Illuminating microalgal biofilms using advanced photonic imaging techniques

In recent years, microalgal biofilms have garnered significant interest primarily due to their potential to transform wastewater treatment and overcome the limitations associated with conventional microalgal planktonic-based cultivation methods. Advances in imaging technologies have provided insight into the complex dynamics of microalgal biofilms, which could help in understanding both biofilm structure and function, and thus to optimize microalgae biofilm-based technologies. In particular, photonic microscopy allows researchers to study the architectural nuances, physiological responses, as well as spatial organization and interactions within biofilm communities. Despite these significant advances, there is still a lack of consistency in approaches and analytical techniques, which hinders standardized studies. Therefore, there is a need for common protocols and benchmarks in photosynthetic biofilm imaging. This review focuses primarily on key photonic imaging technologies, including confocal laser scanning microscopy (CLSM), light-sheet microscopy, histology coupled with a digital slide scanner, and optical coherence tomography (OCT). Principles, advantages/limitations and current applications of each technique in the context of microalgal biofilm studies, are presented allowing researchers to make reasoned decisions for their specific investigative endeavors. • CLSM, light-sheet, histology with slide scanner, and OCT offer unique insights into microalgal biofilm structure and function • Photonic imaging allows real-time, non-destructive biofilm monitoring, key to optimizing biofilm-based cultivation • Autofluorescence plus staining enhances analysis of photosynthetic and non-photosynthetic biofilm components • Standardized protocols and benchmarks are needed for consistent, reliable photosynthetic biofilm imaging studies