| Summary: | Photosynthetic single-celled diatom algae, due to their unique structure and properties, represent promising candidates for various applications in technology and biomedicine. These nanostructured objects, enveloped within a silica cell wall called a frustule, play a significant role in Earth’s ecology. In this study, we proposed new techniques for monitoring the growth of diatoms—in situ fluorescence measurements using the IVIS imaging system and photoacoustic measurements with a raster scanning optoacoustic mesoscopy (RSOM) setup. Two different diatom cultures, Achnanthidium sibiricum and Encyonema silesiacum, were cultivated under the optimal conditions in the incubator and monitored over the period of 70 days. Our results showed that the total radiant efficiency increases with increasing incubation time for E. silesiacum. Simultaneously, for A. sibiricum it slightly decreases after 56 days, indicating that diatoms were at the end of their exponential growth phase. The photoacoustic signal from E. silesiacum was lower than from A. sibiricum, which is in good agreement with spectroscopic characterization results. The IVIS imaging system made it possible to assess the growth and viability of diatom cells without compromising cell integrity. In contrast, photoacoustic imaging has proved to be suitable for the rapid detection and thorough in situ assessment of the density of diatom colonies due to the presence of light-absorbing chromophores. These methods can be used to monitor the growth of diatoms and facilitate the harvesting of bioactive substances derived from diatoms for pharmaceutical and biomedical purposes.
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