent emission. This study strengthens the hypothesis that ambient supermicron particle fluorescence in wavelength ranges used for most FBAP instruments is likely to be dominated by biological material and that such instrumentation is able to discriminate between FBAP and non-biological material in many situations. More detailed follow-up studies on single particle fluorescence are still required to reduce these uncertainties further, however.
    Full-text · Article · Sep 2011 · Atmospheric Measurement Techniques
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