10. Labelling strategies and biosensors
Over the years a variety of labelling strategies and biosensors suitable for imaging GPCR signalling have been developed (Figure 4). Finding the optimal probe or their combination is a cornerstone of any imaging project because different probes have their advantages, limitations, and areas of application. The most common labelling strategies applied in GPCR research include the use of fluorescent ligands, FPs, direct and ligand-directed labelling, self-labelling systems, protein conjugation systems, quantum dots, and nanodiamonds. Existing biosensors are used to detect a multitude of signalling processes, including ligand binding (Rosier et al., 2021), signalling cascade activation (Maziarz et al., 2020), GPCR conformation changes (Banerjee et al., 2022), receptor heteromerization (Sleno et al., 2017), interactions between signalling proteins (Olsen et al., 2020), the release of neurotransmitters (Patriarchi et al., 2018; Sun et al., 2018), signalling in different subcellular compartments (Irannejad et al., 2013), the production of second messengers and their spatial localisation (Anton et al., 2022), and many others.