Resonance Raman and SERRS of fucoxanthin: Prospects for carotenoid quantification in live diatom cells

•Concentration dependence resonance Raman spectra•Concentration dependence SERRS spectra•Fucoxanthin dominance in live diatoms is not consistent with one specific Raman band position•quantification in live cell Fucoxanthin, one of the most abundant carotenoids in brown algae or in unicellular diatoms, plays a crucial role in photosynthetic processes and has a significant contribution to the natural pigments industry and biomedical application as colouring and bioactive agent. Many carotenoids are widely identified using resonance Raman (RR) spectroscopy, however, quantitative estimation of this pigment in solutions and in live cells from RR data is challenging. Here we investigated the concentration dependence resonance Raman and surface-enhanced resonance Raman scattering (SERRS) spectra of fucoxanthin, to prospect the capability of the techniques for quantitative estimation of the carotenoid in live diatom species, Cylindrotheca closterium and Skeletonema costatum. Furthermore, since pools of carotenoids are usually present in live photosynthetic microorganisms, we compared their SERRS signal when exposed to Ag nanoparticles and found distinct SERRS carotenoids signature. Regarding fucoxanthin quantification, we found a nonlinear increase in the resonance Raman intensity of the ν(C=C) mode in the concentration range from 1.190 µM to 3.035 mM and a linear increase in SERRS intensity in the 0.12 to 1.186 µM concentration range, comparable with the signal intensity collected from single diatom cells. Particularly, S. costatum, an opportunistic diatom causing harmful bloom in certain conditions, could provide important information from carotenoids monitoring in relation with its adaptability to various environmental factors, which would certainly consolidate such monitoring approaches relying on Raman spectroscopy techniques.