Characterization of Spontaneous Melanization by Fluorescence Spectroscopy: A Basis for Analytical Application to Biological Substrates

Abstract

Melanin is present in various biological substrates where it may participate in several processes, from innate immunity to the still-unsolved opposite roles in antioxidant protection, including photoprotection and the related ability to interact with light. Melanin–light interaction has also been an important source of inspiration for the development of innovative bioengineering applications. These are based on melanin’s light-energy-absorption ability of its chemically and structurally complex components and precursors, and on the improvement in analytical and diagnostic procedures in biomedicine. In this regard, here, we characterized the fluorescence spectral properties of melanin and of its precursor L-tyrosine in an aqueous solution during spontaneous melanization. Besides the confirmation of the typical fluorescence-emission signature of melanin and L-tyrosine, we provide additional insights on both emission and excitation spectra recorded during melanization. On these bases, we performed a subsequent characterization on the aqueous extracts from two different melanin-containing biological substrates, namely hairs from a domestic black cat and eggs from the Asian tiger mosquito. The results from the mild extraction procedure, purposely applied to obtain only the soluble components, combined with fluorescence spectral analysis are expected to promote further investigation of the melanization processes, particularly in insects.

Gene expression profiles of skin from cyclin dependent kinases 5-knockdown mice

“…Hair and skin color depend on the pigments produced by melanocytes at the base of the epithelium [ 5 ]. Mammalian melanocytes produce two chemically distinct types of melanin, black/brown eumelanin and yellow/red-brown pheomelanin [ 6 ]. The quality and ratio of eumelanin to pheomelanin determine the final color of the hair and skin.…”

Developmental and Nutritional Dynamics of Malpighian Tubule Autofluorescence in the Asian Tiger Mosquito Aedes albopictus

“…The characterization of AF signals in mosquitoes has been recently approached in anatomical structures associated with mechanical and sensory functions, with potential relevance also for vector surveillance and control [ 43 , 44 , 45 ]. A mixed and variable presence of the bluish AF ascribable to the elastic and resilient resilin and of the greenish-reddish AF ascribable to the rigid chitin has been detected in different body compartments, consistently with their already proposed ability to affect the elasticity or stiffness of different structures and their related mechanical and sensory functions [ 44 , 45 , 46 , 47 , 48 ].…”

“…A mixed and variable presence of the bluish AF ascribable to the elastic and resilient resilin and of the greenish-reddish AF ascribable to the rigid chitin has been detected in different body compartments, consistently with their already proposed ability to affect the elasticity or stiffness of different structures and their related mechanical and sensory functions [ 44 , 45 , 46 , 47 , 48 ]. The dependence of the body surface pattern on its scales, black or fluorescing with a reddish or white-bluish signal for the likely presence of melanin and its precursors or resilin, respectively, has been proposed to have implications for mosquito inter- and intra-specific communication [ 43 , 44 ]. Studies on the AF in the MTs of mosquitoes, on the other hand, are currently lacking but anticipated to yield insights into the metabolic and detoxification processes within these organs, shedding light on the mosquito’s physiological status and its reactions to environmental factors or treatments.…”