Raman-based analysis and structural differentiation of potentially harmful algae and cyanobacteria

Algal blooms appear most often during the summertime in marine or fresh water resources and can be harmful to humans, animals, and aquatic life. Especially cyanobacteria blooms can be dangerous as they are able to produce cyanotoxins, which can be harmful already at low concentrations. Consequently, it is very important to analyze algae and cyanobacteria blooms quickly, in situ and without complex sample preparation to identify whether the bloom can be harmful or not and to initiate further steps in time. Raman spectroscopy is capable of analyzing organic samples in situ and non-invasively with high specificity. It allows to investigate the structure of algae and cyanobacteria without physical contact and a time effective sample preparation is possible. In this work, we present a Raman based approach to analyze algae and cyanobacteria in the visible wavelength range. We determine components and the structure of the cells to distinguish potentially harmful species and also non-harmful species. Most of the fluorescence signal from the algae is suppressed so that the Raman signals from components inside the cell can be measured. The acquired spectra are processed to compare them and to retrieve information about the differences in the inner structure. Our Raman-based approach is thus suited for fast analysis and distinction of potentially harmful algae and cyanobacteria.