Fluorescent Probes for Nanoscopic Imaging of Mitochondria

Studying the ultra-fine structure and functions of mitochondria at a nanoscale level has garnered tremendous attention from biologists. Mitochondria perform many more functions than merely generating adenosine triphosphate (ATP), and their functions can vary in different eukaryotic cells. In place of diffraction-limited conventional imaging techniques, advanced nanoscopic technologies have been devised in the past decades to explore the unknown aspects of mitochondrial dynamics and complex structures with a sub-diffraction resolution. The success of these super-resolution microscopy and nanoscopy techniques is complemented by the advancements in designing smart fluorescent probes that target mitochondria. Therefore, this review includes the comprehensive aspects of the recent progress in developing fluorogenic systems for nanoscopic imaging of mitochondria. The review also critically assesses the associated benefits and limitations of such fluorophores when they are employed in practical experiments. Future scope and challenges in developing suitable fluorophores for several nanoscopic techniques are also judiciously evaluated. Accurate, detailed understanding of the biological events occurring in the sub-cellular organelles is important for countering critical physiological disorders and, hence, can promote the welfare and optimal health for mankind. In this regard, fluorescence bio-imaging has paved the way for studying cell biology in depth. However, subcellular organelles such as mitochondria, which perform numerous important functions in the cellular context, cannot be studied in detail because of their very small size, which falls under the diffraction limit. To overcome this issue, several nanoscopic microscopy techniques have come to light recently, and upon being coupled with appropriate fluorophores, these can facilitate the study of the structure and dynamic processes inside mitochondria with nanoscale resolution. In this review, we have carefully assessed both the technical advancements in various nanoscopic techniques and the progress in developing smart fluorophores for mitochondria-specific nanoscale imaging.