Luminescent Metal Complexes as Emerging Tools for Lipid Imaging

Fluorescence microscopy is a key tool in the biological sciences, which finds use as a routine laboratory technique (e.g., epifluorescence microscope) or more advanced confocal, two-photon, and super-resolution applications. Through continued developments in microscopy, and other analytical methods, the importance of lipids as constituents of subcellular organelles, signalling or regulating molecules continues to emerge. The increasing recognition of the importance of lipids to fundamental cell biology (in health and disease) has prompted the development of protocols and techniques to image the distribution of lipids in cells and tissues. A diverse suite of spectroscopic and microscopy tools are continuously being developed and explored to add to the "toolbox" to study lipid biology. A relatively recent breakthrough in this field has been the development and subsequent application of metal-based luminescent complexes for imaging lipids in biological systems. These metal-based compounds appear to offer advantages with respect to their tunability of the photophysical properties, in addition to capabilities centred around selectively targeting specific lipid structures or classes of lipids. The presence of the metal centre also opens the path to alternative imaging modalities that might not be applicable to traditional organic fluorophores. This review examines the current progress and developments in metal-based luminescent complexes to study lipids, in addition to exploring potential new avenues and challenges for the field to take.