Differentiation of algae clones on the basis of resonance Raman spectra excited by visible light

Fourteen algae clones belonging to four different classes, including clones of Pseudo-nitzschia (Bacillariophyceae), some of which are capable of producing the toxin domoic acid, have been studied by means of resonance Raman spectra excited at 457.9 and 488 nm. Spectra taken at both excitation wavelengths are of high quality and are sufficiently distinct to differentiate clones at the algal class level. All spectra contain major features near 1000, 1153, and 1523 cm(-)(1), which are strongly resonance enhanced due to carotenoid pigments. Weaker features between 920-980 and 1170-1230 cm(-)(1), also due to carotenoid pigments, are more characteristic of the algae clones and more directly reflect different carotenoid composition. Similarities and differences among spectra have been analyzed by the method of principal component analysis (PCA). A distinct clustering of spectral data according to algal class has been shown by PCA score plots. All Pseudo-nitzschia clones can be separated from other classes of algae on the basis of spectra, but it is not possible to distinguish toxic Pseudo-nitzschia from nontoxic clones on the basis of these spectra, which reflect only differences in carotenoid composition.

UV resonance Raman detection and quantitation of domoic acid in phytoplankton

Cultures of the phytoplankton diatom, Pseudonitzschia multiseries, have been harvested under controlled growth conditions ranging from late logarithmic to late stationary phase (17-58 days). The amount of domoic acid (DA) present in the growth media and in the homogenized cells has been determined by HPLC. Defined samples of media, homogenized cells, whole cells, and whole cells in media have been laser excited at 251 nm for the purpose of selectively exciting intense UV resonance Raman spectra from DA in the samples. Neither media nor cell component spectra from algae seriously interfere with DA spectra. The spectral cross sections for the dominant 1652-cm-1 mode of DA have been determined for 242-, 251-, and 257-nm excitation. Maximum sensitivities are achieved with 251-nm excitation because cross sections for DA are a maximum, and interference from other algal components becomes very small. DA concentrations that have been determined with 251-nm excitation by resonance Raman methods correlate closely with values determined independently with HPLC, especially at higher DA concentrations. The UV resonance Raman analysis of DA in phytoplankton algae is shown to be very sensitive and quantitative as well as rapid and nonintrusive.