3.4 SIM
SIM is an SRN modality that achieves spatial resolution enhancement by projecting light patterns over a fluorescent sample (Figure 2e) (Gustafsson, 2000). The known structure of such patterns allows for efficient deconvolution of the PSF and improved lateral resolution to 120 nm. Although the resolution improvement achieved with SIM is not as high as that achieved with STED and SMLM techniques, its main advantage is the ability to obtain fast imaging of dynamic processes and high compatibility with the imaging of live samples. In GPCR research, SIM has been used to localise βArrestin-2 in the membrane inside and outside of clathrin-coated pits (Eichel et al., 2016) and detect the differential segregation of activated β2AR molecules phosphorylated by GPCR kinases (GRKs) and protein kinase A (Shen et al., 2018). SIM can be used with a variety of fluorescent sensors, which increases the flexibility of the experimental system design (Wang et al., 2019).