Raman Microscopy in Plant Science, Carotenoids Detection in Fruit Material

Non-destructive nature of Raman analysis makes it exceptionally useful for various investigations of plant materials; such investigations have been performed at both macro- and micro-levels. It afforded the analysis of carotenoids in different fruits using Raman microspectroscopy. The major advantage of this technique is the capability to provide information about concentration, structure, and vibrational fingerprint of molecules within intact cells and tissues (Nikbakht et al. 2011). One of the main problems associated with the use of conventional Raman on plant materials is the very strong autofluorescence that is produced when phenolic compounds are excited by visible light. In addition, the energies required to generate a Raman signal detectable above the autofluorescence, can cause heating and subsequent modification of the plant tissue. For investigation at the cellular level and it’s compartments (i.e. carotenoids inside plant cells) resonance Raman spectroscopy could give promising results (Bhosale et al. 2014). Despite the fact that Raman scattering is an extremely weak by itself, when the energy of the scattered photon matches the energy of an electronic transition of the molecules, absorption and scattering of the chromophore are strongly increased (Meinhardt-Wollweber et al. 2018). The resonance effect may enhance the Raman spectrum by several orders of magnitude, where the molecules can be detected even at lower concentrations inside the sample. In large, complex molecular structures resonance selectivity helps to identify bands originating from vibrational modes of specific parts of the molecule. In that way the target molecules could be recognized and enhanced above the others based on their resonance behaviour.