1 research outputs found
Dispersive Raman spectroscopy allows the identification and quantification of melanin types
Melanins are the most prevalent pigments in animals and are involved in visual
communication by producing colored traits that often evolve as intraspecific signals
of quality. Identifying and quantifying melanins are therefore essential to
understand the function and evolution of melanin-based signals. However, the
analysis of melanins is difficult due to their insolubility and the lack of simple
methods that allow the identification of their chemical forms. We recently proposed
the use of Raman spectroscopy as a simple, noninvasive technique that can
be used to identify and quantify melanins in feathers and hairs. Contrarily, other
authors later stated that melanins are characterized by a lack of defined Raman
signals. Here, we use confocal Raman microscopy to confirm previous analyses
showing that the two main chemical forms of melanins (eumelanin and pheomelanin)
exhibit distinct Raman signal and compare different excitation wavelengths
to analyze synthetic pheomelanin and natural melanins in feathers of different
species of birds. Our analyses indicate that only laser excitation wavelengths
below 1064 nm are useful for the analysis of melanins by Raman spectroscopy,
and only 780-nm laser in the case of melanins in feathers. These findings show
that the capacity of Raman spectroscopy to distinguish different chemical forms
of melanins depends on laser power and integration time. As a consequence,
Raman spectroscopy should be applied after preliminar analyses using a range of
these parameters, especially in fragile biological tissues such as feathersPeer reviewe