Photoacoustic visualization of diatom algae

Abstract

Photoacoustic imaging is a rapidly maturing imaging modality in biological research and medicine. Its underlying principle is the photoacoustic effect. This method can also be used to study algae containing light-absorbing chromophores, which produce a photoacoustic signal under laser irradiation. Here, we demonstrate successful photoacoustic visualization of unicellular diatom algae called Karayevia amoena. These hierarchical micro/nano-structured organisms mixed with an agarose gel were excited by nanosecond pulsed green, 532 nm laser using a raster scanning optoacoustic mesoscopy (RSOM) approach. We observed a strong photoacoustic signal from diatom cells and showed that it decreases with decreasing diatom concentration. The signal originates from chlorophyll a and c and fucoxanthin. We also studied cyanobacteria to prove that the photoacoustic technique can be useful for visualizing this type of object as well. Photoacoustic imaging is a promising method for remote control of algae cultivation in bioreactors and their natural environment.